Harrat Rahat: The Geoheritage Value of the Youngest Long-Lived Volcanic Field in the Kingdom of Saudi Arabia

  • Mohammed Rashad Moufti
  • Károly Németh
Part of the Geoheritage, Geoparks and Geotourism book series (GGAG)


Harrat Rahat is a volcanic field that consists of over 500 individual volcanoes (Fig. 3.1), many of them with multiple vents forming compound edifices (Camp and Roobol 1989; Coleman and Gregory 1983; El Difrawy et al. 2013; Moufti et al. 2013a). Harrat Rahat was formed over the past 10 million of years (Moufti et al. 2013a), and it is still considered to be an active volcanic region as it has had at least two historic eruptions (Camp et al. 1987; Moufti et al. 2013a). The volcanic field consists of extensive lava fields (Murcia et al. 2014) and various types of volcanic cones and explosion craters (Camp et al. 1991; El Difrawy et al. 2013; Moufti and Hashad 2005; Moufti et al. 2011), each of them is perfectly exposed due to the arid climate and lack of vegetation, and many of them are relatively easy to access (Fig. 3.2). The field is located nearby one of the holiest cities of Islam—Al Madinah—and also hosts the youngest volcanoes in the Kingdom of Saudi Arabia, which have historical and cultural significance (Fig. 3.1). Harrat Al Madinah is the northern part of the Harrat Rahat and the best studied in the Harrat Rahat. The distinction between Harrat Rahat and Harrat Al Madinah is loosely constrained and it has a traditional and geographic connotation rather than geological reasoning. In a similar way, different parts of Harrat Rahat have local names that refer to nearby settlements or other geographical features.


Lava Flow Explosive Eruption Volcanic Field Lava Dome Scoria Cone 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

3.1 Introduction

Harrat Rahat is a volcanic field that consists of over 500 individual volcanoes (Fig. 3.1), many of them with multiple vents forming compound edifices (Camp and Roobol 1989; Coleman and Gregory 1983; El Difrawy et al. 2013; Moufti et al. 2013a). Harrat Rahat was formed over the past 10 million of years (Moufti et al. 2013a), and it is still considered to be an active volcanic region as it has had at least two historic eruptions (Camp et al. 1987; Moufti et al. 2013a). The volcanic field consists of extensive lava fields (Murcia et al. 2014) and various types of volcanic cones and explosion craters (Camp et al. 1991; El Difrawy et al. 2013; Moufti and Hashad 2005; Moufti et al. 2011), each of them is perfectly exposed due to the arid climate and lack of vegetation, and many of them are relatively easy to access (Fig. 3.2). The field is located nearby one of the holiest cities of Islam—Al Madinah—and also hosts the youngest volcanoes in the Kingdom of Saudi Arabia, which have historical and cultural significance (Fig. 3.1). Harrat Al Madinah is the northern part of the Harrat Rahat and the best studied in the Harrat Rahat. The distinction between Harrat Rahat and Harrat Al Madinah is loosely constrained and it has a traditional and geographic connotation rather than geological reasoning. In a similar way, different parts of Harrat Rahat have local names that refer to nearby settlements or other geographical features.
Fig. 3.1

Overview map of Harrat Rahat on GoogleEarth image. Arrows outline the boundary of Harrat Rahat. Blue dot marks the 1256 AD historic eruption site near Al Madinah City

Fig. 3.2

General view of Harrat Rahat with cones and flow fields [24° 20′ 14.91″N; 39° 51′ 6.33″E]

In this chapter we will present a detailed summary of the geoheritage value of the geological features that form the backbone of the geoheritage of Harrat Rahat. The most extensive geoheritage research in Saudi Arabia has been undertaken in the Harrat Al Madinah in the northern part of Harrat Rahat, and that is the basis of a proposal to establish the Harrat Al Madinah Volcanic Geopark. As in other harrats in the Kingdom, the geoheritage research is rather fragmental so far; in subsequent chapters we will provide a brief summary of the geoheritage value associated with other harrats. In describing subsequent harrats we will refer heavily back to the identified geoheritage value of the Harrat Rahat, which will provide a firm scientific basis to justify the high geoheritage value of all the harrats of the Kingdom of Saudi Arabia. The harrats could thus be promoted as a continent-scale world heritage site on the basis of the universal value of observing and studying volcanism.

UNESCO promotes conservation of geological and geomorphological heritage through protection of world heritage sites and development of educational programs under the umbrella of geoparks (Dowling 2011; Farsani et al. 2011; Gordon 2012; Henriques et al. 2011; Joyce 2010). In this chapter we identify significant volcanic features that could be organized and promoted as the first geopark, the Al Madinah Volcanic Geopark in the Kingdom of Saudi Arabia (Moufti and Németh 2013a). The Harrat Al Madinah Volcanic Field has numerous volcanic geosites (Moufti and Németh 2013a b, c) relevant to broadening our understanding of the evolution of volcanic fields dominated by Hawaiian and Strombolian style volcanic cones and lava fields (Kereszturi and Németh 2012a, b).

The proposed geopark includes the location of the last historically erupted volcanoes in the Arabian Peninsula (Moufti and Németh 2013a; Moufti et al. 2013b). An historic eruption site in the proximity of Al Madinah City formed a chain of lava spatter and scoria cones formed in a 52 day-long eruption in 1256 AD (Fig. 3.3). This eruption site is located about just 10 km SE of modern Al Madinah city (Fig. 3.1). The violent eruption formed a ~2 km long NW-SE-aligned fissure that produced at least seven volcanic edifices with multiple vents that is now a globally unique volcanic landscape with easy access from a major city of Saudi Arabia. Any geoeducational and geoconservation program designed or proposed for this region in the future must take this location as the core of the project (Moufti and Németh 2013a, b, c).
Fig. 3.3

Overview of the 1256 AD eruption site from the SE [24° 20′ 35.04″N; 39° 46′ 38.49″E]

Harrat Rahat consists of excellent geotopes that illustrate fine details of explosive and effusive volcanism of monogenetic volcanic fields. Thus this is one of the most accessible places on Earth to see the geological context of the birth, evolution and erosion of lava spatter and scoria cone complexes and their associated lava flow fields.

Because Harrat Al Madinah is located so near to Al Madinah city the proposed geopark is easily accessible through highways (and by train in the near future) and it would provide significant economic benefit to Al Madinah city. The park could provide a cost-effective volcanic geoeducation program to pilgrims who are in the city visiting the holy sites.

Through the creation of a world network of natural parks with significant geological features, labelled UNESCO Geoparks, UNESCO promotes conservation of our geological heritage (Dowling 2011; Erfurt-Cooper 2011; Farsani et al. 2011; Joyce 2010). The first step in developing a geopark is to identify geotopes, geosites and geomorphosites which are the key geological features in a region that are easy to access, significant in the global geological sense and that could potentially serve as a basis for broader geoconservation projects (Deraman et al. 2010; Moufti et al. 2013c; Petrovic et al. 2013). Volcanic geoparks are increasingly popular projects worldwide and play a substantial role in geohazard education, including facilitating the dissemination of current research results on the volcanic processes that the ever increasing human society faces (Erfurt-Cooper 2011).

In addition, volcanic geoparks can serve as a geotouristic base that can generate significant economic benefit. Geosites, geomorphosites and geotopes are the smallest “units” of intact geological features that are identifiable through their uniqueness or because they are graphic examples of specific volcanic phenomena or form a vital landscape representative of a specific volcanic processes (Armiero et al. 2011; Erikstad 2013; Fassoulas et al. 2012).

Here we identify significant volcanic features that bear not only regional, but global, volcanic value in a confined area that could be organized and promoted as the first volcanic geopark in the Kingdom of Saudi Arabia: the Al Madinah Volcanic Geopark (Moufti and Németh 2013a). Harrat Al Madinah has many volcanic geosites including the last historically erupted volcanoes in Arabia (Camp and Roobol 1989). Overall, the proposed geopark would provide significant economic benefit to the nearby city of Al Madinah. Pilgrims arrive from every corner of the globe, including countries where volcanic hazard is an everyday aspect of life (e.g. Indonesia); therefore, the proposed geopark would serve as a significant geoeducational hot spot (Moufti and Németh 2013a, b, c).

A major geotope with distinct geosites/geomorphosites has been selected to demonstrate the diversity of volcanic phenomena associated with the intraplate volcanism of the Harrat Al Madinah. Hawaiian to Strombolian type eruptions created lava spatter and scoria cones (Kereszturi and Németh 2012a, b) visible from major highways, allowing visitors to stop near the AD 1256 historic eruption site just 10 km SE of Al Madinah (Fig. 3.4). The 52 day-long eruption formed a ~2 km long NW-SE-aligned fissure which emitted mainly a’a lava flows and lava spatter-dominated pyroclastic cones (Camp et al. 1987) (Fig. 3.5).
Fig. 3.4

The 1256 AD eruption site on a LiDAR image shows the complex nested scoria cone structure of the eruption site. Highway is in the bottom left corner of the image about 600 m from the foothill of the cone complex. The top left corner of the map view is about [24° 21′ 39.72″N; 39° 45′ 57.75″E]

Fig. 3.5

The 1256 AD eruption site fissure aligned nature obvious feature visible for an untrained eyes. View looking toward NW

At least seven vents have been identified, which made nested lava spatter cones (Camp et al. 1987; Murcia et al. 2013, 2014). The main central cones had more energetic explosive eruptive episodes that generated pyroclastic fall deposits, forming an ash-plain (Fig. 3.6) (Murcia et al. 2013). The vents are inferred to be hosted lava lakes and lava lake outbreaks initiated crater wall collapses, as traced on circular fissures along the crater margins (Murcia et al. 2014). The growth of the individual cones was repeatedly interrupted by lava flow outbreaks in the tip of the fissures by rafting away large pieces of the cones that were subsequently rehealed, resulting in a nested and complex volcano morphology (Murcia et al. 2014). The geotopes form the 1256 AD eruption sites as part of the Northern Harrat Rahat (or Harrat Al Madinah) is probably the best exposed and accessible site on Earth to show the diversity of volcanic features a fissure-eruption can produce (Moufti and Németh 2013a).
Fig. 3.6

Ash plain around the 1256 AD cones. View is looking toward the 1256 AD cones in the background from the point of about [24° 20′ 37.33″N; 39° 46′ 54.83″E]

The recent increased seismic activity in 2009 in the region just north of Harrat Rahat in the Harrat Lunayyir region (Duncan and Al-Amri 2013; Hansen et al. 2013; Mukhopadhyay et al. 2013; Pallister et al. 2010; Zahran et al. 2009; Zobin et al. 2013), also justifies the establishment of an educational site that could play a significant role in the dissemination of scientific knowledge to the public, which could help the population better understand the potential outcome of any volcanic unrest the region may face (Moufti and Németh 2013a; Moufti et al. 2013b, c, d and e).

An historic review of seismic and volcanic events in the Arabian Peninsula, based on English translations of original documents, reveals that an earthquake occurred in 641 AD that destroyed houses in Al-Madinah (Ambraseys et al. 1994). It has been suggested that this earthquake is linked with a volcanic event outside of Harrat Rahat that occurred a year before, in 640 AD (Ambraseys et al. 1994). The location of this event is generally accepted to be a chain of four small cones west of Al-Madinah City (Camp and Roobol 1989), but on further examination the evidence justifying these four cones as the site of the 641 AD eruption is lacking (Moufti et al. 2013b). This volcanic event is associated with one or both of the following eruptions mentioned in historic records and occurred near to Tabuk (about 300 km NW of Al-Madinah City): the Hala’l-‘Ishqa (27.58° N, 36.80° E) and/or Hala’l-Badr (27.25° N–37.20° E) (Ambraseys et al. 1994) in the Harrat Uwayrid (Fig. 3.1). Indeed there are young volcanic landforms located in this region judging from their morphological appearance but their historic age is questionable.

Camp and Roobol (1989) report references to a volcanic eruption in 641 AD located in the vicinity of Al Madinah that were reported in the manuscript of “Khulasaf Al-Wafa” which was written in 1568 AD by Nour Al-Dian B. Al-Samhoudy, commonly identified as the historian of Al-Madinah. Interestingly, Camp and Roobol (1989) agree with a report connecting this event to a volcanic eruption in 641 AD associated with a specific harrat called Harrat Layla (Simkin and Siebert 1994). Confusingly, Harrat Layla has been mentioned as the location of a fire (eruption?) in 640 AD—not in 641 AD—to where Umar, the ruler of Al-Madinah, ordered a man to go out, but in the meantime the “fire” was gone (Juynboll 1989a, b), suggesting a short-lived event at a distance from Al Madinah that could have been travelled in a single day (e.g. <100 km). As a conclusion, the eruption of 641 AD and its location are poorly constrained; however there is no doubt that the four small scoria cones that are located about 13 km to the SW from the Holy Mosque are very young cones (Fig. 3.7). These cones are the likely locations of a young volcanic event that could be the result of the 641 AD eruption (Moufti et al. 2013b).
Fig. 3.7

641 AD cones on GoogleEarth satellite image [24° 24′ 42.82″N; 39° 29′ 50.98″E]

3.2 Volcano Types and the Geoheritage Value of the Harrat Rahat

Harrat Rahat is one of the most diverse volcanic regions of the Arabian Peninsula in respect of the presence of well-preserved, young volcanic landforms and their eruptive products. While the Harrat Rahat is viewed as an intracontinental volcanic field with numerous monogenetic (short lived and small volume) volcanoes, its volcanological diversity is far greater from that. The most extensive volcanic features of the region are the various types of lava fields (Murcia et al. 2014). Many of the lava fields are associated clearly with point sources such as scoria and/or spatter cones or they have emerged along fissures defined by some sort of lineaments of relatively small size of cones. The majority of the lava flows are partially confined forming narrow branches of flows following gentle sloping low rimmed valleys (Fig. 3.8) (Murcia et al. 2014). It seems that the lava flow distribution has been strongly controlled by the landscape inundated by successive flow units gradually shifting younger flows side by side. As a result, a characteristic flow pattern can be seen in many places, where older lava flows acted as obstacles for younger flows, especially in the northern side of the Harrat Rahat. Lava flows that outpoured along north to south aligned fissures tend to form distinct lava lobes from the north to south trending dorsal ridge of the Harrat Rahat.
Fig. 3.8

Confined lava flows occupy narrow valley systems in the Northern Harrat Rahat [24° 22′ 38.38″N; 39° 55′ 37.12″E]

The majority of the lava flows fields are transitional types, representing surface textures carry features typical of aa lavas that composed of pieces of broken partially developed cooling lava crusts (Fig. 3.9), commonly defined as rubbly or slabby pahoehoe (Murcia et al. 2014) similar to those flow fields documented in Cameroon (Suh et al. 2011; Wantim et al. 2011), Deccan in India (Bondre and Hart 2008; Duraiswami et al. 2003, 2014) or in Krafla in Iceland (Rossi 1997). The lava fields commonly engulf obstacles such as pre-flow cones (Fig. 3.10). In medial to distal areas, the lava flow fields are commonly littered by pieces of rafted cone material as a sign that the flows might have either emitted in a time when their source cone gradually collapsed or the flow itself bulldozed through pre-existing older cones (Németh et al. 2011; Riggs and Duffield 2008).
Fig. 3.9

Slabby pahoehoe in Harrat Rahat [24° 25′ 5.73″N; 39° 51′ 4.40″E]

Fig. 3.10

Engulfed pre-flow cone in the Northern Harrat Rahat [24° 22′ 36.68″N; 39° 49′ 26.03″E]

The most common types of volcanic edifices in the Harrat Rahat are the scoria cones and spatter cones. While no systematic study has been done on their morphometric parameters some preliminary study documented that their parameters range from the full spectrum of sizes known from such cones on Earth (Kereszturi and Németh 2012a, b). There are a large number of relatively small lava spatter cones closely resembling large hornitos (Wentworth and Macdonald 1953) many of them with very steep slope angles (Fig. 3.11) (Moufti et al. 2013e).
Fig. 3.11

Small and steep lava spatter cone in the volcanic chain of the 1256 AD eruption site in Northern Harrat Rahat [24° 20′ 43.06″N; 39° 46′ 32.13″E]

On the other hand, very large scoria cones are known mostly from the dorsal zone of the Harrat Rahat (Fig. 3.12), that are closely resembling small stratovolcanoes with complex pyroclastic stratigraphy, suggesting their longer activity and larger eruptive volumes as a scoria cone generally considered for (Kereszturi and Németh 2012a, b). In this respect the larger scoria cones are better to view as long lived, small-to-medium sized stratovolcanoes, similar in eruption style and size as the active Cerro Negro in Nicaragua (Hill et al. 1998; McKnight and Williams 1997; Roggensack et al. 1997). In general the majority of the scoria cones of Harrat Rahat are dominated by pyroclastic deposits and demonstrate evidence of intense heat effect, agglutination, welding and accumulation of pyroclasts typical of eruption through vigorous lava fountain events. In many cases, the cones have well-preserved crater rims composed of welded pyroclasts (Fig. 3.13). These features together indicate that the eruptions must have been dominated by lava fountaining that produced spatter-like pyroclasts agglutinated and welded together upon landing (Head and Wilson 1989; Kereszturi and Németh 2012a, b; Martin and Németh 2006; Sumner et al. 2005). As a consequence of such eruption mechanism, the Harrat Rahat scoria cones are commonly associated with clastogenic lava flows that form upon heat retention of landed pyroclasts that then melt together and form a new melt on the proximal areas of the cones. Harrat Rahat is rich in such volcanic features and that makes the field special in this respect. In some occasions the cones show evidences of lateral spreading as a response to the high heat in their proximal areas and the underlying melt that can function as a lubricant to be able to displace large sectors of cones (Fig. 3.14). Cone rafting is also prominent volcano-morphological features in the field (Fig. 3.15) and it has been commonly accompanied with explosive ash-emitting eruptions that then partially covered the still moving lava flows gradually displaced part of individual cones (Murcia et al. 2013; Riggs and Duffield 2008).
Fig. 3.12

Large scoria cone with complex stratigraphy potentially represents an eruption site that was active over prolonged time and better to view it as a polygenetic small-volume stratovolcano [24° 21′ 16.13″N; 39° 48′ 49.43″E]

Fig. 3.13

Lava spatter dominated cone with characteristic “collar” in the lip of its crater as a sign of strong welding that preserved the crater rim [24° 11′ 43.74″N; 39° 52′ 51.14″E]

Fig. 3.14

Collapsing cone of Mosawdah [24° 14′ 13.30″N; 39° 47′ 48.74″E]

Fig. 3.15

An older rafted scoria cone near the young Al Anahi scoria cone and lava flow field [24° 16′ 38.54″N; 39° 46′ 6.11″E]

3.3 Volcanic Precinct Concept and Its Benefits

The proposed Harat Al Madinah Volcanic Geopark (HAMVG) (Fig. 3.16) is based on a holistic geoeducation and geoconservation philosophy in order to demonstrate the diversity of volcanism associated with the evolution of long-lived monogenetic volcanic fields in intra-continental regions (Moufti and Németh 2013a). It has been suggested that volcanic features that would form the core of the geoheritage value of the Harrat Rahat should be arranged into a hierarchical system based on the systematic evaluation of each of the geoheritage sites selected on the basis of their value (Moufti and Németh 2013a). Such a system of the volcanic features and landforms preserved in the territory of the proposed HAMVG could emphasize the scientific (geological—volcanological) entity, the level of importance, and the conditions of access to those sites (Moufti and Németh 2013a). This system therefore would be able to offer a self-explanatory guide for end-users to develop alternative geoeducational programs that are easily linked to specific geological-volcanological topics the designed system can offer (Moufti and Németh 2013a).
Fig. 3.16

Volcanic “precinct” regions as the core of the provisional volcanic geopark of Al Madinah in the Harrat Rahat

Geological (and/or geomorphological) sites have just been started to be catalogued in Saudi Arabia with various level of success and/or detail following the geosite (geomorphosites), geotope and geopark concept that has been successfully used elsewhere (Fuertes-Gutierrez and Fernandez-Martinez 2012; Kazancı 2012; Pulido Fernandez et al. 2014; Vujičić et al. 2011). Recently initiated projects in the Kingdom of Saudi Arabia have identified and documented many volcanic geosites that are significant in their context, such as significant in comparison to the host volcanic region where they are located, as well as carrying value that make them internationally important volcanic features to contribute to the global understanding of specific volcanic processes.

Initially an attempt was pursued to establish the first geopark with a volcanic theme near the culturally important region of Al Madinah city (Moufti and Németh 2013a, b and c). An idea to establish a geopark near Al Madinah was argued on the basis of the high scientific, aesthetic and economic potential the volcanic regions near Al Madinah can carry. A proposal is in consideration currently to evaluate the feasibility to go ahead with focused work to establish such geoparks.

Here we provide the geological and geographical scientific information to provide enough background to show that the region is suitable to develop a volcanic geopark. The scientific research recently intensified on understanding dispersed volcanic systems along the western margin of the Arabian Peninsula that brought a new global interest to explore the volcanic fields abundant in this region (El Difrawy et al. 2013; Murcia et al. 2014; Runge et al. 2014; Wahab et al. 2014; Zobin et al. 2013) many of them was triggered by recent seismic unrest likely been caused by dyke intrusions to a very shallow level of the crust (Baer and Hamiel 2010; Duncan and Al-Amri 2013; Koulakov et al. 2014; Mukhopadhyay et al. 2013; Pallister et al. 2010). The fact that Harrat Rahat also host one of the youngest eruption sites (1256 AD) that are exceptionally well-preserved and located nearby Al Madinah city justify clearly that with the abundance of scientific research that can offer a well-designed volcanic geological model a geopark concept can be developed and distinguish these volcanic areas significantly from others on the global scale while can be linked easily to other similar fields elsewhere in the globe along their scientific as well as landscape aesthetic and accessibility value (Moufti and Németh 2013a).

