Eruptive Scenarios Research Articles

Monti Sabatini and Colli Albani: the dormant twin volcanoes at the gates of Rome

This multi-disciplinary work provides an updated assessment of possible future eruptive scenarios for the city of Rome. Seven new 40Ar/39Ar ages from selected products of the Monti Sabatini and Vulsini volcanic districts, along with a compilation of all the literature ages on the Colli Albani and Vico products, are used to reconstruct and compare the eruptive histories of the Monti Sabatini and Colli Albani over the last 900 ka, in order to define their present state of activity. Petrographic analyses of the dated units characterize the crystal cargo, and Advanced-InSAR analysis highlights active deformation in the MS. We also review the historical and instrumental seismicity affecting this region. Based on the chronology of the most recent phases and the time elapsed between the last eruptions, we conclude that the waning/extinguishment of eruptive activity shifted progressively from NW to SE, from northern Latium toward the Neapolitan area, crossing the city of Rome. Although Monti Sabatini is unaffected by the unrest indicators presently occurring at the Colli Albani, it should be regarded as a dormant volcanic district, as the time of 70 kyr elapsed since the last eruption is of the same order of the longest dormancies occurred in the past.

Testing a Comprehensive Volcanic Risk Assessment of Tenerife by Volcanic Hazard Simulations and Social Vulnerability Analysis

Volcanic activity remains highly detrimental to populations, property and activities in the range of its products. In order to reduce the impact of volcanic processes and products, it is critically important to conduct comprehensive volcanic risk assessments on volcanically active areas. This study tests a volcanic risk assessment methodology based on numerical simulations of volcanic hazards and quantitative analysis of social vulnerability in the Spanish island of Tenerife, a well-known tourist destination. We first simulated the most likely volcanic hazards in the two eruptive scenarios using the Volcanic Risk Information System (VORIS) tool and then evaluated the vulnerability using a total of 19 socio-economic indicators within the Vulnerability Scoping Diagram (VSD) framework by combining the analytic hierarchy process (AHP) and the entropy method. Our results show good agreement with previous assessments. In two eruptive scenarios, the north and northwest of the island were more exposed to volcanic hazards, and the east registered the highest vulnerability. Overall, the northern municipalities showed the highest volcanic risk in two scenarios. Our test indicates that disaster risk varies greatly across the island, and that risk reduction strategies should be prioritized on the north areas. While refinements to the model will produce more accurate results, the outputs will still be beneficial to the local authorities when designing policies for volcanic risk reduction policies in Tenerife. This study tests a comprehensive volcanic risk assessment for Tenerife, but it also provides a framework that is applicable to other regions threatened by volcanic hazards.

From eruption scenarios to probabilistic volcanic hazard analysis: An example of the Auckland Volcanic Field, New Zealand

The dichotomy between probabilistic and scenario-based volcanic hazard assessments stems from their opposing strengths and weaknesses. The quantification of uncertainty and lack of bias in the former is balanced against the temporal narrative and communicability of the latter. In this paper we propose a novel methodology to bridge between the two, deriving a pseudo-probabilistic hazard estimate from a suite of dynamic scenarios covering multiple volcanic hazards and transitions in eruptive style, as designed for emergency management purposes, in a monogenetic volcanic field. We use existing and new models for eruption style transitions, which provide probabilities conditional on local environmental conditions, thus obtaining the relative likelihoods of each scenario at every location in the field. The results are interpreted in terms of the probability of various hazards and combinations of hazards arising from various scenarios at critical locations. Conversely, we also demonstrate that it may be possible to optimise the likelihood of the scenario allocations across desired locations for emergency management training purposes.

