Low but constant seismicity was recorded from mid-April to early May, particularly in the N part of the volcano (12 April) and near the summit. Later in May, seismicity increased, and events remained shallow, below the two summit craters. Rare, deeper events were recorded in the E summit area. Progressive inflation had begun in April. Dry-tilt indicated an average inflation of 70 µrads around Bory Crater. Permanent inclinometers confirmed the dry-tilt data. Around 23 April inclinometers indicated that inflation had stabilized but a permanent magnetic station (6) showed a significant decrease, especially in the 7 x 11 km summit caldera. On 2 June at 1957 an intrusion occurred in the summit area accompanied by a seismic swarm lasting over 30 minutes. When seismicity ceased at 2030 no eruption had occurred.

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 B. Gillet, OVPDLF; P. Bachelery, Univ de la Réunion; A. Hirn, J-L. Le Mouel, J-L. Cheminee, P. Blum, and J. Zlotnicki, IPGP.