The above outlined logical set naturally offer that in a large area such as any of the harrats in western Saudi Arabia, particularly the Harrat Rahat, the best way to follow some sort of “precinct” concept to link geoheritage sites along their common geoeducational value, and of course their geographical locations (Moufti and Németh 2013a). The “precinct” concept naturally groups together the main and most representative volcanic features (including landforms and associated geotopes) to form at least three distinct precincts as the basis of a proposed volcanic geopark (Moufti and Németh 2013a). The HAMVG’s volcanic landforms naturally offer a three-layered precinct hierarchy with an additional extra level which could be linked to more adventure style geotourism as the site located far from the others and can offer a true remote arid region experience to anyone who would visit those locations, in spite that geologically it is not offering anything significantly different than the other precinct (Fig. 3.16). The precinct concept has been applied to geoeducational programs as the core of a geopark concept in other regions, such as the Kanawinka Geopark in southern Australia and Victoria ( In comparison to the Kanawinka Geopark’s precincts, the proposed HAMVG’s precincts are not only thematically but also geographically well-separated, allowing distinct geotourism projects to be designed around them (Moufti and Németh 2013a).

3.4 Volcanic Precincts Versus Volcanic Heritage Routes

Volcanic precinct are favoured against volcanic heritage route design in the case of the Saudi Arabian harrats. Volcanic precincts can offer more than a linear path to explore geoheritage sites along a well-designed route. A precincts can group geosites that are by some reason can be associated with similar geological or geomorphological concept, information or state of research and therefore can be used to target specific audience to visit that sites. In case of the Al Madinah region, the volcanic precincts follow an order that link to the level of adventure tourism needed to explore the grouped geosites with the level of complexity of the volcanological knowledge that could be achieved by a visitor just by completing the specific precinct tours. Near Al Madinah, the 3 + 1 precinct is designed to follow a natural logical path (Fig. 3.16).

Precinct 1 is all about the historic volcanic eruptions that affected the life of the people in the region in the past several centuries, and also had some influence on the cultural development of the region (Fig. 3.16). These sites are easy to access, they are well-preserved, and together they can provide a very good introduction to understanding volcanic processes.

Precinct 2 would involve a little bit longer trip to complete and offers a more detailed understanding of the type of volcanic eruption most common among the harrats, lava spatter cones and extensive lava flows.

In Precinct 3 visitors explore unusual volcano types that formed lava domes, explosion craters, and even produced pyroclastic flows that covered vast areas in the central part of Harrat Rahat, visible on a satellite image (Fig. 3.17). Visiting the selected geosites in Precinct 3 will provide anadventurous geotouristic experience, including evidence to demonstrate the destructive force of explosive volcanism.
Fig. 3.17

Satellite image in the Precinct 3 showing visually different (light coloured) regions in the central part of Harrat Rahat. The top left corner of the map view is about [24° 14′ 46.07″N; 39° 39′ 48.11″E]

Precinct 4 is a more adventurous version of Precinct 3, offered as an alternative for those visitors eager for adventure tourism. The geosites of this precinct are deep inside the interior of Harrat Rahat, and to visit them requires preparation and experience.

Harrat Rahat is appropriate for developing geoeducational and geotouristic projects arranged in precincts rather than in geoheritage routes. Within the precincts, geosites are arranged along routes that link geosites with specific geological value.

3.5 Lava Flow Features and Their Geoheritage Value for Understanding Lava Flow Field Evolution

Harrat Rahat is probably the most accessible harrat in the Kingdom of Saudi Arabia and it is home of a great diversity of lava flow morphotypes (Murcia et al. 2014). The arid climate and the relatively easy access of many of the sites can allow visitors to see most of the lava flow surface textures in their pristine status. The arid climate offers well-preserved lava flow surface textures to be seen. Especially nearby Al Madinah city the extensive road network that are linked to dirt roads across the harrat form an ideal logistic set to select specific lava surface sites to promote and include in various precincts to be listed as key geosites.

The phrase “lava morphotype” refers to the characteristics of the surface morphology of any lava flow after solidification. The lava flow surface morphotypes carry significant information on the cooling history, rheology and the dynamics of the lava flow during its molten stage (Anderson et al. 2012; Duraiswami et al. 2014; Njome et al. 2008; Solana 2012; Suh et al. 2011; Woodcock and Harris 2006). In the Kingdom of Saudi Arabia, young and well-preserved mafic lava fields display a wide range of these morphotypes (Murcia et al. 2014).

At Harrat Rahat a framework of lava surface morphotypes for describing changes in morphotypes down-flow has been proposed (Murcia et al. 2014). The gradual changes of lava surface morphotypes can be traced very clearly along the 23 km long 1256 AD historic lava flows (Fig.  3.18). The changes over distance provide an important scaling aspect for the visitor to appreciate the lava flow emplacement mechanism. The abundance of small-volume and short lava flows can also be used to develop geoeducational projects to demonstrate the variability and the unique nature of a silicate melt to flow on the Earth surface.
Fig. 3.18

Lava surface morphotype change across the 1256 AD lava flow main axis [24° 23′ 2.38″N; 39° 46′ 13.77″E]

Implications of demonstrating the variety of lava flow surface textures through a well-designed geoeducation program can contribute significantly into the volcanic hazard education of the local population. The lava fields of the recently proposed Al-Madinah Volcanic Geopark, and other harrats are commonly mentioned as continental flood basalts or large igneous provinces (White et al. 2009) and they carry important geoeducational value (Fig. 3.19).
Fig. 3.19

Lava surface texture changes in proximal areas through cascading lava flows (dark centre of the flow) over steep slopes [24° 21′ 5.00″N; 39° 46′ 31.09″E]

Overall, the Harrat Rahat lava flow fields extend up to 23 km from the source, and vary between 1–2 and 12 m in lava flow thickness (Murcia et al. 2014). The lava flow fields cover areas between ~32 and ~61 km2, with individual volumes estimated between ~0.085 and ~0.29 km3 (Murcia et al. 2014). The lava flow surface textures exhibit shelly-, slabby-, and rubbly-pahoehoe, platy-, cauliflower-, and rubbly-a’a, and blocky morphotypes roughly in this order to downflow (Murcia et al. 2014). The specific lava flow surface textures are linked to both intrinsic (i.e. composition, temperature, crystallinity and volatile-content/vesicularity) and extrinsic (i.e. emission mechanism, effusion rate, topography and flow velocity) emplacement parameters and their changes over distances (Murcia et al. 2014). In many places along the 1256 AD lava flow one morphotype transitions to another in individual flow-units or lobes and that they dominate zones (Murcia et al. 2014).

Pahoehoe morphotypes (Fig.  3.20) are more related to the simple mechanical disaggregation of the solidified crust over an inflating lava flow body that under mechanical stress gradually disaggregating and carried away by the moving mass (Murcia et al. 2014). A’a morphotypes in the contrary are related to the transitional emergence and posterior fading of clinker, and blocky morphotype to fracturing and auto-brecciation. a’a morphotypes (i.e. platy-, cauliflower-, rubbly-a’a) are those that dominate the lava flow field surfaces in northern Harrat Rahat, which suggests that core-dominated flows were predominant during flow movement (Murcia et al. 2014). Lava structures may be related to some morphotypes once they were well-developed and they are well-preserved. In particular, down-flow changes exhibit key illustrative and easy recognizable features in the lava flow fields and might provide insights into real-time monitoring of future flows in this region. From geoeducational point of view Harrat Rahat offers probably the most accessible and the greatest diversity of lava flow types, and therefore these flow fields can help to show evidence and consequences of potential lava flow eruption event in the future.
Fig. 3.20

Pahoehoe lava surface morpfotype [24° 21′ 8.66″N; 39° 46′ 32.74″E]

3.6 Volcanic Cones and Their Geoheritage Value

Volcanic cones are abundant in the territory of Harrat Rahat and they range from a very small (~10 m high) to cones that are over 100 m above their surroundings. Cone morphology reflects some degree of their age, and potentially could be used for relative age datings such as it has been suggested and trialled elsewhere (Porter 1972; Settle 1979; Wood 1980a, b). Relative age dating of the volcanic cones based on cone morphometry is, however, in arid climate might not work in a way how early studies predicted as the cone geometry modification is a very slow process and cones can appear in a very youthful appearance after significant time as demonstrated in many scoria cone fields (Kereszturi and Németh 2012a, b).

Erosion of scoria cones show a great variety of trends that are commonly linked to relative age (Doniz-Paez 2015; Fornaciai et al. 2012; Inbar et al. 2011; Inbar and Risso 2001; Kervyn et al. 2012) (Porter 1972; Settle 1979; Wood 1980a, b; Hooper and Sheridan 1998; Doniz et al. 2008; Inbar et al. 2011; Fornaciai et al. 2012), but recent studies also show that especially in cases when cones are dominated by lava fountain-fed spatter eruptions, the cone erosion, and cone geometry-modification more commonly linked to the cone genetic history or the substrate morphology than to the time passed since its eruption (Favalli et al. 2009; Kereszturi et al. 2013; Kereszturi and Németh 2012a, b). While scoria cones in Harrat Rahat show a great variety of erosional stages, e.g. common gully formation on their flank, the majority of the cones are easy to recognize and they are spectacular (Fig. 3.21). Young cones are relatively smooth surfaced and their craters have no aeolian dust infill. Their craters are rarely breached however crater breaching across the central part of the Harrat Rahat is common as response to the edifice instability caused by the extensive lava flow outpouring in their flank region.
Fig. 3.21

Typical, moderately erosion modified large scoria cone in the Harrat Rahat [24° 23′ 0.45″N; 39° 49′ 59.20″E]

While the youngest scoria cones are easy to recognize in the field and in satellite imagery, to use their morphometry parameters for relative age dating can be misleading and likely cannot provide high resolution of ages to be able to distinguish even a Pleistocene cone from a Holocene one. An excellent example is the 641 AD four cones just SW of Al Madinah city. The four cones are only inferred to be the eruption sites of the 641 AD historical eruption however their morphology cannot be distinguished from other Pleistocene to Holocene cones. This problem is partially due to the fact that this cones are dominated by lava spatter eruption, similar to many other cones in the Harrat Rahat, that formed collar-like spatter ramparts in their crater rim, that acted as a preventing shield in top of the cones, lowering significantly the erosion speed, and change the style of erosion as predicted in recent studies (Kereszturi and Németh 2012a, b).

3.7 Lava Domes and Explosion Craters as the Results of the Potentially Most Hazardous Volcanism in the Region

Results of silicic volcanism are clearly visible as spectacular volcanic landforms in three of the harrats in Saudi Arabia; in Harrat Rahat (Moufti and Németh 2013a), Harrat Khayber (Moufti and Nemeth 2014) and Harrat Kishb (Moufti et al. 2013c). Harrat Rahat however is the location where these volcanic features are relatively young, about 0.3 to 0.7 Ma (Camp and Roobol 1989; Moufti et al. 2012), therefore well-preserved and in addition they can be accessed through dirt roads by a relatively short highway drive out of Al Madinah city. The centrally located position of these silicic volcanoes can provide a great opportunity to both adventure and eco-tourism as the sites are remote and commonly provide unique landscape forms with unique ecosystems (Fig. 3.22).
Fig. 3.22

Matan lava dome complex is a unique geotop [24° 13′ 26.43″N; 39° 50′ 22.23″E]

The central part of the Harrat Rahat is covered by various silicic (mostly trachytic) pyroclastic deposits forming an extensive ash plain landscape that are surrounded by steep and high lava domes. The lava domes are interestingly commonly associated with older scoria cones and it seems they erupted through pre-existing volcanic landforms. Their composition ranges from mugearite through benmoreite to trachyte (Camp and Roobol 1989).

The volcanic landforms are diverse, and can be seen simple lava domes, lava dome complexes, and lava dome complexes associated with explosion craters commonly deep as over 100 m (Fig. 3.23). The presence of the silicic eruptive centers carries a significant volcanic hazard aspects putting the Harrat Rahat among those volcanic regions where violent explosive eruptions and associated lava dome formation was far more common as it is considered, and in spite of the relative older age of these sites, such future eruptions cannot be excluded. In this respect to develop a geoeducational program around the silicic eruption centers of Harrat Rahat bears a very important aspect of the proposed Al Madinah Volcanic Geopark design. The sites are not only exotic, exciting and visually outstanding, but also offer a different angle to demonstrate the volcanic eruption styles formed the landscape at Harrat Rahat.
Fig. 3.23

Typical explosion crater of the Gura 2 in the central region of the Harrat Rahat [24° 12′ 22.95″N; 24° 12′ 22.95″N]

From the scientific perspective, the common presence of small to medium volume silicic lava domes in a volcanic field suggests that some degree of crustal storage network must exist beneath the Harrat Rahat to form chemically evolved magmas in spite of the general dispersed, volcanic field-forming nature of the volcanism. The relatively small-volume and simple architecture of the lava domes of Harrat Rahat makes them different from those lava domes commonly associated with major central (composite and strato-volcano or caldera) volcanoes such as Merapi, Indonesia (Abdurachman et al. 2000), Unzen, Japan (Fujii and Nakada 1999) or Soufriere Hills in Montserrat (Bourdier and Abdurachman 2001; Carn et al. 2004). The lava domes of Harrat Rahat are single, individual sites that were probably grown over decades, but their eruption was likely controlled by a single or low number of eruptive phases that make them closer relationship with typical monogenetic volcanoes than to those complex and long-lived lava domes commonly developed on top of major long-lived polygenetic volcanoes. In this respect, Harrat Rahat’s lava domes can offer a unique opportunity for scientific research to understand how dispersed lava dome field evolve, and how they contribute to the geological record of volcanic fields.

The silicic lava domes of Harrat Rahat are similar to those lava dome fields documented in association with dispersed small-volume volcanic fields such as those in Central Mexico (Blatter et al. 2001; Guilbaud et al. 2012; Hasenaka 1994; Hasenaka and Carmichael 1985; Riggs and Carrasco-Nunez 2004) or in SW US (Riggs et al. 1997). Similar dispersed lava dome fields have been documented across the Miocene to Pleistocene Carpathian Volcanic Arc (Lexa et al. 2010) that highlight the significance of such small volume lava dome systems in regard to understanding their origin as part of a dispersed volcanic region or volcanic field. In scientific perspective the lava domes of Harrat Rahat are significant features, and can offer key sites to study lava dome formation, their geomorphological evolution and their effect on the surrounding regions through block-and-ash flow eruptions.

In addition to lava domes the Harrat Rahat also host numerous explosion craters (Fig. 3.23). These craters are diverse in their size (crater diameter and depth) and exclusively located in the central part of the field. In the crater wall of these craters commonly half section of older silicic lava domes are exposed indicating some link between lava dome growth and sudden disruption and crater formation. The smallest craters are surrounded by coarse pyroclastic breccias inferred to be explosion breccias. These deposits are rich in accidental lithic fragments and deep crustal origin xenoliths. The juvenile pyroclast content of these pyroclastic rocks are relatively low. The juvenile pyroclasts are low vesicular microlite-rich rocks indicating potential magma-water explosive eruptions as a cause of their fragmentation.

In larger craters such evidence to support potential magma and water explosive interaction is less clear, and the deposits surrounding the craters are more typical block-and-ash flow deposits typical for moderate run-out distance pyroclastic flows. In this respect Harrat Rahat’s explosion craters can be classified as small maar volcanoes to more typical broad craters with even moderate caldera collapse features in their summit. The important aspect of these explosion craters beside the gradual trend from phreatomagmatic to magmatic explosive types of eruption as a driving force to their formation is, that even the largest and most complex craters are relatively simple in comparison to a long-lived silicic volcano. This fact again offer a unique scientific background to establish a scientifically well-established geoeducation program to demonstrate the full spectrum of eruption styles and volcano types associated with a predominantly dispersed, volcanic field building volcanic system such as Harrat Rahat.

3.8 Organisation of Precincts of the Proposed Harrat Al Madinah Volcanic Geopark (HAMVG)

The HAMVG three precincts (Fig. 3.16) are proposed as based on their scientific aspects, level of exposures, geoeducational value and logistical aspects (Moufti and Németh 2013a):
Precinct 1

Historic Eruption Precinct—1256 AD and 641 AD Historic Eruption Sites;

Precinct 2

Lava Lakes, Lava Fountains and Volcano Spreading Precinct—The Mosawdah Volcano and

Precinct 3

From Silicic Lava Domes to Explosion Craters Precinct.

Precinct 4

An additional Precinct has been outlined as an alternative or extension of the Precinct 3 to provide a stronger adventure touristic aspect to fundamentally the same geological processes Precinct 3 can demonstrate.

Precinct 1 groups volcanic features and associated geoeducational and geotourism programs that demonstrate the eruption sites that have been historically documented and are probably the most relevant to the inhabitants of Al Madinha city. The key to establish this precinct is the direct relevance of the demonstrated volcanic features to the life of the locals. This precinct hosts numerous geosites dealing with extensive transitional pahoehoe-to-aa lava fields with world-class examples of lava flow surface textures, lava spatter and scoria cone (Murcia et al. 2014).

Precinct 2 can be viewed as an expansion of the first, offering the visitor a more in-depth understanding of the type of volcanism very common in the Harrat Al Madinah. Precinct 2 is centered around the main volcanic geotope, the Mosawdah Volcano and its lava flows, and its numerous geosites that provide superb examples to understand the life of a highly active effusive volcano that formed lava fountaining. As a result the volcano under its own erupted hot material gradually collapsed and signs of the edifice spreading and collapse are evident. It is more difficult to access the geosites of Mosawdah volcano than the geosites of Precinct 1 and therefore it would involve some “adventure tourism” style trip which makes this precinct available only to those visitors who wish to go deeper into understanding volcanic processes. Precinct 1 and 2 fundamentally cover the majority of the volcanic features that can be located in the Al Madinah Volcanic Field (Moufti and Németh 2013a).

Precinct 3 offers the most adventurous trips for visitors and some unique additions to understanding the full spectrum of volcanic processes in the AMVF. Precinct 3 volcanic features deal with silica-rich volcanism that formed various lava domes (e.g. trachytic), as well as deep explosion craters, many of them at least in their initial phase were formed due to magma and ground-water explosive interaction. Precinct 3 is located far from Al Madinah city, and only well-equipped geotourists with trained guides can visit the sites. While the volcanic features in Precinct 3 can be seen to have a very high aesthetic and scientific value, they are rather an extra addition to the full picture of the volcanism of the AMVF, than something without which the visitor would get a distorted image of the field. However, those who decide to invest energy to visit Precinct 3 would be well rewarded by a truly dramatic volcanic landscape. Precinct 3 could be expanded toward the south (provisional Precinct 4) as an alternative geoheritage site, where a great variety of pyroclastic flow deposits and associated volcanic craters can be visited. These sites have a very unique landscape value. However, visits to these sites can only be done by well-prepared adventure tours.

3.9 Precinct 1—Historic Volcanic Eruption Sites

The largest historic eruption at 1256-AD that lasted ~52 days produced about minimum 0.29 km3 lava forming a maximum of ~23-km long and 8-m thick flow field (Murcia et al. 2014). This complex semi-confined to unconfined lava field is dominated by transitional flow textures typical for fast moving, open channel lava. Gradual transition from a shelly-, slabby-, and rubbly-pahoehoe, toward platy-, cauliflower-, and rubbly-a’a, reflects lava flow rheology changes (Murcia et al. 2014). The resimulation of the 1256-AD flow with MAGFLOW code (Bilotta et al. 2012; Cappello et al. 2011; Del Negro et al. 2008; Herault et al. 2009) suggests also a complex flow evolution, including late stage ponding of lava around the emission points (Nemeth et al. 2013). Flow inflation/deflation features such as lava rises, tumuli, lava blisters, pressure ridges and evidences of cone rafting are common in proximal areas (Camp et al. 1987; Nemeth et al. 2013). The cones of the 1256-AD eruption are dominated by flattened lava spatter, ash, lapilli with Pelee’s hair and tears, and reticulate suggesting lava fountain-dominated eruptions as well as Strombolian style explosive eruptions (Murcia et al. 2013). Textural features are common for lava lake level fluctuations and lava outbreaks inferred to cause edifice spreading (Nemeth et al. 2013). Other historic eruption took place in 641-AD forming four small cones—recently named as Al-Du’aythah volcanic cones (Murcia et al. 2015)—aligned in NNW–SSE in the western edge of Al-Madinah City (Moufti et al. 2013b). Three out of the four cones has basal phreatomagmatic deposits indicating initial phreatomagmatic explosions (Moufti et al. 2013b; Murcia et al. 2015). This is the only location in the younger (<10,000 years) eruptive centers in the northern Harrat Rahat where evidences of phreatomagmatism are known (Murcia et al. 2015). The 641-AD cones’ upper sequences inferred to be produced by typical lava fountain and moderate Strombolian style explosive eruptions that produced small clastogenic flows reaching less than 300 m from their source (Murcia et al. 2015).