Auckland Volcanic Field magmatism, volcanism, and hazard: a review

ABSTRACT Auckland Volcanic Field (AVF) is a basaltic intraplate volcanic field in North Island, New Zealand, upon which >1.6 million people live. Seismic velocity tomography and geochemistry suggest a primary mantle source region at a depth of 70–90 km. Geochemical analysis indicates a range of magma compositions, and that melts ascend with little crustal interaction. Eruptions generally began with a phreatomagmatic phase forming maar and tuff rings with tephra fall, base surges, and ballistic projectiles as the main hazards. Subsequent magmatic phases formed scoria cones, and sometimes produced lava flows. Ages of 47 of the 53 volcanic centres reveal that the AVF first erupted ∼193 ka, and last erupted ∼500 yrs. BP. These geochronological constraints indicate repose periods ≤0.1–13 kyr, which have decreased since ∼60 ka. From known geological and exposure information, and using an interdisciplinary approach, eight future eruption scenarios have been developed for planning processes. Outstanding questions for the AVF concern the cause of mantle melting, the structure of the underlying lithosphere, magma ascent rates, controls on repose periods and eruptive volumes. Answering these questions may improve our understanding of warning periods, monitoring strategies, spatiotemporal risk profiles, and socio-economic impacts of volcanism on New Zealand’s largest city.

Past eruptions and future predictions: Analyzing ancient responses to Mount Vesuvius for use in modern risk management

The Campania region of southern Italy, dominated by Mount Vesuvius, is an enduring volcanic landscape which hosts a wealth of detailed information about human responses to past eruptions. This research taps into rich archaeological, geological, and historical data to bring together the past, present and future of Mount Vesuvius and the populations surrounding it. Records from the Avellino eruption (ca. 1900 BCE), and the Pompeii eruption (79 CE), their impacts, and associated social responses are examined here as two of the largest, most violent events of Vesuvius' eruptive history which impacted human populations. The social impacts of these eruptions are considered as valuable sources of information about worst-case-scenario events which should be utilized in contemporary risk management and emergency planning. The vulnerability and resilience of the Early Bronze Age and Roman societies who experienced the Avellino and Pompeii eruptions, respectively, are contrasted with potential responses of present Campanian communities to a hypothetical future eruption scenario. This work thus makes use of archaeological data from past disasters to engage with contemporary issues of emergency planning and risk management in the Vesuvius region of Southern Italy.

Emplacement of unusual rhyolitic to basaltic ignimbrites during collapse of a basalt-dominated caldera: The Halarauður eruption, Krafla (Iceland)

AbstractDeposits of the ca. 110 ka Halarauður eruption of Krafla caldera (reconstructed volume = 7 ± 6 km3 dense rock equivalent) include the only spatter-rich ignimbrite known in Iceland, and an exceptionally rare lava-like basaltic ignimbrite. We present a revised stratigraphy and new whole-rock major-element data set for products of this unusual event, one of only three Quaternary ignimbrite eruptions identified in Iceland. Compositions of Halarauður products span a broad range (50.0–74.6 wt% SiO2), reflecting mixing of rhyolite with underplating basalt. Small-volume, valley-ponded, basal pumice- and spatter-bearing lithic breccias and ignimbrite (rhyolite to andesite) reflect rapid column collapse during early opening of ring-fault vents. A transition to voluminous, regionally dispersed spatter agglomerates (dacite to basaltic andesite) marks an abrupt eruptive intensification, as gas-poor magma was squeezed into a developing ring-fault system by the subsiding chamber roof. Spatial heterogeneities in ascent rates and outgassing through this variably dilated fault system caused coeval formation of collapsing plumes and spatter fountains at separate vents. Spatter was entrained into flows from the more explosive vents, which deposited proximal spatter agglomerates and more distal spatter-bearing ignimbrite. Overlying lava-like ignimbrite deposits (basaltic andesite to basalt) reflect a final opening of vents, as mafic magma from deep levels of the chamber was squeezed through a dilated ring-fault system by the subsiding roof block and erupted at uncharacteristically high mass flux. Development of a mature ring-fault conduit system during early tapping of silicic magma appears to be a prerequisite for the emplacement of welded basaltic ignimbrites, and it should be considered as a possible eruption scenario in basalt-dominated systems where silicic magma has been known to also accumulate. Poor preservation of the Halarauður deposits exemplifies the challenges of studying ignimbrite eruptions in frequently glaciated regions like Iceland, where they may be more common than the geological record suggests.

