A fast GIS-based risk assessment for tephra fallout: the example of Cotopaxi volcano, Ecuador-Part II: vulnerability and risk assessment

In order to develop efficient strategies for risk mitigation and emergency management, planners require the assessment of both the expected hazard (frequency and magnitude) and the vulnerability of exposed elements. This paper presents a GIS-based methodology to produce qualitative to semi-qualitative thematic risk assessments for tephra fallout around explosive volcanoes, designed to operate with datasets of variable precision and resolution depending on data availability. Due to the constant increase in population density around volcanoes and to the wide dispersal of tephra from volcanic plumes, a large range of threats, such as roof collapses, damage to crops, blockage of vital lifelines and health problems, concern even remote communities. To address these issues, we have assessed the vulnerability and the risk levels for five themes relevant to tephra fallout: (1) social, (2) economic, (3) environmental, (4) physical and (5) territorial. Risk and vulnerability indices for each theme are averaged to the fourth level of administrative unit (parroquia, parish). In a companion paper, Biass and Bonadonna (this volume) present a probabilistic hazard assessment for tephra fallout at Cotopaxi volcano (Ecuador) using the advection-diffusion model TEPHRA2, which is based on field investigations and a global eruption database (Global Volcanism Program, GVP). The scope of this paper is to present a new approach to risk assessment specifically designed for tephra fallout, based on a comprehensive hazard assessment of Cotopaxi volcano. Our results show that an eruption of moderate magnitude (i.e. VEI 4) would result in the possible collapse of ∼9,000 houses in the two parishes located close to the volcano. Our study also reveals a high risk on agriculture, closely linked to the economic sector, and a possible accessibility problem in case of an eruption of any size, as tephra is likely to affect the only major road running from Quito to Latacunga (Panamerican Highway). As a result, this method fits into the ongoing effort to better characterize and evaluate volcanic risk, and more specifically the risk associated with tephra fallout. Although this methodology relies on some assumptions, it can serve as a rapid and efficient starting point for further investigations of the risk level around explosive volcanoe

Aeolian Remobilisation of Volcanic Ash: Outcomes of a Workshop in the Argentinian Patagonia

During explosive volcanic eruptions, large quantities of tephra can be dispersed and deposited over wide areas. Following deposition, subsequent aeolian remobilisation of ash can potentially exacerbate primary impacts on timescales of months to millennia. Recent ash remobilisation events (e.g., following eruptions of Cordón Caulle 2011; Chile, and Eyjafjallajökull 2010, Iceland) have highlighted this to be a recurring phenomenon with consequences for human health, economic sectors, and critical infrastructure. Consequently, scientists from observatories and Volcanic Ash Advisory Centers (VAACs), as well as researchers from fields including volcanology, aeolian processes and soil sciences, convened at the San Carlos de Bariloche headquarters of the Argentinian National Institute of Agricultural Technology to discuss the ?state of the art? for field studies of remobilised deposits as well as monitoring, modeling and understanding ash remobilisation. In this article, we identify practices for field characterisation of deposits and active processes, including mapping, particle characterisation and sediment traps. Furthermore, since forecast models currently rely on poorly-constrained dust emission schemes, we call for laboratory and field measurements to better parameterise the flux of volcanic ash as a function of friction velocity. While source area location and extent are currently the primary inputs for dispersion models, once emission schemes become more sophisticated and better constrained, other parameters will also become important (e.g., source material volume and properties, effective precipitation, type and distribution of vegetation cover, friction velocity). Thus, aeolian ash remobilisation hazard and associated impact assessment require systematic monitoring, including the development of a regularly-updated spatial database of resuspension source areas.Fil: Jarvis, Paul A.. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Bonadonna, Costanza. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Dominguez, Lucia. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Forte, Pablo Brian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Frischknecht, Corine. Universidad de Ginebra. Facultad de Ciencias. Sección de Ciencias de la Tierra; SuizaFil: Bran, Donaldo. Instituto Nacional de Tecnología Agropecuaria; ArgentinaFil: Aguilar, Rigoberto. No especifíca;Fil: Beckett, Frances. No especifíca;Fil: Elissondo, Manuela. Secretaría de Industria y Minería. Servicio Geológico Minero Argentino; ArgentinaFil: Gillies, John. Desert Research Institute; Estados UnidosFil: Kueppers, Ulrich. Ludwig Maximilians Universitat; AlemaniaFil: Merrison, Jonathan. University Aarhus. Institut for Fysik Og Astronomi; DinamarcaFil: Varley, Nick. Universidad de Colima; MéxicoFil: Wallace, Kristi L.. United States Geological Survey; Estados Unido

