The April 2007 eruption and the Dolomieu crater collapse, two major events at Piton de la Fournaise (La Réunion Island, Indian Ocean)

After 10 years of high activity and 24 eruptions, Piton de la Fournaise (PdF) produced on April 2 to May 1, 2007 one of its most voluminous and intense eruption since at least one century. The eruption focused at 590 m elevation in the Grand Brûlé on the south east flank of Piton de la Fournaise, 7 km away from summit. It was located close to the southern cliff of the Grand Brûlé volcano tectonic collapse, the Rempart du Tremblet, and to the nearby village called Le Tremblet, and it highly rattled and incommoded the inhabitants there. Eleven hours after the beginning of the eruption the lava flows reached the sea and created 0.45 km2 of new land until the end of eruption. In the night of April 5 the rock column beneath Dolomieu crater started to collapse with a piston like mechanism into the magma chamber, forming within less than 24 h the most recent and well documented caldera. We report in this paper the chronology of these two related major events in the recent activity of PdF seen by the scientific networks of the volcanological observatory (OVPF/IPGP) and field observations, which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes.