Volcanic Risk Research Articles

Conceptualizing community in disaster risk management

Community resilience is often assessed in disaster risk management (DRM) research and it has been argued that it should be strengthened for more robust DRM. However, the term community is seldom precisely defined and it can be understood in many ways. We argue that it is crucial to explore the concept of community within the context of DRM in more detail. We identify three dominating views of conceptualizing community (place-based community, interaction-based community, community of practice and interest), and discuss the relevance of these conceptualizations. We base this discussion on quantitative and qualitative empirical and policy document data regarding flood and storm risk management in Finland, wildfire risk management in Norway and volcanic risk management Iceland. According to our results, all three conceptualizations of community are visible but in differing situations. Our results emphasize the strong role of public sector in DRM in the studied countries. In disaster preparedness and response, a professionalized community of practice and interest appear to be the most prominent within all three countries. The interaction-based community of informal social networks is of less relevance, although its role is more visible in disaster response and recovery. The place-based (local) community is visible in some of the policy documents, but otherwise its role is rather limited. Finally, we argue that the measured resilience of a community depends on how the community is conceptualized and operationalized, and that the measures to strengthen resilience of a particular community should be different depending on what the focal community is.

Educational Processes for Volcanic Risk Management (Vrm) at an Educational Institution (Ei) in The Department of Nariño (COLOMBIA)

Objective: to analyze the educational processes in Volcanic Risk Management (VRM) of the project of Education in Emergencies (EiE) at the Institución Educativa San Bartolomé (IESBA) in the Municipality of La Florida in the Department of Nariño (Colombia). Method: it is a qualitative study oriented from the historical-hermeneutical paradigm including ethnographic elements. Its participants were students, teachers and administrative staff of the IESBA. The techniques and instruments for collecting information included participant observation, individual and group semi-structured interviews, personal communications and document review. The constant comparison method was used for information analysis. Results: the interaction and the communication in the educational institution, as well as the community participation lead to the adoption and the strengthening of the knowledge referred to the VRM, from the different teaching strategies that involve not only the educational community, but also the community in general. Conclusions: the work done by the IESBA is consistent with the needs and demands of the context in which it is set, highlighting from the EiE project, elements such as community participation and institutional and inter-institutional work. This study shows a strategy that can be replicated in diverse EI that are highly exposed to the volcanic risk. Finally, considering inclusive education is also an indicator of improvement.

Evaluating population vulnerability to volcanic risk in a data scarcity context: The case of Goma city, Virunga volcanic province (DRCongo)

Goma city, at the eastern border of DRCongo, is highly exposed to natural hazards, especially from Nyiragongo volcano, located directly North of it. In January 2002, the city centre of Goma was devastated by lava flows and several thousands of people were temporarily displaced. Defining and quantifying population vulnerability to natural hazards, and lava flow hazards in particular, is a crucial element to evaluate and manage the risk. This paper aims at assessing the vulnerability of the population facing volcanic hazards in Goma, and its spatial variation across the city, in order to support volcanic risk prevention and management at the local levels. In this data scarcity context, two parallel methodologies are tested based on data collected through a large-scale household survey: the Social Vulnerability Index (SoVI) as defined by Cutter et al. (2003) based on a statistical data reduction; the other using fewer significant indicators in order to develop an Operational Vulnerability Index (OVI). Results show that the spatial distribution of the vulnerability levels with both approaches is quite similar, but the construction of an OVI can help to communicate the message more easily to political authorities for risk management actions – e.g., to target neighborhoods where to develop priority prevention programs – but also in terms of spatial urban planning – e.g., to identify areas where to act. Population vulnerability assessment, together with the lava flow hazard invasion probability and population exposure, is one of the crucial steps towards the lava flow risk assessment.

