Challenges in Responding to a Sustained, Continuing Volcanic Crisis: The Case of Popocatépetl Volcano, Mexico, 1994-Present
Popocatépetl Volcano, located in the central Trans-Mexican Volcanic Belt, is surrounded by a densely populated region with more than 20 million people. During the past 23,000 years, this volcano has produced eruptions ranging widely in size and style, including Plinian events and massive sector collapses. However, the historical activity of Popocatépetl, recorded in detail since 1500, consists of only nineteen small to moderate eruptions, several similar in style to the current eruptive episode (1994-present). After nearly 70 years of quiescence since its eruptions in the mid-1920s, Popocatépetl reawakened in December 21, 1994. This eruptive activity, which is still ongoing, has been characterized by a succession of lava dome growth-and-destruction episodes: pulses of effusive and moderately explosive activity alternating with periods of almost total quiescence. This pattern appears to be characteristic of all historical eruptions, several of which lasted for decades, with interspersed lull periods that in some cases make it difficult to identify the end of the eruptive episodes. In this chapter, we discuss the problems and challenges posed by a prolonged, low-level volcanic crisis (or “semi-crisis”) of variable intensity that has lasted for more than 20 years, without showing any signs of coming to an end. Paradoxically, this still-continuing crisis has spawned two opposite developments: (1) during periods of little visible activity, people dwelling near the volcano become somewhat apathetic and indifferent; but (2) during times of easily observed visible activity, awareness of changes at the volcano—and their hazardous implications—is rapidly and greatly enhanced by the common use of social media by people.
Disasters can occur when society fails to identify and foresee the potentially hazardous manifestations of a natural phenomenon. However, disasters may also occur if society fails to adopt adequate measures to reduce the risks—to people, property, and infrastructure—posed by hazardous phenomena even if recognized in advance. Responding effectively to hazards is a process as complex as is the fabric of society itself, as each hazardous phenomenon has a variety of destructive manifestations, and each may affect different sectors of society in particular ways. This is especially true when dealing with volcanic crises. As has been long recognized (e.g., Fiske 1984; Peterson 1986, 1988; Tilling 1989; Voight 1990; Peterson and Tilling 1993; Haynes et al. 2008; Solana et al. 2008; Fearnley 2013), the process of crisis response entails close interaction between three main entities: (1) The scientists studying the hazardous phenomena and their potential social outcomes; (2) the authorities in charge of public safety and infrastructure; and (3) the affected populace. The wide spectrum of backgrounds and attitudes of all the involved stakeholders during such interaction, together with the vague or imprecise information generally available during the crisis, often combine to hinder effective communications among the entities involved. Poor communications in turn complicate the perception of the risk, a factor likely to increase societal vulnerability. Thus, during an evolving crisis, it is critical to develop a perception of risk as uniform as possible among all stakeholders—no easy task when the affected population is measured in millions. To achieve this goal requires searching for communication tools that can describe—as simply as possible—the relations between the level of threat posed by the volcano, and the level of response of the authorities and the affected public. In the case of Popocatépetl, the Civil Protection of Mexico addressed this challenge by developing and implementing the Volcanic Traffic Light Alert System (VTLAS). Distinct from other volcano alert systems (VALs)—typically referenced to the activity of the volcano— used to communicate warning information from scientists to civil authorities managing volcanic hazards (Fearnley 2013; Potter et al. 2014), the VTLAS scheme (discussed in detail below) additionally was intended to reduce the possibility of ambiguous interpretations of intermediate alert levels by the large populations at risk. This additional component marks a significant advance in the management of volcanic crises in Mexico (De la Cruz-Reyna and Tilling 2008).
Before proceeding further, we should summarize how risk is managed by the National Civil Protection System of México (SINAPROC), which was created in 1986 after the catastrophic disaster caused by a M 8.1 earthquake on September 19, 1985. The executive body of the SINAPROC at the federal level is the General Coordination, housed within the Ministry of the Interior (Secretaría de Gobernación). The General Coordination is supported by four agencies: (1) the National Direction of Civil Protection, an operational body in charge of implementing the preventive and relief actions; (2) the General Direction of Integral Risk Management, which provides the funding for prevention and emergency actions; (3) the General Direction of Interlinking and Regulations, which coordinates the different government levels involved with civil protection; and (4) the National Center for Disaster Prevention (CENAPRED), a technical body created in September 19, 1988, with substantial technical and generous financial support from the government of Japan. The mission of CENAPRED is to promote the applications of science and technology for the prevention and mitigation of disasters, to train and inform professionals and technicians on these subjects, and to disseminate the necessary information for preparedness and self-protection.
