Large‐scale flank collapse events during the activity of Montagne Pelée, Martinique, Lesser Antilles

Abstract

[1] A horseshoe-shaped structure already identified on the southwestern flank of Montagne Pelée (Martinique, Lesser Antilles arc) was previously interpreted as resulting of a flank collapse event, but no debris avalanche deposits were observed at the time. New offshore high-resolution bathymetry and geophysical data (Aguadomar cruise; December 1998 to January 1999; R/V L'Atalante) lead us to identify three debris avalanche deposits on the submarine western flank of Montagne Pelée extending down to the Grenada Basin. They display morphological fronts and hummocky morphology on bathymetric data, speckled pattern on backscatter data and hyperbolic facies on 3.5 kHz and seismic profiles. New on-land geological studies lead us to identify two other horseshoe-shaped structures on the same flank of the volcano. The three submarine deposits have been traced back to the structures identified on land, which confirms the occurrence of repeated flank collapse events during the evolution of Montagne Pelée. The ages of the last two events are estimated at $9 ka and $25 ka on the basis of 14 C and 238 U/ 230Th dates. Every flank collapse produced debris avalanches which flowed down to the Caribbean Sea. We propose that the repeated instabilities are due to the large asymmetry of the island with western aerial and submarine slopes steeper than the eastern slopes. The asymmetry results from progressive loading by accumulation of volcanic products on the western slopes of the volcano and development of long-term gravitational instabilities. Meteoric and hydrothermal fluid circulation on the floor of the second flank collapse structure also creates a weakened hydrothermalized area, which favors the recurrence of flank collapses.INDEX TERMS: 3045 Marine Geology and Geophysics: Seafloor morphology and bottom photography; 8414 Volcanology: Eruption mechanisms; 8499 Volcanology: General or miscellaneous;

Numerical modelling of historical landslide-generated tsunamis in the French Lesser Antilles

“…Both the Mattioli et al (2007) simulation and ours show that a limited source volume can indeed generate a tsunami as was observed in Montserrat and in Guadeloupe. Potential volcano flank collapse, especially when considering large volumes of debris, are sometimes associated with tsunami hazards (Le Friant et al, 2003. In fact, the global volume of a potential huge landslide must not be identified as a direct tsunami source, as it would collapse and enter the sea during a noninstantaneous time sequence.…”

Flank instability assessment at Kick-’em-Jenny submarine volcano (Grenada, Lesser Antilles): a multidisciplinary approach using experiments and modeling

“…This recent collapse episode suggests that the sliding surface left by the previous landslide played the role of a weak basal layer. A similar process has been proposed for the generation of multiple landslides at other centers in the arc (see Le Friant et al 2003;Boudon et al 2007). The current conical-shaped edifice also lies within this structure (Boudon et al 1999;Dondin 2010;Dondin et al 2012).…”

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“…On volcanoes of the Lesser Antilles arc, at least 52 flank-collapse events have been identified (Deplus et al, 2001;Le Friant et al, 2002, 2003a, 2003b, 2004Lebas et al, 2011;Boudon et al, 2007). In the northern part of the arc, flank collapses are repetitive, do not exceed 1 km 3 in volume, can occur in all directions, and are promoted by intense hydrothermal alteration and well-developed fracturing of the summit part of the edifices.…”

“…In the southern part of the arc, flank collapses are larger (with volumes up to tens of km 3 ), always directed to the west, and related to the higher overall slopes of the leeward side of the islands. For example, the evolution of the active Montagne Pelée volcano, Martinique, has been marked by three major flank collapses (~0.1 Ma, ~25,000 y ago, and ~9000 y ago) that systematically destroyed the western flank of the volcano (Le Friant et al, 2003a, 2003bBoudon et al, 2005Boudon et al, , 2007. Collapse volumes varied from 2 to 25 km 3 , and debris avalanches flowed down to the Grenada Basin (Fig.…”

“…Two-dimensional seismic surveys around the Lesser Antilles have provided excellent images (Figs. AF01-AF18) of the debris avalanche deposits, including their basal surfaces (e.g., Deplus et al, 2001;Le Friant et al, 2003a), contrary to seismic lines in other geodynamic contexts. For the Lesser Antilles, Le Friant et al (2009, 2010 have shown that as much as 70 vol% of the erupted products along the arc are finally deposited in the surrounding marine environment, emphasizing the need for submarine studies in this tectonic environment to retrieve a complete picture of the constructive and destructive processes associated with arc volcanism.…”