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The off-shore continuation of an active basaltic volcano: Piton de la Fournaise (Réunion Island, Indian Ocean); structural and geomorphological interpretation from sea beam mapping

Journal of Volcanology and Geothermal Research
Publication Date
DOI: 10.1016/0377-0273(89)90003-6
  • Earth Science
  • Physics


Abstract In 1984 a Sea Beam survey of the submarine east flank of Piton de la Fournaise was performed with R/V “Jean Charcot”. Three main types of volcanic or volcano-tectonic features have been identified: 1. (1) The subaerial NE and SE volcanic rift zones of Piton de la Fournaise do not extend more than about five kilometers offshore. Unlike typical Hawaiian rift zones, which form narrow (2–4 km) ridges extending tens of kilometers from the summit, the active rift zones of Piton de la Fournaise widen downslope, attaining more than 10 km at their front. 2. (2) The submarine extension of the Grand Brûlé slide is larger than the subaerial portion. The entire slide forms a 7 × 24 km scar bounded by two ramparts to the north and south. The slumped material may have moved as a debris flow, forming a large talus downslope of the slide. However, the submarine counterpart of the south area of the Grand Brûlé seems to be composed by a slumped block whose structure is apparently not disturbed. 3. (3) Another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone. This “cast flank submarine plateau” cannot be associated with any active structure of Piton de la Fournaise. Its surface generally dips gently (2–3°), and its northern and southern flanks are extensively cut by landslides. Cones of variable dimensions are observed on the plateau and farther to the east. Three hypotheses are examined to account for the origin of this morphology: (a) remnant flank of an ancestral Fournaise volcano associated with a large buried intrusion found by drilling beneath the Grand Brûlé; (b) distinct volcanic massif or (c) material of a huge and ancient landslide. The geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly. This confirms that, as suggested by the bathymetric analysis, this part of the plateau is relatively coherent. Conversely, the eastern portion of the plateau appears to be poorly magnetized and composed of low-density material, probably chaotic materials derived from landslides. The reversed magnetization of the western part shows that the whole structure is older than 0.7 Ma. These results show that the volcanic history of Piton de la Fournaise is more complex than previously thought.

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