Unravelling the magma feeding system of a young basaltic oceanic volcano

A multidisciplinary approach combining petrological, geochemical, and fluid-inclusion studies with seismic monitoring data was used to build a model of the magma feeding system of Pico volcano (Azores islands, North Atlantic Ocean). We explore how magma has ascended to the surface in the last 10 ka and how this ascent is associated with the selective activation of the three tectonic systems intersecting the volcano. The deepest and most important ponding level for all ascending magmas is located at 17.3–17.7 km and corresponds to the Moho Transition Zone (MTZ), which marks the transition from mantle rocks to ultramafic cumulates. At shallower depth ascending magmas carry >30 vol% of clinopyroxene and olivine. Each magma ascent followed a distinct path and ponded often for a limited period. Ponding levels common to all feeding systems are present at 16.3–16.7 km, 12.1–14.5 km, 9.4–9.8 km, and 7.7–8.1 km. These depths mark important discontinuities where magmas formed stacked sills and evolved through fractional crystallisation. Dense and un-decrepitated fluid inclusions show rapid ascent from the MTZ along the Lomba do Fogo-São João fault (N150° system) and along the N120° regional transtensive system, despite multiple intrusions. Magma ponding at 5.6–6.8 km occurs where the N150° and N60° tectonic systems intersect each other. Here magma evolves towards plagioclase-rich and is only erupted at the summit crater and subterminal vents. This region is the source of the frequent microseismicity recorded at 4 to 7 km beneath the southern flank of Pico volcano, which might be associated with the early stages of formation of a more complex magma reservoir. The local and regional tectonics are of paramount importance in the activation of the different magma feeding systems over time. This new information is fundamental to improve the knowledge on the future eruptive behaviour of Pico volcano and can have significant implications on the mitigation of volcanic risk. This multidisciplinary approach can be applied not only to other volcanoes of the Azores but also to poorly monitored oceanic volcanoes, where magma ascent strongly depends on the activation of tectonic systems.

When the Vertical Becomes Horizontal: Experiencing Exploding Mountains in Borderlands

This article uses a case study from Latin America to investigate the geological politics surrounding borderland volcanoes. As scientific technologies for volcano monitoring improve and the number of volcanoes monitored globally increases, a growing awareness of transborder volcanic risk is developing. In parallel to this, developments in geopolitics have started to embrace the idea of vertical territory: territory as a material volume, reemphasizing the geological in politics and the political in geology. This article considers the dynamics of territory through time, with a particular focus on extreme “geo-events” that reshape institutions, reveal cross-border differences in nation-state assemblages, and redistribute the earth in dynamic ways. This raises interesting challenges for scientists because of the diverse scientific histories and institutional structures between nations, but it also raises potential geopolitical challenges. The article thus argues that volcanoes can provide focal points for the politics of the geos, as experienced by communities and by scientists: Awareness of “the other” side of the volcano border and experiencing the activity of the earth in a liminal setting are important in how people interpret the earth and their own identities. Volcanic eruptions highlight the diversity of institutional approaches across the border and can provoke reconfiguration of national priorities. Key Words: disaster risk, geopolitics, political geology, territory, volcanic risk.

Characterizing magma fragmentation and its relationship with eruptive styles of Somma-Vesuvius volcano (Naples, Italy)

Among the active volcanoes worldwide, Somma-Vesuvius is one with the highest volcanic risk as the surrounding areas are highly populated. Somma-Vesuvius is quiescent since 1944, but geological and historical records reveal a frequent violent explosive activity in the last 4000 years, representing a severe risk for the ∼700,000 inhabitants currently living in the area having a high probability for being impacted by pyroclastic density currents (“red zone”) and more than one million people who can be potentially affected by tephra fallout. This study aims to analyze the distribution and grain-size of tephra fallout deposits from several Somma-Vesuvius eruptions of different styles, ranging from Violent Strombolian to sub-Plinian and Plinian, for characterizing the associated magmatic fragmentation through the assessment of their total grain-size distribution (TGSD). Chronologically, we focus on the Avellino (4365 BP) and Pompeii (A.D. 79) Plinian eruptions, the Pollena (A.D. 472) sub-Plinian eruption, and the 1906 and 1944 Violent Strombolian eruptions. The related TGSDs were estimated by means of the Voronoi tessellation method, which requires a suitable number of local grain-size distributions and estimation of the area of minimum tephra loading (zero-line contour). However, field-derived TGSDs can be biased towards the coarse and fine grain-size populations due to the typical paucity of available field outcrops of fallout deposits. To encompass this issue, we performed a sensitivity study on the assumption behind TGSD reconstructions and described TGSDs through analytical grain-size distributions that best fit the field TGSDs. Our main objective is a more robust estimation of the TGSDs associated with the different eruptive styles, which is crucial, together with the other eruption source parameters, for robustly predicting tephra loading and airborne ash dispersal of future eruptions at Somma-Vesuvius.