While lava spatter and scoria cones are among the most common volcanic landforms on Earth (Németh 2010; Valentine and Gregg 2008; Vespermann and Schmincke 2000), to see perfectly exposed and unmodified landforms is becoming increasingly difficult because they are either remotely located, have suffered from significant anthropogenic modifications or they are in areas where the vegetation cover inhibits views of the original landscapes. The Precinct 1 “Historic Eruption Precinct1256 AD and 641 AD Historic Eruption Sites precinct” of the proposed HAMVG comprises volcanic landforms that are well exposed, easy to access and record a unique volcanic process associated with a sustained fissure-fed volcanic eruption, considered to be one of the last major volcanic eruption in the Arabian Peninsula (not counting on those volcanoes erupted recently in the axis of the Red Sea (Xu and Jonsson 2014). Volcanic phenomena represented in this precinct include the results of prolonged lava fountain fed eruptions, such as cone rafting and associated lava lake infill and drain-back, as well as lava flow outbreaks at various points on the fissure-axis edges of the developed volcanic cones. The variety of volcanic features associated with lava fountain type volcanic eruptions is great and ranges from identification of traces of lava-lake level fluctuations in the inner crater walls and clastogenic (rootless) lava flow formation through rapid accumulation of lava spatter in the inner and proximal outer flank of the volcanic cones, to rock records that document fully developed and established volcanic conduit conditions promoted by Strombolian style magmatic gas bubble outburst-driven explosive dispersal of pyroclasts, forming extensive tephra blankets (Hintz and Valentine 2012; Keating et al. 2008; Valentine 2012; Valentine and Gregg 2008; Valentine et al. 2007).

The 1256 AD eruption site with its complex cones along a 2.3 km long fissure form a complete volcanic geotope (Moufti and Németh 2013a; Moufti et al. 2013d and e; Murcia et al. 2013), therefore, it is a significant educational site, where visitors can learn about the complexity of magmatic effusive and explosive eruption styles that may occur along a long lived and evolving fissure, the interaction between effusive and explosive stages of eruptions, as well as the link between changes of eruptive rate and the resulting volcanic landform (and landscape), and the dynamic processes that may take place in volcanic craters. The proximity and easy access to the Precinct 1 “Historic Eruption Precinct1256 AD and 641 AD Historic Eruption Sites” to the Al Madinah city, coupled with the young age of the eruptions and the historical documentation, make this site the perfect location to provide eye-opening evidence of the style of eruptions the region may face in the future.

3.9.1 Geotope of the 1256 AD Historic Eruption Site and Its Lava Flows

The 1256 AD eruption produced Hawaiian and Strombolian style volcanic activity through a ~2.2 km long fissure that created seven individual and nested volcanic cones (Fig. 3.24). The individual cones are aligned along the fissure and some are partially destroyed. The smallest cone is less than 0.1 km wide and 10 m high, while the biggest cone is 0.7 km wide and 90 m high. The smallest cones are typical lava spatter cones with steep flanks and agglutinated and welded banks of spatter and clastogenic flow lobes (Moufti et al. 2013e).
Fig. 3.24

Overview of the 1256 AD eruption site looking from the NW

The 1256 AD eruption site is a perfect geotope in the sense of its geological heritage. It is composed of individual volcanic cones erupted in similar style and produced overlapping pyroclastic rock units as well as multiple lava flows. The link between individual geosites are along the fact that they have been produced by similar geological processes slightly differs from each other as the controlling parameters for each eruption was a little bit different. As a result, it is very clear to define the boundary of the geological feature (as the cones along the fissure), easy to link them together along a common geological process (the Hawaiian to Strombolian style eruptions), they are easy to distinguish from other parts of the volcanic field, e.g. they form the volcanic edifices and their proximal areas, that are different geologically then the inter-cone regions where extensive ash plain formed from pyroclastic falls (tephras).

This distinction and separation of these volcanic landforms from others also logical and scientifically valid as they follow the boundary between the volcanic edifice and the surrounding volcanic ring plains and their deposits as it has been outlined in many other areas and many other type of volcanoes (Kereszturi and Németh 2012a, b; Manville et al. 2009; White 1989, 1990, 1991). The 1256 AD eruption site as a geotope offers a great variety of geoeducational sites to be presented. The individual geosites were identified on the basis of their scientific information they can provide, their preservation potential and attractiveness for both professional and general audience.

Pyroclasts that were ejected beyond the 1256 AD cone’s (medial-to-distal pyroclastic succession), forming a tephra cover composed of angular-to-plastically shaped pyroclasts including Pele’s tears, hair and basaltic reticulate (Kawabata et al. 2015; Nemeth et al. 2013). Recent study of the distribution pattern of the ash plain around the cones reviled that the eruptions that produced the pyroclastic fall fed from multiple eruption plumes each representing individual eruption phases (Kawabata et al. 2015). In proximal areas such tephra sections are particularly well-exposed and can offer great geosites to define where visitors can see that even predominantly effusive and mild explosive eruption-dominated volcanoes such as the 1256 AD eruption sites can be associated with extensive tephra fall-producing eruptions. Such researches are recently been conducted in other places on Earth (Németh et al. 2011; Valentine and Gregg 2008; Valentine and Keating 2007; van Otterloo et al. 2013) and therefore the 1256 AD eruption site geotope can be easily linked to those front-line researches and can offer a new aspect to understanding mafic explosive eruption processes and their volcanic hazard aspects.

Besides the volcanic processes that built the cone and “ash-plain”, cone rafting, as well as central crater floor subsidence, took place frequently, leaving behind truncated cones and pyroclastic raft-covered lava flows to complicate the volcanic landforms. Medial-to-distal ash and lapilli were accumulated on and below lava flows, indicating coeval lava effusion, pyroclastic fall producing explosive eruptions and lava flow outbreaks in cone-flank regions. Horseshoe-shaped cones, multiple rafted cones and nested cones create a diverse and complex volcanic landscape along the fissure. Each of the volcanic cones shows evidence of crater floor subsidence, crater wall collapse (Fig. 3.25), and some degree of rafting of the cone’s outer flank through lava outbreaks in the foothill of the cones, suggesting that the craters of these cones were filled with lava lakes with fluctuating levels. The lava spatter-dominated proximal volcanic successions are interpreted to be deposited from Hawaiian style lava fountaining and Strombolian-style explosive eruptions. Lava spatters erupted through lava fountains accumulated along the vents, where the freshly deposited hot material formed agglutinate that commonly fed clastogenic lava flows (Fig. 3.26). The heat from the lava lakes and from the fast accumulated lava spatter piles favoured the perfect physical conditions for the freshly-landed pyroclasts to coalesce and form increasingly steepening cone morphologies. Slope angles are commonly higher than the angle of repose of any granular material, due to the agglutination and coalescence of individual pyroclasts on the flank of the growing lava spatter cone.
Fig. 3.25

Evidences of crater wall collapse along the crater wall of the 1256 AD cones [24° 21′ 7.64″N; 39° 46′ 21.26″E]

Fig. 3.26

Clastogenic lava flows in the edifice building succession of the 1256 AD eruption site [24° 21′ 22.18″N; 39° 46′ 15.53″E]

The complex semi-confined to unconfined lava fields of the 1256 AD eruption are dominated by transitional flow textures typical for fast moving, open channel lava (Bretar et al. 2013; Duraiswami et al. 2003, 2014; Wantim et al. 2011). The gradual transition from a shelly-, slabby-, and rubbly-pahoehoe, toward platy-, cauliflower-, and rubbly-a’a, reflects lava flow rheology changes (Murcia et al. 2014). Flow inflation and deflation features, such as lava rises, tumuli, lava blisters, pressure ridges and evidence of cone rafting, are common in proximal areas. Textural features of solidified lavas in crater settings are common for supporting repeated lava lake level fluctuations and lava outbreaks inferred to cause edifice spreading.

In the following section a summary of individual identified geosites are listed with a short description. The selection was conducted by a scientific evaluation of the sites ranking their scientific importance, uniqueness and their location. While similar features selected and listed below are abundant in the Harrat Rahat, the selected geosites are those that can be easily accessed and/or linked to a broader educational program including the previously introduced precinct concept. Geosite 1—Southern Cone and Hornito Field [24° 20′ 28.37″N; 39° 46′ 39.97″E]

This geosite is located in the southern margin of the 1256 AD fissure aligned cone chain (Fig. 3.27). It is slightly offset from the main cone edifice which has been partially destroyed by lava flow rafting and the engulfment of flow lobes initiated from the interior part of the crater of the southernmost cone of the 1256 AD eruption site. The southern cone itself is a partially destroyed volcanic landform. Its crater still preserved but its outline difficult to trace due to the thick lava flow covers that truncated its margin. It is relatively well preserved in its eastern side, where it is the highest. In the highest point a large hornito can be seen with a deep cavity as a pipe along magma was squeezed out forming lava spatter-dominated ramparts. In the southern side of the cone, in the outer flank of the edifice a chain of hornitos form a spectacular set of volcanic landforms. Each of the hornitos is around 5 m tall and few metres wide. The lava spatter forms a chain of steep and narrow cones that has a large cavity supported by the agglutinate wall of the hornito (Fig. 3.28). The significance of this site is to demonstrate the fact that lava lake level fluctuations took place along the 1256 AD fissure eruption, and sometimes lava was squeezed out along marginal structures forming chain of hornitos. While similar geosites have been named elsewhere (Gao et al. 2010, 2013) and such processes can be observed in their stage of formation in Hawaii, this site is significant due to its easy access, large geometry and important message to understand late stage volcanic hazards such an eruption site can produce (Ort et al. 2008).
Fig. 3.27

Overview map of the location of identified geosites associated with the 1256 AD eruptions site’s geotope. Geosites numbered as listed in the text. Note that the upper image shows the northern distal lava flow sites while the bottom image shows the geosites identified in the proximal area of the 1256 AD eruption site. Cone numbers are also shown on the bottom image

Fig. 3.28

Chain of hornitos in the southern edge of the southernmost cone of the 1256 AD eruption site [24° 20′ 27.83″N; 39° 46′ 40.27″E] Geosite 2—Southern Cone and Lava Tube Field [24° 20′ 37.01″N; 39° 46′ 37.12″E]

This geosite has been defined in the NE section of the outer edifice margin of the southern cone of the 1256 AD eruption site geotope (Fig. 3.27). In this site thin crusted lava flows forming a complex network of lava tubes (Fig. 3.29). The lava tube are clearly inflational features of low viscosity and fluidal, but gas rich lava as suggested by the high vesicularity of the tube-forming rocks. The tubes are about a meter wide, box-shaped in cross sectional view and surrounded by about 5 to 20 cm thick porous (vesicular) chilled crust. The interior of the tubes are rich in small-scale (cm-scale) lava stalactite and stalagmite. The individual lava tubes are cross-cutting each other and seem to form a positive relief on the landscape indicating that the low viscosity melt outpoured and quickly run down on the emitting cone flan. The significance of this geosite is to demonstrate the effect of low viscosity of lava on the resulting lava tubes. Similar features are common elsewhere in the Saudi harrats, but this site easy to access nature makes this location a valuable geosite. This geosite also highlight the need of nature conservation projects in the region, as these sites are fragile and easy to be demolished.
Fig. 3.29

Lava tubes forming a complex network of small and narrow lava tubes in the NE sector of the southernmost cone of the 1256 AD eruption site geotope [24° 20′ 36.70″N; 39° 46′ 36.75″E] Geosite 3—Steep Lava Spatter Cones [24° 20′ 42.23″N; 39° 46′ 32.01″E]

This geosite [24° 20′ 45.53″N; 39° 46′ 30.55″E] is the third distinct cone (Fig. 3.27) of the 1256 AD Al Madinah Volcanic Eruption Geotope. This geosite is located between cone 2 and 4 (Fig. 3.27) and its morphology differs significantly from the morphology of the cone 2 and 4 (Fig. 3.30). It has a very steep slope angle, being almost 60° along the crater rim and over 35° at its base that makes this cone among the steepest known cones on Earth (Moufti et al. 2013e). These slope angles are higher than the angle of repose of any granular material, and account for the agglutination and coalescence of individual pyroclasts on the flank of the growing lava spatter cone to maintain these slope angle value (Moufti et al. 2013e). The cone has a crater about 20 m deep with vertical wall that is drapped by lava spatter suggesting some drainage and refill of the crater by repeated lava injection. While steep lava spatter cones are common features on Earth, this site is unique as this cone probably would fit to the largest of such cones on Earth. In addition its architecture closely resembling a large hornito and raises an important question how it was fed. Was it directly connected to a feeder dyke below, or was it just fed from sideway, as a response to the changes of the physical conditions of the lava lakes hosted in the nearby large cones? The existence of such questions ensure that the location indeed can provide valuable information to our common understanding of lava spatter cone formation particularly to their plumbing system. Such questions and aspects of a geosite can just make stronger why this location been selected as a geosite (Fig. 3.31).
Fig. 3.30

Steep lava spatter cone (right) as a geosite along the fissure aligned cones of the 1256 AD eruption site geotope [24° 20′ 44.74″N; 39° 46′ 30.72″E]

Fig. 3.31

Hummocky surface of ponded lava flow region west of the main cones of the 1256 AD eruption side geotope [24° 20′ 44.50″N; 39° 46′ 18.70″E] Geosite 4—Ponded Pahoehoe Proximal Lava Fields and Lava Caves [24° 20′ 48.06″N; 39° 46′ 16.35″E]

In the western side of the main central cone of the 1256 AD eruption side geotope is a proximal area of lava flows erupted from the 1256 AD fissure (Fig. 3.27). This location is one of the most diverse and easy to access in the entire Harrat Rahat in respect of the variety of lava ponding types one can visit in a relatively small area. Its diversity is great in regard of the variety of lava surface textures the visitor can explore as well as the numerous evidences of inflation and deflation of ponded lava flows. The site is an easy walk distance from a sealed road from where with a less than an hour walk the visitor can explore the effect of lava ponding and formation of various features define significant time (days to weeks) when magma was just ponded in the depressions surrounded the growing cones.

The area is best defined as a large silver, grey smooth surfaced region where hummocky surface of the lava flow can be observed (Fig. 3.31). The lava surfaces are smooth with some pahoehoe surface texture marks. Large blocks of smoothed surfaced lava flow fragments are separated by fractures along some dm-scale displacements are common, where the internal texture of the lava crust can be studied. The lava crusts are normally in a dm-scale in their thickness but nearly 1 m thick crusts are also known in the interior of this field indicating that lava ponding must have been taking place over several days or weeks (Holcomb 1981; Polacci and Papale 1997). This observation fits well to the known longetivity of the 1256 AD eruption and this geosite can provide some graphic insight how such historic account could be justified by pure geological observations, which made this geosite an important addition to the geoeducational programs the Harrat Al Madinah Volcanic Geopark could provide.

This geosite also show fantastic examples of lava inflations and deflations in the form of lava tubes (Fig. 3.32). One of the largest and longest lava tubes has been found in Harrat Al Madinah area. Complex lava tube network as a main artery of the proximal feeding system of the 1256 AD eruption main lava flow is suspected to be located in this area (Murcia et al. 2014). The geosite is a unique and an easy to access location where the visitors can get an immediate insight how the proximal feeding system of major lava flows can function. This site has a very high educational value as it provides evidence that magma can stay hot and fluid long time beneath the growing and thick crust. Such information is very important to convey as it carries important volcanic hazard aspects to the local population.
Fig. 3.32

Large lava tube exposed just west of the main cone of the 1256 AD eruption site geotope [24° 20′ 49.00″N; 39° 46′ 16.05″E]

The evidences of lava ponding, inflation and deflation also provide better understanding how large volume of lava be able to accumulate prior it can break out and feed long lava flows. The evidences of the inflation and deflation in this geosites are the large tumuli (Fig. 3.33), collapsed and displaced lava tube roof blocks and abundant occurrences of lava marks in the tubes. This geosite potentially could function as a main site to educate the public about volcanic hazards.
Fig. 3.33

Tumuli on the surface of the smooth pahoehoe lava flow field just west of the main cone of the 1256 AD eruption site geotope [24° 20′ 45.24″N; 39° 46′ 15.63″E] Geosite 5—Pressure Ridges, Flow Channels and Convection Zones [24° 21′ 4.74″N; 39° 45′ 46.32″E]

This geosite is located right next to a sealed highway, and therefore it is very easy to access (Fig. 3.27). It shows lava surface features indicating for the lava flow field dynamics and mechanical properties. The elongated, “pathway-like”, slightly twisted zone shows that lava flow must have been fairly viscous to form some squeezed zones in what the still molten lava formed draping features as well as the degassing formed a highly vesicular but chilled outer margin of the flow (Fig. 3.34). An almost 50 m-long spreading ridge with a central crack is exposed and ready to be examined by the visitors that form the core of this geosite (Fig. 3.34). Such spreading ridge indicates that the lava crust has formed by lateral spreading from a convective plume similar to other open channel transitional flows such as those located and documented from Krafla in Iceland (Rossi 1997). The rugged vesicular surface of the lava was fed from the crack in the middle as an up-flow of the cooling viscous melt along the ridge. The asymmetry of the features (in map view) can be associated with the differential shear acted upon the entire lava flow field. Along this location abundant evidences can be observed to see, that the lava flow field was time to time fed by newly arrived open-channel fed melt that cut through and just gradually mingled with the ponded interior of the lava. This location provides insight into the dynamic nature of a large ponded lava zone in the proximal areas of a volcano. In addition this geosite contributes to our understanding of the unstable nature of a ponded lava body that can collapse and cause catastrophic flow inundation downhill from the crater.
Fig. 3.34

Rotational feature as a pressure ridge in just west of the main cone of the 1256 AD eruption site geotope suggesting dynamic picture of the lava flow movement in the proximal areas [24° 21′ 4.05″N; 39° 45′ 45.99″E] Geosite 6—Reticulite Field [24° 20′ 51.22″N; 39° 46′ 17.88″E]

In the western foothill of the central cone of the 1256 AD eruption site geotope red scoria with dark glassy lava spatter bomb fields together provide the location for this geosite (Fig. 3.27). This location is part of the transition of the cone edifice and the surrounding ash plain. The presence of reticulite (Mangan and Cashman 1996; Powers 1916) in this site is an important indicator that this eruption erupted very low viscosity magma that was able to produce highly vesicular glassy pyroclasts that are very light and ready to be carried away for long distances (Fig. 3.35). This physical property of a pyroclast is important to constrain the potential that such eruption is capable to produce eruption cloud that can be carried away far and produce ash plain such as in the case of the 1256 AD eruption. The presence of reticulite and Pelee’s tears and hair also indicates that the magma fragmentation was largely controlled by sheer of the low viscosity melt upon exiting the crater, and likely to be associated with a lava fountain fed eruption (Mangan and Cashman 1996). This geosite therefore plays an important role to explain the explosive phase of the 1256 AD eruption and carries key volcanic hazard aspect the local community could learn here.
Fig. 3.35

Reticulate and Pelee’s hair and tear are abundant in the western edge of the lower section of the 1256 AD main cone flank [24° 20′ 51.92″N; 39° 46′ 17.31″E] Geosite 7—Cone 3—Pit Crater [24° 20′ 45.82″N; 39° 46′ 30.32″E]

Pit craters form due to sudden withdrawal of magma below a crater through flank eruptions leading to a fast collapse of the crater floor (Carter et al. 2007; Harris 2009; Németh and Cronin 2008). As a result the internal part of the crater wall will be mantled by draping lava and spatter. The outflow points are commonly marked as “boccas” in the outer edifice lower flank. Recognition of pit crater formation bears an important role to establish the eruption mechanism a volcano followed.

