The March–April 2007 Eruptions of Piton de la Fournaise as Recorded by Interferometric Data

Abstract : Piton de la Fournaise is one of the few volcanoes in the world to be monitored on a regular basis from space, by use of Interferometric Synthetic Aperture Radar (InSAR) data. Thirty of the 39 eruptions that occurred during the 1998–2010 period were imaged by various radar satellites. In this chapter, we present one of the best examples of surface deformation mapping achieved at Piton de la Fournaise volcano. From March 30 to May 1 2007, Piton de la Fournaise experienced a major eruptive crisis, characterized by the largest historical flank eruption (210 × 106 m3), and by a 340 m caldera collapse. The event was captured by InSAR data from the ENVISAT and ALOS-1 satellites. Large and unusual displacements of the Central Cone and the Eastern Flank of Piton de la Fournaise occurred during the co-eruptive period and in the following months. Analysis of the InSAR displacement combined with other geophysical and field observations allows us to propose conceptual models to explain the Central Cone and the Eastern Flank displacements. The April 2007 caldera collapse induced a sudden decompression of the hydrothermal system contributing to the strong centripetal subsidence of the Central Cone. This then decreased exponentially with poro-elastic compaction and creep of the Central Cone. For the Eastern Flank, the displacement is related to the combined effect of a sill and slip on a detachment. Dense olivine-rich magma from the deeper part of the main magma storage was injected as a dyke which may have encountered a pre-existing structural discontinuity, intruded it as a sill and activated it as a detachment surface. Magma then further propagated to the April 2 eruption site.