Geology and morphostructural evolution of Piton de la Fournaise
Résumé
The morphology of Piton de la Fournaise volcano results from the succession of construction, destruction and deformation processes that occurred since at least 530 ka. The chaotic surface of the gently dipping submarine flanks indicates that volcaniclastic deposits related to massive flank landslides and erosion cover most of the submarine flanks. Only a few seamounts like Cône Elianne and the submarine continuation of the rift zones are built by lava flows. In the subaerial domain, Piton de la Fournaise exhibits deeply incised canyons evidencing intense erosion and eastward verging scarps whose origin is still controversial. The different interpretations invoking flank landslides and/or summit collapse calderas are summarized. Geological data indicate a twofold construction of Piton de la Fournaise. Between 530 and 60 kyrs, the volcanic centre located in the current Plaine des Sables led to the building of the western part of the massif. The volcanic centre migrated eastwards to its current location, possibly at 60–40 kyrs. Then Piton de la Fournaise experienced caldera collapses and recurrent phreatomagmatic eruptions especially between 4880 and 2340 yr BP as evidenced by the Bellecombe ash deposit. Most of the recent volcanic activity is now currently focused restricted inside the Enclos Fouqué caldera where lava flow accumulation and rare explosive events built the 400-m-high Central Cone.
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