The sudden withdrawal of melt likely means that the crater was filled with active lava lakes and that was commonly acted as point source of low lava fountains (Okubo and Martel 1998; Rymer et al. 1998). The 1256 AD eruption site along the 2.3 km-long fissure shows numerous evidences of active lava lake formation then pit crater development. The repeated nature of pit crater formation attests the drainage and refill of magma to a crater. An example provides an ideal geosite to be defined as Cone 3 (Fig. 3.27). This crater is in a short walk from the main access point to the 1256 AD geotope and it provides a perfect view into a twin pit crater. In the inner wall of the crater lava spatters form ramparts and multiple layers of lava lake level markers suggest that the lava lake hosted in this crater changed its level more than once. This geosite has a high educational value to demonstrate that craters can form in a passive way, and explosive activity is not the only way to form a crater (Roche et al. 2001). Geosite 8—Cone 4—Large Scoria Cone with Complex Crater [24° 20′ 52.39″N; 39° 46′ 26.66″E]

Cone 4 is one of the large volcanic cone of the 1256 AD volcanic geotope (Fig. 3.27). It is a complex scoria cone that exposes edifice sections dominated by lava spatter beds, while other sectors are more typical to pure scoria ash and lapilli accumulation. In the crater of the cone is complex and provides a good view to understand the gradual step-like growth of the cone commonly accompanied with magma withdrawal (Stovall et al. 2009) and small pit formation in the center of the cone (Fig.  3.36). The core of the cone is welded, and agglutinate layers tend to show slow plastic deformation features indicating that the heat of the high level lava in the crater and upper conduit welded the edifice significantly (Martin and Nemeth 2006; Sumner et al. 2005; Vespermann and Schmincke 2000). In the crater, large cracks suggest that the cone was slightly spread and tend to fall apart due to the hot base it was sitting on. The top of this geosites are ideal to have a look out on the 1256 AD eruptions and its extensive lava fields. The significance of this geosite is to demonstrate the potentially explosive nature of an eruption this type of volcanoes in the Harrat Rahat functioned in the past. The dominantly Hawaiian style eruptions in combination with the more typical Strombolian style eruptions suggest that this volcano was a complex volcano with complex eruption styles where the physical conditions in the upper conduit determined the style of eruption (Stovall et al. 2011).
Fig. 3.36

Crater zone of the Cone 4 demonstrate complex intra-crater processes in a growing edifice [24° 20′ 52.27″N; 39° 46′ 25.62″E] Geosite 9—Inter-cone Ponded Pahoehoe Lava Field [24° 21′ 2.09″N; 39° 46′ 26.84″E]

Just NW from Cone 4, a very special area defines the geosites where ponded lava and its surface features can be studied (Fig. 3.27). This area is located on the eruptive fissure of the 1256 AD eruption site and it is a question if it is underlain by a feeder dyke or it is just a ponding feature in a depression between cones. Currently there is not enough data to decide this. The inflational features however are evident. The center is composed of shiny, smooth surfaced pahoehoe lava fields that are partially cracked and rotationally and/or vertically displaced. The cracks are commonly healed by more viscous lava (Fig. 3.37). The center part of the ponded zone is about 1–5 m below to its margin where dragged lava forming rampart like feature like a skin over an area indicating deflational force that collapsed the dm-thick crust of the lava pond (Harris et al. 2009; Head and Wilson 1989; Patrick and Orr 2012; Stovall et al. 2009). This region can be accessed by long walk through a rugged lava field and is only recommended to those can handled such conditions. The geological and educational value of this geosite is illustrating lava ponding, which is a common event with this type of volcanism (Anderson et al. 1999; Ball et al. 2008; Crown and Baloga 1999; Hoblitt et al. 2012; Parcheta et al. 2012; Self et al. 1998). Moreover lava ponding can host large volume of magma that can quickly be released that needs to be viewed as potential volcanic hazard (Patrick and Orr 2012).
Fig. 3.37

Ponded lava in between Cone 4 and 5 showing exceptional inflational and deflational features [24° 21′ 1.82″N; 39° 46′ 25.69″E] Geosite 10—Lava Flow Cascade and Lava Flow Termination [24° 21′ 5.04″N; 39° 46′ 31.13″E]

A spectacular lava flow cascade is defined as a geosite just N-NE from the intra-cone ponded lava field explained above (Fig. 3.27). The geosite represents an about 500 m long confined lava flow that shows a perfect transition from the ponded pahoehoe lava flow textures to a typical slabby and rubble pahoehoe textures. The steep slope and the magmatic pressure from the ponded lava together are inferred to be responsible for the formation of a high speed cascading lava flow that broke apart the earlier formed lava crusts and carried them away from their original position (Duraiswami et al. 2014; Guest et al. 2012; Peterson and Tilling 1980; Rowland and Walker 1990). As a result a typical small-scale rubble pahoehoe lava unit formed. The geosite is unique because in a relatively short distance and easy walk the visitor can access the entire lava flow and see the flow transition very clearly. An extra speciality of this geosite is that the visitor can walk out to the end of individual lava flow units and examine the flow termination of this type of flow (Fig. 3.38).
Fig. 3.38

Typical lava flow terminus of a small, transitional lava flow [24° 21′ 4.44″N; 39° 46′ 32.28″E] Geosite 11—Lava Flow Ponding and Draining Effect [24° 20′ 59.47″N; 39° 46′ 19.87″E]

In the other side of the ponded lava flow between Cone 4 and 5, another fine example can be seen to demonstrate the drainage effect of ponded lavas (Fig. 3.27). In this region the visitor can trace the lava tube that connected to the central ponded region, which has a collapsed and ripped off roof, probably caused by the mechanical erosion by the cascading lava flow already carried large rafts of lifted and rotated lava crusts. Along the open lava flow channels’ margins, spatter levels mark previous lava level stages (Fig. 3.39).
Fig. 3.39

Unroofed lava tube with lava level markes in the preserved channel margin [24° 21′ 0.12″N; 39° 46′ 21.48″E] Geosite 12—Cone 5—Bomb-Dominated Cone [24° 21′ 5.21″N; 39° 46′ 21.72″E]

Cone 5 is a cone nearly entirely composed of cannon ball-like bombs and lapilli slightly agglutinated in the flank of the cone (Fig. 3.27). The abundant lava cannonballs indicates that lava must have left the crater in larger packets and travelled through a significant length in the air, where surface tension and rotation of the bombs that formed the clasts now cover the entire flank of the cone (Fig. 3.40). The cannonball bombs and lapilli can be interpreted to represent the complex origins of the particles. The spherical shaped bombs and lapilli are commonly smoothed surfaced with textures indicate some rotational movement of the clast prior to solidification, resulting some degree of textural separation of the core and the rim of the particle closely resembling some sort of armoured lapilli or bomb texture. These can be interpreted as a sign that these pyroclasts originated when degassed magma ejected as separate fragments that tended to be pulled into lava spheres due to mechanical rounding upon rolling down fast in a semi-molten state on the growing edifice flank (Francis 1973).
Fig. 3.40

Cannon ball-like lava bombs littered on the flank of Cone 5 [24° 21′ 5.03″N; 39° 46′ 19.64″E]

However, cannonball lapilli and bomb with more uniform and smoothed rim and more dense core with entrapped vesicles or older (different textured) lava can be interpreted as recycled colder particle that were ejected subsequently by younger melt from a relatively stable lava lake constantly digested rolled back material and erupted them out through discrete explosions and/or fountain (Alvarado et al. 2011; Bednarz and Schmincke 1990).

The cone flank shows a spectacular view. This geosite can provide information to the visitor that active lava lakes must have existed in this crater, where recurrent bubble coalescence exploded the degassed magma that then formed cannonball-like fragments. This is a more calm explosive processes in comparison to those where reticulate formed and therefore this geosite can provide a reference to two end-member style of explosivity a future eruption would likely cause in the Harrat Rahat. The crater of the cone is also well-exposed and provides further evidences for pit crater formation and crater floor subsidence by drainage of the lava lake. Geosite 13—Cone 6–7—Main Cone [24° 21′ 17.45″N; 39° 46′ 18.82″E]

Cones 6 and 7 are considered to be the main cones of the 1256 AD eruption (Fig. 3.27). This double cone is the largest by volume, and it has a deep, elongated crater that can be traced over 400 m (Fig.  3.41). In the crater floor of the cones coarser crystalline lava represent the base of former lava lakes that solidified and crystalized slowly. Accessing the crater floor is challenging but not impossible and not necessary becausecircling the crater rim can provide insight to understanding the eruption mechanism of the main cone of the Al Madinah 1256 AD eruption. It is evident that that the elongated craters functioned as host of lava lakes. The lava lakes commonly changed their level, and they were likely drained in the NW outer flank of the cone edifice, where a small “bocca” looks as an initial point of the major long lava flows. The highest easterly crater rim and edifice composed of step-like crater rims that are separated by faulted zone of flank blocks suggest a gradual subsidence of the central part of the cone accompanied with some tendency to rebuild the cone through subsequent eruptive activity. This is a similar process as documented elsewhere and it seems that it is a common feature for a long-lived scoria cone that gradually emitted lava flows which is the case of this cone (Németh et al. 2011; Riggs and Duffield 2008). This geosite therefore can be used to demonstrate the causes and consequences of the edifice growth, rafting and lava flow initiation associated with long-lived scoria cones.
Fig. 3.41

Elongated crater zone of the main cone of Cone 6 and 7 [24° 21′ 21.70″N; 39° 46′ 23.93″E] Geosite 14—Collapsing Cone Zone [24° 21′ 15.61″N; 39° 46′ 16.78″E]

In the western margin of the Cone 6–7, there are good examples to demonstrate the cone’s instability during the edifice growth (Fig. 3.27). In this crater rim, large (tens of metres wide) radially fractured zones can be traced, where agglutinated lava spatter beds tend to be displaced forming a mosaic-like pattern in map view (Fig. 3.42). This geosite is excellent to demonstrate the mechanical response of a still hot and semi ductile spatter bed to deform in a rigid fashion, and collapse towards the center of the growing pit crater. This geosite is unique and easy to access, and visitors could learn a lot how the edifice growth and destruction can play together in the shaping of the cone morphology.
Fig. 3.42

Radially jointed agglutinated spatter fragments gently dipping toward the pit craters provide good evidence to imagine the pit crater and crater wall collapse formation event [24° 21′ 14.78″N; 39° 46′ 16.80″E] Geosite 15—Lava Flow Field Slope Angle Changes, Flow Transitions [24° 22′ 30.41″N; 39° 46′ 5.46″E]

In proximal areas it has been demonstrated clearly in a relatively small-scale (hundreds of metres) that lava ponding and sudden break outs from the ponded zones can form transitional lava flow morphotypes. In more distal areas in the main artery of the 1256 AD 23 km-long lava flow there are very graphic examples to explore this phenomena in large scale. This geosite is one of the best examples to demonstrate that lava ponding can take place en-route along the main long lava flows, especially when morphology barriers or depressions are common. This geosite shows such ponded lava zones, that then quickly cascaded through an about 20 m drop in the topography, leading to form a channelized rubbly pahoehoe texture to develop on the fast moving lava flow. This geosite has an important role to demonstrate to the visitors that lava behaves very differently in comparison to water, and unexpected inflational events and ponding can occur frequently. When such ponded zones break out, fast moving transitional type lava flows tend to form. Thus this geosite provides a fine example of the paheohoe to aa lava flow transition as strongly controlled by the viscosity of the melt due to cooling and the slope angle on the flow move (Duraiswami et al. 2003; Kilburn 1981; Peterson and Tilling 1980; Rowland and Walker 1990). Geosite 16—Lava Flow Squeeze Outs in Distal Areas [24° 26′ 23.07″N; 39° 46′ 17.45″E]

In the most distal areas of the 1256 AD lava flows unconfined lava terminus formed (Fig. 3.27). In these areas there are numerous small to medium-scale lava flow zones where squeezed out lava can be seen (Fig. 3.43). These squeeze out zones are important geosites as they provide some insight to the visitor that lava flows can be active long after the main flow body was emplaced (Rowland and Walker 1987; Sheth et al. 2011). This information is also important to volcanic hazard aspects of similar lava flows telling us that lava can stay in molten stage long after the emplacement of the flow.
Fig. 3.43

Distal lava squeeze outs in the margin of the 1256 AD main lava flow [24° 26′ 33.07″N; 39° 46′ 24.28″E]

Fig. 3.44

Suggested study pathes across the 1256 AD eruption site of Al Madinah Georoutes

The above listed geosites of the 1256 AD Al Madinah eruption are best to visit by following three suggested study paths (Fig.  4.44). There are three levels of study paths recommended to be developed. Two of them can be done by walking off from a general starting or access points, while the third one offer an introductory dirt road experience that follows a full circle around the 1256 AD cones and the medial part of the main lava flows of the eruption.

Northern Circuit Walking Path
The Northern Circuit walking path takes the visitor to the main cones—Cone 6 and 7—through a near complete circle (Fig. 3.45). Its access point is located in the northern edge of the main cones. The main goal of this walking path is to link geosites demonstrate the eruption mechanism of the main, most obvious cone(s) of the 1256 AD eruption site. In addition this walking path provides unique vantage points to explore the proximal lava flow region that fed the 23 km long lava field.
Fig. 3.45

Northern Circuit walking path

Southern Circuit Walking Path
The Southern Circuit walking path is a slightly easier walking track in comparison to the Northern Circuit one (Fig. 3.46). The visitor by completing this study path will see the geosites demonstrate features associated with the lava inflation and deflation, formation of lava tubes and their collapses, and provide some information on the lava flow initiation through ponded lava regions. Because the access point for this walking track is nearby to a sealed road, this walking path can be separated into smaller segments that general physical condition visitors or school children can also complete.
Fig. 3.46

Southern Circuit walking path

Cone and Lava Field Car Route

The Cone and Lava field car route (Fig. 3.44) follows dirt roads that completely circle the 1256 AD eruption’s 7 cones and their proximal to medial lava flow fields. This trip can be offered to visitors who are not interested in exploring the proximal areas by foot, and/or have limited time. This trip can provide multiple vantage points to the main cones of the 1256 AD eruption. En-route the circle provides short stop options to examine specific geosites, especially those associated with the lava flow surface textures. This study path also recommended as a test trip to those wish to explore the Harrat Rahat in its more remote geosites in the Precinct 2, 3 and 4.

3.9.2 Geotope of the 641 AD Historic Eruption Site

Al-Madinah City is located in a basin that is filled with thick alluvial deposits derived from the higher basement rocks standing as horsts blocking the western and northern side of the basin (Fig. 3.1). An historic eruption that took place in this basin in 641 AD is inferred to be sourced from four small volcanic cones (Fig. 3.47), aligned NNW—SSE (Fig. 3.48), located west of Al-Madinah City (~12 km from the Holy Mosque) (Camp and Roobol 1989; Moufti et al. 2013b; Murcia et al. 2015; Nemeth et al. 2013). This cones recently been named as the Al-Du’aythah volcanic cones (Murcia et al. 2015). Three out of the four cones have basal phreatomagmatic deposits indicating initial phreatomagmatic explosions (Fig. 3.49). These are the only centers of all the younger (<10,000 years) volcanoes in northern Harrat Rahat where evidence of phreatomagmatism is known.
Fig. 3.47

Overview of the four cones of the 641 AD eruption site nearby Al Madinah city looking from the point of [24° 24′ 20.65″N; 39° 29′ 21.68″E] toward N

Fig. 3.48

Map view of the four cones inferred to be the source of the 641 AD historic eruption near Al Madinah city on GoogleEarth image (a), on LiDAR (b and c) and on a schematic cross section (d) with calculated eruptive volume values after Murcia et al. (2015)

Fig. 3.49

Basal phreatomagmatic tephra indicates phreatomagmatic explosive eruptions three out of the four cones formed during the 641 AD eruption [24° 24′ 48.47″N; 39° 29′ 44.88″E]

The four cones have young volcanic morphology, such as steep cone flanks, near angles of repose slope, intact crater rims, and limited gully formation on its outer flank, all of which is suggestive of young eruption ages, when their geomorphology features are compared to other young cones elsewhere (Murcia et al. 2015). Each of the four cones is similar in size, with a base diameter of about 200–250 m and relative heights of about 30–50 m. The tallest, but simplest, volcano is the most southern and is composed of a conical shaped edifice with an enclosed single crater. The other three cones are somewhat more complex and exhibit multiple craters and complex volcanic stratigraphy, ranging from a basal tuff ring abundant in accidental lithic fragments commonly cored in lapilli and bombs to various types of scoria cones, lava spatter cones, small lava coulee and short lava flows. The upper sequences of the cones are inferred to be produced by typical lava fountain and moderate Strombolian style explosive eruptions that also initiated small clastogenic lava flows reaching less than 300 m from their source.

The thickest tuff ring sequence has been recorded as a 5 m thick succession of lapilli tuff that is inferred to have been formed by an initial explosive eruption triggered by the interaction of rising basaltic magma and the shallow ground-water table, and the resulting pyroclastic rocks are defined as a basal phreatomagmatic succession. While phreatomagmatism is inferred to be the cause of the initial explosive, vent opening stage in many older (0.3–0.7 Ma old) volcanoes of the Harrat Rahat (Moufti and Németh 2013a), such records in association with small basaltic volcanoes are not known in the vicinity of Al-Madinah City, especially not in other young or historic eruption sites.

The basal tuff ring deposits also expose numerous cored bombs that are the spectacular results of the interaction between cold country rocks and low viscosity basaltic magma, capable of engulfing particles and being ejected as a cored bomb (Fig. 3.50). The fact that three out of the four cones have a basal tuff ring indicates that during this eruption, at least in the initial phase, magma interacted with shallow ground-water and triggered base surges that accumulated a relatively thin tephra unit (Rosseel et al. 2006). This also indicates that, if a future eruption were to occur in the area of the Al-Madinah basin, there is a chance that the initial stage of the eruption could be phreatomagmatic and therefore to promote and preserve this location as an intact volcanic geotope is important for volcanic hazard education (Moufti et al. 2013b).
Fig. 3.50

Cored bombs from the 641 AD eruption sites

The 641 AD volcanic geotope can host several individual geosites that are each can be used as a standalone geoeducational location to promote several aspects of mafic explosive and effusive volcanism. The proximity of the location to Al Madinah city, the site relatively small size and the complexity of volcanic features well preserved and exposed make this geotope a unique location future geoeducation programs could use, and as proposed could be the gateway to the great Al Madinah Volcanic Geopark (Moufti et al. 2013b). This geotope also contains the majority of the volcanic features the visitor can come across by visiting the greater Harrat Rahat region, and therefore it can be used as a jump-desk to develop any further geoeducational programs to a remote and fairly large region of Harrat Rahat. Geosite—Cone 1—Intact Scoria Cone [24° 24′ 33.44″N; 39° 29′ 56.10″E]

Cone 1 is the most southerly cone of the four cones and it is also the simples (Fig. 3.51). It has a circular crater that is well-preserved. In the crater lava spatter banks exposed. In the flank of the cone is steep, typical to a scoria cone in spite that the majority of the edifice is composed of agglutinated lava spatter. To access the top of the cone needs some care as there is no path and the flank is steep. The geosite educational value is that the cone is still intact, its shape demonstrating a young volcanic landform and its pyroclastic rocks units indicates a relatively simple and short lived eruption mechanism (hours to days).
Fig. 3.51

Cone 1 has an intact and simple cone [24° 24′ 33.44″N; 39° 29′ 56.10″E] Geosite—Cone 2—Thin Veneer of Phreatomagmatic Base and Spatter-Covered Crater Interior (S3–4) [24° 24′ 42.18″N; 39° 29′ 51.17″E]

Cone 2 is a smaller cone than Cone 1 and its flank is not as perfect as Cone 1 (Fig. 3.52). The base of the cone in its southern edge are composed of a thin lapilli tuff succession indicating that the eruption of this cone must have started by an initial mild phreatomagmatic explosive phase that quickly evolved to be magmatic explosive with some intermittent lava fountaining events. The geosite educational value is to see clearly how an initial phreatomagmatic explosive eruption can turn to be more magmatic explosive and eventually build a scoria cone over the course of the eruption.
Fig. 3.52

Cone 2 has a broad crater mantled with lava spatter [24° 24′ 42.18″N; 39° 29′ 51.17″E] Geosite—Cone 3—Scoria Section (S1–1) [24° 24′ 49.63″N; 39° 29′ 48.40″E]

Cone 3 is a complex scoria cone (Fig. 3.53) with a phreatomagmatic lapilli tuff base that is covered by typical scoriaceous ash and lapilli upsection. The scoria section is important as it composed of vesicular typical scoria indicating that the eruptions were controlled by regular bubble outbursts in the upper conduit of the growing scoria cone. The black scoria contains numerous cannonball lapilli and bomb suggesting that some recycling must have been taken place in the crater where ejected bombs and lapilli fell back. The scoria section also shows some exhalation minerals that make the scoria deposits colourful in places. The geosites educational value is that it can help to the visitor to understand the nature of magma fragmentation and provides good evidence that ash can be produced in such small eruptions.
Fig. 3.53

Cone 3 is a complex scoria cone with a phreatomagmatic lapilli tuff base that covered by scoria beds and lava spatter [24° 24′ 49.63″N; 39° 29′ 48.40″E] Geosite—Cone 3—Lava Dome (S1–2) [24° 24′ 51.50″N; 39° 29′ 49.08″E]

The top of the Cone 3 is covered by a lava dome and spine that fed a very short blocky lava flow. The lava flow is rather a lava dome that uplifted the internal part of the scoria cone and partially protruded through the edifice sliding fragments. This location provides a good example that volcano destabilisation and collapse can take place in such small volcanoes and they can pose a syn-eruptive hazard. This geosite also provides a good introduction to an intra-crater intrusive process that can be explored in large scale in the remote parts of the Harrat Rahat. Geosite—Cone 3—Exposed Phreatomagmatic Base (S3–2) [24° 24′ 48.03″N; 39° 29′ 45.25″E]

The base of the Cone 3 is composed of about 4 m thick exposed lapilli tuff and tuff that is bedded, well-bedded to cross-bedded and contains abundant country rock fragments. Many of the country rock fragments are partially or fully covered by thin lava coat, indicating a low viscosity melt that entrapped them. The cored bombs are inferred to have been derived from the alluvial fan filling a basin nearby the bounding Precambrian horsts. The phreatomagmatic base is the thickest at the Cone 3 suggesting that the initial phase might have been short, but it has been excavated significant portion of country rocks that ended up in the accumulating basal pyroclastic succession.