Hydrothermal eruptions at El Humazo, Domuyo geothermal field, Argentina: Insights into the eruptive dynamics and controls

Hydrothermal eruptions are explosive events driven by the sudden and violent vaporization of the water present in many hot water geothermal fields worldwide. Over recent years, thermodynamical conditions of fluids and petrophisical-geomechanical features of host-rocks were mentioned as responsible of the wide range of eruptive styles and deposits of hydrothermal eruptions. Nevertheless, geological and historical records show that PDC and fallout processes are underestimated as common processes linked to hydrothermal eruptions. This paper analyzes from a multi-disciplinary approach —virtual outcrops modeling, sedimentology, petrographic and XDR studies, facies modeling, eye-witness source analysis, and stratigraphy— the pristine Holocene–historic hydrothermal eruptive record of El Humazo manifestation (Domuyo Geothermal Field, Patagonia, Argentina). Different eruptive scenarios are characterized by ballistic ejection, PDC and/or fallout mechanisms with discernible tefra-composition and granulometry, associated with both excavational and/or aggradational landforms. We show how diverse eruptive dynamics are controlled by pre-eruptive internal and external factors, such as reservoir energy, depth of the explosion/fragmentation levels, physical properties and structural anisotropy of the host-rocks and eruptive center migrations. We consider that this case study may be useful not only for the application in the assessment of the volcanic hazard associated with the Domuyo geothermal field, but also contributes to the knowledge of the eruptive dynamics in other geothermal systems with similar characteristics.

Practising an explosive eruption in Iceland: outcomes from a European exercise

A 3 day exercise simulating unrest and a large explosive eruption at Katla volcano, Iceland, was conducted in January 2016. A large volume of simulated data based on a complex, but realistic eruption scenario was compiled in advance and then transmitted to exercise participants in near-real time over the course of the exercise. The scenario was designed to test the expertise and procedures of the local institutions in charge of warning and responding to volcanic hazards, namely the volcano observatory, national civil protection, and the local university-science sector, as well as their interactions with the European science community and the London Volcanic Ash Advisory Centre. This exercise was the first of this magnitude and scope in Iceland and has revealed many successful developments introduced since the 2010 Eyjafjallajökull and 2011 Grímsvötn eruptions. Following the exercise, 90% of participants said that they felt better prepared for a future eruption. As with any exercise, it also identified areas where further development is required and improvements can be made to procedures. Seven key recommendations are made to further develop capability and enhance the collaboration between the volcano observatory, volcano research institutions and civil protection authorities. These recommendations cover topics including notification of responders, authoritative messaging, data sharing and media interaction, and are more broadly applicable to volcanic institutions elsewhere. Lessons and suggestions for how to run a large-scale volcanic exercise are given and could be adopted by those planning to rehearse their own response procedures.

Developing a suite of multi-hazard volcanic eruption scenarios using an interdisciplinary approach

Understanding future eruptions and their potential consequences is an important component of volcanic disaster risk reduction. Suites of scenarios are a useful compromise between fully probabilistic and fully deterministic (single scenario) approaches. In this paper, we present an interdisciplinary approach that combines stakeholder (volcanologists, disaster risk researchers, policy advisors, infrastructure managers, and emergency managers) requirements with fundamental science to produce multi-hazard eruption scenarios for a high-risk volcano. We apply this approach to the Auckland Volcanic Field (AVF) to develop a suite of scenarios (‘DEVORA Scenarios’) that cover the wide spectrum of credible expected eruption activity. Demand was driven by a desire from stakeholders for scenarios that are scientifically credible and relevant for disaster risk management purposes, including evacuation, welfare, recovery, and critical infrastructure disruption planning. Stakeholders were embedded throughout the scenario development process, most importantly at the scoping and design stage, and through multiple formal and informal review cycles. Balancing scientific credibility whilst ensuring the scenarios is relevant to stakeholders was a challenge that required considerable time by all parties. Importantly, the process of scenario development was just as useful as the final product: it facilitated open discourse on major scientific uncertainties and information gaps on AVF volcanism, hazards, and risk. This served two important ends: 1) it allowed scientists to communicate areas of uncertainty to other stakeholders such as emergency managers, and 2) it identified potential future research avenues with an obvious and tangible societal benefit. It is anticipated that the DEVORA Scenarios will serve as a foundation for studies exploring the societal ramifications of a future AVF eruption. The process we outline here can be followed to develop credible and relevant suites of eruption scenarios for disaster risk management purposes in other environments.