Public response to news reports on the Mount Kusatsu-Shirane volcanic eruption: A content analysis of online reader comments

This paper reports on the real-time public responses to the eruption disaster on Mt. Kusatsu-Shirane in January 2018. This volcanic disaster attracted significant media coverage, with many people again acknowledging the risk of volcanic hazards from the many news reports. These days, as it has become increasingly common for people to express their opinions using online sites, online reader comments can be important sources of public opinion. This paper used a content analysis approach to analyze the comments posted in online news reports on the volcanic disaster to determine the public's perspective of the risks associated with volcanic disasters and volcanology. Applying an inductive category-extraction strategy, the comments were sorted into six categories of comments (1) that made reference to volcanic risk perception, (2) on volcanology or volcanologists, (3) that had fatalistic perceptions of natural disasters as blameless misfortunes, (4) on eruption predictability, (5) on disaster risk reduction measures implemented by central/local governments and disaster management agencies, and (6) explaining the phreatic explosion mechanism. It was found that many comments tended to have a negative tone, and a prominent criticism was that modern science could not detect volcanic activities reliably. However, some commenters suggested that experts with a sophisticated knowledge of volcanology should be available to support local communities in a similar way to the “home doctor”. Volcanologists need to disseminate information, such as the current state of geological and earth science education systems, volcanological knowledge, and application of the lessons learned from volcanic disasters.

Enhancing Social Resilience Through Fruition of Geological Heritage in the Vesuvio National Park

The Vesuvio National Park, established in June 1995, is the green area closest to Napoli megacity, which suffers the absence of urban green spaces and could hence offer to citizens the opportunity to enjoy healthy places in a peculiar environment as the landscape of an active volcano. We here propose two trails with several stops, named the Ancient Railway Track and the Valle dell’Inferno. They start from San Sebastiano al Vesuvio and Ottaviano towns, located on two opposite sides of northern Somma-Vesuvio area, and are both directed towards the Vesuvio crater. Along the trails, the visitors can enjoy several volcanic forms and products (the Somma caldera rim, dykes, lava domes, ropy lava flows, pyroclastic fall deposits) together with historical remains, such as the Cook Railway track, and the typical botanic association, the Mediterranean bush. The stops were illustrated with panels describing in detail both geological and landscape features with pictures and simple text boxes, clear and engaging for a wide set of excursionists of different ages and cultural backgrounds. The quality of the two trails was assessed through a quantitative evaluation of the single stops considering the different typologies of expected visitors. The project of promotion and fruition of green spaces in an active volcanic area here proposed contributes to encourage healthy living and raise well-being and could represent one of the means to achieve a better level of resilience for a society exposed to high volcanic risk.

Risk perception and organizational capacity building in the Azores (Percepción del riesgo y desarrollo organizacional de capacidades de las Azores)

ABSTRACTAt an organizational level, effective communication and coordination are vital elements of capacity building to foster disaster resilience. The aim of this study is to verify differences in volcanic hazard risk perception and knowledge of Civil Protection agents with responsibilities in disaster management in the Azores, assuming that these can influence communication. Risk perception and knowledge were evaluated on a convenience sample of 373 participants. Results indicate moderate levels of volcanic risk perception, lack of knowledge and significant differences in the risk perception of agents from the Civil Protection System. Questions on the efficacy of risk communication between agents, the dissemination of information pertaining to volcanic risk, the dissemination of information on emergency and preparedness measures implemented and on the forms of communication between Civil Protection agents were raised. This study can be regarded as a first effort to analyse the capacity of public officials in the Azores to deal with a volcanic event and points to areas to enhance if resilience is to be promoted.