This geosite bears with a very significant educational value to be able to show the differences of the pyroclastic succession formed due to explosive magma and water interaction. As phreatomagmatic successions are rare in the Harrat Rahat, the presence of them in relationship with the small cones of the 641 AD eruption site can keep the public attention on the fact that in low-land and in more humid periods, phreatomagmatism can take place in an otherwise arid region. This fundamental volcanic hazard aspect cannot be underestimated. Geosite—Cone 3—Exposed Transition Between Phreatomagmatic Base to Scoria Deposits (S3–3) [24° 24′ 47.41″N; 39° 29′ 47.58″E]

A transitional section in the southern flank of the Cone 3 can provide another unique geosite where the visitor can explore how continuous the transition between the phreatomagmatic and magmatic eruption driven pyroclastic succession. This indicates that the eruption were likely continuous (e.g. no break) and the eruption style must have changed during the evolution and growth of the cone. This geosite therefore can convey important messages such as (1) initial phreatomagmatic explosive eruptions can change to be more magmatic gas-driven if the water supply drops or vanishes in the course of the eruption and (2) if the magma eruption rate is large enough, the initial phreatomagmatic pyroclastic successions can be completely covered by a large scoria cone. This later message is important as other scoria cones, especially in the Al Madinah basin where ground water is available, might have had the similar thin phreatomagmatic base. Geosite—Cone 4—Exposed Phreatomagmatic Base (S3–1) [24° 24′ 52.48″N; 39° 29′ 40.59″E]

Cone 4 is the most northerly cone of the four 641 AD cones (Fig. 3.48). The base of this cone similar to Cone 3 and this geosite demonstrate similar features but in different volcanoes as the previous geosite. The significance to of this geosite is that such thin phreatomagmatic veneers can form very irregular base of this cones that can be partially or entirely covered by subsequent eruptive products. Probably the Cone 3 and 4 are those cones where the magma eruption volume and rate were too small and the basal phreatomagmatic pyroclastic unit were not covered completely, and therefore we still can see that initial phreatomagmatic explosive eruption took place. Geosite—Cone 4—Short Lava Flow Terminus (S2–1) [24° 25′ 1.91″N; 39° 29′ 40.92″E]

The Cone 4 is the source of a short lava flow that poured out toward the North (Fig. 3.54). This lava flow is short (<200 m) but still showing typical flow morphological features such as rubbly pahoehoe texture as it can be seen in many of the Harrat Rahat lavas. In this respect this geosite has geoeducational significance because it can be used as an introduction site to the lava flow emplacement processes common across the harrats of Saudi Arabia.
Fig. 3.54

Lava flow terminus of the Cone 4 [24° 25′ 1.91″N; 39° 29′ 40.92″E] Geosite—Cone 4—Partially Collapsed Cone (S2–2) [24° 24′ 58.58″N; 39° 29′ 44.21″E]

The top of the Cone 4 is composed of a double crater. It seems that an initial crater has been truncated by the outpouring lava flow that partially rafter the flank of the cone away. As a result, the surface of the lava flow is littered by cone flank remnants and large pyroclasts such as fluidal bombs and blocks. This geosite therefore is important to demonstrate that the crater of a volcano is an active playground where gravitational collapse, rafting by outpouring of lava flows and explosive eruptions can act and shape it to their final form. This is again and important aspect to introduce in this geosites, because similar processes but in larger scale are very common across the Harrat Rahat, and therefore this geosite can be used as a starting point for such geoeducational programs. Geosite—Cone 4—Crater of Cone 4 (S2–3) [24° 24′ 55.74″N; 39° 29′ 45.47″E]

The Cone 4 has a well-developed crater from where the visitor can have a nice view toward the short lava flow. From this point as a geosite the visitor can get an insight to the dynamic processes of how volcanic craters evolve. Georoutes

Along the four cones of the 641 AD eruption site four study paths (Fig. 3.55) are recommended (Moufti et al. 2013b). These study paths are linked together and following the above described geosites. The basic concept suggested is that these four study paths combined with a visitor center could act as a gateway visitor center for the Harat Al Madinah Volcanic Geopark. Beside that the visitor center could act as a geoeducational center, the four study path can provide all the details in a short distance walk or drive that can give to the visitor a very good start to plan their more adventure-rich trips to the interior to the Harrat Rahat.
Fig. 3.55

Study paths of the 641 AD eruption sites. Green start marks the potential information center from where the walking pathes can be started

Walking Path 1

Walking path 1 is the shortest and easiest walking path exploring the Cone 4 (Fig. 3.55). The main goal of this study path to provide a first-hand easy experience to the visitor to see the conditions of a lava field, cone flank and the potential features they can come across in the harrats.

Walking Path 2

Walking path 2 requires a little bit better physical conditions from the visitor as it explores the Cone 3 (Fig. 3.55). It takes the visitor up to its summit and it also provides a good way to connect the basalt phreatomagmatic successions to the capping magmatic explosive and effusive units. From the top of the Cone 3 a perfect view can be enjoyed toward Al Madinah city. This walking path can emphasize the volcanic hazard aspect of the proposed geopark as the visitor will see clearly how much the city expanded since the 641 AD eruption, and today its outskirts are located in the harrat.

Walking Path 3

Walking path 3 takes the visitor around the Cone 3 (Fig. 3.55). Instead of walking up to the cone, the visitor can stay in level and just complete a circle to see the phreatomagmatic successions and the overview of the complex scoria cone that is capped by a lava spine.

Car Touring

For an easy overview, a driving tour can be arranged that takes the visitor around the four cones allowing stops at key geosites focussing on the basal phreatomagmatic succession (Fig. 3.55). The car tour option also can provide opportunity for families to stop by and explore the volcanic features with good options for picnicking.

3.9.3 Scoria Cone with Ottoman Fortress Geotope [24° 20′ 17.47″N; 39° 35′ 13.14″E]

Just south of Al Madinah city around the ring motorway a complex scoria cone form an intact volcanic geotope (Fig. 3.56). This scoria cone seems to be a young scoria cone complex capped with historic site of an Ottoman fortress, and therefore it has a complex geoheritage value. The scoria cone was used as a perfect lookout point for centuries, and the fortress constructed on the top of the cone used the natural crater rim as a wall. The complex scoria cone also show evidences that it is a relatively young volcanic landform as based on its stratigraphy position in comparison to basal and capping lava flows nearby.
Fig. 3.56

GoogleEarth satellite image of the complex scoria cone host an Ottoman fortress [24° 20′ 17.47″N; 39° 35′ 13.14″E] Geosite—Cone Base

The base of the complex cone demonstrates a fine example to examine the erosional processes of a scoria cone. The thick reworked scoria fan resulted from the gradual erosion of the cone itself, and its base now covered by modified grain flow-dominated volcaniclastic sediments. The way up to the cone follows the gradual transition from the reworked part of the cone to the more primary volcanic explosive eruption dominated scoria and bomb beds in the top of the cone. The geoeducational value of this geosite is based on its good exposure and graphic examples, that the scoria cone edifices’ base are dominated by volcaniclastic deposits that were formed due to the mass movement on the flank of the cones. Geosite—Cone’s Double Crater and Fortress

The top of the geotope is an ideal place to see the volcanic craters of a scoria cone (Fig. 3.57). The crater rim is composed of agglutinated scoria especially around the lip of the crater. The agglutinated spatter-dominated beds of the crater rim were used to form the natural base of an Ottoman fortress upon the construction was based (Fig. 3.58). The collar-like crater lip also show a graphic example that the erosion of a scoria cone in such conditions are likely controlled by rock falls due to the undercutting of the softer scoria layers below the agglutinated more stable beds (Kereszturi and Németh 2012a, b; Martin and Németh 2006; Németh 2010; Németh et al. 2003, 2005).
Fig. 3.57

Double crater of the complex scoria cone indicates vent shifting during the eruption [24° 20′ 9.84″N; 24° 20′ 9.84″N]

Fig. 3.58

Agglutinated spatter collar functioned as a foundation of an Ottoman fortress demonstrates well the natural base of human developments on a scoria cone [24° 20′ 11.27″N; 39° 35′ 18.82″E]

3.9.4 Al Madinah Water Management Geotope

Around Al Madinah, water management in early history produced some spectacular and less known water management systems. Especially in the northern side of the greater Al Madinah region (Fig. 3.59), such remains are common, and they can serve good understanding on the water availability of the Al Madinah basin. This geotope plays and important role to demonstrate the ground and surface water is available, and probably was more abundant in the past historic time. This information can be connected well to demonstrate that phreatomagmatic explosive eruptions are likely eruption scenarios in areas where shallow aquifers are common. In this aspect this geotope fits very logically to the geoeducational concept of the Precinct 1 educational concept particularly to the demonstration of the formation of the 641 AD volcanic cones.
Fig. 3.59

GoogleEarth maps of water dams just north of Al Madinah city Geosite—Water Dam 1 [24° 26′ 34.15″N; 39° 55′ 8.38″E]

A large water dam form this geosite with a fantastic architecture constructed in a narrow gorge of old, Proterozoic rocks (Fig. 3.60). The water dam demonstrates that surface water can be captured and used for water management. In addition it is also an important site to appreciate the fact the in more humid climatic conditions even surface water can be abundant in the Al Madinah basin, that then can be diverted by lava flows and or trigger phreatomagmatic explosive eruptions at least in the initial stage of the eruptions as it has been demonstrated in the 641 AD cones just west of Al Madinah city.
Fig. 3.60

Overview of one of the ancient water dam (1), part of the greater Al Madinah water management system [24° 26′ 34.15″N; 39° 55′ 8.38″E] Geosite—Water Dam 2 [24° 26′ 28.80″N; 39° 55′ 2.74″E]

A second major water dam show a smaller construct with lower but wider dam. The presence of this dam highlight the fact that in early time water management was fairly advanced in the region and surface water availability was great enough to invest to build such complex structures. This also indicates that especially in humid conditions, the potential to have phreatomagmatic explosive eruptions in the future if new vents would be opened in this region cannot be excluded.

3.10 Precinct 2—Collapsing Cones, Lava Spatters and Lava Flows

This proposed precinct focuses on a single location that can be accessed only by 4WD tours. It is relatively far from Al Madinah city, but a well maintained 4WD track leads straight to the crater rim of a spectacular volcano (Fig. 3.61). On the way to the geosites of this precinct, the visitor will be able to see other lava spatter cones and extensive lava fields with tumuli, surface features and flat ephermal river and lake beds. The main geosites can be visited as a single full day trip or can be combined with a short morning visit to the Historic Eruption Precinct—1256 AD and 641 AD Historic Eruption Sites and then a visit to the Lava Lakes, Lava Fountains and Volcano Spreading Precinct—The Mosawdah Volcano.
Fig. 3.61

Overview of the Mosawdah volcano and its surroundings on a GoogleEarth image [24° 14′ 10″N; 39° 47′ 51″E]. GSM1 and GSM2 refer to the location of the two geosites documented from Mosawdah volcano

Mosawdah volcano (24° 14′ 10″N; 39° 47′ 51″E; 1010 m asl) is a complex nested lava spatter cone with multiple crater rims, spreading fractures across the eruptive products surrounding the main crater (Fig. 3.62) and an at least 30 meters deep, perpendicular walled pit crater exposing a welded and rheomorphic lava spatter rim. The volcanic cone of Mosawdah volcano itself represents a single well-defined geotope where several individual geosites can be defined in accordance with the visible volcanological details. Each potential geosite is within walking distance of the other.
Fig. 3.62

Overview of the crater of the Mosawdah volcano looking from the SE

The volcano has been assigned to be ~0.6 Ma and 4500 BP in age (Camp and Roobol 1989), based on relative stratigraphy relationships with nearby volcanic landforms. At least three concentric nested crater rims can be identified around the main pit crater (Fig. 3.62). Each crater rim has a steep, near-perpendicular crater wall and relatively flat outward dipping outer rim. The entire volcano appears as a large (about 700 m wide) nested volcanic landform with multiple craters. Mosawdah volcano shows some similarities to the 1256 AD nested volcanic cones and logically can be connected to the geoeducational programs developed for the 1256 AD cones as part of the Precinct 1 of the proposed Al Madinah Volcanic Geopark. Mosawdah volcano however can provide a much more graphic example of an eruption that produced fast-moving, large-volume lava flows, high eruption rate driven lava fountaining and a complete rheomorphism of the accumulated pyroclasts along the active vents, similar to those that have been described during the Izu Oshima eruption in Japan in 1986 (Sumner 1998; Sumner et al. 2005). The Mosawdah volcano is open toward the northwest, from where a ~10 km long lava flow initiated toward the SW at about the same elevation from the outside flank of the cone as the base of the central pit crater.

The lava flows are relatively thin (few metres) tube fed pahoehoe flows and channelized a’a lavas that spread broadly across the low lying areas around the cone. The lava fields are clearly visible from the top of this geotope and provide a spectacular view of a lava flow field that partially engulfs the central cone, leading to its gradual spreading and rafting. The main volcanic cone is about ~0.6 km in diameter at the base, with a maximum height of ~50 m, suggesting some sort of gradual spreading of the cone on top of a hot and fluid lava base.

Large lava spatter cones are common volcanic landforms associated with extensive low viscosity basaltic eruptions on intra-continental to ocean island settings (Kereszturi and Németh 2012a, b). There are numerous, well described examples of active lava spatter cone formation from Hawaii (Lefevre et al. 1991; Parfitt and Wilson 1995, 1999; Parfitt et al. 1995) or Iceland (Ilyinskaya et al. 2012). Lava spatter cone remnants are common volcanic landforms among many of the Miocene to Pleistocene European or western US intra-continental volcanic fields (Carracedo Sanchez et al. 2014; Valentine et al. 2000); however, they are commonly heavily vegetated and only sporadic outcrops of preserved rocks are visible. The Mosawdah volcano offers a perfectly exposed, non-vegetated, large volume example of the result of lava spatter eruptions. Mosawdah volcano also has a regional significance in terms of understanding the full spectrum of volcanic processes in the Harrat Al Madinah. The volcanism that created the Mosawdah volcano represents an end-member of the eruptive style spectrum, characterized by continuous and prolonged activity of relatively low lava fountains that provided fast accumulation of lava spatter around the active vent(s), promoting the formation of localized agglutinate and clastogenic lava flows.

The high heat source and the fast accumulation rate of lava spatter, in concert with a stable lava lake in the center of the volcano, created a ductile, partially molten base of the volcano, promoting gradual spreading and repeated lava lake drain-back and infill associated with extensive lava flow outbreaks. In this respect, the Mosawdah volcano is probably the best exposed and easiest to access site in the Harrat Rahat to provide an insight into the active lava fountain and lava lake driven eruption style that was common in the eruptive history of many of its volcanoes. Therefore, Mosawdah volcano and the proposed precinct around it bear significant geoeducational value to demonstrate the highly effusive, moderately explosive style of volcanism the region has experienced in the past and could experience in the future.

3.10.1 Mosawdah Volcano Geotope Geosite—Pit Crater, Lava Outflow and Spatter Rampart [24° 14′ 13.80″N; 39° 47′ 48.37″E]

The Mosawdah volcano proximal crater rim forming successions are typical for fast accumulating lava spatters that locally form welded and clastogenic zones that squeezed re-melted material between individual lava spatter clasts (Sumner et al. 2005). The outline of lava spatters can be recognized; however, their recognition is becoming increasingly difficult toward the centre of the volcano (Sumner et al. 2005). This facies architecture indicates that the volcano erupted dominantly lava fountains, which must not have been very high (in the range of up to tens to few hundreds of meters) in order to be able to retain enough heat upon landing to allow the lava spatters to agglutinate and weld together locally, feeding clastogenic lava flows (Wolff and Sumner 2000). The near continuous section exposed in each of the preserved inner crater walls suggests no time break or interruption in lava fountaining (Fig.  3.63). The fast accumulation of lava spatters and the ongoing clastogenic lava flow formation must have generated an inferno in the proximal areas of the volcano, providing a soft, molten base to slowly slide and spread apart the cone itself, promoting repeated lava lake drawbacks, refill, volcanic sector dilation and partial cone rafting (Wolff and Sumner 2000). This geotope also shows a fantastic example to see how lava outpouring and pit crater formation can be connected. The central crater of the volcano is very deep and show evidences of plastic deformation of the accumulating spatter. The geoeducational value of this geosite is to highlight the fast rate of spatter accumulation needed to be able to form clastogenic lavas and therefore it provides a very important location to appreciate the significance of eruption rate in the formation and growth of scoria and spatter cones.
Fig. 3.63

Lava spatter dominated section of the crater wall area of the Mosawdah volcano [24° 14′ 11.31″N; 39° 47′ 51.55″E] Geosite—Collapsing and Spreading Section of Cone [24° 14′ 12.73″N; 39° 47′ 53.48″E]

Due to the fast accumulation of hot pyroclasts and their agglutination and remelting to form clastogenic lava flows has a strong implication on the volcanic edifice stability (Németh et al. 2011; Sumner 1998; Sumner et al. 2005; Wantim et al. 2011). This geosite provides a graphic example to demonstrate this process and show how the volcanic edifice slowly spread apart along fractures (Fig. 3.64) over a hot still ductile deforming lava pond partially forming the lava lake in the growing crater. This site also poses another important aspect to form disintegrating scoria cones by potential bulging of shallow intrusive bodies due to the gravitational instability of large blocks of the core of the cone that can be uplifted by some upward moving melt packets in the base of the cone.
Fig. 3.64

Fractures likely formed due to the gradual spreading of the core of the growing volcanic edifice due to gradual outpouring of lava from the central lava lake and to the hot and plastically deforming base of the cone itself [24° 14′ 12.62″N; 39° 47′ 53.88″E]

3.10.2 Al Anahi Volcano Geotope [24° 15′ 34.03″N; 39° 47′ 18.51″E]

Just north from the Mosawdah volcano, a remote scoria cone form a remarkable landform. The Al Anahi cone is a large scoria cone with complex crater and an extensive lava flow, all showing young morphological stages. The Al Anahi volcano can be defined as an intact geotope and can form an alternative site to visit for those wish to have adventure style geotourism. Geosite—Al Anahi Cone [24° 15′ 34.03″N; 39° 47′ 18.51″E]

Al Anahi cone is a scoria cone that is among the largest cones in the Harrat Rahat (Fig. 3.65). The scoria cone is unique and it can be defined as a geosites on the basis that it has fairly high amount of fine ash and fine lapilli as an edifice building pyroclasts, and therefore suggests that its eruption was likely more explosive Strombolian style than pure Hawaiian lava fountain-dominated. The cone has an elongated crater that is easy to access by a short low grade ascend to the top. Around the crater rim the visitor can make a full roundtrip by walk, and see above the outflow point of a long lava flow partially rafter away small part of the cone.
Fig. 3.65

Al Anahi scoria cone [24° 15′ 34.03″N; 39° 47′ 18.51″E] Geosite—Al Anahi Flow Field [24° 14′ 51.53″N; 39° 45′ 3.01″E]

The lava flow of Al Anahi is defined as a geosite where the visitor can explore a thick and long lava flows with aa-type lava flow surface textures. The Al Anahi lava flow is one of the best examples in the Harrat Rahat to show typical aa lava surface textures. The lava flow is steep walled, contain abundant rugged lava spines, collapsed blocks and have milled cauliflower textures all indicative to more viscous lava to be emplaced. The flow itself acts as a major barrier to cross the harrat, and visits to this geosites are only recommended along its margins. In the marginal areas this lava flows show lots of evidences of late stage squeeze outs and collapse of the lava fronts exposing sheared conchoidal shape lava surfaces with pressure ridges. This geosite has a high educational value to demonstrate the lava morphology type varieties the lava viscosity can create, and also provide graphic example to demonstrate the volcanic hazard caused by a fundamentally aa-type lava emplacement.

