The N-flank fissure eruption was continuing at a low level on 26 July. Occasional tephra ejections stopped 1 July but degassed lava remained in Durandal crater to roughly 15-20 m below the rim. Lava drained directly into tubes and surfaced in the Plaine des Osmondes, > 1 km downslope. Little change in lava flow volume has occurred since 10 June. Harmonic tremor continued at a low level except at Soufrière station, just NE of the summit, where continuous NE-flank deflation had been recorded by tilt stations since the eruption's onset. Deflation progressively decreased before stopping on 12 July. Average rates were 8 µrads/day 18-24 May, 3.5 µrads/day 25 May-3 June, and 1.7 µrads/day after 4 June. There were no significant changes in the magnetic data.

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, D. Vandamme, P. Nerbusson, J. Delmond, and P. Taochi, OVPDLF; J. Dubois, J-L. Cheminée, A. Hirn, P. Blum, and J. Zlotnicki, IPGP ; P. Bachelery, Univ de la Réunion.