Report on Piton de la Fournaise (France) — July 1999
Bulletin of the Global Volcanism Network, vol. 24, no. 7 (July 1999)
Managing Editor: Richard Wunderman.
Piton de la Fournaise (France) A fissure eruption begins 19 July
Please cite this report as:
Global Volcanism Program, 1999. Report on Piton de la Fournaise (France) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 24:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199907-233020.
Piton de la Fournaise
21.244°S, 55.708°E; summit elev. 2632 m
All times are local (unless otherwise noted)
A new eruption on 19 July was preceded by ten days of seismic activity. On 14 July, there was an earthquake of magnitude 2.3, but otherwise activity was low (3.5 events per day). At 1817 on 19 July, there was a seismic swarm of 77 earthquakes measuring under M 1.0 and one measuring M 1.2; later, at 1856, tremors began being registered at the summit seismic stations. Earthquake epicenters were at Dolomieu crater; focal depths were between slightly above sea level and the ground surface. In the evening lava fountains of up to 100 m height could be observed from the national highway in the "Grand Brûlé."
Weather conditions did not permit field observations until 21 July, when a 500-m-long fissure with small cones was discovered trending N to W across Dolomieu crater and beyond it to the ESE. On Dolomieu crater's W margin a larger cone straddled the crater's border. About 25% of the Dolomieu surface was covered by the new lava field. On 21 July, volcanic activity inside Dolomieu was limited to degassing on the E side of the new crater. Only steaming could be observed on the E flank and bad weather subsequently closed in.
On 23 July seismicity increased for 11 hours. Again, weather conditions did not allow field observations for another two days. Then, during a helicopter flight on 25 July, observers saw two lava fields. The first contained aa lava on the N of the crater (100 m across, 1.5 km long, and 1-2 m thick). The second contained pahoehoe lava on the E of the crater; these were still active, with dozens of small (under 1 m thick) flows. The first lava field was probably emplaced during the 19 July eruption and the second during the eruption on the night of 23 July. As of 26 July tremor and eruptions continued.
A basaltic shield volcano, Piton de la Fournaise forms the SE half of Réunion Island, 700 km E of Madagascar. It has been one of the most active oceanic volcanoes, with more than 100 eruptions in the last 300 years. Three calderas formed at around 250,000, 65,000, and <5,000 years ago by progressive eastward slumping of the volcano. Most historical eruptions originated from the summit and flanks of a 400-m-high lava shield within the youngest caldera.
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.
Information Contacts: Thomas Staudacher and Jean Louis Cheminée, Observatoire Volcanologique du Piton de la Fournaise (OVPF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.