After the eruptive episode of late March-early April, seismic events were due primarily to collapse in the summit zone, especially inside Dolomieu Crater and in the walls of its newly formed pit crater. Some deeper events were recorded in the SE part of the Enclos Caldera at depths of 2 km below sea level. The lava that had cascaded into the pit crater 29 March-5 April was originally extruded during the 29 December eruption. Summit tilt stations indicated a continuation of low deflation. The SE flank fissures (~8 km from Dolomieu Crater, near Piton Takamaka) continued to emit vapor for a few days. Fumaroles, some emitting SO₂, covered the floor of Dolomieu Crater. Reoccupation of the radial leveling profile (3 km long, from the Enclos Caldera rim to the summit) did not show significant movement since October 1985.

Geological Summary. Piton de la Fournaise is a massive basaltic shield volcano on the French island of Réunion in the western Indian Ocean. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three scarps formed at about 250,000, 65,000, and less than 5,000 years ago by progressive eastward slumping, leaving caldera-sized embayments open to the E and SE. Numerous pyroclastic cones are present on the floor of the scarps and their outer flanks. Most recorded eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest scarp, which is about 9 km wide and about 13 km from the western wall to the ocean on the E side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures outside the scarps.

Information Contacts: H. DeLorme and J-F. DeLarue, OVPDLF; P. Bachelery, Univ de la Réunion; J-L. Le Mouel, J-L. Cheminée, A. Hirn, P.A. Blum, and J. Zlotnicki, IPGP.