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Les déstabilisations de flanc des volcans de l'Ile de La Réunion (Océan Indien): Mise en évidence, implications et origines

Abstract : The joint study of the emerged and submerged parts of Reunion Island (Indian Ocean), based on the evaluation of marine multibeam data collected these last 20 years and confronted with previous geological and geophysical works, demonstrates the considerable importance of flank landslide processes in the evolution of this volcanic oceanic system. Fifty or so mass-wasting events recurrently dismantled Piton des Neiges, Les Alizés, and Piton de La Fournaise volcanoes during the last 2 million years at least. They are multi-scale, primary or secondary, and of aerial, coastal or submarine origin. Most correspond to instantaneous and catastrophic phenomena of debris avalanche type. Their deposits are mainly accumulated at sea, within four gigantic topographic bulges named "Reliefs Sous-Marins", located to the east, north, west and south of the island. These fans are 20-30 km wide at the coastline and 100-150 km wide at their end, 70-80 km offshore. They were built gradually by the superimposition and/or the juxtaposition of products displaced during landslide episodes implying up to several hundreds of km3 of materials. A very small proportion is recognized on land, in Piton des Neiges central part or at its littoral edges, and constitutes the proximal facies of the deposits recognized offshore. The main structural features of Reunion sub-aerial morphology are interpreted as (1) relatively recent landslide scars, often remodelled by erosion and/or filled by subsequent volcanic activity, or (2) remnants of old debris avalanches amphitheatres whose border faults could have been reactivated by volcano-tectonics (caldera collapses, gravitational spreading, Piton des Neiges hypovolcanic complex subsidence,...) and/or during younger landslide events. These faults have probably guided the mass-wasting of the edifice by erosion, thus facilitating the digging of Piton des Neiges central depressions (the three Mafate, Salazie, Cilaos cirques and the Marsouins paleo-cirque) and of the main valleys of the island. The study of Mount Haddington volcano (James Ross Island, Antarctica) and analogue experiments show that the ductile deformation of low strength layers existing within shield volcanoes, and in particular of volcanoclastic deltas, made up mostly of debris avalanche deposits, is a key for the generation of rotational slides and subsequent debris avalanches. This model is privileged for Reunion volcanoes, considering a predominant role of gravitational processes in flank landslides triggering.
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Contributor : Jean-François OEHLER Connect in order to contact the contributor
Submitted on : Friday, October 14, 2005 - 9:29:07 AM
Last modification on : Tuesday, October 19, 2021 - 6:59:06 PM
Long-term archiving on: : Friday, November 25, 2016 - 9:36:19 AM


  • HAL Id : tel-00010498, version 1


Jean-François Oehler. Les déstabilisations de flanc des volcans de l'Ile de La Réunion (Océan Indien): Mise en évidence, implications et origines. Géologie appliquée. Université Blaise Pascal - Clermont-Ferrand II, 2005. Français. ⟨tel-00010498⟩



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