Growth and collapse of the Reunion Island volcanoes

Abstract

International audienceThis 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

Seamount chain–subduction zone interactions: Implications for accretionary and erosive subduction zone behavior

“…Large-scale flank collapse can transport 100-mto kilometer-scale megablocks into the moats (e.g., Moore et al, 1994). The moat has a maximum of 3 km thickness by up to 160 km width at Hawaii (e.g., ten Brink and Watts, 1985;Moore et al, 1994), a maximum of 455 m thickness by up to 250 km width at the Canary Islands (Collier and Watts, 2001;Gee et al, 2001), and a maximum of 520 m thickness by up to 130 km width at La Réunion island (southwestern Indian Ocean; de Voogd et al, 1999;Oehler et al, 2008) (widths as measured from Figure 1 and from Oehler et al [2008]). Relatively little sediment is deposited on the flanks of the actual seamounts; these are dominated by sediment erosion and bypass into the moat (Leslie et al, 2002).…”

Bathy-morphological setting of Terceira Island (Azores) after the FAIVI cruise

“…Conversely, while dismantling and large-scale mass-wasting processes are widely detected on the submarine flanks of other active volcanic islands (e.g. Boudon, Le Friant, Komorowski, Deplus, & Semet, 2007;Coombs, White, & Scholl, 2007;Mitchell, Masson, Watts, Gee, & Urgeles, 2002;Moore, Normark, & Holcomb, 1994;Oehler, Lénat, & Labazuy, 2007;Romagnoli, Casalbore, Chiocci, & Bosman, 2009a;Romagnoli, Kokelaar, Casalbore, & Chiocci, 2009b), these features are subordinate in the offshore areas. They are mainly represented by small and medium-scale slope failures affecting the outer edge of the insular shelf, similar to that observed on nearby Faial Island (Quartau et al, 2012).…”

Potential and Limitation of SPOT-5 Ortho-Image Correlation to Investigate the Cinematics of Landslides: The Example of “Mare à Poule d’Eau” (Réunion, France)

“…Therefore, the vertical extent of the landslide remains unknown. The landslide body is composed of recent breccia of differentiated volcanic rocks (the "MAPE breccia", [31,32]) overlying a layer of old breccia, which is characterized by alteration and clay facies. This layer plays the role of detachment surface on which the upper mass slides toward the north [31].…”