3.10.3 Fissure Vent and Five Fingers Flow Field Geotope

One of the enigmatic locations in the Northern Harrat Rahat region is a chain of volcanoes along some visible surface fissures that look like a fissure source of some young lava flow field cited as “five fingers lava flow” (Fig. 3.66). The fissure oriented scoria and spatter cones are spectacular examples of a proximal source region of a major lava flows that initiated fine major lava flows filled valley networks in the NE side of the volcanic field. This region can be defined as a single major geotope on the basis of the unique link of its volcanic features demonstrate the evolution of a fissure aligned volcanic chain that emitted significant volume of fluidal magma through pahoehoe to aa lava flows.
Fig. 3.66

Five fingers” lava flow system on GoogleEarth image Geosite—Fissure [24° 15′ 41.63″N; 39° 51′ 34.99″E]

An open fissure exposed in a lava flow field just west of a sealed road that can be defined as a key geosite to demonstrate the ground movement and fissure formation associated with volcanic eruptions (Fig.  3.67). The fissure is 2-10 m wide, deep, and exposes half section of whaleback type lava flows. The fissure can be traced over kilometres of length in satellite images and likely associated with some regional tectonic features along dyke movement took place. This geosite is very significant in geoeducational perspective as it can be shown to visualise the failed eruption took place in 2009 in the Harrat Lunayyir that caused seismic unrest and forced to evacuate thousands of people due to the fair of a volcanic eruption (Duncan and Al-Amri 2013; Jonsson et al. 2010; Koulakov et al. 2014; Mukhopadhyay et al. 2013). While the origin of this fissure is unknown its presence and its location in relationship with other fissure aligned vents indicates that it had some link with dyke intrusions and eventual fissure eruptions that formed and shaped of the face of this part of the volcanic field.
Fig. 3.67

Open fissure cut through a thick lava flow field aligned in the same orientation as the scoria and spatter cones nearby [24° 15′ 41.63″N; 39° 51′ 34.99″E] Geosite—Southern Fissure Cones [24° 17′ 52.80″N; 39° 50′ 59.83″E]

The region commonly referred as the fissure vent zone (Murcia et al. 2014) can be divided into a southern and northern segment. This division is purely based on practical sense by the accessibility of the area. The southern segment is a very rugged region and to access this part needs great deal of orientation and potentially to visit this geosite would require organized tour. The fissure region when the visitor passing through, difficult to see due to the great variety of lava surface textures, and small spatter cones littered the terrain. The southern segment of the fissure aligned vent connected well with the exposed fissures explained in the previous geosite. Along a zone of about 7 km length what this geosite defines numerous individual scoria cones can be identified. Many of these scoria cones are rather chains of cones, and many of them have elongated craters. The southernmost part of this geosite is difficult to access, and only a look out can be taken from its southernmost locations toward a rafted and partially collapsed fissure network that is the inferred source of the southernmost arm of the five fingers lava flows. Further in the north the fissure aligned cones can be accessed on dirt roads, however, to navigate in the harrat in this rugged terrain needs lot of attention. Along a dirt road a spectacular spatter cone that looks like a giant hornito can be seen (Fig. 3.68), that acted as appoint source of lava fed from the southernmost arms of the five fingers flows. Along the fissure small lava flows forming a ribbon-like network of flow surfaces indicating the running nature of the low viscosity melt that must have just outpoured along this fissure (Fig. 3.69). Further to the north a complex and well-developed large lava spatter cone chain forming a fantastic landscape showing the dynamic nature of the entire fissure network feed lava over tens of km2 areas.
Fig. 3.68

Giant hornito-like spatter cone feeding fluidal (low viscosity) lava flows [24° 20′ 0.08″N; 39° 51′ 2.59″E]

Fig. 3.69

Low viscosity lava formed amazing lava network on the surface of a fissure-fed spatter cone. Individual lava tube is about a meter wide Geosite—Northern Fissure Cones [24° 20′ 49.16″N; 39° 49′ 56.73″E]

The northern sector of the fissure aligned vent system in the Northern Harrat Rahat is the apparent source of the northern two arms of the five fingers lava flow (Murcia et al. 2014). In this location older cones form an obstacle for the outpouring of the lava however some remains of the original lava spatter cones can be recognized alongside with a great variety of collapsed pits and lava tube roofs. This geosite has a geoeducational value because it shows clearly that the rejuvenation of volcanic activity in a same place can form amalgamated volcanic landforms that overlap each other. The interaction of the vents emitted the lava flows with older cones aligned to the same direction than the fissure suggests that the region was common area where volcanic eruptions took place. This site therefore can contribute significantly to our understanding of the volcanic hazard aspect of a long-lived volcanic field. Geosite—Five Fingers Lava Flow Field Proximal Section—South [24° 20′ 49.16″N; 39° 49′ 56.73″E]

The proximal section of the lava flow fields of the five finger lava flow is an important geosite. While on the satellite image and on the field the region is an area where only thin lava flow preserved, it can provide a very important eruption mechanism aspects to the visitors. Interestingly in these regions only the marginal chilled crust of a former inflated flow system is preserved, and scattered lava crust rubbles, that form a field with thin obscured lava blocks (Fig. 3.70). The preserved lava crusts and marginal fragments with some squeeze out flows suggest that the majority of the flow must have been removed gravitationally. Such situation can be envisioned that a ponded lava flow formed nearby the fissure that inflated, and then when it has reached a threshold volume value it has been collapsed and emptied its fluid interior fast, that has carried away the broken crustal regions. This geosite provides a very graphic image for this potentially dangerous process we need to consider in eruption scenario developments for future lava flow eruptions in the region.
Fig. 3.70

Proximal region of the southern segments of the five finger lava flow Geosite—Five Fingers Lava Flow Field Proximal Section—North [24° 21′ 12.61″N; 39° 49′ 14.15″E]

In the northern sector the proximal lava flow regions of the five finger flows show large scale hummocky surface morphology (Fig. 3.71). These features can be interpreted as an inflated flow field that has been partially preserved, e.g. they have not been removed by gravitational collapse and drag of the fast emptying of the ponded lava. In this respect this geosite is an important one to compare the lava pond emptying processes that can be seen in detail in these sites.
Fig. 3.71

Whaleback style lava morphology of a large inflated and preserved flow part of the source region of the northern sectors of the five finger lava flows [24° 21′ 12.61″N; 39° 49′ 14.15″E] Geosite—Five Fingers Lava Flow Field Median Section [24° 24′ 56.11″N; 39° 50′ 56.18″E]

The medial sections of the five fingers lava flows show typical transitional lava flow morphotypes (Fig. 3.72). This geosites all along the middle sections of any of the five fingers five arms can be visited with an aim to demonstrate the nature of the pahoehoe to aa flow transition in the form of ripping off solidified lava crusts that then homogenized and mixed with the moving lava flow main body. This geosite can provide a very insight to the visitor about the flow transition and the gradual ponding and breakout as an important movement mechanism of transitional type lava flow movement.
Fig. 3.72

Pahoehoe to aa transitional lava flow morphotypes in the medial sections of the five fingers lava flow [24° 24′ 56.11″N; 39° 50′ 56.18″E] Geosite—Five Fingers Lava Flow Terminus [24° 23′ 42.79″N; 39° 59′ 18.36″E]

The terminus of the five fingers lava flow five arms provide a good example to envision how a transitional, more aa type lava stops in the end (Fig. 3.73). This geosite also very graphic example to imagine the momentum of such a long (over 10 km) lava flow can have and how it come to a rest by forming an unconfined fan in its end that hit the pre-existing topography.
Fig. 3.73

Lava terminus of a nearly 15 km long lava flow [24° 23′ 42.79″N; 39° 59′ 18.36″E] Geosite—Five Fingers Lava Flow Field’s Rafted Cone Material and Northern Flow Terminus [24° 26′ 42.78″N; 39° 50′ 23.48″E]

One of the most intriguing textural feature of most of the lava flows in the Harrat Rahat is the potential of this type of lava flows to carry bulldozed flow material as well as pre-existing cone material as rafted debris (Fig. 3.74). This geosite has a significant message for volcanic hazard of large lava flows inundate inhabited human built environment, as they can move building fragments far, and apparently they cannot be stopped easily by obstacles (Fig. 3.75).
Fig. 3.74

Rafted nearly completely homogenized cone material (lighter textured fragments among darker coherent lava clasts) incorporated in the aa lava in the distal facies of the five finger lava flow arms [24° 26′ 42.78″N; 39° 50′ 23.48″E]

Fig. 3.75

Zargat Abu Zaid scoria cone rafted cone and ash covered lava field. Photo was taken from the point of [24° 16′ 32.70″N; 39° 50′ 19.38″E]

3.10.4 Zargat Abu Zaid Geotope [24° 16′ 32.83″N; 39° 50′ 25.16″E]

Zargat Abu Zaid is a large scoria cone just west of the fissures fed five fingers lava fields. The cone is very likely an older cone as its flank has extensive gully network in spite of its steep cone flank. The crater rim is well-preserved as a collar-like feature as a result of the preservation of softer scoria beds capped by lava spatter banks. This scoria cone is a perfect example to demonstrate the syn-eruptive eruption style influences on the volcanic facies architecture that then controls the post-eruptive erosion style of the cone (Kereszturi and Németh 2012a, b). The scoria cone also has an extensive lava field that partially rafter away its northern sector that have been partially rebuilt by the ongoing eruption. This scoria cone with its lava field can demonstrate the cone rafting processes that took place in a time when the cone was still erupting and producing ash and lapilli that then partially covered the moving lava flow. The cone with its lava field together is a geotope due to the intact geological features they can demonstrate. Geosite—Crater Infill [24° 16′ 30.02″N; 39° 50′ 17.88″E]

The crater of Zargat Abu Zed scoria cone is partially filled with reworked volcaniclastic material as a sheet wash deposit accumulated in the crater of the cone (Fig. 3.76). The crater rim composed of agglutinated and partially welded lava spatter that acted as an erosion resistant cover protecting the cone from significant erosional lowering. Along the crater rim outer margin the erosion is dominated by rock falls due to undercutting of the solid and erosion resistant agglutinate. In the inner part of the crater steep dipping agglutinate beds forming the upper section of the crater that gradually covered by volcaniclastic sediments in the lower section of the crater. The northern edge of the crater rim is truncated and repeatedly rebuilt during rafting event of lava flows exited the lower northern flank of the cone. This geosite has a high geoheritage and geoeducation value because it is an easy to access location where the visitor can learn great variety of volcanic processes. In addition the geosite also can provide a good reference to show to the public that the final shape of a volcano can be the result of a combination of primary, edifice building and secondary, syn- and post-eruption related erosional processes.
Fig. 3.76

Complex volcaniclastic sedimentary infill in the Zargat Abu Zaid scoria cone’s crater looking from the point of [24° 16′ 30.02″N; 39° 50′ 17.88″E] Geosite—Rafted and Ash-Covered Flow Field

The northern sector of the Zargat Abu Zed scoria cone has been partially destroyed and partially rebuilt by subsequent eruptions. The northern sector of the cone composed of hummocky surface that is primarily a lava flow (Fig. 3.77) field initiated from the lower sector of the cone flank through a lateral “bocca”. The lava flow is nearly completely covered by thick ash and lapilli nearly in its entire length making difficult to see the original surface and texture of the lava flow. The lava flow is initiated from the lower part of the cone and its movement is likely rafted part of the cone away. Larger cone sections on top of the lava flow is supporting this idea however the thick ash cover on the lava flow hinder further, more detailed interpretation. The fact that the lava flow field also covered by ash and lapilli suggest that the time the lava flow was still moving the scoria cone still had an explosive ash- and lapilli-producing eruption. This geosite has a high geoeducational value because it helps to link the cone (edifice)-building eruption styles with those forming the lava flows. Visiting this geosite and the entire Zargat Abu Zed geotope can help the visitor to recognize the link between explosive and effusive processes associated with the harrats’ volcanism. A geotope like this can serve well to develop a realistic volcanic image in the mind of the visitor in what the various volcanic processes are linked and not presented only as individual singular events and processes.
Fig. 3.77

Rafter lava flow field of Zargat Abu Zaid with ash cover looking toward Al Madinah City (north) from the crater rim of the cone

3.10.5 As-Sahab Geotope [24° 21′ 16.42″N; 39° 48′ 48.00″E]

As-Sahab is large and complex slightly older scoria cone that is in the region where the five fingers lava flow fields erupted along the main fissure system (Fig. 3.78). The cone complex has no assigned lava flow fields or at least it is too difficult to link the many old lava flows located nearby this cone complex to be able to say confidently which one belongs to the cone. The cone together however can be looked at as a complex geotope due to its special location. The cone acted as a barrier and obstacle for the five fingers fissure eruption and its lava flows were diverted by the cone itself. This location can show a perfect site to the visitors to appreciate the effect of a pre-existing topography in the potential path of subsequent lava flows. This geotope also poses a fundamental question the visitors could see clearly, that older cones exists in the area where young fissure-fed lava flows erupted, moreover they are aligned in the same way as the young fissures and flows, and seemingly erupted in the same style. This has a significant message and high geoeducational value as this geotope can show very graphically that the NNW—SSE dorsal zone of the Harrat Rahat was/is one of the main eruption site of the volcanic field, and it is very likely structurally controlled as modern fissures and associated cone chains indicate it.
Fig. 3.78

As-Sahab scoria cone complex on a GoogleEarth image. Top left corner of the map view is [24° 21′ 47.07″N; 39° 48′ 6.99″E] Geosite—Cone Complex

The As-Sahab scoria cone is a large cone in its advanced erosion stage (Fig. 3.78). The cone southern side is open and the cone has been eroded and lowered significantly. The geosite can be accessed by foot through the southern open crater. In the interior of the crater the inner crater wall is filled with lava spatters forming hanging lava drapes on the agglutinated steeply crater-ward dipping beds. Large clastogenic lava zones can be seen from below, however, access to those sites and in general to the crater rim’s higher part is not advisable due to high potential for rock falls. The crater internal part is partially filled with volcaniclastic deposits mixed with aeolian dust. In spite of the infilling, the crater is still forming a shallow depression suggesting that its original depth and geometry must have been dramatic, and likely hosted a lava lake that have been drained laterally by “boccas” feeding the older lava flow fields located in this area. The significance of this geosite is that it can show a link between young and older volcanic landforms and demonstrate clearly that similar volcanic processes must have taken place over thousands and thousands of years. This geosite also provides a good example to compare the older and younger volcanic landforms. Geosite—Interaction Between Fissure Flow and Cone

Jabal Al Malsa cone northern and eastern sector is partially covered by the five finger fissure-fed lava field (Fig. 3.78). Previously the cone was under debate as a potential main source of the fissure fed young Quaternary lava flows nearby. Recent fieldworks however suggest that Jabal Al Malsa is an older cone due to its morphological appearance. Along the contact between the young fissure-fed lava flows and the cone it is perfectly visible how an obstacle can divert and interact with a pahoehoe to aa transitional lava flow field. Along this contact zone the visitor can see complex lava surface textures while in the distant regions the proximal lava flow fields show a stunning volcanic landscape with open channels, pressure ridges, inflation features, tumuli and large rotate blocks of ripped up lava crusts. The geosite geoeducational value is high as it is also provide a very good vantage point to demonstrate that the older scoria cones in the region are also aligned to the same fissure orientation along the younger extensive lava flows were emitted.

3.10.6 Halat Khamisah Scoria Cone and Lava Flow Field Geotope [23° 55′ 25.18″N; 39° 54′ 38.53″E]

The Halat Khamisah scoria cone is defined to be a young scoria cone located near a major trans-Arabian gas pipeline (Fig. 3.79). The cone and its lava flows are remote and only dirt road access is available that might change in the future when a service road along a major gas pipeline is constructed. It is located in the central part of Harrat Rahat, and it can be selected as a type locality to demonstrate that Harrat Rahat had some other young volcanic region where scoria cones and lava flows erupted probably in the same time as the five fingers lava flows near Al Madinah. The cone and its single lava flow are together defined as a geotope on the basis of its volcanologically common features that can tell a unique story to the visitor. The geotope has a great educational value as it can demonstrate that young eruptions are not restricted to specific northern regions of the Harrat Rahat but they are known elsewhere. This geotope also can show that extensive ash-producing eruptions are also not restricted to the 1256 AD eruption but similar eruptions took place elsewhere. This geotope also can provide insight to understand the complexity of the evolution of Harrat Rahat and appreciate its volcanism’s time and space dispersion.
Fig. 3.79

Halat Khamisah scoria cone and lava flow is a young volcanic region in the southern central part of Harrat Rahat clearly visible by its young lava flows shown up with different textures on a GoogleEarth image. Top left corner of the map view is [23° 56′ 43.04″N; 39° 46′ 45.92″E] Geosite—Ash Plain [23° 55′ 39.00″N; 39° 54′ 48.01″E]

The Halat Khamisah scoria cone forms a fairly large scoria cone that has steep cone flank indicating its young age. The edifice is covered by dark (black) scoria ash and lapilli that is littered by well-developed spindle bombs especially in the proximity of the cone. Where the cone slope angle reduced, black ash plain can be traced over few kilometres away from the cone foothill. This ash plain is exposed in cross-sectional view in few wadis about a km away from the cone, providing unique window to the internal texture, thickness and vertical variations of a scoriaceous ash and lapilli succession. The ash plain as a geosite beside its aesthetic value provides an important insight to understand the explosive eruptions associated with the cone building. The extensive nature of the ash plain suggests that at least in few stages, the eruption of the Pipeline cone might have been more violent than a normal Strombolian style explosive eruption, and it has been able to produce large volume of finer grained pyroclasts that were dispersed across the landscape as documented elsewhere (Kawabata et al. 2015; Németh et al. 2011; Pioli et al. 2008; Rowland et al. 2009). This geosite has a great geoeducation value as it demonstrates that in Harrat Rahat violent Strombolian style eruptions took place and we have every reason to assume that such eruptions might take place in the future. Geosite—Cone Crater [23° 55′ 11.93″N; 39° 54′ 28.45″E]

The Pipeline cone crater can be accessed relatively easily from the cone southern foothill. The walking path to the crater is a gentle ascending path going through various lithofacies of the edifice building pyroclastic units. There are large spindle bomb-rich parts and fine grained more scoriaceous lapilli- and ash-dominated successions suggesting that the eruption style of this cone through its growth has changed many times. The crater of the cone is partially open toward the west and it is occupied by an outflow of a major blocky—aa lava. In the breaching point of the lava flow the cone flank is destroyed and displaced by rafting, however rafter materials cannot be traced long from the breach point suggesting that the crater rim might have been originally low in the west. The proximal zone of the lava filling the crater is typical aa lava with spines, large lava columns and lifted and rotated angular, crystalline lava blocks (Robert et al. 2014; Wantim et al. 2011). This geosite has a reasonable geoeducational value as this is among those rare sites where typical aa and block lava is exposed from their proximal section. Pahoehoe lava surface types are rare in this lava flow field. Geosite—Block Lava Flow Field [23° 54′ 58.21″N; 39° 53′ 3.59″E]

This geosite refers to a lava flow cross sectional point about 3 km from the crater down-flow. Going up to the crater and follow the lava flow down is a very challenging track and it is not advised as the danger of injury is high due to the numerous steep and deep fissures between lava blocks. In this geosite however it is clearly visible how a typical aa-lava looks like. The lava is composed large blocks, and in places it closely resembles block lavas rather than aa. The lava flow interior has numerous large rounded cauliflower type lava balls, and vertically oriented spines as typical features of aa lavas. This geosite geoeducational value s to demonstrate that a seemingly block-dominated lava that is generated from a higher viscosity melt (more crystalline for instance) can produce lava flows that can travel over 10 km from their source even in a relatively flat surface.

3.11 Precinct 3—From Silicic Lava Domes to Explosion Craters

Explosive volcanic processes are typically the most hazardous aspect of volcanism to human life and associated built environments of the modern society. Explosive volcanism registers on a broad scale from weak to highly explosive eruption styles.

The Precinct 3 at the proposed Harrat Al Madinah Volcanic Geopark named as “From Silicic Lava Domes to Explosion Craters precinct” offers a very dramatic insight for the visitors into the eruptive products that result from various types of explosive volcanism from different magma compositions (Fig. 3.16).

Explosive volcanism associated with monogenetic intra-continental volcanic fields is typically caused by magmatic gas expansion of volatile-rich magmas, commonly more silicic in composition, and/or by magma-water interaction, causing phreatomagmatic explosions that form base-surges and other pyroclastic density currents and construct maars and tuff rings (Valentine and Gregg 2008). The central part of Harrat Al Madinah contains the best closely spaced examples to see the results of explosive volcanism in the form of extensive pyroclastic density current deposits and broad and deep explosion craters (Camp and Roobol 1989). These violent types of volcanism are inferred to be several hundreds of thousands of years old (Camp and Roobol 1989), seemingly forming a concentration of specific volcano types in a remote but accessible region of the proposed volcanic geopark. As it is the furthest precinct from Al Madinah city, as well as it contains some of the oldest volcanism in the Harrah Al Madinah, it is logical to offer this precinct as the last for the visitor. The logistical difficulties in visiting this precinct also make this location suitable for the more adventurous tourist with higher levels of fitness (Moufti and Németh 2013a). However, visitors to the precinct will be rewarded with probably the most dramatic, and one of the most unique, volcanic landscapes anywhere on Earth.

As is typical of arid areas with limited ground and surface water availability, the Al Madinah Volcanic Field has dominantly produced scoria cones, spatter cones and large lava flows, all derived from “dry” magmatic eruptions as presented in the previous two precincts (Moufti and Németh 2013a). However climate changes over the lifespan of a volcanic field (millions of years) can dramatically change the hydrology and hydrogeology of the region, and an otherwise “dry” eruption style-dominated field can quickly can be switched to a “wet” eruption dominated system, even without requiring dramatic magmatic composition changes (Kereszturi et al. 2011). As a result such volcanic fields can produce phreatomagmatic volcanoes such as maars and tuff rings.

Beside the dramatic volcanic landscapes of the explosion craters, the Precinct 3 includes truly unique volcanic landforms that record silicic lava dome formation and associated features. It is an interesting aspect of the Harrat Al Madinah’s volcanism, which has global significance, that silicic (mostly trachytic) lava domes have been produced in the same region where basaltic scoria and lava spatter cone forming eruptions were dominant (Moufti and Németh 2013a). There has been a diverse range of silicic volcanism through non-explosive lava dome eruptions to block-and-ash flow generating violent eruptions (Moufti and Németh 2013a). Seeing these features coexist with features from basaltic and trachytic monogenetic volcanism is one of the most geologically intriguing aspects of the proposed geopark, in terms of understanding the origin of the evolved volcanism in dispersed, intra-continental systems commonly referred to as monogenetic fields.

In the proposed precinct, three well distinguished and easy to access trachytic lava domes as individual volcanic geotopes are included in the selected list of high value locations. However, from these lava domes such as local high points of the region, further distant lava domes can be seen toward the east and northeast as completing the picture for the visitor to appreciate that the region is very rich in silicic lava domes (Fig. 3.80). The geotopes and their geosites of the Precinct 3 provides very graphic insights to the physical processes associated with lava dome formation to be compared, with cryptodomes through to explosion craters, and complex volcanic structures showing evidence for multiphase, and commonly multi-chemical (basaltic to trachytic), eruptions.
Fig. 3.80

Distant silicic lava domes dominate the horizon in the southern margin of the proposed Harrat Al Madinah Volcanic Geopark demonstrating that the visitor has entered to a region the intracontinental volcanism produced a great variety of volcanic landforms [24° 13′ 19.65″N; 39° 50′ 59.90″E]

The variety of trachytic lava domes exposed in is precinct are spectacular and they offer a good geoeducational program to build on them to link this geotopes and geosites to other well-known, recently erupted silicic lava domes, including Unzen in Japan (Kaneko et al. 2002; Yamashina and Shimizu 1999) and Mount St Helens (USA) (Anderson et al. 1995). The similarity in size, volume and eruptive products of the trachytic lava domes of the Harrat Al Madinah to those lava domes generally associated with subduction-related strato- and/or composite- volcanoes, makes the HAMVG truly unique and globally significant; and can make the proposed Harrat Al Madinah Volcanic Geopark as a potential “Makkah of Volcanologists” (Moufti and Németh 2013a). The scientific value of this precinct is self-defined. The perfect exposures, the lack of vegetable cover, the great visibility and the numerous longitudinal sections along gullies offer great research potential in these locations to scale the physical parameters of pyroclastic flow forming eruptions. In addition, the availability of pyroclastic deposit-engulfed scoria cones and other morphological obstacles can help to calibrate the energy budget of pyroclastic flows and therefore the precinct could serve as an important study location for such scaling volcanological work. Considering the “monogenetic volcanism” on display, this precinct offers a dramatically new view that will enable visitors to appreciate the complexity of such volcanism and see the link between focused (strato- and composite volcano-producing) and dispersed (purely monogenetic volcano-producing) magmatic plumbing system-associated volcanism, which will potentially make this volcanic geopark globally very significant (Moufti and Németh 2013a).

