After a long period of heavy weather where fog and low clouds prevented aerial photography over the Fagradalsfjall eruption sites, new measurements were finally obtained on September 9 (transmitted September 13). The measurements show that the average lava flow over the last 32 days is 8.5 m³ / s. The fairly powerful eruption was active about half the time. The average flow at the time of the eruption could therefore have been about twice as high.
The lava emitted has a volume of 143 million cubic meters and the covered area of 4.6 square kilometers. During the month following the last investigation, lava flowed in the western part of Meradalur, Syðri Meradalur and the northern part of Geldingadalur and Nátthaga. The area has increased very little, as the lava flows mainly to the surface, and has not reached the edge of the pre-existing field.
Fagradalsfjall - evolution of the tremor from 04.09 to 14.09.2021 - Doc. Hraun.vedur.is - one click to enlarge
These results will need to be reassessed, as there are good indications that the rash did not stop during this 8.5-9 day break. However, it is evident that the eruption channel to crater # 5 became blocked and this dam prevented magma from flowing into it. It also prevented the formation and flow of large gas bubbles, and therefore the visual disturbances were similar.
But weak pulses of turbulence, a constant flow of gas from the crater, glowing magma in the sky above internal lava channels and at the lava edges at Geldingadalur show that the magma was rising through the eruption channel. to the surface during this disruption of surface activity.
The "hot magma springs" formed in several places in the lava field west of Geldingadalur (photos on this link). This lava eruption is obviously not the result of the surface activity that was in the crater at that time, as the lava fields are separated and some of the lava that formed around this " hot magma springs " flowed to the east.
Magma has flowed and accumulated in Geldingadalur over the past 8-9 days. Yesterday, the internal pressure in this pond was high enough to force its way through the lava crust, to form the "hot springs of magma"
Sources: Jardvis & icelandmonitor.mbl.is
Þorvaldur Þórðarson, a volcanologist, says it's pretty clear that Askja has been gradually preparing for the eruption in recent years. In this context, he mentions that the ice on Öskjuvatn melted in 2012 due to increased thermal activity at the bottom of the lake. An increase in heat flow has been observed in the underlying plumbing, which means that magma can move through the system. The 2014 landslide that fell from Suðurbotnar to Öskjuvatn and caused a great tidal wave is also part of this rise.
"So there have been signs in the air for almost nine years that something is going to happen in Askja", he says. When asked how an eruption could be expected in Askja, Þorvaldur mentions an explosive eruption as a possibility. Such eruptions occur when hot magma comes in contact with water; cooling turns it to ash before it rises from the ground. If the ashes rise to the surface, they can travel long distances, as happened during the Askja eruption in 1875, but the ashes then spread to Fljótsdalshérað and Austfjörður, from Borgarfjörður in the south to in Fáskrúðsfjörður.
During the week of September 6 to 12, the eruptive activity of Sabancaya remained at a moderate level, with an average of 31 explosions per day, accompanied by plumes of gas and ash up to 4,000 meters above the summit.
The IGP recorded and analyzed 1,326 earthquakes of volcanic origin, associated with the circulation of internal magmatic fluids. The VT earthquakes occurred mainly to the north and north-east of the volcano, with a magnitude between M2.5 and M3.5.
The deformation does not show any significant anomalies. Six thermal anomalies were detected by Mirova, with a max. of 56 MW, associated with the presence of a lava body on the surface of the crater.
The volcanic alert remains in Naranja, with an inaccessible area of 12 km radius around the crater
La Palma - the Cumbre Vieja massif is in the foreground - photo archives Sergio Socorro 10.2017 via InVolcan
In recent years, the Cumbre Vieja / La Palma volcano - Canary archipelago - has experienced 10 seismic swarms: 1 in 2017, 1 in 2018, 5 in 2020 and 3 in 2021, including the one that started last Saturday, September 11.
This latest swarm, which started at 4:18 a.m. (Canary Island time) on September 11, 2021, currently has more than 400 earthquakes located under Cumbre Vieja at depths of about 12 km (according to IGN, the hypocenters are located between 8 and 11 km deep). The depth of previous seismic swarms oscillated between 20 and 30 km.
The magnitude of the earthquakes has increased in the past few hours with 10 earthquakes of magnitude 3 mbLg or greater, the highest magnitude being 3.4 mbLg which was recorded at 23:46:55 UTC on September 12 with the epicenter north of Fuencaliente.
The geochemical monitoring program for volcanic monitoring on La Palma allowed us to detect in 2020 (16/09/2020), the highest helium-3 emission value observed on La Palma in the last 30 years , and after this detection, the observatory recorded the highest number of seismic swarms in La Palma since 2017 (7 out of a total of 10).
Without a doubt, the current seismic swarm represents a significant change in the activity of the Cumbre Vieja volcano and is linked to a process of magmatic intrusion into the interior crust of the island of La Palma.
The management of PEVOLCA recommends changing Cumbre Vieja from green to YELLOW, and does not exclude an intensification of the seismicity felt in the coming days, depending on the evolution of the activity.
Sources: Instituto Volcanológico de Canarias, PEVOLCA & I.G.N.