Insulation effects of Icelandic dust and volcanic ash on snow and ice
In the Arctic region, Iceland is an important source of dust due to ash production from volcanic eruptions. In addition, dust is resuspended from the surface into the atmosphere as several dust storms occur each year. During volcanic eruptions and dust storms, material is deposited on the glaciers where it influences their energy balance. The effects of deposited volcanic ash on ice and snow melt were examined using laboratory and outdoor experiments. These experiments were made during the snow melt period using two different ash grain sizes (1 ϕ and 3.5 ϕ) from the Eyjafjallajökull 2010 eruption, collected on the glacier. Different amounts of ash were deposited on snow or ice, after which the snow properties and melt were measured. The results show that a thin ash layer increases the snow and ice melt but an ash layer exceeding a certain critical thickness caused insulation. Ash with 1 ϕ in grain size insulated the ice below at a thickness of 9–15 mm. For the 3.5 ϕ grain size, the insulation thickness is 13 mm. The maximum melt occurred at a thickness of 1 mm for the 1 ϕ and only 1–2 mm for 3.5 ϕ ash. A map of dust concentrations on Vatnajökull that represents the dust deposition during the summer of 2013 is presented with concentrations ranging from 0.2 up to 16.6 g m−2.
KeywordsIceland Insulation Ash Dust Snow Albedo
The physical and optical properties of snow are influenced by the presence of impurities, in particular by absorbing material such as aerosol particles deposited on the snow surface (e.g., Doherty et al. 2010 and Painter et al. 2012). Effects of aerosol particles on, for instance, snow melt and albedo (e.g., Meinander et al. 2013) and bidirectional reflection (Peltoniemi et al. 2009) have been studied for natural snow and during campaigns where impurities were deposited on snow in different quantities (e.g., Meinander et al. 2014). Commonly, the effects of impurities, such as black carbon, are studied, which are transported from their source regions to the snow-covered northern latitudes. The properties of snow and ice on the surface of glaciers in Iceland are influenced by the deposition of dust (Arnalds et al. 2014) and, during volcanic eruptions, by volcanic ash. The 2010 eruption of Eyjafjallajökull (Thorsteinsson et al. 2012) not only influenced the whole global air traffic by tephra release into the atmosphere up to 10 km a.s.l. reaching as far as the southern parts of Europe (e.g., Bonadonna et al. 2011; Bursik et al. 2012; Gudmundsson et al. 2012a) but also drastically influenced the albedo of glaciers in Iceland (Gudmundsson et al. 2012b and Pálsson et al. 2013). The majority of Icelandic tephra is basaltic in origin resulting from the mid ocean ridge basalt, but the chemical composition of tephra varies between different volcanic systems and even eruptions. Phreatomagmatic basaltic eruptions are typical in Iceland and occur from subglacial, subaerial, and submarine volcanoes (Thordarson and Larsen 2007). Therefore, Icelandic ash and dust is mainly basaltic volcanic glass which is deposited in Iceland’s sandy deserts which cover an area over 22.000 km2. Deserts of this composition are globally unique (Arnalds 2010). The ash from Eyjafjallajökull 2010 was of andesitic composition, slowly progressing from benmorite to thrachyte as the eruption proceeded with a silicic content ranging from ∼58–69 % SiO2. (Gislason et al. 2011 and Gudmundsson et al. 2012a)
Several dust storms occur in Iceland every year with deposition of dust or ash on the ice caps (Arnalds et al. 2014) with varying amounts at different altitudes which influence their melting behaviour. These dust storms are as well volcanic in origin (Arnalds et al. 2013) but redistributed and deposited in the glacier forefield where it is mixing with glacial till. From the forefield, it can be resuspended into the air by the action of wind and carried onto the glacier. After the 2010 eruption, the entire Eyjafjallajökull ice cap and most of the neighbouring Mýrdalsjökull were covered with a thick tephra layer, insulating the glacier surface whereas a thin tephra layer on Vatnajökull, Hofsjökull and Langjökull significantly increased the absorption of shortwave radiation and therefore enhanced melting (Gudmundsson et al. 2012b and Pálsson et al. 2013). In this paper, effective and critical thicknesses for Eyjafjallajökull (2010) ash are studied and compared with the help of outdoor and laboratory experiments. The effective thickness is the thickness when the material-covered ablation is maximized The critical thickness is the thickness of the material covering the ice or snow where the ablation rate of the material-covered ice or snow equals that of clean snow or ice; more material will start to insulate. (Brock et al. 2007).