3.11.1 Matan Lava Dome Geotope [24° 13′ 31.71″N; 39° 50′ 23.56″E]

In the NW entry to the precinct, a dirt road follows a dry valley that connects to a broad alluvial fan which is bordered by the large Matan lava dome (Fig. 3.81). It is a complex volcano with a basal diameter of about 1.8 km. The dome is clearly a composite lava dome (Fig. 3.81) recording multiple styles of silicic magma emplacement that range from rigid to more plastic emplacement. Lava dome rock facies are diverse as a reflection of variously degassed and viscous trachyte being emplaced in a relatively confined area. Lithological domains can be seen in outcrops and they are commonly reflected by colour differences in the exposed rocks. The lava dome itself is dominated by coherent lava dome cores with some rock-fall and lava dome carapace breccias, some short run-out distance (<500 m) and relatively thin pyroclastic flow deposits can be traced around the main body of the lava dome complex all typical for a lava dome anywhere (Brenna et al. 2012; Costa et al. 2012; de Vries et al. 2014; Fink and Griffiths 1998; Miallier et al. 2010; Riggs et al. 1997). On the SW side of the lava dome, a volcanic crater with a flat crater floor suggests some initial explosive volcanic eruptions prior to the emplacement of the main Matan lava dome complex. This explosion crater is the source of at least two pyroclastic flow units traceable over a kilometre from the preserved crater rim. This location not only provides a graphic example of trachytic lava dome formation, but it also links the trachytic explosion craters with trachytic lava dome forming events, giving an example of the interplay between dramatically different eruptions styles.
Fig. 3.81

The Matan lava dome geotope from the air showing a superb complex lava dome easy to access Geosite—Matan Lava Dome Side [24° 13′ 12.97″N; 39° 50′ 2.40″E]

This geosite is the base of the lava dome complex in the southern side of the volcano. To access higher portions of the lava dome require some rock climbing skills and still it would be a difficult and demanding climb. In the base of the lava dome however a great variety of large blocks are ready to be observed and they can provide enough information to understand the lava dome-forming processes. Large blocks of flow banded trachytic rocks are the most common rock type among the debris apron. These type of rocks are typically representative for the lava dome growth and they can form zones across the original cliff faces representing specific parts of the lava dome complex. From the distance the shape of the lava dome is noteworthy especially its steep upper segment (Fig. 3.82). There are no obvious pyroclastic rock units exposed around the lava dome complex suggesting that lava dome collapse and associated explosive eruptions were plazed just a minor role in the evolution of this volcano. The geoeducational value of this geosite is that the visitor can get an immediate insight of the highly viscous nature of the magma formed this volcano. This view can be contrasted by nearby basaltic spatter cones and lava flows which are much smaller and more flat volcanic landforms. In addition, this location is in easy access from a sealed road.
Fig. 3.82

Matan lava dome complex from the geosite located in its southern foothill. Photo was taken from [24° 13′ 12.97″N; 39° 50′ 2.40″E] toward the NE Geosite—Matan Lava Dome Side Crater [24° 13′ 11.75″N; 39° 50′ 5.15″E]

In the southwestern side of the Matan lava dome complex a shallow, broad crater is visible that is surrounded by a low pyroclastic rim. This location can be accessed by walking track from the previous geosite through a gentle ascending path that take the visitor to the southern crater rim’s top. Along this walk, the visitor can examine the debris apron surrounding the main lava dome, a typical volcaniclastic debris apron that is composed of short run-out distance block-and-ash flow deposits mixed with fluvial and aeolian deposits and rock falls from the main dome region. The crater itself hosts voclaniclastic debris from the western segment of the Matan lava dome suggesting that it was formed earlier than the main lava domes. The crater rim is composed of welded pyroclastic rocks interbedded with some unconsolidated trachyte fragment-rich pyroclastic succession interpreted to be small-volume block-and-ash flow deposits. There are no clear indications to support magma and water explosive interaction as the main process to be responsible for the formation of the crater in spite the fact that the flat-floored crater and its broad shape very common among tuff rings. The significance of this geosite is to demonstrate that explosion craters can be common features in association with lava dome-dominate eruptions. The easy access and the rewarding fantastic view can be used as main promotion features to attract visitors to this site. In addition from this location the visitor can see the Mosawdah volcano and its extensive lava field just north of the Matan lava dome.

3.11.2 Mouteen Lava Dome Geotope [24° 12′ 51.79″N; 39° 50′ 38.82″E]

Along the 4WD road to the heart of the Precinct 3, just about 3 km from the Matan lava dome toward the SE, the visitor can view the Mouteen lava dome (Fig. 3.83). The lava dome seems to be smaller than the Matan lava dome with an about 800 m diameter. It also seems simpler than the Matan lava dome structure by having a simple flat toped lava dome (Fig. 3.84). The very unique nature of this lava dome however in comparison to the Matan lava dome is, that the silicic lava dome nearly completely intruded, invaded and truncated an earlier basaltic scoria cone that is exposed in the SE side of this volcanic complex.
Fig. 3.83

GoogleEarth image of the Mouteen lava dome complex showing its complex geometry. The top left corner of the map view is [24° 14′ 5.32″N; 39° 49′ 29.02″E]

Fig. 3.84

Lava dome top of the Mouteen lava dome (middle view). Matan lava dome is visible in the right side of the view Geosite—Mouteen Lava Dome Hosting Cinder Cone [24° 13′ 3.80″N; 39° 51′ 11.35″E]

From the 4WD road taking the visitor to the interior of the Precinct 3 a short walk the visitor can access the Mouteen lava dome. Prior reaching the lava dome itself, the walking track pass through the flank of a cinder cone that has been truncated and invaded by the lava dome. The cinder cone composed of black to red scoria that is littered by large spindle bombs especially in the region of the crater rim (Fig. 3.85). The contact between the lava dome and the cinder cone is covered by debris apron however it is clear that the more viscous lava dome truncated the host cinder cone. It is difficult to constrain what timeframe the lava dome extrusion took place, e.g. how long after the cinder cone formed the lava dome grown in its crater. However there are no strong evidences to support that the lava dome formation was immediately followed the scoria cone formation and it is more likely that there was significant time gap between these two strikingly different eruption style and magma composition to reach the surface. This geosite therefore has a great geoeducational value as it records rejuvenation of volcanism in the same place where previously different composition magma formed volcanoes through a very different eruption mechanism.
Fig. 3.85

Spindle bombs form ballistic bomb region in the crater rim region of the cinder cone hosting the Mouteen lava dome [24° 13′ 3.80″N; 39° 51′ 11.35″E] Geosite—Mouteen Lava Dome Main Dome Complex [24° 13′ 3.55″N; 39° 50′ 50.37″E]

This geosite can be accessed by further walking to the top of the Mouteen lava dome. The visitor can examine the lava dome material with great detail and in the end of the track the top of the lava dome can be explored where spines, rock falls and inter-dome aeolian silt pans can be seen. From the end of the track in the North of the Mouteen lava dome top perfect view shows the Matan lava dome and in the distance the Mosawdah cone and lava field.

3.11.3 Jabal Al Malsaa Matam Volcanic Complex Geotope [24° 12′ 18.43″N; 39° 51′ 6.65″E]

Jabal al Malsaa Matam is a large volcanic complex with multiple vents and cone segments. From the top of Mouteen lava dome a perfect view shows its full extent as sitting on a large flat region covered by various pyroclastic density current deposits, lava flows, inter-cone stream valleys and accumulation zones of aeolian dust in lee sides of landforms (Fig. 3.86). The cone itself is large, and its volcanic architecture indicates that it must have been active long time, and it is likely represents a transitional volcano type between pure monogenetic and polygenetic volcanoes. This complexity of the volcano is apparent in its SW sector where various lava flows, craters, and pyroclastic rock units provide a complex set of volcanic edifice.
Fig. 3.86

Jabal al Malsaa Matam volcanic complex is a volcano with multiple vents and compound volcanic edifice [24° 12′ 18.43″N; 39° 51′ 6.65″E] Geosite—Benmoreite Lava Flow [24° 11′ 35.78″N; 39° 51′ 21.37″E]

In the SW foothill of the volcano a spectacular benmoreite lava flow is exposed. The lava flow shows intensive flow banding and a very unique flow top morphology closely resembling clastic rock textures. In several places the flow is partially cross cut by wadis where the rock surface is more polished exposing the coherent texture of the rock. This geosite is important as it shows a graphic example to the visitor that the distinction between clastic and coherent rock textures is not easy when we deal with silicic rocks (McPhie et al. 1993). The disadvantage of this geosite is that it is difficult to access. Geosite—Explosion Crater and View to the Main Cone [24° 11′ 41.26″N; 39° 51′ 21.13″E]

Just slightly above the benmoreite lava flow geosite, a low rimmed explosion crater exposes a thin pyroclastic succession indicative for magma and water explosive interaction (Fig. 3.87). This crater is flat floored and filled nearly completely with voclaniclastic debris eroded from the southern flank of the southern cone of the Jabal al Malsaa Matam volcanic cone complex. The broad crater is partially surrounded by accidental lithic-rich silicic lapilli tuff and tuff beds. The significance of this geosite is that it provides some evidences to support that phreatomagmatism took place in the formation of this crater. In this respect this crater can be contrasted with that located in the west of the main Matan lava dome. It also highlights the fact that small and single silicic craters (e.g. just more west from the Matam lava dome complex) can likely be resulted from single and short-lived phreatomagmatic explosive eruptions similar to those reported elsewhere (Herrero-Hernandez et al. 2012; Németh et al. 2012; Zimmer et al. 2010).
Fig. 3.87

Exposed phreatomagmatic pyroclastic rock units surrounding a single explosion crater in the southern sector the Jabal al Malsaa Matam volcano [24° 11′ 39.75″N; 39° 51′ 28.15″E]

3.11.4 Um Junb Lava Dome Geotope [24° 11′ 59.43″N; 39° 53′ 27.63″E]

Um Junb is a lava dome complex with a 1.5 km diameter volcanic cone and lava dome structure (Fig. 3.88). The pyroclastic cone forming the base of the volcanic edifice has been invaded by benmoreitic magma that formed explosive and effusive eruptive products. The pyroclastic record of this volcano indicates an initial explosive eruption that produced pyroclastic flows that engulfed nearby obstacles, such as pre-existing scoria cone that lower flank is partially covered by the pyroclastic flow deposit. The pyroclastic flow deposits from Um Junb volcano are restricted and hardly traceable further than 500 m from the preserved, otherwise eroded volcanic edifice (Fig. 3.89). The volcano is only accessible by intensive walking. The geotope itself has significance that its crater has been filled by a lava dome, while the silicic tuff ring is still reasonable intact. In this respect the volcano represents a stage of volcano development where the subsequent explosive eruptions and intense lava dome emplacement has not reached that degree that the initial volcanic edifice suffered significant truncation of its geometry.
Fig. 3.88

Um Junb lava dome on GoogleEarth satellite image. Top left corner of the map view is [24° 14′ 40.01″N; 39° 49′ 6.05″E]

Fig. 3.89

Um Junb lava dome complex from about 3 km distance. Photo was taken from the point about [24° 13′ 20.22″N; 39° 52′ 42.24″E]

3.11.5 Dabaal Al Shamali Lava Dome Geotope [24° 13′ 20.02″N; 39° 54′ 19.07″E]

Dabaal al Shamali is a well-developed lava dome easy to access from a sealed road (Fig. 3.88). The lava dome has an asymmetric shape from side view (Fig. 3.90). The lava dome is surrounded by a rampart-like feature that is an earlier stage lava dome remnant truncated by the subsequent extrusion of further lava. The volcano southern side exposes large and deep fractures. These fractures are inferred to be related with the gravitational dilation caused by the extruding lava in the centre of the lava dome. While this part of the volcano is spectacular, and the cone flank in spite of its steep slope fairly stable it is not recommended to be visited alone and without proper gears due to potential collapse of some of the rim of these deep fissures. This geotope has a significant geoeducational value as it can show clearly that a lava dome can be gravitationally instable and such instability can cause a collapse (de Vries et al. 2014). It is also evident from this geotope that such collapse can take place accidentally during the lava dome growth or well after the growing ceased.
Fig. 3.90

Dabaal al Shamali lava dome from the distance at a point of about [24° 12′ 6.21″N; 39° 54′ 58.36″E]

3.11.6 Gura 1 Explosion Crater Geotope [24° 13′ 5.58″N; 39° 53′ 29.36″E]

The Gura 1 volcano in the northern part of the Precinct 3 (Fig. 3.88) is a typical example of a “simple” explosion crater, which is a low-rimmed crater of 600 m diameter that has been partly overlapped by later a’a lava flows with abundant tumuli (Fig. 3.91). The crater rim of Gura 1 exposes pyroclastic surge-dominated sequences and poorly sorted explosion breccias that are dominated by a range of country rock lithologies. The deposits of the Gura 1 crater are confined to the rim around the crater and quickly pinch out over a few hundreds of metres from its crater rim. There are no widespread pyroclastic deposits (neither fall nor flow) associated with this crater, indicating that its formation was dominantly controlled by the explosive interaction of rising magma and ground water where the explosions generated ground-hugging base-surges that travelled a few hundreds of metres from their source (Austin-Erickson et al. 2011; Lorenz 2007; Németh and Cronin 2011). The basal deposits of the tuff ring are dominated by dense, angular trachytic lithologies, indicating the presence of silicic lava dome associated rocks beneath the vents that were disrupted by the explosive eruptions through the formation of Gura 1. Gura 1 can be interpreted as a shallow maar volcano, and highlights the potential effect of the presence of ground water on the resulting volcanic landform.
Fig. 3.91

Look out to the Gura 1 explosion crater from the distance looking toward Dabaal al Shamali lava dome. Photo was taken from a point about [24° 13′ 1.82″N; 39° 53′ 22.43″E]

3.11.7 Gura 2 Explosion Crater Geotope [24° 12′ 11.68″N; 39° 52′ 42.02″E]

Gura 2 volcano is a large volcanic crater (Fig. 3.88) that has produced the one of the most widespread pyroclastic flow deposits in the area of the proposed Precinct 3 (Fig. 3.92). The widespread pyroclastic deposits cover the surrounding low lands and climb over small obstacles, and can be traced high up on distant and tall volcanic cones (Fig. 3.92). The pyroclastic flow deposits’ light colour provides a dramatic landscape to the area that the visitor cannot miss. The pyroclastic flow-forming eruption style and the silicic (trachytic) composition of the magma involved in this eruption make Gura 2 volcano a unique place where a devastating and significant landscape-modifying volcanic eruption can be demonstrated to the visitors. This is a fundamental concept in the design of the geoeducational program of the proposed Precinct The general preconception for the eruption style and eruption effect of a mafic intra-continental volcanic field is generally mildly explosive and largely effusive. While this is certainly the case for the youngest eruptions of the Harrat Rahat—presented in the area of Precinct 1 and 2—Gura 2 volcano provides a graphic example that highly destructive and explosive eruptions took place in the Harrat Al Madinah in the not too distant pass (about 0.7 Ma). Gura 2 is also a spectacular volcanic landform with enormous aesthetic and adventure volcanic tourism value. It consists of a crater of 500 m diameter within a tuff ring of 700–800 m diameter (Fig. 3.93). The inner crater wall at the eastern edge of the volcano exposes an earlier constructed evolved basaltic cone and lava flow complex, which was cut in half by the explosion and potential crater floor subsidence (Fig. 3.93). While the crater gives the impression that its floor is below the syn-eruptive landscape, and therefore it should be defined as a maar volcano, the reality is different. The crater floor is about 100 m above the base of the volcano and therefore the entire volcano forms a broad lensoid shape positive landform. The tuff ring surrounds the main crater dissected the pre-tuff ring scora cone and lava dome forms a low angle outward dipping rim that is gradually transforming into a pyroclastic flow deposit-covered landscape mantling successions traceable over several kilometres from the crater. The primary pyroclastic deposits further form reworked pyroclast-fans entering into neighbouring valleys, providing a valuable, perfectly exposed volcanic facies association traceable from the source to its reworked fans (Fig. 3.94). Gura 2 volcano in this respect gives an opportunity to study the interaction between pyroclastic flows and pre-existing topography, as well as post-depositional reworking processes and therefore this geotope has a significant geoeducational value rarely visible such clearly elsewhere (Brown et al. 2003; Brown and Branney 2004; Edgar et al. 2007). The accumulated pyroclastic successions are perfectly exposed and the lack of vegetation cover makes it a perfect playground for experts and general public to investigate the effect and style of pyroclastic flow deposit accumulation.
Fig. 3.92

Gura 2 volcano produced block-and-ash flow deposits (light coloured cover over landscape) covered the older cones and inter-cone regions up to 10 km from the source. Photo was taken from the southern crater rim of Gura 2 [24° 12′ 16.42″N; 39° 52′ 31.50″E] toward south

Fig. 3.93

Crater of the Gura 2 volcano exposes older lava domes and half sectioned scoria cone segments suggesting complex eruption history of the volcano

Fig. 3.94

Gura 2 volcano forms a positive landform with a deep and wide crater on top. Block-and-ash flow deposits derived from Gura 2 volcano cover the landscape several kilometres away from the volcano (light cover over landscape). Note the crater of Gura 3 volcano in the left side of the view Geosite—Western and Northern Crater Rim

The crater rim of Gura 2 volcano can be accessed from the south. To the southern crater rim a 4WD track can take the visitor then a westerly round trip can be taken by foot to the northern rim. On the way to the southern crater rim lookout the path follow a typical block-and-ash flow fan surface littered by moderately vesicular trachyte lapilli and block hosted in a fine ash matrix. This rock texture is evident in the crater rim where proximal sections of the block-and-ash flow deposits exposed. Toward the north it is clearly visible how the pyroclastic flow deposits mantle over the disrupted trachytic lava domes as an older volcanic landform dissected by the explosive eruptions of Gura 2. This geosite has a high geoeducational value as it demonstrates clearly how crater formation, pre-existing volcanic landforms and the depositing pyroclastic successions from the disrupting explosive events form together the volcanic landscape. Geosite—Eastern Gully [24° 12′ 11.33″N; 39° 53′ 4.83″E]

Gura 2 volcano provides a more violent and complex eruption scenario in comparison to Gura 1 that can be closely examined in a deep incised gully network in the eastern margin about 1 km from the crater rim that can be defined as a key geosite. In this gully a at least three major pyroclastic flow unit is exposed in their proximal facies that initiated from the Gura 2 volcano suggesting major explosive eruption that give birth to this volcano (Fig. 3.95). It is inferred that the explosive eruptions were initiated by an explosive interaction of trachyte intrusion with groundwater, leaving behind the basal dense, green tuff breccia. The initial vent opening was quickly followed by eruptive phases producing pyroclastic flows that travelled up to several kilometres. The initial cratering and un-roofing that was likely triggered by phreatomagmatism was followed by volatile-rich trachyte magma emplacement, triggering a series of explosive eruptions, generating dense and particle-charged, “heavy” eruption clouds—probably about 3 to 10 km tall—that quickly collapsed and inundated an area of about 20 km2 by pyroclastic flow and surge deposits.
Fig. 3.95

Proximal pyroclastic flow units in the eastern sector of the Gura 2 volcano about 1 km from its crater rim [24° 12′ 11.33″N; 39° 53′ 4.83″E]

3.11.8 Gura 3 Explosion Crater Geotope [24° 11′ 22.71″N; 39° 52′ 24.36″E]

Gura 3 volcano is another volcanic crater in the Precinct 3 (Fig. 3.88); it has a crater diameter of about 500 m (Fig. 3.96) and similar geometry and deposits as documented for Gura 1. The crater rim exposes pyroclastic surge deposits and consists of rare dense trachyte-dominated juvenile pyroclasts that are predominantly accidental lithics clasts of altered syenite and meta-sedimentary rocks. A small spine-like trachytic lava dome occupies the centre of the flat crater floor and indicates that in the late stage of the eruption, after the crater formed, some degassed melt was able to squeeze through (Fig. 3.97). The laterally restricted deposits of the Gura 3 volcano are covered by pyroclastic flow deposits derived from the Gura 2 volcano, providing a relative stratigraphic age; however there is no evidence of significant erosion and/or soil formation on top of the Gura 3 and below the Gura 2 deposits. Similarly to Gura 1, Gura 3 is also the result of an explosive interaction between rising trachytic magma and ground water. The volcano can be accessed directly by 4WD car, and a short walk can complete a perfect view of a well-developed maar volcano, that is unique feature in the Harrat Rahat and therefore it has a significant geoeducational value.
Fig. 3.96

View of the Gura 3 maar [24° 11′ 28.50″N; 39° 52′ 23.97″E] from the south showing its deep crater with a small toloid. View is toward NE

Fig. 3.97

Typical pyroclastic succession of the Gura 3 maar geotope’s western crater rim and the small toloid in the middle of the crater. Picture was taken from [24° 11′ 30.52″N; 39° 52′ 14.02″E] toward SE

