Amy Donovan

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Driven to collapse Volcanic eruptions occur frequently, but only rarely are they large enough to cause the top of the mountain to collapse and form a caldera. Gudmundsson et al. used a variety of geophysical tools to monitor the caldera formation that accompanied the 2014 Bárdarbunga volcanic eruption in Iceland. The volcanic edifice became unstable as magma from beneath Bárdarbunga spilled out into the nearby Holuhraun lava field. The timing of the gradual collapse revealed that it is the eruption that drives caldera formation and not the other way around. Science, this issue p. 262 Magma flow from under the Bárdarbunga volcano drove caldera collapse during the 2014 eruption. INTRODUCTION The Bárdarbunga caldera volcano in central Iceland collapsed from August 2014 to February 2015 during the largest eruption in Europe since 1784. An ice-filled subsidence bowl, 110 square kilometers (km2) in area and up to 65 meters (m) deep developed, while magma drained laterally for 48 km along a subterranean path and erupted as a major lava flow northeast of the volcano. Our data provide unprecedented insight into the workings of a collapsing caldera. RATIONALE Collapses of caldera volcanoes are, fortunately, not very frequent, because they are often associated with very large volcanic eruptions. On the other hand, the rarity of caldera collapses limits insight into this major geological hazard. Since the formation of Katmai caldera in 1912, during the 20th century’s largest eruption, only five caldera collapses are known to have occurred before that at Bárdarbunga. We used aircraft-based altimetry, satellite photogrammetry, radar interferometry, ground-based GPS, evolution of seismicity, radio-echo soundings of ice thickness, ice flow modeling, and geobarometry to describe and analyze the evolving subsidence geometry, its underlying cause, the amount of magma erupted, the geometry of the subsurface caldera ring faults, and the moment tensor solutions of the collapse-related earthquakes. RESULTS After initial lateral withdrawal of magma for some days though a magma-filled fracture propagating through Earth’s upper crust, preexisting ring faults under the volcano were reactivated over the period 20 to 24 August, marking the onset of collapse. On 31 August, the eruption started, and it terminated when the collapse stopped, having produced 1.5 km of basaltic lava. The subsidence of the caldera declined with time in a near-exponential manner, in phase with the lava flow rate. The volume of the subsidence bowl was about 1.8 km3. Using radio-echo soundings, we find that the subglacial bedrock surface after the collapse is down-sagged, with no indications of steep fault escarpments. Using geobarometry, we determined the depth of magma reservoir to be ~12 km, and modeling of geodetic observations gives a similar result. High-precision earthquake locations and moment tensor analysis of the remarkable magnitude M5 earthquake series are consistent with steeply dipping ring faults. Statistical analysis of seismicity reveals communication over tens of kilometers between the caldera and the dike. CONCLUSION We conclude that interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual near-exponential decline of both the collapse rate and the intensity of the 180-day-long eruption. By combining our various data sets, we show that the onset of collapse was caused by outflow of magma from underneath the caldera when 12 to 20% of the total magma intruded and erupted had flowed from the magma reservoir. However, the continued subsidence was driven by a feedback between the pressure of the piston-like block overlying the reservoir and the 48-km-long magma outflow path. Our data provide better constraints on caldera mechanisms than previously available, demonstrating what caused the onset and how both the roof overburden and the flow path properties regulate the collapse. The Bárdarbunga caldera and the lateral magma flow path to the Holuhraun eruption site. (A) Aerial view of the ice-filled Bárdarbunga caldera on 24 October 2014, view from the north. (B) The effusive eruption in Holuhraun, about 40 km to the northeast of the caldera

Social studies of volcanology: knowledge generation and expert advice on active volcanoes

This paper examines the philosophy and evolution of volcanological science in recent years, particularly in relation to the growth of volcanic hazard and risk science. It uses the lens of Science and Technology Studies to examine the ways in which knowledge generation is controlled and directed by social forces, particularly during eruptions, which constitute landmarks in the development of new technologies and models. It also presents data from a survey of volcanologists carried out during late 2008 and early 2009. These data concern the felt purpose of the science according to the volcanologists who participated and their impressions of the most important eruptions in historical time. It demonstrates that volcanologists are motivated both by the academic science environment and by a social concern for managing the impact of volcanic hazards on populations. Also discussed are the eruptions that have most influenced the discipline and the role of scientists in policymaking on active volcanoes. Expertise in volcanology can become the primary driver of public policy very suddenly when a volcano erupts, placing immense pressure on volcanologists. In response, the epistemological foundations of volcanology are on the move, with an increasing volume of research into risk assessment and management. This requires new, integrated methodologies for knowledge collection that transcend scientific disciplinary boundaries.