The aim was to study the influence of ash layers of variable thickness, as would result from dust storms or eruptions and how they influence glacier surface mass balance, whether they insulate the ice or enhance melting. The thickness of dust layers in dust storms is rather thin and is expected to enhance melting, whereas during eruptions layers can be very thick. In Gudmundsson et al. (2012a), it was reported that the maximum thickness of the ash layer from the Eyjafjallajökull 2010 eruption exceeded 30 m close to the vent and 1 m thickness 2 km away from the vent, whereas on SW Vatnajökull it was reported to be a 0.1 mm thick tephra layer covering the ice. In the 2011 eruption of Grímsvötn, observations showed ash thicknesses on Tungnaárjökull (W-Vatnajökull) in a cm to mm scale.
Effective and critical thicknesses for Mt St Helens (1980) tephra are 3 and 24 mm, respectively (Driedger 1981). For the Icelandic volcano Hekla (1947), where tephra was covering ice at Gígjökull, these values were 2 and 5.5 mm, respectively (Kirkbride and Dugmore 2003). For rock debris effective and critical thicknesses are much thicker than for tephra (usually ∼10 and ∼15–50 mm, respectively) due to its low thermal conductivity. Because of the typically darker colour of tephra, small concentrations can dramatically reduce snow or ice albedo and increase ablation rates (Driedger 1981).
Effective and critical thickness for different materials such as tephra, rock debris and dust
Effective thickness (mm)
Critical thickness (mm)
Mt St Helens (1980) asha
Hekla (1947) tephrab
Villarrica tephra (lapilli)c
Dust (largely organic matter)d
Eyjafjallajökull ash (2010, 1 ϕ)
Eyjafjallajökull ash (2010, 3.5 ϕ)
Materials and methods
Four outdoor and laboratory experiments have been carried out at the Finnish Meteorological Institute (FMI) at Kumpula Kampus in Helsinki, Finland. These experiments contribute to a better understanding of insulation characteristics of ash and dust deposition on Icelandic glaciers. The modalities of different experiments are related to natural conditions, which are described below.
Dust distribution 2013 on Vatnajökull
Dagsson-Waldhauserova et al. (2014) suggest that about half of all dust storms in south Iceland each year occur at temperatures at or below 0 °C; therefore, dust can be mixed together with snow. The deposition of dust on snow or ice has an important climatic effect due to influence on surface albedo reduction and enhanced melt.
Origin and properties of ash used in the experiments
Material used for experiments at FMI was ash from the 2010 Eyjafjallajökull eruption in Iceland. The material was collected on Eyjafjallajökull (sample site in Fig. 1) at 1420 m a.s.l., about 3 km east of the vent. It was collected just after the eruption ended in late May 2010.
Four outdoor (AoS-2015, Roof 2015 and AiC-2015) and laboratory (AoI-2015) experiments were carried out using snow (AoS-2015), ice (AoI-2015, Roof 2015) and snow over ice (AiC-2015). Ash of 1 ϕ grain size was used for the AoS-2015, AoI-2015 and AiC-2015 experiments, whereas ash of 1 and 3.5 ϕ was used for Roof 2015 experiment. Layer thicknesses were measured above 1 mm and in dry condition of the ash.
Snow depth and temperature were then monitored for 17 days when the snow was melted naturally.
A controlled experiment with ash on ice was made both indoors (AoI-2015) and outdoors (Roof-2015), to identify and separate the effects of temperature and solar irradiance.
Roof 2015 experiment
The laboratory experiments were repeated outside on the roof of the FMI building in sunny conditions to study effects of solar irradiance in addition to that of temperature above zero. The experiment was repeated with the same volume of impurities, but using two different grain sizes of the Eyjafjallajökull 2010 ash: 1 ϕ (samples A) and 3.5 ϕ (samples B). The concentrations for the 3.5 ϕ B-samples were: 2.46 g (1 ml, 292 g m−2); 36.8 g (15 ml, 4385 g m−2, 1-mm layer thickness), 73.7 g (30 ml, 3–5-mm layer thickness, 8772 g m−2) and 294.7 g (120 ml, 35,086 g m−2, 9–13-mm layer thickness). The concentrations for the 1 ϕ ash were the same as used in AoI-2015.