CENAPRED also acts as an active interface between the operative, decision-making authorities of the SINAPROC and the academic scientific community. In conducting its work, CENAPRED utilizes four advisory scientific committees on topics relevant for disaster prevention, composed of prominent, experienced Mexican scientists in the areas of Earth sciences, hydro-meteorological sciences, social sciences, and chemical and industrial hazards. There are also ad-hoc sub-committees, as is the case of the Advisory Committee for Popocatépetl Volcano, on which several international volcanologists—especially from the U.S. Geological Survey (USGS)—have actively participated. This advisory sub-committee will be herein referred as the Popocatépetl Scientific Committee (PSC).
Popocatépetl has remained persistently active for over 20 years, thereby creating a long-standing volcanic crisis that has imposed additional difficulties in the management of the volcanic risk. CENAPRED has been and remains in charge of the monitoring of Popocatépetl volcano, and it also continues to host and coordinate PSC sessions as needed.
2 Popocatépetl Volcano: Geologic Setting and Eruptive History
Geological evidence indicates that a large eruption about 23,000 years destroyed a pre-existing volcanic edifice, generating massive debris avalanches (Robin and Boudal 1987; Boudal and Robin 1989; Siebe et al. 1995). Since then, Popocatépetl’s eruptive history has been characterized by at least seven major explosive eruptions and many smaller eruptions that have produced large volumes of ash and pumice. Three of the most recent explosive eruptions (ca. 3000 B.C., between 800 and 200 B.C., and ca. A.D. 800) affected human settlements, as indicated by archaeological remains buried by ashfall deposits and pottery shards incorporated by mudflows (Siebe et al. 1996; Siebe and Macías 2004). After the last of these major eruptions, activity at Popocatépetl has remained moderate for nearly 1200 years. Batches of magma were extruded, producing lava domes and associated moderate explosions and ashfalls. Eyewitness reports since 1354 (in the native Nahuatl and Spanish language translations) describe episodes of activity, while more recent and detailed written reports since 1500 document that about 16 small and 3 moderate eruptive episodes have occurred within the past 500 years, some of them probably involving dome growth-and-destruction processes similar to those of the current, ongoing activity (De la Cruz-Reyna et al. 1995; De la Cruz-Reyna and Tilling 2008).
3 Ongoing Unrest, Eruptive Activity, and Volcanic Crisis
Management of risk posed by volcanic unrest requires a comprehensive understanding of the natural phenomenon. In this regard, a sustained activity makes it particularly difficult to forecast the future activity and its consequences, because the commonly employed methodologies to recognize and assess the relevance of precursors of increased activity are obscured by the persistent low-to-medium level of activity. It is thus important to define and establish the context of the unrest to develop decision-making criteria.
Before the current activity, there was little public awareness outside the scientific community about Popocatépetl being an active and potentially hazardous volcano. The previous eruption of Popocatépetl was not a major event. It began in 1919, and the available descriptions of that activity (Friedländer 1921; Waitz 1921; Dr. Atl 1939) indicate that it consisted of a succession of dome emplacements and destructions, similar to the current eruptive episode, probably lasting until 1927. Then, after nearly 70 years of quiescence (except for a minor fumarolic event in 1947), Popocatépetl volcano reawakened in 1993 with increased fumarolic and seismic activity (De la Cruz-Reyna et al. 2008). By October 1994, this unrest further escalated, culminating with a series of moderately large phreatic explosions at the crater during the early hours of 21 December 1994. These explosions produced ashfalls on several towns to the east and northeast of the volcano, including the large city of Puebla.
At the time of the explosions, glaciers with an estimated total area of 0.54 km2 blanketed the northern flank of the cone, below the crater (Delgado-Granados 1997; Huggel and Delgado-Granados 2000). With the vivid memories of the 1985 Nevado del Ruiz disaster in the minds of authorities and scientists, nearly 25,000 people living in some of the most vulnerable towns located along the likely paths of pyroclastic flows and lahars were evacuated in the afternoon of 21 December as a precautionary measure. A week later, the eruptive activity decreased and its largely phreatic nature became better understood, the evacuated residents were allowed to return home. Ash emissions or protracted explosions consisting mostly of gas and steam with relatively low concentrations of ash and a characteristic emerging seismic signal were referred to as “exhalations.” This type of relatively low-level activity persisted through 1995 and into early 1996, with decreasing intensity (De la Cruz-Reyna and Siebe 1997).
