Print this pageHow an Intraplate Volcanic Island May Generate True Volcanoclastic Deep-Sea Fans — La Réunion Island, Indian Ocean
Bruno Savoye1, Francky Saint-Ange2, Emmanuelle Sisavath1, Christine Deplus3, and Patrick Bachelery2
1Ifremer, Plouzane, France
2La Réunion University, Saint Denis, France
3Institut de Physique du Globe, Paris, France
Recent studies carried out off North Western Africa showed that the presence of volcanic islands along the Morocco and Mauritanian passive continental margins increased the complexity of deep-sea sediment distribution. The growth and the dismantling of these volcanoes modified the pre-existing seafloor topography and produced numerous submarine avalanches. However in spite of the numerous studies led around volcanic archipelagos like Canary and Hawaii, no true volcanodetritic deep sea fans were never observed around theses islands.
Two cruises had been performed by french oceanographic vessels in 2006 around La Reunion island : FOREVER and ERODER 1 ; they led to the discovery of four volcanodetritic deep sea fans, whose sources are 4 big erosional features located on La Reunion. This oceanic intraplate island consists of two juxtaposed volcanic massifs: Piton des Neiges, which is a dormant volcano and Piton de La Fournaise, which is a highly active basaltic shield volcano that has grown continuously since at least 0.527 Ma. It is currently one of the most active volcanoes in the world.
The geometry of the discovered fans depends both on the topography of the abyssal plain and the renewal of sediment supply allowed by the volcanic activity. They show many similarities with continental turbiditic systems. They are as long and wide as classical silicoclastic systems, the relatively small area of the sediment source being compensated by the fast renewal of potential sediments, an effect that does not exist in classical continental systems.
The wider fan, named the Cilaos fan, extends over an area of more than 15000 km2, i.e. 6 times the island area of 2500 km2 and 40 times the watershed surface. At present, we observe several branches which shapes and extensions are influenced by the presence of debris avalanche deposits and a set of NE-SW trending volcanic ridges.
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