Probabilistic volcanic impact assessment and cost-benefit analysis on network infrastructure for secondary evacuation of farm livestock: A case study from the dairy industry, Taranaki, New Zealand

Evacuation is often a necessary volcanic risk mitigation measure. However, the focus is typically on primary evacuation from immediate life safety from the eruption, compared to secondary evacuation from loss of critical services and networked infrastructure. Evacuation, and the associated decision-making process, can be streamlined if probable evacuation can be forecast, and hence prepared for. This paper provides a framework using geospatial data, probabilistic modelling and cost-benefit analysis to produce a geospatial evacuation decision support tool. In this paper, we present a case study for the tephra fall hazard to dairy livestock for Mt. Taranaki, New Zealand, applying Bayesian Event Tree for Volcanic Hazard (BET_VH) modelling in conjunction with tephra dispersal modelling using TEPHRA2. We model two eruption types: 1) smaller Merapian; and 2) larger sub-Plinian, estimating tephra fall coverage with associated probabilities of occurrence. A comprehensive geospatial inventory is compiled, associating dairy farms with essential services: modelled electricity and water supply sources, and road access. Fault tree analysis and fragility functions are used to assess impact to: 1) feed supply; 2) water supply; and 3) milking ability for both on farm and external services e.g. electricity and water supply for each farm in the region. Without any of these, animal welfare will be threatened, even within a short timeframe e.g. two weeks. Cost-benefit analysis establishes if and where it will probably be beneficial to evacuate. This paper provides the first quantitative geospatial inter-dependency study for the Taranaki dairy industry from tephra fall, but also provides a framework that can be used to assess the impact to any geophysical hazard for any community or sector.

Tephra clean-up after the 2015 eruption of Calbuco volcano, Chile: a quantitative geospatial assessment in four communities

Reliable methods for volcanic impact and risk assessments are essential. They provide constructive information to emergency and disaster managers, critical infrastructure providers, the insurance industry, and wider society. Post-eruption clean-up of tephra deposits is a prevalent and expensive (time and resource) activity which is often not planned for. Here, we present an overview of the clean-up efforts undertaken in four communities after the VEI 4 eruption of Calbuco volcano in 2015. We narratively reconstruct clean-up efforts in Ensenada (Chile), Junín de los Andes (Argentina), San Martín de los Andes (Argentina), and Villa La Angostura (Argentina) using semi-structured interviews, syn- and post-deposition photographs, pre- and post-event visual spectrum satellite imagery, and media reports. We compare these reconstructions with estimates based on a geospatial modelling approach adapted from Hayes et al. (Journal of Applied Volcanology 6:1; 2017). Specifically, we compare reported and geospatially derived estimates for volume of tephra removed, and clean-up operation duration. Our modelling approach performed well for Junín de los Andes but did not adequately capture volume and clean-up operation duration for the three remaining case study locations. We discuss several sources of uncertainty (including observational errors and natural variance of tephra deposit thickness), reported tephra removal volume estimates, clean-up methods, land use, and temporal evolution of clean-up operation demand. Our work demonstrates the utility of using simple geospatial data to develop assessments for tephra clean-up for use in response and recovery planning, and quantitative volcanic impact and risk assessments.

Natural disasters, land and labour

Abstract We study the behaviour of farmers living under the threat of the Tungurahua Volcano in Ecuador. Recent eruptions have caused significant damage, including crop loss, death of livestock and destruction of dwellings. We collected a unique data set after a major eruption in 2016. We interviewed 222 farmers in the area affected by the eruption and 260 in a nearby control zone to understand why they choose to remain in the risky zone despite the existence of public programmes aimed at relocating them to safe zones. We examine land and labour, which are farmers’ primary productive assets. First, we investigate the capitalisation of volcanic hazards in farmland values and find a negative price premium of 21 per cent compared to the control zone. Second, we explore non-farm labour in response to volcanic risk. Finally, we argue that repeated ash fall events increase the illiquidity of farm household assets, such as farmland, and that agricultural human capital is difficult to convert into non-agricultural capital. Our results convey important information for public policies aimed at supporting adaptation and resilience of people living under the threat of volcanoes and other natural disasters.