About a year later, seismicity and exhalation activity increased again, and on 26 March 1996 a lava dome was first observed growing on the crater floor. This dome was partially destroyed by an explosion on April 30, 1996, which propelled ejecta several kilometers into the sky and hot debris as far as 4 km and caused the only reported fatalities to date directly related to the Popocatépetl activity. Despite public warnings not to enter the 12 km-radius restricted area around the mountain, five members of a sports club climbed to the summit crater rim to obtain good images and videos of the activity. These climbers were struck and killed by incandescent fragments during their descent, a few hundreds of meters downslope from the crater, as evidenced by the images recovered from their cameras. Dome-building activity resumed mid-March 1997 (GVN 1996, 1998). These 1996–1997 events marked the beginning of a series of dome growth-and-destruction cycles that have continued up until this writing. Although most of the explosions have been moderate, some of them have been large enough to produce pyroclastic flows (in 2001) and lahars (in 1997 and 2001; Capra et al. 2004).
A level of activity of the volcano is defined by the PSC and translated into the most likely scenarios, describing them in specific terms, including time scales, names of threatened areas, etc. In general terms, these sets of scenarios may be grouped according to seven levels of response of the SINAPROC, which in turn are managed as phases within each of the Traffic light colors: two for Green, three for Yellow, and two for Red.
SINAPROC authorities translate the level of volcanic hazard defined by the PSC into one of three alert levels for the population (not of the volcano) that leave no room for uncertainty: Green, everything is fine; Yellow, you must be aware of the hazard and pay attention to any official announcements; and Red, you must leave the area according to the instructions given by the authorities.
All decisions involving mitigative actions are undertaken by the Civil Protection authorities according to the selected phase within the color level. It is important to emphasize that, in Mexico, the management of risks associated to natural phenomena is by law a responsibility assumed by the three levels of government: federal, state, and municipal. The Scientific Committees are officially appointed advisory groups of “more than 10 but less than 15 experts in the subject, which can emit opinions and recommendations about the origin, evolution and consequences of hazardous phenomena, aimed to technically induce decision making for prevention and mitigation to the population…”, as stated by the Organization and Operation Manual of the National System of Civil Protection within the General Law of Civil Protection.
4 Evolution of the Activity Influences Public Perception of Hazards
5 Development of Risk—Mitigation Strategies Since 1994
Perhaps the main challenge in managing the response to the ongoing volcanic activity of Popocatépetl has been posed by its rather pedestrian, anti-climactic character, particularly during the 2003–2010 period. The initially impressive phreatic eruption of 1994 that sharply contrasted with the quietness of the previous 70 years prompted the frenzied making of a Popocatépetl’s volcanic hazards map (Macías et al. 1995) in only a few months under high-stress conditions. This map—the first such for Popocatépetl specifically intended for use by civil authorities—was made with a general consensus of the involved Mexican and U.S. experts. The high-urgency 1994–95 scientific and governmental response, which also included the development of the VTLAS, then gradually declined until the onset of effusive magmatic activity in 1996. The VTLAS was set at Yellow for the population at the moment of its implementation in mid-1995. The slow decline of the ash–emission events, the direct source of public and authority awareness, was not much in agreement with the data from the volcano-monitoring instruments. The VTLAS thus remained in Yellow even when the volcano appeared to be in a relative state of rest. News media and the public started to joke about a “busted” traffic light. However, in March 1996, the emplacement of the first lava dome confirmed an ongoing level of eruptive activity, and thereby rekindled public and media interest and concern. Unlike the initial 1994 episode, the now much-improved monitoring data allowed a better understanding of the 1996 activity. Because the character of the dome -emplacement processes was effusive and confined within the summit crater, the PSC continued to recommend maintaining the VTLAS in Yellow, as the probabilities of pyroclastic flows or lahars were still low. It was at that time that some members of a sport clubs climbed to the crater rim. Tragically, this imprudent action resulted in the above-mentioned casualties caused by the first dome-destruction explosion, again rekindling the interest of public and media.
Dome-emplacement and destruction activity continued in the ensuing years with a somewhat increasing trend, but without exceeding the levels set by the scenarios marked by the VTLAS, so it continued in condition Yellow. However, the dome-destruction explosions in 1997, and particularly the 13 km-high ash column of 30 June that caused ashfalls in Mexico City and impelled closing its airport for 12 h, prompted changing the VTLAS to Red for a few hours. However, no evacuations of populations were ordered, thereby generating some confusion among people and authorities. Studies at other volcanoes (Solana et al. 2008) indicate that, although civil authorities are aware of the volcanic hazards, their understanding of how to respond during an emergency can be incomplete, and that understanding how people perceive risk is important for improving risk communication and reducing risk-associated conflicts (Haynes et al. 2008).
