Hazard implications of small-scale edifice instability and sector collapse: a case history from Soufrière Hills Volcano, Montserrat
S. R. YoungB. VoightJenni BarclayRichard A. HerdJean‐Christophe KomorowskiA. D. MillerR. S. J. SparksR. C. Stewart
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Abstract During the 1995 to 1998 phase of dome growth at Soufrière Hills Volcano on Montserrat, we documented instability of the steep southern rim of English's Crater, known as Galway's Wall. The horseshoe-shaped English's Crater provided good evidence for previous sector collapses, and assessments undertaken in late 1996 anticipated the possibility of a partial sector collapse and a SW-directed explosion, hazards previously unrecognized on Montserrat. A change from predominantly endogenous to exogenous growth of the lava dome at the end of 1996 eased the stress on the southern sector. However, rapid dome growth in November and December 1997 led to severe reloading and eventual sector failure at the base of the buried Galway's Wall and in the adjacent hot-spring area. This failure resulted in the debris avalanche and lateral blast of 26 December 1997. Similar sector collapses at a number of small volcanoes in the Caribbean, as well as worldwide, are evidence that edifice instability develops commonly in dome-forming eruptions. The hazards from a sector collapse and a consequent lateral blast are extreme, and monitoring operations and disaster planning at such volcanoes should focus on these, as well as on the more common hazards of conventional pyroclastic flows associated with dome growth.Keywords:
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While volcanic events are commonly characterized by multiple eruptive stages, most probabilistic tephra hazard analyses only simulate the major (paroxysmal) stage. In this study, we reconsider this simplified treatment by comparing hazard outcomes from simulated single‐ and multistage eruption sequences, using the Okataina Volcanic Center (OVC) in New Zealand as a case study. Our study draws upon geological evidence particular to the OVC as well as generalized patterns of eruptive behavior from other analogous volcanic centers. Exceedance probabilities of simulated tephra thickness, the cumulative duration of explosive behavior, and the duration of the entire eruptive sequence were all compared. Multistage simulations show an increased hazard with the greatest differences lying close to the vent for long duration and high thickness thresholds and at intermediate distances between the vent and the maximum extent of the deposit for lower thickness and duration thresholds. Multiple explosive stages increase the likelihood of an event lasting longer than 1 month by up to sevenfold and, for given low‐probability events, accumulated tephra thicknesses in some locations may increase by 1 order of magnitude and impact up to 22% more of New Zealand's North Island. Given our understanding of the eruptive history of the Okataina Volcanic Center, multistage simulations provide a better understanding of the potential hazard from this source.
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Since the most reliable volcanic hazard map will be of little use unless it is presented in a meaningful format, the Volcanic Hazard Map of Nevado del Huila Volcano (Colombia) was combined with remote sensing data and visualized in 3-D. This visualization methodology could be used with any volcanic hazard map available, in order to generate products that could help improving the communication between volcanologists and people not familiar with volcanoes. The right understanding of any volcanic hazardous situation will avoid or minimize damaging consequences to people exposed to such natural risk.Volcanoes with their eruptions and other related hazards had lo
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In the case of the volcanic eruption of Mount Usu in 2000, there were no victims because the evacuation activities were carried out smoothly, as people made great use of the hazard map of Usu Volcano as a source of information. Also, the Mount Fuji Hazard Map Committee started work in 2001, scheduled to publicize the results in the near future. Although volcanic hazard maps have only recently captured the attention to people in Japan, they have been used in various overseas countries for many years. This paper summarizes the definition of volcanic hazard maps and the method of making volcanic hazard maps, classifies and analyzes the collected foreign cases, and introduces representative examples.
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Abstract. The possible emplacement of pyroclastic fall and flow products from Campi Flegrei and Somma-Vesuvio represents a threat for the population living in Napoli city. For this area, the volcanic hazard was always partially investigated to define the hazard related to the Campi Flegrei or to the Somma-Vesuvio activity one at a time. A new volcanic hazard and risk assessment, at the municipality scale, as a vital tool for decision-making about territorial management and future planning, is presented here. In order to assess the hazard related to the explosive activity of both sources, we integrated the results of field studies and numerical simulations, to evaluate the future possibility for Napoli to be hit by the products of an explosive eruption. This is defined for the Somma Vesuvio central volcano through the sum of "field frequency" based on the thickness and distribution of past deposits (Lirer et al., 2001), and for the Campi Flegrei volcanic field by suitably processing simulated events based on numerical modelling (Alberico et al., 2002; Costa et al., 2009). Aiming at volcanic risk assessment, the hazard areas were joined with the exposure map, considered for our purposes as the economical value of artefacts exposed to hazard. We defined four risk classes, and argued that the medium and low-very low risk classes have the largest extent in Napoli municipality, whereas only few zones located in the eastern part of the city and in the westernmost coastal area show a high risk, owing to the correspondence of high economical value and high hazard.
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This book provides the discussion of a survey of short-term and long-term volcanic hazard and risk, including types of potentially hazardous volcanic events, the information necessary for volcanic-hazards assessments. It also provides cartographic representation of volcanic hazard (with examples ranging from the French West Indies to the Philippines) and suggestions for the preparation of hazards-zonation maps.
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Volcanoes represent complex geological systems capable of generating many dangerous phenomena. To evaluate and manage volcanic risk, we need first to assess volcanic hazard (i.e., identify past volcanic system behavior to infer future behavior. This requires acquisition of all relevant geological and geophysical information, such as stratigraphic studies, geological mapping, sedimentological studies, petrologic studies, and structural studies. All this information is then used to elaborate eruption scenarios and hazard maps. Stratigraphic studies represent the main tool for the reconstruction of past activity of volcanoes over time periods exceeding their historical record. This review presents a systematic approach to volcanic hazard assessment, paying special attention to reconstruction of past eruptive history. It reviews concepts and methods most commonly used in long- and short-term hazard assessment and analyzes how they help address the various serious consequences derived from the occurrence (and nonoccurrence in some crisis alerts) of volcanic eruptions and related phenomena.
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Abstract. Nowadays, tephra fallout hazard is based on coupling the physical modeling of the tephra dispersion processes with a probabilistic analysis that takes into account the natural variability of the volcanic phenomena in terms of eruption probability, eruption sizes, vent position and meteorological conditions. In this framework, we present a prototypal methodology to carry out a multi-volcano long-term tephra fallout hazard assessment in Southern Italy from the active Neapolitan volcanoes: Somma-Vesuvius, Campi Flegrei, and Ischia. FALL3D model (v.8.0) has been used to run thousands of numerical simulations (1,500 per eruption size class), considering the ECMWF ERA5 meteorological dataset over the last 30 years. The output in terms of tephra ground load has been processed within a new workflow for large-scale, high-resolution volcanic hazard assessment, in order to quantify the mean annual frequency with which the tephra load at the ground exceeds given critical thresholds at a target site within a 50-years exposure time, and the relative epistemic uncertainty. This work provides, for the first time, a multi-volcano probabilistic hazard analysis for tephra fallout, fully comparable with those used for seismic phenomena and other natural disasters in which multiple sources are integrated together, and it accounts for potential changes in regimes of each single considered volcano. This allows us to discuss also how the full information can be traced back to provide specific information about the prevalence of different volcanoes and eruptive style in the different target areas, based on hazard disaggregation. The methodology is applicable to any other volcanic areas or over different exposure times.
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