Near-Real-Time Tephra Fallout Assessment at Mt. Etna, Italy

During explosive eruptions, emergency responders and government agencies need to make fast decisions that should be based on an accurate forecast of tephra dispersal and assessment of the expected impact. Here, we propose a new operational tephra fallout monitoring and forecasting system based on quantitative volcanological observations and modelling. The new system runs at the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo (INGV-OE) and is able to provide a reliable hazard assessment to the National Department of Civil Protection (DPC) during explosive eruptions. The new operational system combines data from low-cost calibrated visible cameras and satellite images to estimate the variation of column height with time and model volcanic plume and fallout in near-real-time (NRT). The new system has three main objectives: (i) to determine column height in NRT using multiple sensors (calibrated cameras and satellite images); (ii) to compute isomass and isopleth maps of tephra deposits in NRT; (iii) to help the DPC to best select the eruption scenarios run daily by INGV-OE every three hours. A particular novel feature of the new system is the computation of an isopleth map, which helps to identify the region of sedimentation of large clasts (≥5 cm) that could cause injuries to tourists, hikers, guides, and scientists, as well as damage buildings in the proximity of the summit craters. The proposed system could be easily adapted to other volcano observatories worldwide.

Ceboruco hazard map: part I - definition of hazard scenarios based on the eruptive history

Of the 48 volcanoes in Mexico listed as potentially active by the National Center for Disaster Prevention (CENAPRED), Ceboruco, located in the western Trans-Mexican Volcanic Belt, is considered among the 5 most hazardous. Its recent eruptive history includes a large magnitude Plinian (VEI 6) eruption ~ 1000 years ago and the historical 1870–1875 vulcanian (VEI 3) eruption, as well as recent fumarolic and seismic activity.Ceboruco is a relatively young (< 400,000 years) stratovolcano characterized by abrupt changes in eruptive behavior. Individual eruptive episodes have great variations in style (effusive andesitic to highly-explosive rhyodacitic) and duration. These factors complicate hazard assessment.Three main eruptive scenarios of different magnitudes (large, intermediate, small) and eruption characteristics (likelihood of occurrence: high, medium, small) have been identified and will be presented as a background to build the volcanic hazard map for Ceboruco volcano (presented in part II of this work). Here, we report on the detailed eruptive history, with emphasis on the volcanic products of each of the eruptions, in order to identify those deposits that can serve as a reference for calibrating the modeling software (Tephra2 and Hazmap for ash fallout, Eject! code for ballistics, Etna Lava Flow Model for lava flows, Titan2D for pyroclastic density currents, and Flo-2D and LaharZ for lahars) that will be used in further steps to simulate different volcanic phenomena and lead to the construction of the hazard map.

How the variety of satellite remote sensing data over volcanoes can assist hazard monitoring efforts: The 2011 eruption of Nabro volcano