At this stage, the need of an embedded scale within the three-color alert levels designating the alert level of authorities became immediately evident; see De la Cruz-Reyna and Tilling (2008) for a detailed account of the VTLAS levels. The quick return to condition Yellow, as no evacuations were needed, again prompted the news media and public to joke about a “busted” traffic light. Public discussions on this subject, however, ultimately proved to be beneficial, because it helped to convey to the general public and many authorities that the color of the Traffic Light is not a description of the state of the volcano, but rather it is a description of the threat on people and thus reflects the state of awareness of individuals. Hence, the VTLAS remained in Yellow, although the phase, i.e., the level of alert for Civil Protection authorities, has changed several times.
The December 2000–January 2001 explosive activity marked a watershed in the evolution of the ongoing volcanic crisis at Popocatépetl. Before 2001, the accumulation rate of dome lavas and debris exceeded the rate of removal by explosive activity. After a period of irregular activity lasting until 2003, that trend slowly reversed, and the main crater slowly began to recover some of its former capacity (Gómez-Vázquez et al. 2016). After 2003, a lower lava emplacement and explosion rates (shown as a diminishing slope of the cumulative RSEM counts in the inset of Fig. 5) prompted a reduction of the VTLAS phase from Y-3 to Y-2, and then to Y-1 in 2004, still maintaining however condition Yellow on affected populations. The slightly increased seismic activity in late 2005 and 2006 raised the VTLAS phase back to Y-2. Overall, between 2005 and 2009, the rate of dome-lava growth did not exceed the rate of debris removal by explosions and exhalations, so that the crater continued to deepen slightly. Explosive activity gradually increased again in mid-2010 and continued with minor fluctuations through 2011. On 20 November 2011, a powerful explosion ejected large ballistic blocks to distances of 4 km; this explosion also generated a shock wave that was felt by some people as far away as 10 km from the volcano, but luckily with no damaging consequences.
Since 2001, dome building, exhalations, and explosions have continued sporadically to the date of this writing (July 2016). Accordingly, this persistent, though irregular, activity has necessitated that the VTLAS remains for long times in condition Yellow, leading to some wearisomeness and complacency among the populace and some municipal authorities of towns near the volcano during protracted lull periods. However, no complacency existed among authorities at the federal level. During periods of relative inactivity, the PSC and the CP authorities discussed in depth the pros and cons of making the VTLAS more dynamic, particularly lowering it to Green during relative quiescences. However, after much debate, a strong argument finally gained consensus: Green conditions would immediately allow the occupation and/or reoccupation of previously restricted areas close to the limit of the National Park, and well within the exclusion radius of 11 km. Then, should a new episode of more intense explosive activity arise, it would be much more difficult to evacuate people than it would be had the VTLAS remained in Yellow. Thus, it was decided to retain the current protocols, until there was solid evidence that the now two-decade-long eruptive episode had completely finished and the volcano had re-entered another long repose period.
6 Scientific Strategies and Scientific Challenges
The main difficulties faced by the scientists of the PSC may be summarized in two different realms: firstly, the scientific and technical one related to understanding of volcanic processes and, secondly, the operational aspects in effectively communicating hazards information to the CP authorities, news media, and the affected populace. With regard to the former, apart from the typical instrumental and technological inadequacies and limitations in the amount and quality of monitoring data, an important issue has been the evolution of the precursors’ meaning and possible implications. Specifically, what do the variations in precursory activity portend what the volcano might do next? During the initial years of the crisis at Popocatépetl, acquired experience allowed identification of clear precursors to explosions, such as harmonic tremors; repetitive short-duration, low-amplitude LP events (drumbeats); accelerated rate of RSAM counts, etc. However, and with no clear watershed (although it may be related to the change of eruptive regime in 2001–2003), in several instances such seismic signals were not necessarily followed by explosions. On the other hand, cumulative volcano-tectonic (VT) energy release, rate of dome growth, and VT appearing in specific locations seemed to have become more relevant precursors.
