The Observatoire Volcanologique du Piton de la Fournaise (OVPF) reported that a magmatic intrusion was detected beneath the E rim of Dolomieu Crater at Piton de la Fournaise during 2225-2330 on 5 December based on seismic data. The seismic network recorded 227 shallow volcano-tectonic earthquakes with magnitudes less than 1 at depths of 1.8-2.3 km. Some of the located earthquakes showed that magma migrated less than 500 m from an area below the SE rim to an area below the NE rim. The seismicity was accompanied by rapid, low-magnitude deformations at the summit area that lasted less than an hour. Seismicity continued after the intrusion ceased, with a decreasing rate through the next day. The Alert Level was raised to 1 (or an Orange Alert). During 7-8 December seismicity had returned to a rate of 1-3 earthquakes per hour, comparable to before the intrusion. The Alert Level was lowered back to "Vigilance" (or a Yellow Alert) was initiated on 28 November and described as “a possible eruption in medium term (a few days or weeks) or presence of risks on the sector (rockfalls, increase of gas emissions, still hot lava flows)”.

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.

Source: Observatoire Volcanologique du Piton de la Fournaise (OVPF)