New behaviour of the Piton de La Fournaise volcano feeding system (La Réunion Island) deduced from GPS data: Influence of the 2007 Dolomieu caldera collapse

After 15 months of summit deflation, the unrest of Piton de La Fournaise renewed in August 2008 with several seismic crises and the re-pressurization of the plumbing system. The successive seismic crises, sometime accompanied by ground displacements detected by GPS, were associated with inter-eruptive dyke intrusions. It was the first time since the implementation of the observatory that such successive inter-eruptive magma migrations, not reaching the surface, were observed at Piton de La Fournaise. The change in the volcano activity, with an increase in the frequency of pure dyke intrusions, have followed the Dolomieu caldera collapse of April 2007 and reveals its strong influence on the new eruptive regime. Stress changes in the volcanic edifice have, temporarily at least, favoured the arrest of dykes in depth. During these successive dyke intrusions, magma stopped at shallow depth to form transitory magma storages before to erupt during three successive small summit eruptions (September 21st–October 2nd, 2008; November 27th; and December 14th, 2008–February 4th, 2009). The same kind of change in the pre-eruptive and eruptive behaviour can be expected on other volcanoes having experienced a summit caldera collapse.