Report on Piton de la Fournaise (France) — 23 February-1 March 2005
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 23 February-1 March 2005
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2005. Report on Piton de la Fournaise (France). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 23 February-1 March 2005. Smithsonian Institution and US Geological Survey.
Piton de la Fournaise
21.244°S, 55.708°E; summit elev. 2632 m
All times are local (unless otherwise noted)
Contrary to reports that volcanic activity had ceased at Piton de la Fournaise on 19 February, the eruption continued through at least 25 February. After a period of low activity around the 19th, eruption tremor increased to high levels again on 21 February. Two eruption sites were active: the principal vent at 1,600-m elevation above the Plaine des Osmondes, and a vent at about 1,200-m elevation in the Plaine des Osmondes. The principal vent released a volcanic plume and several pahoehoe lava flows, but no lava fountains were visible. The second vent also released a very fluid pahoehoe lava flow. The lava flows covered a large area within the Plaine des Osmondes, and smaller lava flows traveled to about 600-m elevation in the Grand Brûlé.
On 24 February, shallow seismicity began beneath Dolomieu crater. It increased over time and by the 26th several hundreds of seismic events up to M 3 occurred. According to OVPDLF, these events may have indicated the possibility of a new pit crater forming within Dolomieu crater. On the 24th, visible signs of volcanic activity stopped within the Plaine des Osmondes, while eruption tremor slowly increased.
On the evening of 25 February, a lava flow from Plaine des Osmondes traveled down the Grandes Pentes, cutting the national road on its way to the sea. The lava flow covered a distance of ~5 km in about 2 hours. At the same time, seismicity on the North East rift zone above "Bois Blanc" appeared and a new vent opened within the "Trou de Sable" on the northern border of the "enclose" at 450-m elevation. This lava flow stopped about 100 m from the national road.
Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. 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 calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern 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 on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.