For the past few weeks, the area of the Fagradalsfjall lava field has not increased and lava has not flowed into new land, says Magnús Tumi Guðmundsson, professor of geophysics at the University of Iceland, speaking about the rash on mbls.
The intermittence of the eruption (see the fluctuations of the tremor) causes more or less long periods without lava flow ... the lava tunnels close.
When the eruption resumes, it takes several hours to fill the crater before the lava begins to flow. Lava then flows to the surface in the valleys of Meradalir, Geldingadalir and Nátthagi, but stops before reaching the edge of the lava field. It piles up near the crater.
The lull periods allowed the bottom of the crater to be seen active: The crater basin is about 60 to 70 m deep, and the drain is deeper, below the earth's surface, as before the start of the eruption
Sources : mbls & Hraun
Fagradalsfjall eruption - Event # 5 crater - photo Jón Steinar Sæmundsson 27.07.2021 / via mbls - one click to enlarge
Continuous GPS measurements and satellite data from Sentinel-1 (InSAR) show that expansion began in Askja (Dyngjufjöll) in early August 2021. The center of the expansion is at the western end of 'Öskjuvatn near Ólafsgígar near the GPS station which now shows the earth at about 5cm per month.
Askja is an active volcano and there are regular earthquakes, but the last eruption was in Askja in 1961. Regular measurements also showed landslides in the years 1970-1972, but these measurements were discontinued and when regular measurements resumed in 1983, the land had subsided. Since then, a regular landslide of 1 cm per year has been measured so far.
The cause of the current expansion is not entirely clear, but it is believed most likely to be an influx of magma. Volcanoes often show periodic activity as they remain dormant with little activity for years and decades, but in between there are periods of activity with overheating, earthquakes, and geothermal energy. There is no way to predict in advance how such periods of activity will develop, but it is very common for such periods to end without a rash.
The Meteorological Office is closely following the evolution of the situation and will keep you informed of any development of the activity.
Askja - The image shows the quasi-vertical deformation in mm for the period August 1 to 21. The InSAR image is obtained from two passes of the Sentinel-1 satellite. Red color indicates increase and blue indicates subsidence (see scale). The area with the highest inflation is northwest Öskjuvatn. The black triangle indicates the location of the nearest GPS station Ólafsgíga (OLAC). - Doc. IMO
Askja - data from GPS station OLAC: the uprising started between late July and early August (mainly visible in the Up component) and it is still ongoing (September 2, 2021). The dotted red line indicates the estimated rate of climb at ~ 5 cm / month. / Doc. IMO
Jökulhlaup underway in Skafta. The flood comes from the W-Skaftárcauldron.
The water level in Grímsvötn rose sharply last month and has not been higher since before the eruption of Gjálpar in 1996. About 0.75 cubic kilometers of water accumulated there, according to Eyjólfur Magnússon, scientist at the Institute of Earth Sciences of the University of Iceland. This significant build-up can be attributed to the fact that there has been no ice breakout since 2018.
The flow has been fairly stable at Skaftá near Sveinstindur for the past few hours and now measures around 520 cubic meters per second. It is not unlikely that the runoff has reached its peak if we look at the previous floods from the western cauldron.
When asked if the Icelanders should prepare for a blowout after the next race, Eyjólfur said it was a realistic possibility.
Sources: mbls & IMO
The Jökulhlaup in Skaftá may have reached its peak yesterday, but it looks like it will continue in the same way for the next two or three days - photo mbl.is / Jónas Erlendsson - 02.09.2021
The increase in electrical conductivity in the Skaftá River is likely due to steam explosions from the geothermal area under the ice cauldron. Steam explosions occur as the geothermal area adjusts to the decrease in water pressure resulting from the drainage of the cauldron. Explosions increase the amount of dissolved material in flood water, which is detectable downstream as an increase in conductivity in the river. - Doc. IMO
The lava eruption in the summit crater of the Great Sitkin volcano continued over the past week. Satellite data showed the new lava dome has grown from ~ 90m to ~ 1090m in diameter. Lava filled the crater from the May explosion on August 4 and is now flowing down the sides of the 1974 lava dome. and through the floor of the summit crater. These images show some distortion caused by the oblique illumination angle of the satellite, but capture the changes at the top of the Great Sitkin well.
Gas plumes were visible on satellite images throughout the week, but no explosive activity or ash emissions were detected. Small earthquakes were detected throughout the week, possibly associated with the lava effusion.
There is no indication of how long the lava effusion will continue during the current eruption, and it is possible that explosive activity will occur with little or no warning.
The Great Sitkin volcano is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks. The alerts are at Watch / Orange.