Volcanic hazard assessment for tephra fallout in Martinique

Audrey Michaud-Dubuy,Guillaume Carazzo,Edouard Kaminski

doi:10.1186/s13617-021-00106-7

Abstract

Mount Pelée (Martinique) is one of the most active volcanoes in the Lesser Antilles arc with more than 34 magmatic events in the last 24,000 years, including the deadliest eruption of the 20th century. The current volcanic hazard map used in the civil security plan puts the emphasis on the volcanic hazard close to the volcano. This map is however based on an incomplete eruptive history and does not take into account the variability of the expected source conditions (mass eruption rate, total erupted mass, and grain-size distribution) or the wind effect on ash dispersal. We propose here to refine the volcanic hazard map for tephra fallout by using the 2-D model of ash dispersal HAZMAP. We first simulate the maximum expected eruptive scenario at Mount Pelée (i.e., the P3 eruption) using a seasonal wind profile. Building upon the good agreement with field data, we compute probability maps based on this maximum expected scenario, which show that tephra fallout hazard could threaten not only areas close to the volcano but also the southern part of Martinique. We then use a comprehensive approach based on 16 eruptive scenarios that include new field constraints obtained in the recent years on the past Plinian eruptions of Mount Pelée volcano. Each eruptive scenario considers different values of total erupted mass and mass eruption rate, and is characterized by a given probability of occurrence estimated from the refined eruptive history of the volcano. The 1979-2019 meteorological ERA-5 database is used to further take into account the daily variability of winds. These new probability maps show that the area of probable total destruction is wider when considering the 16 scenarios compared to the maximum expected scenario. The southern part of Martinique, although less threatened than when considering the maximum expected scenario, would still be impacted both by tephra fallout and by its high dependence on the water and electrical network carried from the northern part of the island. Finally, we show that key infrastructures in Martinique (such as the international airport) have a non-negligible probability of being impacted by a future Plinian eruption of the Mount Pelée. These results provide strong arguments for and will support significant and timely reconceiving of the emergency procedures as the local authorities have now placed Mount Pelée volcano on alert level yellow (vigilance) based on increased seismicity and tremor-type signals.

Highlights

Mount Pelée (Martinique) is one of the most active volcanoes in the Lesser Antilles arc with more than 34 magmatic events in the last 24,000 years (Smith and Roobol 1990; Westercamp and Traineau 1983; Boudon et al 2005; Michaud-Dubuy 2019)
These studies, based on more than 200 outcrops and robust age determinations highlight that Plinian eruptions are more frequent at Mount Pelée than previously thought, and provide important Eruptive Source Parameters (ESPs, total volume, mass eruption rate, total grain-size distribution, column height, exit velocity) retrieved from field observations and measurements combined with physical models of volcanic columns
In this work, we proposed an integrated approach to refine tephra fallout hazard assessment in Martinique, based on eruptive scenarios determined from our revisited Plinian eruptive history of Mount Pelée volcano, and considering daily wind variability for the first time

Summary

Introduction

Mount Pelée (Martinique) is one of the most active volcanoes in the Lesser Antilles arc with more than 34 magmatic events in the last 24,000 years (Smith and Roobol 1990; Westercamp and Traineau 1983; Boudon et al 2005; Michaud-Dubuy 2019). These studies, based on more than 200 outcrops and robust age determinations highlight that Plinian eruptions are more frequent at Mount Pelée than previously thought, and provide important Eruptive Source Parameters (ESPs, total volume, mass eruption rate, total grain-size distribution, column height, exit velocity) retrieved from field observations and measurements combined with physical models of volcanic columns Another major outcome is that the associated hazards, including tephra fallout whose dispersal strongly depends on wind speed and direction, and pyroclastic flows due to column collapse, are largely underestimated in the current evacuation plans (Michaud-Dubuy 2019). The most probable eruptive scenario for Mount Pelée volcano in the future may be a phreatic eruption (Boudon et al 2005), the possibility of a more powerful Plinian eruption occurring is non-negligible and could threaten the entire Caribbean region

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