The Ash in Container (AiC) experiment was performed in a cold container where ash was deposited on snow over ice. This experiment should evaluate to see if the ash starts insulating as in the outdoor experiments even with a slight different setup of snow over ice. This setup shows more realistically the surface of a glacier with ice below and therefore cooling from above and melting temperatures only from the surface.
Dust distribution map 2013
Figure 6 shows a map representing the spatial distribution of dust concentration deposited in the summer 2013 on Vatnajökull, a year without volcanic eruptions. This should show that very small amounts of dust or ash are getting deposited on the glacier. The map in Fig. 6 shows the location points (called stations) where dust samples were collected, and the colours show the spatial distribution of the dust concentration obtained by interpolation of the measured values (interpolation with the geostatistical analyst method Inverse Distance Weighting (IDW) in ArcMap). Topography was not taken into account in the interpolation. The point locations are not evenly distributed over the glacier area, and the southern part of Vatnajökull was not included in the interpolation due to too large distance from the measurement stations. The southern part of Vatnajökull was left out mainly due to the course of watersheds and snow line at Breiðamerkurjökull.
More dust was deposited in the western part of Vatnajökull than in the north eastern part (Fig. 6). The highest concentration, 16.6 g m−2, was found at station T05 on Tungnaárjökull (SW Vatnajökull). Much lower amounts were found on the upper part of the ice cap, namely at D09, Br7 and BB0. As observed in nature, the highest amounts of dust do not necessary have to be at the lowest altitudes of the glacier (closest to the dust source). Whether the material stays on the surface or is accumulated at a certain spot depends on the local topography, the exposure to wind, the material properties, local weather and melt conditions.
The Ash on Snow (AoS-2015) outdoor experiments were started on 6 February (day 0) and lasted for 17 days, until all the snow had melted.
The snow on top of the ice had melted inside the container after 1 week. When the control snow was in some parts totally melted, only snow spots of 5 mm thickness were left. In contrast, below the large impurity (425 g) snow of 15 mm thickness with a 5 mm ash layer (wet condition) on top remained. Therefore, the high concentration ash layer supported our assumption to insulate the snow from melt even with temperature influence only. The difference to the other ash on ice experiments was that there was ice beneath the snow so it was cooling from below and the container temperature influenced from above on the snow.
Discussion and conclusions
Our findings suggest that if the ash concentration on snow or ice is small, so the layer thickness is very thin, it has the potential to increase snow melt, but after a threshold the insulation effect begins, and the snow melt is decreased compared to clean ice.
In Table 1, critical and effective thickness of different materials is shown in comparison with the results of our experiments. The two grain sizes of the Eyjafjallajökull 2010 ash behave differently in terms of insulation. The Eyjafjallajökull ash has similar values for effective thickness to the thicknesses of the Icelandic volcano Hekla, it is in the range of 1–2 mm thickness. The critical thicknesses are comparable and visible in all our experiments: in the experiments AoS (at the large deposition with 425 g and 15 mm layer thickness), in the AoI experiment (deposition of 283 g, 120 ml, 33,749 g m−2 and 9–13 mm layer thickness), in the Roof 2015 experiment (A5 with 33,749 g m−2 and 9 mm layer thickness) as well as in the AiC experiment (425 g deposition and 15 mm layer thickness). The effective thickness was reached at Hekla tephra at 2 mm and at Eyjafjallajökull ash at 1 mm, in the Roof experiment (at A3 with a deposition of 4219 g m−2). The 3.5 ϕ grain size needs a thickness of 13 mm to start insulating as observed in the Roof experiment (B5 with a deposition of 35,086 g m−2). The Roof 2015 experiment shows as well that only 1–2 mm (B4) or smaller (B3, too thin layer to measure) are enough to enhance melt to a maximum for a grain size of 3.5 ϕ.
Different redistribution behaviours of the two grain sizes at the AoI-2015 experiments were observed. The smaller ash particle fraction of 3.5 ϕ slipped off the ice, whilst the layer of 1 ϕ ash stayed on the ice in-tact. It is suggested that the reason for this difference is to be found in the different surface morphologies. Due to the considerable clustering with fine adhesive particles (see e.g., Fig. 2b and d), the coarser material shows a larger specific surface area than 3.5 ϕ particles which feature smooth surfaces (see Fig. 2f and g). Hence, it is likely that the coarse grains are characterized by a larger coefficient of friction than the finer particles. This effect is even increased by the fact that 1 ϕ grains often feature a high vesicularity (Fig. 2c), which facilitates the absorption of water and is expected to enhance static friction. The majority of 3.5 ϕ particles however is blocky and shows no vesicles (see Fig. 2e). Furthermore, the 1 ϕ grains often feature vesicles, which facilitate the absorption of water. This is not the case for the blocky 3.5 ϕ particles characterized by smooth surfaces. This finding implies that finer, smooth particles, are washed away easier by melt streams on the glacier surface than coarser grains with a rough, irregular surface and high vesicularity. Hence, coarser material could have a much greater effect on the albedo.