3.11.9 Al Shaatha Volcanic Complex Geotope [24° 8′ 39.75″N; 39° 53′ 35.62″E]

The Al Shaatha volcanic complex is a difficult to access region in the centre of the Harrat Al Madinah (Fig. 3.98). A poor quality 4WD dirt road need to be followed leaving the Gura 2–3 volcanoes that made a circle toward the southern edge of the Al Shaatha volcanic complex. It seems that the volcanic complex erupted through an older mafic (basaltic) volcanic chain and the trachytic eruption(s) partially destroyed the pre-trachyte cones leaving behind a moon-like landscape very difficult to travel and be oriented. The Al Shaatha volcanic complex seems to form a large broad crater that is filled with trachytic pyroclastic deposits that leap over the crater rim largely defined by the pre-trachyte volcanic morphology. Toward the south a major block-and-ash flow fan similar to those reported elsewhere (Freundt et al. 2000; Siebe et al. 1993) filling a flat floored wide valley, while toward the east fine grained pyroclastic debris covers a large area in the centre of the Harrat Al Madinah.
Fig. 3.98

GoogleEarth satellite image of the Al Shaatha volcanic complex geotope (GSAS—Geosite Al Shaatha). Top left corner of the map view is about [24° 9′ 37.86″N; 39° 51′ 8.83″E]. Note the white tone of the image representing trachytic ash plain and block-and-ash flow fans Geosite—Pyroclastic Flow Fan [24° 8′ 50.34″N; 39° 52′ 4.31″E]

This geosite is a unique place as it preserves a 500 m wide block-and-ash fan (Charbonnier and Gertisser 2008; Freundt et al. 2000) proximal to medial section that is gradually feeding into a normal volcaniclastic fan accumulating in a wadi (Fig. 3.98). The block-and-ash fan can be accessed easily from the dirt road and a short walk can take the visitor to the region where more than a metre across pumiceous trachyte fragments can be seen close (Fig. 3.99). From the access point the visitor can view the proximal areas of the block-and-ash fan as the deposits leap over the crater rim of the volcano about 150 m above the wadi floor. The geosite has great geoeducational value as it demonstrate the valley-confined nature of the dense block-and-ash flows that can fill valleys (Gertisser et al. 2012; Schwarzkopf et al. 2005; Sulpizio et al. 2010; Suzuki-Kamata et al. 2009).
Fig. 3.99

Large pumiceous trachyte block with radial jointing pattern typical for a block-and-ash flow that generated by a lava dome collapse and associated explosive event [24° 8′ 54.32″N; 39° 52′ 6.25″E] Geosite—Trachytic Ash Plain [24° 7′ 50.00″N; 39° 53′ 56.61″E]

In the eastern side of the Al Shaatha volcanic complex, the terrain is covered by light coloured, pumiceous deposit forming an extensive ash plain that shown up clearly on the satellite images (Fig. 3.98). The ash plain is soft and aeolian remobilisation of pyroclasts is intensive. This geosite has a high geoeducational value as it can demonstrate the potential aftermath of a silicic eruption that covers large regions with fine, light coloured pumiceous ash. The frequent sand storms and the aeolian remobilisation of this sediment can provide valuable ideas to scale the devastation a large silicic pyroclast-producing explosive eruption can cause through block-and-ash flow inundation and airfall (Major et al. 2013; Pittari et al. 2006; Vernet and Raynal 2008). Also, the silicic ash plain shows numerous sedimentological features to better understand the resetting of the landscape after a major silicic ash-producing eruptions through various fluvial and aeolian processes similarly to those regions commonly experienced recent silcic eruptions (Aceves Quesada et al. 2014; Cuitino and Scasso 2013; Umazano et al. 2014). In this respect this geosite provide a complementary site to the basaltic ash plain sites such as those documented near the 1256 AD historic eruption site (Kawabata et al. 2015) as part of the proposed Precinct 1.

3.11.10 Gura 4 Explosion Crater Geotope [24° 6′ 47.80″N; 39° 55′ 56.70″E]

Gura 4 explosion crater is a large and deep crater that can be accessed from the Al Shaatha volcanic complex by a truly adventure style trip. The Gura 4 volcano sits in a middle of a major block-and-ash fan region where trachytic block-and-ash flow deposits from various sources covered the region (Fig. 3.100). The crater is nearly 700 m wide and its shape is fairly irregular with some scalloped surfaces and rock falls (Fig. 3.101). In the crater wall red scoriaceous pyroclastic rock untis are exposed that are mantled by silicic tephra partially originated from the Gura 4 vent. The exact stratigraphy order of the pyroclastic rock units in this region is not established yet, and therefore it cannot be said more about the relative timing of events formed the major craters and major block-and-ash flow fans in this region. This geotope is significant not only by its spectacular landscape but also the deep crater in what the pre-crater scoria cones are half-sectioned indicating that pre-eruption volcanic morphology has some effect on the volcanic landform an explosive, crater-forming event can create.
Fig. 3.100

The Gura 4, 5, Um Rgaibah and Al Efairia crater in GoogleEarth satellite image. Top left corner of the map view is about [24° 7′ 8.28″N; 39° 53′ 21.40″E]

Fig. 3.101

The Gura 4 crater [24° 6′ 47.55″N; 39° 55′ 56.30″E] from the air showing that’s the crater cut through pre-existing scoriaceous successions probably part of a chain of an older scoria cone system

3.11.11 Gura 5 Explosion Crater and Block-and-Ash Fan Geotope [24° 6′ 14.86″N; 39° 57′ 9.94″E]

Gura 5 is a relatively small crater which is located relatively far from other craters (Fig. 3.100). The crater is unique by its appearance as being separated from other craters as indicates that it might represent a single explosive event that occurred in this region without any major development of lava domes. The peculiarity of this volcano is that it forma a rather positive landform and therefore it differs from the Gura 1 single explosion crater where the crater is clearly wide, broad and the tephra ring surrounding it inferred to have formed by phreatomagmatic explosions. Gura 5 is inferred to be a positive landform and probably erupted through moderate explosive eruptions of trachytic magma. There is no clear evidence to support phreatomagmatism in the formation of this volcano. This region also hosts another unique geological feature that has great geoeducational significance. Just west of the Gura 5 crater a deep canyon exposes a thick (30 m +) complex pyroclastic flow successions clearly deposited from multiple eruption events, and potentially from multiple sources. The landscape forms a flat surface that cut through deep box canyon where the typical block-and-ash flow units are exposed. The landscape is very unique in volcanic fields and it is more common feature in areas where long-lived silicic volcanoes exist, and produced multiple pyroclastic flow (e.g. ignimbrite) sheets that covered the landscape such as those in Tenerife (Brown and Branney 2013; Bryan et al. 1998; Garcia et al. 2011; Smith and Kokelaar 2013), or Central Anatolia (Aydar 1998; Le Pennec et al. 2005). This well-preserved “ignimbrite landscape” in spite its remoteness can provide a very unique view on Harrat Al Madinah and therefore this geotope and its geosites bear a major geoeducational value. This geotope shows clearly that on a volcanic field that is largely composed of basaltic volcanoes that erupted small-volume eruptive products that resulted mostly scoria cones and lava flows, extensive sheet like ignimbrite eruptions can take occur. This has a fundamental geohazard message. This geotope can provide to the visitor key information that this geotope and all the nearby sites as part of Precinct 3 can offer a very important volcanic hazard education tool for the public to be utilized through volcanic geoheritage, geoconservation and geotourism.

3.11.12 Um Raqubah Lava Dome Geotope [24° 5′ 23.44″N; 39° 57′ 45.18″E]

Um Raqubah lava dome is a spectacular lava dome in the southern edge of Harrat Al Madinah (Fig. 3.100). It can be accessed from a sealed road that joins to a dirt road toward the interior of the Harrat Al Madinah’s Precinct To visit this site well equipped 4WD car and good navigational gear and expertise are needed, as the road follows Bedouin hunting tracks winding around older aa lava fields. The lava dome is a major landmark as it can be visible from far by its typical telescope shape lava dome that has a major spine in its top (Fig. 3.102). The lava dome surrounded by a steep block-and-ash fan that gradually diminishes in wadi networks about a km from the lava dome centre. Walking track can take the visitor to the first steep wall of the lava dome relatively easily by following the top of the block-and-ash fans. Further climb needs more care as the top spine is steep and cross cut by abundant fractures. This lava dome stands as a single lava dome with multiple growth stage in a volcanic field, and in this respect it is similar to lava dome-fields reported in intracontinental settings such as those in Anatolia (Seghedi et al. 2015; Sen et al. 2002; Siebel et al. 2011). The significance of this geotope is that it provides a very nice view of the architecture of a lava dome formed by multiple intrusive stages and also fed some block and ash flows that deposited their block-and-ash fans around the growing lava dome. This gradual step-by-step growth of the dome and the evolution of the block-and ash fan is clearly visible in this region. In the southern margin of the lava dome a deep gully network exposes a fantastic set of block-and-ash flow deposits inferred to be derived from the nearby Al Efairia volcanic complex. While to visit this geosite it is not important from where the block-and-ash flow came from, the significance of this site is the perfect cross-sectional view of a block-and-ash flow fan where block- and pumice-rich part of the units are well exposed (Fig. 3.103). The top of the block-and-ash fan are typically littered by large convolute and rugged blocks of trachyte mimicking the surface of a lava flow (Fig. 3.104). The significance of this geosite is to demonstrate the typical surface morphology of a block-and-ash fan typical to the Precinct 3 in the proposed Harrat Al Madinah Volcanic Geopark.
Fig. 3.102

Um Raqubah lava dome with its telescopic lava dome complex and block-and-ash fan [24° 5′ 23.44″N; 39° 57′ 45.18″E]

Fig. 3.103

Block-and-ash flow units derived from the Al Efairia volcanic complex showing graphic example of the internal architecture of a block and ash flow fan common in the region of the Precinct 3 (and 4) [24° 4′ 38.70″N; 39° 57′ 52.93″E]

Fig. 3.104

Surface of a block-and-ash fan littered by variously vesicular trachytic clasts closely resembling fragments of lava flow surfaces. The slopes are also difficult to path by 4WD or even by walking. Note Um Raqubah lava dome in the back

3.11.13 Al Efairia Volcanic Complex Geotope [24° 4′ 29.28″N; 39° 56′ 19.40″E]

Al Efairia is a large volcanic complex in the southern part of the Precinct 3 of the proposed HArrat Al Madinah Voclanic Geopark (Fig. 3.100). This complex volcano is best to be defined as a large silicic eruptive center that likely produced some shallow volcanic crater and multiple lava dome complexes. It closely resembling many complex lava domes sitting in silicic tuff rings in dome-tuff ring fields commonly reported from the geological record in various geotectonic settings (Brooker et al. 1993; Henry et al. 1997; Lexa et al. 2010; Riggs et al. 1997). The actual crater (or main eruptive vent) of the volcanic complex is difficult to reconstruct as just part of one of the crater is preserved well. The volcano also complicated by the fact that it has been erupted through a pre-existing scoria cone dominated volcanic chain that has been partially dissected by the formation of the Al Efairia volcano. It is also evident that the volcano had multiple vents and vent shifting produced some slightly migrated vent setting along lava domes formed. While the volcano proximal area is complicated and rather resembles a compound lava dome-dominated silicic volcano, the extensive block-and-ash flow fans are relatively simple and covering probably the largest surface area of the Harrat Al Madinah’s silicic volcanoes. This volcanic geotope has huge geoeducational significance as it provides the largest and most explosive style eruption scenario any volcanic hazard study needs to deal with in future eruptions in the Harrat Al Madinah region. Geosite—Caldera View [24° 4′ 35.58″N; 39° 56′ 56.45″E]

From the NE edge of the crater rim a view can be seen toward the crater (small caldera) of the Al Efairia volcanic complex (Fig. 3.105). The crater is slightly east-west elongated and filled with aeolian dust as reworked pumiceous ash from the nearby ash plains. The crater rim is clearly formed by block-and-ash flow deposits that mantle the landscape toward the north. The geosite is an important lookout point as from here the block-and-ash flow run out distances can be seen clearly, and that information can provide important data for eruption scenario studies for future volcanic eruptions. From this look out it is also evident that the southern side of the volcano is truncated by lava dome complexes, while the northern crater rim partially covers disrupted scoria cones.
Fig. 3.105

View of the main crater of the Al Efairia volcanic complex. Photo was taken from [24° 4′ 35.58″N; 39° 56′ 56.45″E] toward W Geosite—Half-Sectioned Pre-caldera Cone [24° 4′ 54.86″N; 39° 56′ 35.69″E]

In the northern crater rim half section of a scoria cone core exposed (Fig. 3.106). The exposed scoria cone composed of welded and agglutinated basaltic scoria. The cone itself is covered by light coloured pumiceopus block-and-ash flow deposits of the Al Efairia volcano. The block-and-ash flow deposits cover nearly the entire pre-crater scoria cone. Along an east—west line several scoria cones are half-sectioned and partially covered by block-and-ash flow deposits inferred to be derived from the Al Efairia cone. This geosite is probably the best geosite in the entire proposed Al Madinah Volcanic Geopark, where the rejuvenation of silicic volcanism along a pre-existing mafic volcanic chain is clearly visible. This volcanic facies architecture has a major significant on the melt source stability and maybe some structural influence on the rejuvenation of volcanism. Therefore this geosite has a fundamental significance for geoeducation program the proposed geopark intend to promote (Fig. 3.107).
Fig. 3.106

Half section of a proximal scoria cone in the northern crater rim of the Al Efairia volcanic complex [24° 4′ 54.86″N; 39° 56′ 35.69″E]

Fig. 3.107

Well-developed block-and-ash fan in the SW margin of the Al Efairia volcano. In the background the large trachytic lava domes are apparent. Photo was taken from [24° 4′ 47.68″N; 39° 56′ 0.42″E] toward NW Geosite—Al Efairia Lava Dome Complex [24° 4′ 29.28″N; 39° 56′ 19.40″E]

The lava domes of the Al Efairia volcanic complex are not as spectacular visually than optehr previously described lava domes, however they bear geological significance as they seem to grown into a broad crater formed the major and extensive block-and-ash fans derived from the AL Efairia volcanic complex. The lava domes expose flow banded trachyte that is partially flanked by short run-out distance block-and-ash flow deposits with coarse units. The geoeducational value of this geosite is the potential of the clear demonstration to the link between explosive and effusive phase of a silicic volcanic complex in the region. Similar relationships have been demonstrated elsewhere in the Precinct 3, however this site provides the most complex scenario and the largest volume of deposits. Geosite—Complex Volcaniclastic Succession of a Block-and-Ash Fan [24° 4′ 8.49″N; 39° 56′ 38.49″E]

In the SW edge of the Al Efairia volcanic complex a well-developed block-and-ash fan is exposed. The block-and-ash fan shows perfectly the intermixing of primary and secondary deposits on this exposed gentle sloping region. The geosite has a geoeducational significance to demonstrate that in an active inter-con/inter-dome region primary and secondary volcanic processes together forming the landscape and the depositional environment. Moreover from this geosite the crater filling lava domes are clearly visible with their block-and-ash fan also fed material to the distal silicic ash plain.

3.11.14 Al Wabarah Volcanic Complex Geotope (Precinct 4) [24° 0′ 52.87″N; 39° 53′ 16.22″E]

About 5 km south from Al Efairia is the very remote Al Wabarah volcanic complex. This region doesn’t provide extra geological information to understand the volcanism of the Harrat Al Madinah, but by its remote location and rugged, untouched nature can be promoted as an alternative small scale version of Precinct 3, and could be defined as Precinct 4. The remoteness of the region ensures that the landscape has no human influence (yet) and can be promoted as a destination of ecotourism especially with some combination of promoting value of botany and zoology. The region composed of scoria cones similar to those detailed in the Precinct 1, and between these older scoria cone fields there is a double volcanic edifice with two broad craters that are seemingly the source of a succession of silicic block-and-ash flow deposits (Fig. 3.108). The region exposes block-and-ash fans where the visitor can see clear transition between primary and reworked volcaniclastic deposits to demonstrate the terrestrial sedimentary environment influenced by silicic explosive eruptions.
Fig. 3.108

GoogleEarth satellite image of the Al Wabarah volcanic region as the provisional location of Precinct 4 [24° 0′ 52.87″N; 39° 53′ 16.22″E]

3.12 Geopark Potential of the Harrat Al Madinah—A Discussion

Organisation of a geopark along volcanic features with high geoheritage value is the way to maximaze the potential of a region to be promoted successfully as a geopark. In this chapter it has been demonstrated that a systematic arrangement of volcanic geoheritage value of the Harrat Al Madinah has a great potential to provide firm scientific basis to develop and function a geopark in the region. The presented precinct concept showed a logical approach to demonstrate the volcanic geoheritage of the region which is by surface area very large, and by its logistical aspects need to be designed in a way that visitors can cover areas that present logically set geoheritage sites that all together can provide extra added value to understand not only the volcanism behind the formation of the Harrat Al Madinah, but also its volcanic hazards the local population faces with. The main aim to develop a volcanic geopark in the youngest volcanism in the Kingdom of Saudi Arabia is to show the fundamental geological features a typical harrat can have. Harrat Al Madinah with its perfect logistical background and proximity to a cultural focal point on Earth that act as a magnet of large number of visitors is a logical start point to develop projects that promote a geological feature in the Arabian peninsula, which is a very common landscape in the western Arabian region and has numerous cultural implications as well. We demonstrated that potential geoeducational routes and trails across Harrat Rahat, particularly in its northern sector, the Harrat Al Madinah can offer endless world-class geosites that can serve significant knowledge transfer on volcanic landscape evolution and understanding the volcanic hazards a young harrat may indicate. It has been demonstrates that some suggested visitor itineraries through a carefully design geological precincts and their geotopes and geosite could be logically linked together to demonstrate specific volcanic features or processes associated with dispersed volcanism such as formation of intracontinental volcanic fields. The international volcanological significance of the Harrat Al Madinah especially its potential link to volcanic researches on intracontinental volcanic fields hold the potential of its international linkages to similar trails with other volcanic regions’ geopark programs. The proposal and establishment of the HAMVG is the first such attempt in the territory of the Kingdom of Saudi Arabia. The success of this project will likely affect future geoconservation and geoeducation projects planned elsewhere in the Kingdom especially in other harrats. In the next chapters a brief summary will be given about the geoheritage and geoeducational potential of other, less known harrats of the Kingdom. In the following chapters we will not provide such detailed geosite level description of the geoheritage value of each of the harrats as such work would be way to extensive, but will provide significant link to Harrat Al Madinah, and will demonstrate the potential to develop a national network of volcanic geoparks that all together could even provide firm basis to apply candidature for being listed as a world heritage site as a fine example of dispersed intracontinental volcanism on Earth. The success of the Harrat Al Madinah Volcanic geopark potentially could provide an example for future similar activities elsewhere in the Arabian Peninsula and it could be designed as a flagship projects in the region. The impact of the proposed geopark on geotourism is expected to be huge. The Harrat Al Madinah’s volcanic geology is the perfect place to see a wide array of volcanic features, dramatic volcanic landscapes and the interaction between the extreme climate and volcanic landforms associated with intra-continental monogenetic volcanism. The Harrat Al Madinah is a globally unique intra-continental monogenetic volcanic field due to (1) the large number of young (<1 Ma) monogenetic volcanoes it hosts, (2) the wide range of chemical compositions of magma that formed the specific volcano types (from basaltic to trachytic), (3) the diverse eruption styles (e.g. from Hawaiian-style and Strombolian-style magmatic explosive eruptions to phreatomagmatic maar and/or tuff ring forming eruptions) and (4) the dramatically different volcanic landforms and associated volcanic rocks (e.g. from lava spatter cones and scoria cones to trachytic maar volcanoes and lava domes) that can be seen in a perfectly exposed manner. The diversity of volcano types in the proposed geopark that can be visited and seen perfectly is probably among the greatest in comparison to other intra-continental monogenetic volcanic fields. It is suggested that the proposed geopark is linked informally with geoeducation, geoconservational and geotouristic activities conducted and promoted by potential “sister geoparks” elsewhere, such as the Bakony- Balaton Geopark (Hungary), Nógrád/Novohrad Geopark (Slovakia/Hungary), Vulkaneifel Geopark (Germany), Jeju Island Geopark (Korea), Unzen Volcanic Area Geopark (Japan), Kanawinka Geopark (Australia) and Wudalianchi Geopark (China). These “sister geoparks” demonstrate volcanic features associated with similar types of volcanism to the Harrat Al Madinah, but with differences that make the parks complementary, including the level of vegetation cover (e.g. vegetation covered maars with lakes from the Vulkaneifel Geopark that are in contrast with the Harrat Al Madinah’s dry maars and explosion craters), exposure level (e.g. exposed volcanic conduits of similar monogenetic volcanoes to those at the Harrat Al Madinah are visible from the Bakony- Balaton and Nógrád/Novohrad Geopark), and variations in volcano types in accordance with variations in the volcanic eruption styles that formed them (e.g. active lava domes from Unzen Volcanic Area Geopark or the great size, shape and volcanic succession variations in Jeju Island, Korea). Linking and partially coordinating the scientific research, geoeducational/geoconservation programs and the geotouristic aspects of these “sister geoparks” would be a desirable approach in the future.


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© Springer International Publishing Switzerland 2016

Authors and Affiliations

  1. 1.JeddahSaudi Arabia
  2. 2.Palmerston NorthNew Zealand

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