Temporal evolution of roof collapse from tephra fallout during the 2021-Tajogaite eruption (La Palma, Spain)

Although dominantly effusive, the 2021 Tajogaite eruption from Cumbre Vieja volcano (La Palma, Spain) produced a wide tephra blanket over 85 days of activity. About one month after the eruption onset, clean-up operations were implemented to mitigate the impact of tephra load on primary buildings. Here, we present a post-event impact assessment of 764 primary buildings, which expands our empirical knowledge of building vulnerability to tephra fallout to include impacts from long-lasting eruptions. Field observations are analyzed in the perspective of existing fragility curves, high-resolution satellite imagery and a reconstruction of the spatio-temporal evolution of the tephra blanket to characterize the evolution of roof collapse due to static loads over time. Thanks to a chronological correlation between the temporal evolution of tephra sedimentation and the timing of clean-up operations, we quantified their effectiveness in mitigating roof collapse. If no clean-up measures had been taken 11% of the surveyed buildings would have exceeded a 75% probability of roof collapse, while only 10 roof collapses have been observed (1.3% of the analysed buildings). This work provides key insights for further development of emergency plans for the management of long-lasting eruptions characterised by the sustained emission of tephra over weeks to months

Mapa regional y ranking de riesgos volcánicos de la zona volcánica central de los Andes

La Zona Volcánica Central de los Andes (ZVCA) es una de las zonas volcánicas más activas de América del Sur y es una de las áreas en las que la mayoría de los volcanes se encuentran dentro de los 25 km de una frontera internacional comprendiendo Argentina, Chile, Bolivia y Perú, con importantes desafíos transfronterizos (Donovan & Oppenheimer, 2019). En esta región, los volcanes se ubican en el Altiplano-Puna (sobre los 4000 m de altitud) y, por lo tanto, varios volcanes superan los 6000 m s.n.m., entre ellos el Ojos del Salado que es la cumbre volcánica más alta del mundo. Durante décadas, la ZVCA ha sido un sitio importante para entender una gran cantidad de procesos geológicos (e.g, evolución geológica, tectónica, espesor de la corteza, erosión y geometría por subducción, segmentación del arco volcánico y génesis del magma), pero debido al difícil acceso, los registros de erupciones eran bastante escasos, hasta hace muy poco. Durante los últimos 20 años, la agitación volcánica en varias partes de la ZVCA ha permitido la implementación de nuevas capacidades de monitoreo e inversiones en investigación (Aguilera et al., 2022) y como consecuencia, se ha puesto a disposición nueva información detallada. La priorización de estrategias de reducción de riesgos es especialmente importante para la ZVCA debido a su gran cantidad de volcanes. Además, el número de personas expuestas a la actividad volcánica en la ZVCA depende de la dinámica eruptiva y la magnitud de las erupciones potenciales

Seismic soil amplification in alpine valleys: a case study : the Rhône valley, Valais, Switzerland

Alpine valleys are characterized by peculiar conditions, such as thick and young quaternary unconsolidated deposits (several hundred meters deep), steep slopes, rapid lateral variation of surficial deposit and a shallow water-table. In order to better appreciate the role of these elements on the seismic response, two areas were studied using different methodological approaches depending on the available data. In the Sion region, the soil amplification was evaluated in the frequency domain. Two-dimensional (2D) modeling and horizontal to vertical component (H/V) ratio on ambient seismic noise were independently used in order to cross-check their reliability and usefulness. Both techniques are consistent with the general trend, i.e. low frequency value where the deposit is thicker and higher values towards the edges where the sediment is thinning out. 2D modeling makes possible to demonstrate the influence of the asymmetry of the valley geometry, the importance of the slope gradient and the role of structure like shoulders on the amplification distribution. In the upper part of the Rhône valley, in the Susten-Brig area, the influence of local geologic conditions on soil amplification has been examined through a qualitative rating scheme. This approach not only integrates data on the surficial geology, depth to the water table, and thickness, but also on the slope gradient of the quaternary deposit because its influence on the amplification distribution has been demonstrated in the Sion region. The resulting relative maximum amplification map shows that the amplification distribution is mainly controlled by the steep slopes, although the level of amplification at a site depends on all of the present conditions. These results demonstrate the importance of considering not only the surficial characteristics but also the hidden morphological structure of a valley for a seismic hazard assessment in Alpine regions since both elements contribute to modify the seismic response of a site

Seismic soil effect in an embanked deep alpine valley : a numerical investigation of two-dimensional resonance

