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Marginally stable recent Plinian eruptions of Mt. Pelée volcano (Lesser Antilles): the P2 AD 280 eruption

Abstract : Major volcanic hazards in the Lesser Antilles arc include powerful Plinian explosive eruptions that inject ash high into the atmosphere and produce dangerous pyroclastic density currents (PDC) on the ground. Understanding the key physical processes governing the dynamics and stability of past volcanic columns is a fundamental problem in volcanology as well as being central to assessing specific hazards in this region and elsewhere. However, the number of cases for which the transition of regime between a stable and collapsing eruptive plume is described in detail remains too small to constrain fully theoretical models of volcanic plumes. Here we present a detailed reconstruction of the time evolution of the P2 AD 280 eruption at Mt. Pelee volcano in Martinique, to expand the database available to test physical models. The P2 sequence, which forced the first inhabitants to flee to other islands for decades as suggested by archaeological evidence, starts with a basal ash layer interpreted as the result of an initial violent laterally directed explosion to the NE of the volcano. Most of the deposit sequence is made of a pumice fall deposit interbedded with a low-concentration PDC deposit interpreted as the result of a partial column collapse. The upper pumice fall unit shows an inverse gradation and is overlain by a final high-concentration PDC deposit or locally by the correlative low-concentration PDC deposit. Field data on deposit dispersal, thickness, and grain-size distribution are used together with physical models to reconstruct the dynamic evolution of this eruption. Empirical models of deposit thinning suggest that the minimum volume of pyroclastic deposits is 0.67-0.88km(3) dense rock equivalent (DRE), much larger than the 0.17km(3) DRE previously estimated. We find that the mass eruption rate increased from 6x10(7) to 1.1x10(8)kgs(-1), producing an initially stable 23- to 26-km-high Plinian plume, which ultimately collapsed to form a fountain. We discuss the mechanisms leading to column collapse based on published data on magmatic water contents and our estimates of grain-size distributions and mass discharge rates. The eruption started close to the plume/fountain transition and the volcanic column ultimately collapsed mainly due to an increase in mass discharge rate. This marginally stable evolution was also inferred from analysis of the P1 AD 1300 eruption deposits, suggesting consistent behavior during the recent Plinian eruptions of Mt. Pelee volcano. In these two eruptions, the transition occurred at conditions well predicted by our theoretical model of volcanic plumes.
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https://hal-insu.archives-ouvertes.fr/insu-02920463
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Submitted on : Monday, August 24, 2020 - 4:42:49 PM
Last modification on : Tuesday, September 1, 2020 - 3:07:07 AM

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Guillaume Carazzo, Stephen Tait, Edouard Kaminski. Marginally stable recent Plinian eruptions of Mt. Pelée volcano (Lesser Antilles): the P2 AD 280 eruption. Bulletin of Volcanology, Springer Verlag, 2019, 81 (1), ⟨10.1007/s00445-018-1265-6⟩. ⟨insu-02920463⟩

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