Satellite remote sensing is becoming an increasingly essential component of volcano monitoring, especially at little-known and remote volcanoes where in-situ measurements are unavailable and/or impractical. Moreover the synoptic view captured by satellite imagery over volcanoes can benefit hazard monitoring efforts. By monitoring, we mean both following the changing styles and intensities of the eruption once it has started, as well as nowcasting and eventually forecasting the areas potentially threatened by hazardous phenomena in an eruptive scenario. Here we demonstrate how the diversity of remote sensing data over volcanoes and the mutual interconnection between satellite observations and numerical simulations can improve lava flow hazard monitoring in response to effusive eruption. Time-averaged discharge rates (TADRs) obtained from low spatial/high temporal resolution satellite data (e.g. MODIS, SEVIRI) are complemented, compared and fine-tuned with detailed maps of volcanic deposits with the aim of constraining the conversion from satellite-derived radiant heat flux to TADR. Maps of volcanic deposits include the time-varying evolution of lava flow emplacement derived from multispectral satellite data (e.g. EO-ALI, Landsat, Sentinel-2, ASTER), as well as the flow thickness variations, retrieved from the topographic monitoring by using stereo or tri-stereo optical data (e.g. Pléiades, PlanetScope, ASTER). Finally, satellite-derived parameters are used as input and validation tags for the numerical modelling of lava flow scenarios. Our strategy is applied to the first historic eruption of Nabro volcano (Eritrea), occurred in June 2011. This eruptive event was characterized by the extraordinary quantity of SO2 emitted into the atmosphere and the extent of the long lava flows, which had a significant impact on the inhabitants of the Eritrea-Ethiopia border region despite the low population density. Because of its remote position, little was known about this eruption regarding the quantity of volcanic deposits and the timing and mechanisms of their emplacement. We found that the total volume of deposits, calculated from differences of digital elevation models (DEMs), is about 580 × 106 m3, of which about 336 × 106 m3 is the volume of the main lava flow that advanced eastward beyond the caldera. Multi-spectral satellite observations indicate that the main lava flow had reached its maximum extent (~16 km) within about 4 days of the eruption onset on midnight 12 June. Lava flow simulations driven by satellite-derived parameters allow building an understanding of the advance rate and maximum extent of the main lava flow showing that it is likely to have reached 10.5 km in one day with a maximum speed of ~0.44 km/h.

Mapping the susceptibility of rain-triggered lahars at Vulcano island (Italy) combining field characterization, geotechnical analysis, and numerical modelling

Abstract. The characterization of triggering dynamics and remobilized volumes is crucial to the assessment of associated lahar hazards. We propose an innovative treatment of the cascading effect between tephra fallout and lahar hazards based on probabilistic modelling that also accounts for a detailed description of source sediments. As an example, we have estimated the volumes of tephra fallout deposit that could be remobilized by rainfall-triggered lahars in association with two eruptive scenarios that have characterized the activity of the La Fossa cone (Vulcano, Italy) in the last 1000 years: a long-lasting Vulcanian cycle and a subplinian eruption. The spatial distribution and volume of deposits that could potentially trigger lahars were analysed based on a combination of tephra fallout probabilistic modelling (with TEPHRA2), slope-stability modelling (with TRIGRS), field observations, and geotechnical tests. Model input data were obtained from both geotechnical tests and field measurements (e.g. hydraulic conductivity, friction angle, cohesion, total unit weight of the soil, and saturated and residual water content). TRIGRS simulations show how shallow landsliding is an effective process for eroding pyroclastic deposits on Vulcano. Nonetheless, the remobilized volumes and the deposit thickness threshold for lahar initiation strongly depend on slope angle, rainfall intensity, grain size, friction angle, hydraulic conductivity, and the cohesion of the source deposit.

Volcano-Seismic Transfer Learning and Uncertainty Quantification With Bayesian Neural Networks

Over the past few years, deep learning (DL) has emerged as an important tool in the fields of volcano and earthquake seismology. However, these methods have been applied without performing thorough analyses of the associated uncertainties. Here, we propose a solution to enhance volcano-seismic monitoring systems, through probabilistic Bayesian DL; we implement and demonstrate a workflow for waveform classification, rapid quantification of the associated uncertainty, and link these uncertainties to changes in volcanic unrest. Specifically, we introduce Bayesian neural networks (BNNs) to perform event identification, classification, and their estimated uncertainty on data gathered at two active volcanoes, Mount St. Helens, Washington, USA, and Bezymianny, Kamchatka, Russia. We demonstrate how BNNs achieve excellent performance (92.08%) in discriminating both the type of event and its origin when the two data sets are merged together, and no additional training information is provided. Finally, we demonstrate that the data representations learned by the BNNs are transferable across different eruptive periods. We also find that the estimated uncertainty is related to changes in the state of unrest at the volcanoes and propose that it could be used to gauge whether the learned models may be exported to other eruptive scenarios.