This paper presents a 2D numerical study of the seismic response of a deep embanked sediment-filled valley (Rhône valley, Switzerland) to incident SH and SV waves. The 2D modeling is performed with a program developed by Pedersen et al. (1995), based on the IBEM technique. This valley exhibits variation in subsurface geometry. Therefore, three representative cross-sections are considered in order to investigate the influence of symmetric and asymmetric morphology on the seismic response. Comparison between 1D and 2D modeling shows that both resonant frequencies and amplification values differ to a large extent. Looking in the central part of the valley, the 2D predicted amplification value is about twice higher than in the 1D case, whereas the fundamental resonant frequency value is higher by a factor of 1.7. Moreover 2D modeling results show that this valley presents a twodimensional resonance due to its shape ratio and shear-wave velocity contrast. The main characteristic is the unchanged position of the fundamental resonance frequency, regardless of the surface site along the cross-section under consideration and the incidence angle. However, the asymmetric cross-section induces a specific spectral amplification pattern at the surface site and along the cross-section, which is also a function of the direction of incidence of the seismic wave. Such results show the importance of considering the morphology of a deep and narrow valley when investigating the local seismic response

A fast GIS-based risk assessment for tephra fallout: the example of Cotopaxi volcano, Ecuador. Part II: vulnerability and risk assessment

In order to develop efficient strategies for risk mitigation and emergency management, planners require the assessment of both the expected hazard (frequency and magnitude) and the vulnerability of exposed elements. This paper presents a GIS-based methodology to produce qualitative to semi-qualitative thematic risk assessments for tephra fallout around explosive volcanoes, designed to operate with datasets of variable precision and resolution depending on data availability. Due to the constant increase in population density around volcanoes and to the wide dispersal of tephra from volcanic plumes, a large range of threats, such as roof collapses, damage to crops, blockage of vital lifelines and health problems, concern even remote communities. To address these issues, we have assessed the vulnerability and the risk levels for five themes relevant to tephra fallout: (1) social, (2) economic, (3) environmental, (4) physical and (5) territorial. Risk and vulnerability indices for each theme are averaged to the fourth level of administrative unit (parroquia, parish). In a companion paper, Biass and Bonadonna (this volume) present a probabilistic hazard assessment for tephra fallout at Cotopaxi volcano (Ecuador) using the advection-diffusion model TEPHRA2, which is based on field investigations and a global eruption database (Global Volcanism Program, GVP). The scope of this paper is to present a new approach to risk assessment specifically designed for tephra fallout, based on a comprehensive hazard assessment of Cotopaxi volcano. Our results show that an eruption of moderate magnitude (i.e. VEI 4) would result in the possible collapse of ∼9,000 houses in the two parishes located close to the volcano. Our study also reveals a high risk on agriculture, closely linked to the economic sector, and a possible accessibility problem in case of an eruption of any size, as tephra is likely to affect the only major road running from Quito to Latacunga (Panamerican Highway). As a result, this method fits into the ongoing effort to better characterize and evaluate volcanic risk, and more specifically the risk associated with tephra fallout. Although this methodology relies on some assumptions, it can serve as a rapid and efficient starting point for further investigations of the risk level around explosive volcanoes

Challenges of SAR interferometry on Mount Cameroon

Mount Cameroon is the only active volcano of the Cameroon Volcanic Line and is located in an inhabited area. Consequently ground deformation monitoring is crucial. DinSAR has demonstrated its capability in various volcanic contexts. However Mount Cameroon is located close to the Equator and is under the influence of the Africa branch of the Inter-Convergence Tropical Zone (ICTZ), which plays a major role on the precipitable water vapor content in the atmosphere. This volcano also exhibits an elliptical shape and strong slope gradients. We discuss these factors that may hamper the use of radar images on Mount Cameroon

Simulation and Visualization of Volcanic Phenomena Using Microsoft Hololens: Case of Vulcano Island (Italy)

This article describes an interactive holographic visualization of volcanic eruption application for Microsoft HoloLens device. The aim of the project is to use this technology to visualize different eruptive phenomena on an active volcano for public education, emergency training, preparedness planning purposes, and raising awareness among tourists. We have selected La Fossa volcano on Vulcano island (Italy) as a case study and, thus, the application is named HoloVulcano. Unity game engine and Microsoft Visual Studio were used to develop the HoloVulcano augmented/virtual reality visualization application. The current version of HoloVulcano visualizes volcanic phenomena typically associated with unrest (fumaroles) and explosive eruptions (e.g. eruptive plumes, ejection of ballistic blocks, bombs, and pyroclastic density currents). The eruption types are developed based on existing literature using Unity game engine's particle systems component. HoloVulcano is a Microsoft HoloLens device application. Wearing the HoloLens, users can interact with the application through voice, gazing, and gestures and view different volcanic phenomena from different sites and angles on the island. HoloVulcano can be used by emergency managers and teachers for training, emergency exercises, and public educati