Análisis comparativo 2002-2014 del riesgo volcánico en las localidades de Cherquenco y Melipeuco, Región de la Araucanía, Chile

Las fases subplineanas del volcán Llaima (Región de la Araucanía, Chile) representan un alto riesgo para la población de los dos asentamientos humanos más cercanos: Melipeuco y Cherquenco. De esta forma, el objetivo principal de este trabajo es calcular y analizar el riesgo volcánico en ambos pueblos, para los años 2002 y 2014. Para esto, el trabajo se dividió en tres etapas. Primero, una fase de recopilación bibliográfica, donde se buscó sentar las bases de la dinámica del volcán Llaima y su amenaza. En una segunda etapa, se determinó la vulnerabilidad de los asentamientos susceptibles a ser afectados. Finalmente, se realizó un análisis multicriterio con el objetivo de tener una primera aproximación al riesgo volcánico en el área de estudio para los años 2002 y 2014. Los resultados mostraron que las dos áreas de estudio analizadas alcanzan valores de riesgo que aumentan considerablemente en estos doce años de análisis comparativo; sobre todo en el caso de Melipeuco, donde el riesgo pasó de alto a extremo.

From sink to volcanic source: Unravelling missing terrestrial eruption records by characterization and high‐resolution chronology of lacustrine volcanic density flow deposits, Lake Inawashiro‐ko, Fukushima, Japan

AbstractEruption records in the terrestrial stratigraphy are often incomplete due to erosion after tephra deposition, limited exposure and lack of precise dating owing to discontinuity of strata. A lake system and sequence adjacent to active volcanoes can record various volcanic events such as explosive eruptions and subaqueous density flows being extensions of eruption triggered and secondary triggered lahars. A lacustrine environment can constrain precise ages of such events because of constant and continuous background sedimentation. A total of 71 subaqueous density flow deposits in a 28 m long core from Lake Inawashiro‐ko reveals missing terrestrial volcanic activity at Adatara and Bandai volcanoes during the past 50 kyr. Sedimentary facies, colour, grain size, petrography, clay mineralogy, micro X‐ray fluorescence analysis and chemistry of included glass shards characterize the flow event deposits and clarify their origin: (i) clay‐rich grey hyperpycnites, extended from subaerial cohesive lahars at Adatara volcano, with sulphide/sulphate minerals and high sulphur content which point to a source from hydrothermally altered material ejected by phreatic eruptions; and (ii) clay‐rich brown density flow deposits, induced by magmatic hydrothermal eruptions and associated edifice collapse at Bandai volcano, with the common presence of fresh juvenile glass shards and low‐grade hydrothermally altered minerals; whereas (iii) non‐volcanic turbidites are limited to the oldest large slope failure and the 2011 Tohoku‐oki earthquake events. The high‐resolution chronology of volcanic activity during the last 50 kyr expressed by lacustrine event deposits shows that phreatic eruption frequency at Adatara has roughly tripled and explosive eruptions at Bandai have increased by ca 50%. These results challenge hikers, ski‐fields and downstream communities to re‐evaluate the increased volcanic risks from more frequent eruptions and far‐reaching lahars, and demonstrate the utility of lahar and lacustrine volcanic density flow deposits to unravel missing terrestrial eruption records, otherwise the recurrence rate may be underestimated at many volcanoes.