The highest concentration of dust deposited on Vatnajökull was 16.6 g m−2, which represents dust collection over the summer of 2013. This value is much lower than the mean deposition of 400 g m−2 years−1 suggested by Arnalds et al. (2014). As the results of the Roof 2015 experiments show for both grain sizes that very small amounts (1–2 mm or smaller) of ash (or dust) deposition are enough to enhance melt, it is possible that the small amounts of dust or ash deposited on Vatnajökull have a comparable melt effect. Similar experiments with volcanic particles of different origins would help to clarify.
The study described in this manuscript was supported by NordForsk as part of the Nordic Centre of Excellence within the framework of Cryosphere-atmosphere interactions in a changing Arctic climate (CRAICC), which is a part of the Top-level Research Initiative (TRI); Part of this work was supported by the Centre of Excellence in Atmospheric Science funded by the Finnish Academy of Sciences Excellence (project no. 272041), by the Finnish Academy of Sciences project A4 (contract 254195). Gratefully acknowledged are Matti Leppäranta for using his cold laboratory for experiments, the glaciology group of the University of Iceland as well as the Icelandic Glaciological Society for fieldwork support and the Earth Science Institute of the University of Iceland for providing the Eyjafjallajökull tephra. We thank the reviewer and editors for their constructive support.
- Adhikary S, Nakawo M, Seko K, Shakya B (2000) Dust influence on the melting process of glacier ice: experimental results from Lirung Glacier, Nepal Himalayas. IAHS Publ. 264Google Scholar
- Arnalds O (2010) Dust sources and deposition of aeolian materials in Iceland. Icel Agric Sci 23:3–21Google Scholar
- Arnalds O, Thorarinsdottir EF, Thorsson J, Waldhauserova PD, Agustsdottir AM (2013) An extreme wind erosion event of the fresh Eyjafjallajokull 2010 volcanic ash. Sci Rep 3Google Scholar
- Björnsson H, Pálsson F (2008) Icelandic glaciers. Jökull 58:365–386Google Scholar
- Bonadonna C, Genco R, Gouhier M, Pistolesi M, Cioni R, Alfano F et al (2011) Tephra sedimentation during the 2010 Eyjafjallajökull eruption (Iceland) from deposit, radar, and satellite observations. J Geophys Res Solid Earth (1978–2012), 116(B12)Google Scholar
- Dellino P, Gudmundsson MT, Larsen G, Mele D, Stevenson JA, Thordarson T, Zimanowski B (2012) Ash from the Eyjafjallajökull eruption (Iceland): fragmentation processes and aerodynamic behavior. J Geophys Res Solid Earth (1978–2012), 117(B9)Google Scholar
- Driedger CL (1981) Effect of ash thickness on snow ablation. In: Lipman P, Mullineaux DR (eds) The 1980 eruptions of Mount St Helens. USGS Professional Paper, 1250, 757–760Google Scholar
- Gudmundsson MT, Thordarson T, Höskuldsson Á, Larsen G, Björnsson H, Prata FJ, et al (2012) Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland. Sci Rep 2Google Scholar
- Gudmundsson S, Pálsson F, Björnsson H, Magnússon E, Thorsteinsson T, Haraldsson HH (2012) The impact of volcanic aerosols on the energy-and mass balance of Langjökull ice cap, SW-Iceland. In AGU Fall Meeting Abstracts (Vol. 1, p. 0659)Google Scholar
- Pálsson F, Björnsson H, Guðmundsson S, Haraldsson H (2013) Vatnajökull: mass balance, meltwater drainage and surface velocity of the glacial year 2010-11. Institute of Earth Sciences, University of Iceland and National Power Company, December 2013, RH-24-2013Google Scholar
- Thorsteinsson T, Jóhannsson T, Stohl A, Kristiansen NI (2012) High levels of particulate matter in Iceland due to direct ash emissions by the Eyjafjallajökull eruption and resuspension of deposited ash. J Geophys Res Solid Earth (1978–2012), 117(B9)Google Scholar
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