Report on Piton de la Fournaise (France) — May 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 5 (May 1985)
Managing Editor: Lindsay McClelland.
Piton de la Fournaise (France) Eruption with premonitory seismicity
Please cite this report as:
Global Volcanism Program, 1985. Report on Piton de la Fournaise (France). In: McClelland, L. (ed.), Scientific Event Alert Network Bulletin, 10:5. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198505-233020.
Piton de la Fournaise
21.244°S, 55.708°E; summit elev. 2632 m
All times are local (unless otherwise noted)
"Since the last eruption, seismicity and deformation measured at the four summit stations had remained at very low levels (0-5 earthquakes and 1-7 µrad of tilt per month). The pattern of tilt vectors implied a progressive deflation of the area that had undergone large deformation during the last eruption.
"Beginning on 15 May, several small earthquakes (M <1) were recorded at depths of 1.5-2.5 km beneath the summit. Simultaneously, the summit dry tilt stations began to show an inflationary pattern. The number of seismic events progressively increased. Seismic activity peaked on 8 June with 13 events, and decreased to a low level on the 13th. No significant migration of the earthquakes was observed. Inflation appeared to have been almost continuous except during two episodes when deformation slowed (3 June) or reversed (8 June) corresponding to the periods of largest seismic energy release.
"This activity differed from the 1983 pre-eruptive crisis. The late 1983-early 1984 eruption was preceded by two weeks of seismic activity (48 events) with no associated deformation. The most recent activity lasted for at least four weeks. The earthquakes are located in the same area as before, but summit tilt stations show inflation of 15-40 µrads."
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: J. Lenat, OVPDLF; M. Kasser, Inst. Geographique National (IGN), Paris; A. Nercessian, IPG, Paris; R. Vie le Sage, Délégation aux Risques Majeurs (DRM), Paris; P. Bachelery, Univ. de la Réunion; A. Bonneville, Univ. du Languedoc; G. Boudon, Obs. Volc. de la Mt. Pelée; M. Halbwaks, Univ. de Chambéry.