Growth and collapse of the Reunion Island volcanoes |
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Authors: | Jean-François Oehler Jean-François Lénat Philippe Labazuy |
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Institution: | (1) Laboratoire Magmas et Volcans, UMR 6524 CNRS, OPGC, Université Blaise Pascal, 5 rue Kessler,, 63038 Clermont-Ferrand Cedex, France |
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Abstract: | This work presents the first exhaustive study of the entire surface of the Reunion Island volcanic system. The focus is on
the submarine part, for which a compilation of all multibeam data collected during the last 20 years has been made. Different
types of submarine features have been identified: a coastal shelf, debris avalanches and sedimentary deposits, erosion canyons,
volcanic constructions near the coast, and seamounts offshore. Criteria have been defined to differentiate the types of surfaces
and to establish their relative chronology where possible. Debris avalanche deposits are by far the most extensive and voluminous
formations in the submarine domain. They have built four huge Submarine Bulges to the east, north, west, and south of the
island. They form fans 20–30 km wide at the coastline and 100–150 km wide at their ends, 70–80 km offshore. They were built
gradually by the superimposition and/or juxtaposition of products moved during landslide episodes, involving up to several
hundred cubic kilometers of material. About 50 individual events deposits can be recognized at the surface. The landslides
have recurrently dismantled Piton des Neiges, Les Alizés, and Piton de La Fournaise volcanoes since 2 Ma. About one third
are interpreted as secondary landslides, affecting previously emplaced debris avalanche deposits. On land, landslide deposits
are observed in the extensively eroded central area of Piton des Neiges and in its coastal areas. Analysis of the present-day
topography and of geology allows us to identify presumed faults and scars of previous large landslides. The Submarine Bulges
are dissected and bound by canyons up to 200 m deep and 40 km long, filled with coarse-grained sediments, and generally connected
to streams onshore. A large zone of sedimentary accumulation exists to the north–east of the island. It covers a zone 20 km
in width, extending up to 15 km offshore. Volcanic constructions are observed near the coast on both Piton des Neiges and
Piton de la Fournaise volcanoes and are continuations of subaerial structures. Individual seamounts are present on the submarine
flanks and the surrounding ocean floor. A few seem to be young volcanoes, but the majority are probably old, eroded seamounts.
This study suggests a larger scale and frequency of mass-wasting events on Reunion Island compared to similar islands. The
virtual absence of downward flexure of the lithosphere beneath the island probably contributes to this feature. The increased
number of known flank–failure events has to be taken into consideration when assessing hazards from future landslides, in
particular, the probability of landslide-generated tsunamis.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Reunion Island Landslides Multi-beam bathymetry Sonar backscatter Digital terrain model Oceanic islands |
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