A series of volcanic edifices discovered a few kilometers off the coast of SW Sicily

The Graham and Terrible banks, located about 35 km from the south-western coast of Sicily, host a large number of volcanic constructs, the most famous being the ephemeral Ferdinandea Island. These volcanoes occur along two N-S trending strike-slip lineaments that constitute the lithospheric-scale Capo Granitola-Sciacca Fault Zone. Here we present recently acquired swath bathymetric data and magnetic measurements, in conjunction with high-resolution seismic profiles, which reveal the presence of another six volcanic edifices located very close to the Sicilian coasts, one of which is only 7 km away. Three of these volcanic constructs have been previously identified only on the basis of available seismic profiles, but their morphology and their volcanic nature had so far not been documented. Two edifices to the north show a possible tuff cone/ring-like morphology modified by crater breaching, while the three southernmost volcanoes have a truncated-conical shape. The northwestern-most volcano (here called Actea) shows a more complex morphology, probably representing the remnants of a previous crater rim. Seismic data analysis suggests that the six volcanic edifices were generated during a pre-Last Glacial Maximum (LGM, ca. 20 ka B.P.) magmatic phase associated with a tectonic event. Only the Actea volcano shows indications of magmatic reactivation, possibly between the LGM and the initial post-LGM transgressive phase. This reactivation is evident by the emplacement of a prominent young lava flow. The discovery of submerged volcanoes so close to the populated coast of Sicily demonstrates that there are large submerged areas near the littoral that are still little known and studied, and underlines how crucial it is to analyze the issue of volcanic risk for densely inhabited coastal areas like Sicily.

Towards Global Volcano Monitoring Using Multisensor Sentinel Missions and Artificial Intelligence: The MOUNTS Monitoring System

Most of the world’s 1500 active volcanoes are not instrumentally monitored, resulting in deadly eruptions which can occur without observation of precursory activity. The new Sentinel missions are now providing freely available imagery with unprecedented spatial and temporal resolutions, with payloads allowing for a comprehensive monitoring of volcanic hazards. We here present the volcano monitoring platform MOUNTS (Monitoring Unrest from Space), which aims for global monitoring, using multisensor satellite-based imagery (Sentinel-1 Synthetic Aperture Radar SAR, Sentinel-2 Short-Wave InfraRed SWIR, Sentinel-5P TROPOMI), ground-based seismic data (GEOFON and USGS global earthquake catalogues), and artificial intelligence (AI) to assist monitoring tasks. It provides near-real-time access to surface deformation, heat anomalies, SO2 gas emissions, and local seismicity at a number of volcanoes around the globe, providing support to both scientific and operational communities for volcanic risk assessment. Results are visualized on an open-access website where both geocoded images and time series of relevant parameters are provided, allowing for a comprehensive understanding of the temporal evolution of volcanic activity and eruptive products. We further demonstrate that AI can play a key role in such monitoring frameworks. Here we design and train a Convolutional Neural Network (CNN) on synthetically generated interferograms, to operationally detect strong deformation (e.g., related to dyke intrusions), in the real interferograms produced by MOUNTS. The utility of this interdisciplinary approach is illustrated through a number of recent eruptions (Erta Ale 2017, Fuego 2018, Kilauea 2018, Anak Krakatau 2018, Ambrym 2018, and Piton de la Fournaise 2018–2019). We show how exploiting multiple sensors allows for assessment of a variety of volcanic processes in various climatic settings, ranging from subsurface magma intrusion, to surface eruptive deposit emplacement, pre/syn-eruptive morphological changes, and gas propagation into the atmosphere. The data processed by MOUNTS is providing insights into eruptive precursors and eruptive dynamics of these volcanoes, and is sharpening our understanding of how the integration of multiparametric datasets can help better monitor volcanic hazards.

