Report on Piton de la Fournaise (France) — 29 July-4 August 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 29 July-4 August 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Piton de la Fournaise (France). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 29 July-4 August 2015. 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)
OVPDLF reported that a sharp increase in seismicity at Piton de la Fournaise, increased gas emissions, and deformation recorded on 30 July prompted an Alert Level increase and an evacuation. A fissure eruption began the next day at 0920, preceded by 90 minutes of high seismicity and 80 minutes of major deformation; it was confirmed by a hiker and then by observation of a gas plume. A 1-km-long fissure opened in the NE part of the l'Enclos Fouqué caldera and produced dozens of lava fountains. Based on satellite images and gas data the flow rate was estimated to be 28 cubic meters per second initially and then 11 cubic meters per second later that day. A gas plume rose to altitudes of 3.2-3.5 km (10,500-11,500 ft) a.s.l. By the evening there were only five fountains, and a lava flow had traveled as far E as Plaine des Osmondes (NE part of the caldera). According to a news article, lava fountains were 40 m high, forming 20-m-high cones on 31 July. At 1115 on 2 August tremor stopped, after several hours of fluctuating intensity, and lava was no longer being effused.
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.