After 3 months of high seismicity at Piton de la Fournaise and three small seismic crises, a strong seismic crisis with several hundreds of earthquakes started on 15 November at 2336. The earthquakes were accompanied by strong deformation at the summit, including tilt of up to 300 µrad. An eruption began on 16 November at 0433 with the appearance of eruption tremor. Fissures opened on the volcano's E flank between elevations of 1,900 and 1,600 m and lava flowed down the E flank. A small cone formed on one of the most active fissures at ~1,600 m elevation. On 18 November, continuous emissions from the cone rose up to 1,600 m above the crater rim.

During 20-26 November, visual observations were largely hampered by inclement weather. Eruptive tremor was constant on the 20th and 21st, and fluctuated on the 22nd. Tremor showed short-term variations during 23-26 November. Lava flows traveled in lava tubes between the active cone and 1,200 m elevation and traveled on the land surface at elevations between about 1,200 and 500 m.

On 27 November, eruptive tremor had decreased to 25% of that seen since this eruption's start. On that day the fissures located on the S at ~1,850 m and at ~1750 m elevation were no longer active. Instead, two fissures at ~1,600 m elevation were active. The smallest and lowest produced a small lava flow. The largest fissure was located 100 m higher and slightly to the N; it emitted a significant lava flow. Sprays of lava there on 16 November reached up to 80 m high. On 17 November they reached only up to 30 m high, at least in part owing to drag imposed by a small lava lake that had then developed within the cone's interior.

On 29 November eruptive tremor increased by a factor of two, and there were 89 seismic events recorded that day. On the 30th, 329 seismic events were recorded, all located about 1 km above sea level, beneath the floor of Dolomieu crater. A lava flow in the Grand Brûlé area approached the national road, crossing it around 2300. By about 0500 on 1 December the lava flow had reached the sea. At this time almost constant seismicity occurred, with more than 1,500 earthquakes recorded with magnitudes up to 2.8. Eruption tremor was stable; numerous long-period earthquakes were also recorded, indicating the presence of magma beneath the summit. On the morning of 2 December seismicity increased by about a factor of about three, but decreased the next day.

Lava emissions from Piton de la Fournaise ended on 3 December. Permanent tremor decreased significantly that day, although seismic events beneath the summit continued at a rate of 1 per minute. Seismicity continued to decline over the next two days. Poor weather conditions prevented helicopter observations during 3-5 December. Inspection on 6 December revealed some collapses between Bory and Dolomieu craters, and white fumes were being released from the new Guanyin cone, but there was no evidence of surface activity coincident with larger seismic events that occurred while scientists from the OVPDLF were on the edge of Dolomieu.

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: Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), 14 RN3, le 27Km, 97418 La Plaine des Cafres, La Réunion, France.