A 12-hour earthquake swarm occurred 15 July at Piton de la Fournaise, the first seismic crisis there since shortly after the 3 February-5 May 1981 eruption, which produced 10 x 10⁶ m³ of lava during three active phases. Since then, background seismicity had been less than 0.5 events/day. The 21 events between 0830 and 2015 on 15 July occurred in the central area at shallow depth but were poorly located because they were recorded on only 1-3 stations, have emergent onsets, and poorly-defined phases. Event durations ranged from 15 to 150 seconds. The seismic crisis prompted the resurvey of deformation networks, but no significant changes were measured.

The Observatoire Volcanologique du Piton de la Fournaise noted that for the past 50 years the mean eruption frequency has been one every 12-14 months. The 27 months since the last eruption is one of the longer repose intervals during that period.

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), Réunion.