Viscoelastic relaxation: A mechanism to explain the decennial large surface displacements at the Laguna del Maule silicic volcanic complex

Silicic systems generate the most explosive eruptions on Earth. In contrast to basaltic systems, they can accumulate large volumes of magma without systematically erupting, confronting the classical interpretation that a volcano inflates when a magmatic intrusion occurs. Understanding the mechanisms of volcanic inflation and unrest is thus one of the most important challenges in volcanic risk assessment. Laguna del Maule (LdM) in the Southern Volcanic Zone (SVZ) of Chile, is one of the most active Holocene silicic complexes in the world and it has been inflating since 2007, accumulating 2 m of uplift without erupting. Several geophysical and geochemical studies conclude that a large crystal rich reservoir would be residing beneath LdM, in consistency with other multi-disciplinary studies showing that such crystal-rich reservoirs (“mush zones”) can be maintained beneath silicic volcanoes, fed by mafic magma recharge from below. Nevertheless, the mechanical state of such reservoirs remains unclear. Here, we characterize for the first time the mechanical properties of such a mush reservoir, able to promote large surface displacements such as those measured at LdM. Using a 3D finite element method we simulate a recharge of magma at the base of a crystal rich reservoir, by assuming an overpressurized source surrounded by a large viscoelastic shell. Inversion results show that this model fits the observed temporal and spatial evolution of ground displacements measured with InSAR data and GNSS data between 2007 and 2017. We interpret the temporal behavior of ground displacement at LdM as resulting from two contributions. A magma recharge occurred within the first 4 yr of the active inflation, followed by the viscous response of the large viscoelastic shell, set to a viscosity of 1017 Pas. Compared to a purely elastic solution, our model suggests that up to 50% of the accumulated surface displacement during the ten-year period can be explained by this viscous response, and predicts ongoing displacements 50 yr after the onset of inflation. This model agrees with geophysical and geochemical observations and offers a simple explanation of the temporal evolution of surface displacements. It further allows to reconsider the mechanical behavior of large partially crystallized domains in the upper crust; such significant transient stress transfer over large viscoelastic areas should thus be accounted for in other studies of silicic volcanic complexes.

Impact of wind direction variability on hazard assessment in Martinique (Lesser Antilles): The example of the 13.5 ka cal BP Bellefontaine Plinian eruption of Mount Pelée volcano

The threat posed by powerful Plinian explosive eruptions, which inject large quantities of ash into the atmosphere and produce pyroclastic density currents (PDC) on ground, is mainly controlled by eruptive parameters and by the direction and strength of the wind field during the eruption. In most studies, mean wind profiles are used to investigate potential tephra deposit dispersion and to assess volcanic risk. Here we present a detailed reconstruction and reinterpretation of a poorly-understood eruption of Mount Pelée volcano (Martinique), and use it to demonstrate that exclusive use of the average trade wind profile can lead to a misrepresentation of the volcanic risk. The great interest of this eruption stems from its unusual southward dispersion, which encompasses areas that are considered to be safe in current hazard maps and that host major infrastructure. Our new field study and radiocarbon dating show that these deposits are not part of the 2010 BP P3 eruptive sequence as previously thought, but define a so far unknown eruptive event dating back to 13,516 cal BP, which we propose to name the Bellefontaine eruption. The Bellefontaine sequence consists of a basal grey lithic-rich layer resulting from an explosive opening phase that destroyed a pre-existing lava dome, immediately followed by a much thicker, slightly reverse-graded white pumice-fall layer. Their dispersal, thickness, and grain-size distribution are used together with physical models of a volcanic plume to reconstruct the time evolution of the eruption. We find that the mass eruption rate reached 5 × 107 kg s−1, producing a 20-km-high Plinian plume, and that the minimum volume of pyroclastic deposits was 0.18 km3 DRE. 2D simulations of tephra dispersion in the atmosphere performed with HAZMAP show that, unlike the recent eruptions at Mount Pelée volcano, mean seasonal wind profiles cannot explain the southward dispersal of the Bellefontaine deposits. To understand the origin of this unusual dispersion axis, we retrieve forty years of wind data over Martinique by using global atmospheric reanalyses from 1979 by the European Center for Medium-Range Weather Forecasts ERA Interim (hereafter ERA-Interim) and ERA5 (hereafter ERA5). We find that, contrary to previous assumptions, this eruption did not necessarily occur during extreme weather conditions associated with the passing of a hurricane. Looking in detail into the ERA Interim datasets, we observe that the wind direction variability over the past 40 years is very low during the dry season (from December to May), and much larger during the wet season (from June to November), even in the troposphere (≈0 to 18 km), which can occasionally result in northerly winds in the mid- to high troposphere over Martinique. As a similar eruption today would spread volcanic material as far as the prefecture of Fort-de-France and its international airport, a zone classified as safe in current hazard maps, this study highlights the importance of including daily variability of winds in hazard assessment models when considering Plinian eruptions.