Science at the policy interface: volcano-monitoring technologies and volcanic hazard management

This paper discusses results from a survey of volcanologists carried out on the Volcano Listserv during late 2008 and early 2009. In particular, it examines the status of volcano monitoring technologies and their relative perceived value at persistently and potentially active volcanoes. It also examines the role of different types of knowledge in hazard assessment on active volcanoes, as reported by scientists engaged in this area, and interviewees with experience from the current eruption on Montserrat. Conclusions are drawn about the current state of monitoring and the likely future research directions, and also about the roles of expertise and experience in risk assessment on active volcanoes; while local knowledge is important, it must be balanced with fresh ideas and expertise in a combination of disciplines to produce an advisory context that is conducive to high-level scientific discussion.

Scientists’ views about lay perceptions of volcanic hazard and risk

We present data from a survey of scientists from volcano observatories and monitoring institutions around the world. The scientists were asked about the hazards from the volcanoes that they work on, their perception of the likely magnitude and impacts of eruptions, and their views about local people’s awareness of the risk. They were also asked about how well different groups are trusted by local people, and about their views concerning the need to warn people about changes in the volcanic risk. We show that scientists were generally concerned about risk from the volcanoes that they worked on, and also that many scientists felt that their own view of the risk was different from that of locals. Perceived trust in scientists depended upon both social factors and volcanic risk. We discuss the implications of these results for precautionary decision-making on active volcanoes.

Risk perceptions and trust following the 2010 and 2011 Icelandic volcanic ash crises.

Eruptions at the Icelandic volcanoes of Eyjafjallajökull (2010) and Grimsvötn (2011) produced plumes of ash posing hazards to air traffic over northern Europe. In imposing restrictions on air traffic, regulators needed to balance the dangers of accidents or aircraft damage against the cost and inconvenience to travelers and industry. Two surveys examined how members of the public viewed the necessity of the imposed restrictions and their trust in different agencies as estimators of the level of risk. Study 1 was conducted with 213 British citizens (112 males, 101 females), who completed questionnaires while waiting for flights at London City Airport during May 2012. Study 2 involved an online survey of 301 Icelandic citizens (172 males, 127 females, 2 undeclared gender) during April 2012. In both samples, there was general support for the air traffic restrictions, especially among those who gave higher estimates of the likelihood of an air accident or mishap having otherwise happened. However, in both countries, the (minority of) respondents who had personally experienced travel disruption were less convinced that these restrictions were all necessary. Scientists, the International Civil Aviation Organization, and (in Iceland) the Icelandic Department of Civil Protection were all highly trusted, and seen as erring on the side of caution in their risk estimates. Airlines were seen as more likely to underestimate any risk. We conclude that perceptions of the balance between risk and caution in judgments under uncertainty are influenced by ones own motives and those attributed to others.

Chapter 17 Petrological and geochemical variation during the Soufrière Hills eruption, 1995 to 2010

Abstract The andesite lava erupted at the Soufrière Hills Volcano (SHV) is crystal-rich with 33–63% phenocrysts of plagioclase (65%), amphibole (28%), orthopyroxene (7%), and minor Fe–Ti oxide and clinopyroxene microphenocrysts. The andesite hosts mafic enclaves that have similar mineral phases to the andesite. The enclaves are generally crystal-poor but can have up to 27% of inherited phenocrysts from the andesite, the majority of which are plagioclase. The eruption is defined by discrete periods of extrusion called phases, separated by pauses. The enclaves exhibit bulk geochemical trends that are consistent with fractionation. We infer that the intruded mafic liquids of Phases I and II interacted and assimilated plutonic residue remaining from the multiple prior mafic intrusions, while the basaltic liquids from Phases III and V assimilated relatively little material. We also infer a change in the basaltic composition coming from depth. The bulk Fe contents of both magma types are coupled and they both show a systematic interphase variation in Fe content. We interpret the coupled Fe variation to be due to contamination of the andesite from the intruding basalt via diffusion and advection processes, resulting in the erupted andesite products bearing the geochemical imprint of the syn-eruptive enclaves.

