Alert raised after resumption of seismicity at Piton de la Fournaise volcano, Reunion

A resumption of seismicity has been observed at the Piton de la Fournaise volcano in Reunion since June 16, 2020, prompting the national volcanological observatory to raise the Alert Level to "Vigilance" on June 22.

The Volcanological Observatory of Piton de la Fournaise (IPGP) reported that 18 superficial volcano-tectonic earthquakes were recorded, 2 km (1.2 miles), under the summit zone between June 16 and 22.

This seismicity is accompanied by swelling or resumption of inflation at the base and at the top of the volcano.

"This inflation of the building is synonymous with pressurization of the surface magmatic reservoir located around 1.5 to 2.5 km (1 to 1.5 miles) below the summit," IPGP said. 

Histogram representing the number of surface volcano-tectonic earthquakes recorded between June 1 and June 21, 2020. Image credit: OVPF-IPGP

Illustration of the deformation over the past two months. Image credit: OVPF-IPGP

The carbon dioxide fluxes in the far-field soil, which had reached maximum values at the end of the April 2 – 6 eruption this year, continue to reduce, corresponding to the deep ascent of magma to the surface areas of the feeding system.

"Even if the trend is downward, the absolute values ​​of the CO₂ flux through the soil remain very high."

IPGP noted that this process of recharging the surface reservoir can take several days to weeks, before the reservoir roof becomes fragile and breaks, allowing injection of magma towards the surface and an eruption. It can also stop quickly without leading to an eruption.

Map of ground movements. Image credit: OVPF-IPGP

Geological summary

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 histories 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 5 000 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 (1 312 feet) lava shield that has grown within the youngest caldera, which is 8 km (26 247 feet) 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 (IPGP), monitors this very active volcano. (GVP)

Featured image credit: OVPF-IPGP