Forecasting future volcanic eruptions at Mount Cameroon within the time interval 2000–2200

Mount Cameroon is currently the only active volcano in Central Africa. It supports an active farming population due to the fertility of its soil. Its two most recent eruptions were in 1999 and 2000. They were associated with serious costly material damages that impoverished part of the local population. Some people were evacuated from their villages to neighboring localities. The population that lives on these flanks is therefore exposed to volcanic risk. Risk assessment starts with an evaluation of the hazard, which is here an estimation of the probability of an eruption of a given magnitude within a given time interval. The present study exploits the time series of quiescent time periods of Mount Cameroon volcano to predict the likelihood of its future eruptions. Only eruptions with VEI > 0 are considered in this study. The time series of repose intervals of Mount Cameroon is proved to be stationary based on the Kolmogorov–Smirnov (K–S) test on the cumulative number of eruptions and Dickey–Fuller unit root tests, and the successive repose time intervals are proved to be independent using the serial correlation scatterplot and Spearman correlation coefficient. Renewal processes (exponential, Weibull, log-logistic) are each best fitted and tested for goodness of fit. The parameters of the processes were calculated using the maximum likelihood functions. From the K–S and the chi-square tests, all three applied theoretical processes are found to be a good fit to the data. The exponential process is the best characteristic of the series as supported by the Akaike information criterion (AIC) best-to-fit test. The three models offer different predictions of the occurrences of future eruptions of Mount Cameroon. For elapsed time lower than or equal to 30 years, the probabilities estimated from the log-logistic and the Weibull distributions are higher than those calculated from the exponential. For higher elapsed time, the probabilities from the exponential distribution are intermediary between the probabilities from the log-logistic (lower) and the Weibull (higher). These two latter distributions predict different hazard rates than the exponential.

Reservoir Structure and Hydraulic Properties of the Campi Flegrei Geothermal System Inferred by Audiomagnetotelluric, Geochemical, and Seismicity Study

AbstractThe Campi Flegrei caldera is a large volcanic complex lying in the Campanian Plain, Southern Italy. During its history the caldera experienced episodes of bradyseism and intense swarm seismicity. The mechanism leading to unrest episodes is still debated, and great efforts are ongoing to improve the knowledge of this structure and its evolution due to the high volcanic risk in such a densely populated area. Here we present a resistivity model from a two‐dimensional inversion of audiomagnetotelluric data acquired along an approximately 5.6‐km long profile crosscutting the Solfatara‐Pisciarelli district and the Agnano plain. The resistivity model shows (1) very low resistivity values confined in the first 500 m of depth both in correspondence of the Solfatara‐Pisciarelli districts and the Agnano depression; (2) a resistive plume that extends underneath the Solfatara crater down to 2,000‐ to 3,000‐m depth, and (3) an adjoining relative conductive unit eastward. We discuss the resistivity structures in a multidisciplinary framework integrating inedited geochemical and seismological observations with existing surface geology and subsurface information. The Solfatara‐Pisciarelli district and the Agnano plain, both being expression of intense hydrothermal activity, show different characteristics. Below the Solfatara‐Pisciarelli area, the shallow conductive zone is interpreted as a faulted clay cap that overlies a highly active vapor‐dominated reservoir characterized by a convective mechanism. Conversely, below the Agnano plain, a liquid phase seems to prevail in the reservoir. The spatiotemporal variations of seismicity imply a combined action of preexisting tectonic lineaments and fluid interaction between the gas/steam reservoir and the outflow zone.