Slope Stability in a Multi-Hazard Eruption Scenario (Santorini, Greece)

Under the European FP7 SNOWBALL project (2014–2017), the island of Santorini was used as a case study to validate a procedure to assess the possible multiple cascading effects caused by volcanic eruptions. From January 2011 to April 2012, the area was affected by low to moderate (Mw &lt;3.2) seismic shaking, which caused concern regarding a possible volcanic eruption that ultimately failed to materialize. Assuming the worst-case scenario of a sub-Plinian eruption, this study provides insights into the approach adopted by the SNOWBALL project to identify the most critical areas (hot spots) for slope stability. Geological field surveys, thematic maps, and geomorphological data on aerial photos and landform interpretation were adopted to assess the static susceptibility. The eruption scenario is related to two different phenomena: a pre-eruption earthquake (Mw 5.2) and the subsequent ash fallout deposition following the prevailing winds. Landslide susceptibility in seismic conditions was assessed through the HAZUS approach and the estimate of Newmark displacements (u), while the critical areas for ash fallout mobilization were assessed adopting empirical relationships. The findings are summarized in a scenario map reporting the most critical areas and the infrastructures most vulnerable to such phenomena.

Modeling Ash Dispersal From Future Eruptions of Taupo Supervolcano

AbstractHazard analysis at caldera volcanoes is challenging due to the wide range of eruptive and environmental conditions that can plausibly occur during renewed activity. Taupo volcano, New Zealand, is a frequently active and productive rhyolitic caldera volcano that has hosted the world's youngest known supereruption and numerous smaller explosive events. To assess ashfall hazard from future eruptions, we have simulated atmospheric ash dispersal using the Ash3d model. We consider five eruption scenarios spanning magma volumes of 0.1–500 km3 and investigate the main factors governing ash dispersal in modern atmospheric conditions. Our results are examined in the context of regional synoptic weather patterns (Kidson types) that provide a framework for assessing the variability of ashfall distribution in different wind fields. For the smallest eruptions (~0.1‐km3 magma), ashfall thicknesses &gt;1 cm are largely confined to the central North Island, with dispersal controlled by day‐to‐day weather and the dominance of westerly winds. With increasing eruptive volume (1–5‐km3 magma), ashfall thicknesses &gt;1 cm would likely reach major population centers throughout the North Island. Dispersal is less dependent on weather patterns as the formation of a radially expanding umbrella cloud forces ash upwind or crosswind, although strong stratospheric winds significantly restrict umbrella spreading. For large eruptions (50–500‐km3 magma), powerful expansion of the umbrella cloud results in widespread ashfall at damaging thicknesses (&gt;10 cm) across most of the North Island and top of the South Island. Synoptic climatology may prove a useful additional technique for long‐term hazard planning at caldera volcanoes.

Impacto socioeconómico por lahares y caída de ceniza ante la erupción del volcán Cayambe en la actividad florícola en Cayambe y Pedro Moncayo

El complejo volcánico Cayambe representa una potencial amenaza para poblaciones que basan su economía en la floricultura. En este trabajo, se presenta: 1) modelar espacialmente escenarios de erupción del volcán, 2) modelar espacialmente el potencial impacto de estos escenarios de riesgos por afectación de lahares y de ceniza; y 3) evaluar los impactos socioeconómicos de escenarios de erupción modelados por caída de ceniza mediante un análisis estadístico de simulaciones numéricas de escenarios eruptivos y zonas de afectación por lahares tomadas del nuevo mapa de amenazas del Cayambe. Así se determinó que espesores de ceniza de 20 a 50 mm serían el principal problema cubriendo el 81.46% de la superficie con pérdidas que ascienden los 300 millones de dólares en plantas e invernaderos. En el caso de lahares las pérdidas se darían en los suelos y se estiman pérdidas de 45 millones de dólares en el caso de lahares primarios y 15 millones de dólares en caso de lahares secundarios.Los resultados obtenidos en las simulaciones tienen mejor nivel de detalle que los obtenidos en años anteriores por la información cartográfica disponible del sector y las herramientas computacionales utilizadas; los mismos que concuerdan con los depósitos del Cayambe y pueden ser manejados para la toma de decisiones en beneficio de las poblaciones afectadas, considerando que una erupción del volcán Cayambe merece una atención especial por su alto impacto socioeconómico local y nacional por ser las exportaciones de flores un rubro importante para el país.