Geopower: Reflections on the critical geography of disasters

This paper discusses disaster risk reduction (DRR) in the context of emerging geographical ideas about topologies and assemblages. It focuses on the role of expert advice in DRR and the resulting political and epistemological issues. The critical geography of disasters still struggles to communicate with persistent scientific technical-rational approaches to hazard assessment. Furthermore, recent studies have shown the potential for expert advice to be (mis)used for political purposes. Assemblage theory might be useful in opening up this hybrid area of research, as it allows a nuanced view of disasters and DRR that can incorporate complex human-environmental relationships and diverse knowledges.This paper discusses disaster risk reduction (DRR) in the context of emerging geographical ideas about topologies and assemblages. It focuses on the role of expert advice in DRR and the resulting p...

Quantifying gas emissions from the “Millennium Eruption” of Paektu volcano, Democratic People’s Republic of Korea/China

Measurements of S and other volatiles during pre-eruptive crystallization suggest high gas flux during the 946 CE Paektu eruption. Paektu volcano (Changbaishan) is a rhyolitic caldera that straddles the border between the Democratic People’s Republic of Korea and China. Its most recent large eruption was the Millennium Eruption (ME; 23 km3 dense rock equivalent) circa 946 CE, which resulted in the release of copious magmatic volatiles (H2O, CO2, sulfur, and halogens). Accurate quantification of volatile yield and composition is critical in assessing volcanogenic climate impacts but is challenging, particularly for events before the satellite era. We use a geochemical technique to quantify volatile composition and upper bounds to yields for the ME by examining trends in incompatible trace and volatile element concentrations in crystal-hosted melt inclusions. We estimate that the ME could have emitted as much as 45 Tg of S to the atmosphere. This is greater than the quantity of S released by the 1815 eruption of Tambora, which contributed to the “year without a summer.” Our maximum gas yield estimates place the ME among the strongest emitters of climate-forcing gases in the Common Era. However, ice cores from Greenland record only a relatively weak sulfate signal attributed to the ME. We suggest that other factors came into play in minimizing the glaciochemical signature. This paradoxical case in which high S emissions do not result in a strong glacial sulfate signal may present a way forward in building more generalized models for interpreting which volcanic eruptions have produced large climate impacts.

Reactive halogens (BrO and OClO) detected in the plume of Soufrière Hills Volcano during an eruption hiatus

Volcanic plumes are sites of dynamic chemistry involving halogen gases. Here we present new data on the relative abundances of SO2, BrO and OClO gases emitted from Soufriere Hills Volcano [SHV). They were collected during an eruptive hiatus but during sustained degassing at this halogen-rich volcano. By comparison with data from a previous study during an eruptive phase and application of the data and modeling of Villemant et al. (2008), we suggest that, after consideration of errors, either the rate of HBr conversion to BrO is variable, ranging from ∼30% to ∼15%, and/or the relative partitioning of Cl and Br into the gas phase from the melt changes according to eruptive activity. We examine the potential implications of this for fluid-melt partitioning, and compare our results with data from the experimental literature. Our work contributes toward understanding the controls on the BrO/SO2 ratio for volcano monitoring purposes; the changes in plume chemistry with regard to bromine at the onset of lava extrusion may be large and rapid. OClO was detected in the plume at SHV for the first time. This species has only previously been detected in emissions from Mount Etna (using ground-based methods) and from Puyehue Cordon Caulle (using satellite-based methods). No HCHO or NOy species were detected in the spectra.

At the Mercy of the Mountain? Field Stations and the Culture of Volcanology

This paper discusses the role of volcano observatories as local sites of knowledge production through the monitoring of volcanoes, and links this with the global production of knowledge in volcanology. The paper initially discusses the institutional geography of volcanological science, and relates this broadly to the geography of science and science studies. It then focuses on interview data to draw some insights into the experiences of observatory and university scientists. Observatories have to provide scientific advice to local authorities and also engage with the international scientific community. They may act as gatekeepers to the field, and as rich sources of baseline data for research projects. As such, they have a pivotal role in the production of knowledge beyond the field sites—and are also involved in the protection of populations. The paper argues that the tension between academic research and volcano monitoring that occurs at many observatories is an important part of the process of knowledge production in volcanology, and also reveals the complex geographies of social responsibility and collaboration that exist around active volcanoes as scientific networks and territorial governance structures interact.