With regard to effective communications of hazards information, in addition to the general factors considered previously discussed, an additional recurrent hindrance during the Popocatépetl crisis has been the frequent changes of decision-making authorities over time scales shorter than the duration of the volcanic activity. Federal and state governments change every 6 years, so that within each period of administration the responsible CP authorities with whom the scientists interact may be replaced more than once. Thus, it is always necessary to train the new authorities in the communication process. Fortunately, in all cases, the communication of volcanic risk based on likely scenarios has made it possible to deal with this problem relatively easily.
Although the basic tools for scientific assessment of the hazards and systematic monitoring of the activity have not always been sufficient, CENAPRED has made, and is making, a major effort in maintaining the highest technological standards in the volcano-monitoring networks. In addition, a new volcanic-hazards map by a team of volcanologists at the Instituto de Geofísica, and other UNAM institutes has replaced the current one (Macías et al. 1995), which was prepared under rushed conditions with minimal data available at the time. The new hazards map considers a wealth of new geological information collated over the past 2 decades (in particular, extent of lahar inundation areas, magnitude and timing of past Plinian eruptions, ash dispersal data, etc.). The updated hazards map and assessment were released by CENAPRED in (2016). Participants in the current map include some of the authors of the 1995 map: Siebe, Macías, Capra, Delgado, and Martin del Pozzo, plus their associates (e.g., postdocs, students). The CP system provided a special fund (FOPREDEN. Disaster Prevention Fund) to finish the new map, although much of the new scientific data were obtained with research projects financed by CONACYT (Mexican National Science Council) and DGAPA (The UNAM fund to support major research projects).
7 Concluding Remarks and Future Challenges
Grouping of the 19 known historical eruptions of Popocatépetl volcano (De la Cruz-Reyna and Tilling 2008) into six long-duration episodes involving successive dome-emplacements and dome-destruction explosions, interspersed with long periods of quiescence
Estimated minimum duration (y)
Estimated lapse until next episode (y)
VEI range of eruptions in the period
Identifying the end of the current, relatively minor eruptive episode or the possible precursors of a much more explosive activity poses other major challenges. In particular, as seismic records constitute the dominant volcano-monitoring data for Popocatépetl and most other active volcanoes, it is crucial to better understand the empirical relationships between the seismic signals recorded since 1994 and the nature and vigor of the observed volcanic activity preceding, during, and following the seismicity. Physical models then can be developed to explain the source of the diverse seismic signals. Such method is inherently non-unique, and in some cases the ambiguity of the possible causes may lead to inadequate or even incorrect assessment of the hazards. Reduction of such levels of non-uniqueness based on integral analysis of different types of geophysical and geochemical data is a critical need to be fulfilled in the future with additional data and more diagnostic analytical methodologies. In the meanwhile, however, some pragmatic actions must be implemented. That it is why the Popocatépetl Scientific Committee, in attempting to reduce such a complex problem, has strongly emphasized the consensual approach in its deliberations. In a broader context, experience gained over recent decades at volcanoes worldwide indicates a sobering reality: despite the considerable advances in volcano-monitoring techniques, except for very rare exceptions, current state-of-the-art volcanology still lacks a routine, reliable capability to always correctly interpret a volcano’s precursory signals and to accurately predict the outcomes of volcano unrest (e.g., Tilling 2014).
Maintaining a continuous flow of up-to-date information to the public about volcanic activity, hazards, and risk reduction seems to be the best and most practical solution to minimize the weariness and indifference that at times develop among the authorities and populations at risk during lulls of visible activity. In this regard, the daily posting of the activity reports of Popocatépetl on the CENAPED website (http://www.cenapred.gob.mx/reportesVolcan/BuscarReportesVolcan?optBusqueda=1) apparently has been quite effective. This, together with the exponentially growing influence of fixed webcam sites and social media networks, has greatly increased public awareness of the occurrence of even minor events at Popocatépetl and other volcanoes in Mexico or elsewhere. Nonetheless, we recognize that the influence of user-generated social media reporting needs to be regarded with caution, because there is no assurance of the accuracy of the content of the transmitted information. Although most reports and comments diffused via social media are generally informative, at times scientifically unsupported remarks and predictions are also included, thereby contributing to possible confusion and generating a negative impact on the general awareness. To deal with this problem, SINAPROC opened a twitter account to spread reliable information. Dealing with modern-day modes of information dissemination poses another major challenge for all those involved in the management of volcanic risk.
This research has been partially supported by the UNAM-DGAPA-PAPIIT project IN-106312. We wish to express our appreciation to Jose Luis Macías and an anonymous reviewer for helpful constructive reviews of an earlier version of this paper.
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