A 3D imaging textural characterization of pyroclastic products from the 1538 AD Monte Nuovo eruption (Campi Flegrei, Italy)

The explosive volcanic event of the 1538 AD Monte Nuovo eruption (Volcanic Explosivity Index, VEI = 2) in the Campi Flegrei high-risk caldera (Italy) has a strategic significance in the framework of volcanology and volcanic hazard of caldera-forming magmatic systems. In fact, it represents the last and unique historical eruption of the highly populated Phlegraean restless-caldera, and its precursory and eruptive phenomena are well-known because they were described in detail by contemporaneous eyewitnesses.In this study, a set of samples representative of the complete stratigraphic sequence of the Monte Nuovo eruption was characterized using phase-contrast synchrotron radiation computed microtomography and quantitatively investigated through the development of a new protocol for 3D textural analysis of highly-vesiculated volcanic rocks. Previous studies of products from this eruption are available in the literature, mostly based on 2D imaging techniques, and thus provide a useful data set for comparison.The 3D textural measurements allow us to investigate the subvolcanic processes (mechanisms and timing of magma degassing) that occurred during magma ascent in the conduit for each stage of the eruption and their relationship with the variations in the eruptive style described in the contemporaneous accounts of the eruption. This information is fundamental for the definition of a volcanic eruption scenario for such low-VEI events, often recurrent in the history of the caldera, and is useful both for hazard assessment and emergency planning.

Numerical simulation of block-and-ash flows for different eruptive scenarios of the Tacaná Volcanic Complex, México-Guatemala

The Tacaná Volcanic Complex (TVC), shared by México and Guatemala, is considered an active volcano that resumed phreatic explosions in 1949 and 1986. The TVC has recorded at least eight eruptions emplacing block-and-ash flows (BAFs) around the volcanic edifice during the past 42,000 years. The largest event generated the Mixcun deposit some 1950 yr B.P. from San Antonio Volcano, the youngest structure of the complex. Based on the eight mapped BAF deposits of the complex, we perform numerical simulations with the TITAN2d code to recreate the distribution and extent of these deposits. The results were used to prepare the zonation of the TVC based on the surface bed friction angles, which are related to the different morphologies of the volcano. From this zonation and the features of the past BAF deposits, we define three new eruptive impact scenarios (low, medium and high), to perform a hazard assessment of this phenomenon but considering the present morphology of the complex of the four eruptive centers. Next, we ranged the input parameters for each case scenario to analyze the dispersal, thickness and maximum runout of simulated flows. From the numerical simulations, we found that the most influential parameter in the model outputs is the basal friction angle, which varied from 23° to 12°. Then, we merged the eruptive scenarios simulated to construct new hazard maps for the different mass volumes simulated for each scenario. These maps clearly evidenced that the Mexican territory would be seriously affected in case of a renewed explosive activity of the TVC. In fact, even the partial collapse of any of the TVC domes would produce BAFs capable to flow over ~70 communities affecting ca. 20,000 inhabitants, as well as promote the generation of syn-and-post eruptive lahars if they flow into the main rivers that drain the volcano. Therefore, these maps are a great advance to evaluate the destructive potential of the TVC and must serve as the basis for the construction of a new risk map by the local authorities to update the operative and evacuation plans of the region. These actions would help to the >350,000 inhabitants living in a 35 km radius from the volcano's summit to be aware of the perils posed by the volcano, and how to act and evacuate in case of a volcanic crisis.

Eruption Scenarios of Active Volcanoes in Indonesia

Eruption scenarios were prepared as possible sequences in event trees for six active volcanoes in Indonesia, that are located near populated areas or have erupted in recent years (Galunggung, Guntur, Kelud, Merapi, Semeru, and Sinabung). The event trees prepared here show sequences of possible eruption phenomena without probabilities on branches and cover sequences experienced in historical and pre-historical eruptions based on archives and field research results. Changing magma discharge rates during eruption sequences were considered for the event tree of Merapi. This conceptual event tree can also be used as a short-term event tree in which forecasting the coming eruption became possible with geophysical and geochemical monitoring data. Eruption event trees prepared for selected time windows cannot illustrate all plausible hazards and risks associated with an eruption. Therefore, hazards and risks generated from an eruption should be considered in different domains from the event tree.