News from Poas, La Fournaise, Mayotte, and the Dieng Plateau.

The Ovsicori reports the detection of a bubbling at the northern mouth of Lake Poas. Frequent gurgling pulses are still observed in the lake near Crater A, along with frequent short shaking. A slight extension of the crater continues to be detected. Gas ratios remain stable.

On August 2, the aerial fumaroles on the north and east walls of the crater are active, as are the sub-lacustrine fumaroles to the south and north of the lake. Frequent low-frequency volcanic earthquakes and short-lived tremors associated with fumarole activity are recorded. The gas concentrations are measured in small quantities and the deformation of the volcanic building remains stable.

Source: Ovsicori

Poas - evening bubbling and convection cells - Doc. Ovsicori 07.31.2021

In July 2021, the OVPF recorded at the Piton de La Fournaise massive a total of:

- 33 superficial volcano-tectonic earthquakes (0 to 2.5 km above sea level) under the summit craters;

- 0 deep earthquake (below sea level)

- 256 collapses (in the Dolomieu Crater, the ramparts of the Fouqué enclosure, Piton de Crac, and the East River).

The inflation of the building, which began in April 2021, continued throughout July 2021. This inflation showed a pressurization of the superficial magmatic reservoir located around 2 km deep.

Piton de La Fournaise - Deformation from June 2 to August 2, 2021 - Here are shown the base lines (variation in distance between two GPS receivers) crossing the Piton de la Fournaise building, at the top (top), at the base of the terminal cone (in the middle) and in the far field (below) (cf. location on the associated maps). An increase is synonymous with elongation and therefore swelling of the volcano; conversely, a decrease is synonymous with contraction and therefore deflation of the volcano. Any periods colored in light pink correspond to eruptions. - Doc. OVPF

Following the eruption of December 2020, a continuous increase in CO₂ emissions from the soil was recorded at the level of the distal sites (Plaine des Cafres sectors) but also proximal (Gîte du volcano). At remote sites, a trend reversal (decrease in CO₂ emissions) occurred on February 12, 2021, witnessing a possible transfer of magma to more superficial crustal levels. A further increase followed this phase, with the largest increase recorded between April 4 and April 16. At the proximal sites, the increase was continuous until early May, heralding the onset of the long-lasting rash from April 9 to May 24, 2021.

In June 2021, a new trend of increasing CO₂ fluxes was recorded both in the far field, and to a lesser extent in the near field (monthly bulletin for the month of June 2021). Since the distant field CO₂ fluxes are stable on high values.

The inflation of the building and the CO₂ contents in the soil which remained high in July 2021 witnessed magmatic transfers from deep areas to the superficial magmatic reservoir which continued after the end of the eruption of April 9-May 25, 2021.

Source: OVPF Monthly bulletin

Piton de La Fournaise - the Dolomieu crater - photo archives © Bernard Duyck

Since July 31, 2021 at 4:33 p.m. (UTC time; 7:33 p.m. local time), strong seismic activity of the Long-Period (LP) type has been recorded in Mayotte.

For the day of July 31, 186 LP type earthquakes were recorded during 3 distinct swarms, each associated with a Very Long Period (VLP) type earthquake. LP and VLP earthquakes are seismic signals usually associated in the literature with resonances and fluid movements (magmatic or hydrothermal) at depth. Work is underway to try to better understand these signals. Some of these LP earthquakes are located about ten kilometers east of Petite-Terre in the area of the most active proximal seismic swarm, about thirty km deep, at the same place where LP earthquakes are usually localized (REVOSIMA monthly bulletins).

These earthquakes are small in magnitude and were not felt by the population. A new swarm started on August 2 at 13:31 (UTC time; 16:31 local time) and is still in progress.

REVOSIMA closely follows this activity and its development.

Source: REVOSIMA - Exceptional press release 02.01.2021

Mayotte - location of earthquakes in time and theoretical idea of the mode of activity - Doc. S. Hicks 2018 - one click to enlarge

In recent days, the Siglagah crater in the hamlet of Rejosari, village of Pranten, on the Dieng plateau, central Java has again emitted a torrent of mud.
Siglagah Crater is approximately 200 meters from the residential areas of the Dieng Plateau

According to the official statement from the PVMBG, on July 30, 2021, the Siglagah crater spat mud within a radius of less than 10 meters from the source. The center of activity is in one of the fractures in the Siglagah crater region which sits on the hillside.

The activity level is at 1 / normal.

Sourcess: PVMBG and TribunJateng.com / Siglagah Crater Spewing Mud, Dieng Volcano Activity Still Normal Level.