Five months of slow inflation at Piton de la Fournaise and the eruptive series that occurred between May and July 2003 (BGVN 28:05 and 28:06) were followed by new activity in August. Ongoing eruptions in June at the Dolomieu crater had ceased by mid-July, but at 1848 on 22 August seismic activity was again detected beneath the crater. Around 2120 that night an eruptive fissure opened in the Bory crater (adjacent to Dolomieu on the W), followed at 2210 by a second fissure at ~2,450-2,470 m elevation on the N flank. Both fissures remained active for a short time.

At 2330 a final fissure opened on the N flank ~250 m below the second fissure, at 2,200 m elevation. Most of the activity was focused at this third fissure, opening a new crater ~50 m E of the 1998 Piton Kapor crater. During this activity on 22 August lava flowed down into la Plaine des Osmondes. The 36 hours following the initial activity were characterized by a substantial increase in tremor intensity and lava emissions, but by 2152 on 27 August the eruption abruptly ceased. A series of long-period events were observed after 27 August through at least 1 September.

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: Observatoire volcanologique du Piton de la Fournaise, Institut de Physique du Globe de Paris, 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.