At Piton de La Fournaise, after a decrease in the number of earthquakes, the seismic crisis (in the strict sense of the term), which began on September 28, 2020 at 12:04 p.m. local time, ended at around 12 p.m. local time on September 30.
On the other hand, the seismicity still persists with on average over the last hours, 4 earthquakes or landslides / hour. Given the sharp decrease in the number of earthquakes, the term "seismic crisis" is therefore no longer applicable at present.
Between September 28th and 30th (12pm local time), around 2300 earthquakes (1551 superficial summit volcano-tectonic earthquakes, 472 deep volcano-tectonic earthquakes, 48 long periods, and 217 earthquakes classified as "undetermined" because of low magnitudes) and 543 landslides / superficial collapses were recorded by the OVPF. This seismicity was located under the summit and under the eastern flank of the volcano (between 1.6 and 5.2 km deep.
Piton de La Fournaise - Location map (epicenters) and north-south and east-west sections (showing the location in depth, hypocenters) of the earthquakes recorded and located by the OVPF-IPGP between 28/09/2020 and 01 / 10/2020 (9h00) under the Piton de la Fournaise massif. Only localizable earthquakes have been shown on the map (© OVPF-IPGP).
During the day of 09/30, the deformations continued on the eastern flank of the volcano, so the GPS station "GPNG" of the OVPF located in the upper part of the Grandes Pentes, at 1414 m altitude, has continued its eastward slide of 10 cm, or about 70 cm in total since the onset of the crisis, and has risen by about 25 cm since the onset of the crisis.
The persistence of seismicity and deformation under the eastern flank shows that the intrusion of magma towards the eastern flank is still active and that an eruption cannot be excluded. The observatory teams remain mobilized.
Source: OVPF / FB
Piton de La Fournaise - Movements of the GPS station "GPNG" of the OVPF located in the upper part of the Grandes Pentes, at an altitude of 1414 m, on the East-West component (above), North-South (at middle) and Vertical (bottom) over the last two weeks. In blue the raw data, in red the corrected data of the movement of the plate (© OVPF-IPGP).
In Sinabung, these last three days are marked by some blast earthquakes, and the growth of the summit dome.
This development is particularly rapid by comparing the photos taken between early and late September 2020
The level of activity remains at 3 / siaga, with a prohibited zone of 3 to 5 km in radius, depending on the sector.
Sources: PVMBG and Beidar Sinabung
Sinabung - evolution of the topography of the summit between 2018 and 09/21/2020 - Doc. Sadrah Peranginangin
A unique phenomenon was discovered on September 28, 2020 on the Sheveluch volcano. A block of lava of the most acidic composition in the entire development history (since 1980) of the lava dome of the volcano is being extruded. The probable composition of lava is dacitic. The dome is called "Dolphin".
Sources: Olga Girina and Yuri Demyanchuk / IVS FEB RAS
The Icelandic Met Office has changed the aviation color code of the Grímsvötn volcano from green to yellow.
Volcanic activity at Grímsvötn has gradually increased over time, as indicated by several regularly monitored geophysical and geochemical parameters that are now above known background level:
- Seismicity over the past month has been above average.
- Geothermal activity has increased in recent months with clear signs of cauldron deepening in several places around the caldera.
- The deformation of the surface has exceeded the level it was at before the 2011 eruption.
- Magmatic gases were measured in geothermal emissions this summer.
- In addition, the water depth in the subglacial lake is comparable to the level prior to the 2004 and 2010 floods, which increases the likelihood of flooding in the months to come.
Several datasets now indicate that the Grímsvötn volcano has reached a level of unrest comparable to that seen before the historic eruptions.
For these reasons, the aviation color code has changed from green to yellow. This does not mean that a rash is imminent. However, an eruption could be triggered by depressurization if the subglacial lake inside the caldera would drain and cause flooding or occur anyway, possibly with very low precursor activity and short warning time, as seen during the 2011 eruption.