The image of the Soufrière St. Vincent volcano’s summit crater depicts uplifted area accompanied by venting of steam and gas (image: @News_784/twitter)
After little more than one month since the last eruption on 22 April, the volcano continues at seismic unrest.
A volcanologist Dr. Adam Stinton from the Belmont observatory noted: „Since the morning of Friday 21st, there have been a handful of earthquakes, just around 20-25. None of the earthquakes are large enough to be felt at the moment; the average per day is about 10-15 since the last explosion on April 22nd“.
A near-constant gas and steam venting continues from the summit crater. Satellite-based images confirmed that no actively growing lava dome appears within the summit crater at this moment and there is no indication that the volcano will return to a dome growing phase again. Judging from the attached image, an uplifted area in the inner summit crater may indicate either extruded magma towards the surface or tephra accumulation immediately after the last eruption.
According to NASA FIRMS a high thermal anomaly continues to be detected within the summit crater. Sulfur dioxide (SO2) emissions reached to a 461 tonnes/day on 20 May. The Volcanic Alert Level remains at Orange. Source: News 784 25 May 2021
The seismic activity of the volcano quickly intensified after the eruption and continues at elevated levels although lava flows have stopped. The seismic network detected continuous volcanic tremor between midnight and 04:00 local time today indicating magma moving upwards through the volcanic conduits. This may be typical sign for an upcoming eruption. The strong volcanic tremor at roughly regular intervals has been felt in Goma city by local observers as huge cracks started to appear in the roads and buildings.
Huge cracks in the roads and buildings caused by elevated tremor (source: @Melaniegouby/twitter)
Significant seismic activity is still happening following the Nyiragongo’s #eruption, people are reporting strong, regular tremors. I received this video (origin unknown but it appears to be in Gisenyi), showing huge cracks in the road and buildings. pic.twitter.com/rvr7yEcxuT
Earthquakes detected near Nyiragongo on 24 May (source: www.rmb.gov.rw)
Sadly, the death toll from the recent eruption rose to at least 20, after 5 people were found choked to death from toxic fumes when they attempted to cross one of the recent and barely cooled down lava flows that had cut through their neighborhood in an area 13 km north of Goma.
What gas exactly caused their death was not mentioned, but one speculation is it could odorless carbon dioxide trapped in depressions on the surface of the flow – the slopes of Nyiragongo are infamous for many fissures and ground vents emanating accumulating sometimes deadly concentrations of the highly toxic gas.
Nature of eruption still unclear
While the eruption is probably over or at least in a pause, it’s still not clear whether the lava erupted was from a sideways fissure connected with the central conduit that drained the lava lake from the volcano’s summit caldera, or from a new lateral conduit tapping a separate reservoir.
During an overflight, the scientists from the Goma Volcano Observatory were not able to see whether the lava lake in the summit caldera was still present or not due to thick cloud cover.
What seems to worry local people almost as much as a potential re-activation of the eruption and new lava flows are frequent earthquakes that have started to occur under the flanks of the volcano since the eruption.
It is hoped that these reflect internal re-adjustments after the dike and the connected reservoir that had caused the eruption had been emptied. A more concerning prospect would be if the tremors are being caused by magma movements underground, something that cannot be ruled out.
„If there is lava in the crater, the fracturing caused by the movement of the earth would represent new activity.“
„If there is no lava in the crater, then these earthquakes are happening because the earth is in the process of refinding its balance.“, the director of the volcano observatory, Kasereka Mahinda said.
According to the Rwanda Seismic Monitor, the quakes had magnitudes of up to 5 and most of their epicenters were located in Cyanzarwe and Rubavu sectors (SE of the volcano). The strongest so far was a 5.1 event under Lake Kivu in the Rubavu district at 08:37 GMT. A 4.5-magnitude quake followed at 11:53 GMT. According to information via AFP, many people are afraid to stay indoors due to the quakes.
It appears that schools and most other public buildings remain closed, and electricity is still down in much of Goma
Link: Volcano death toll rises as aftershocks shake DR Congo (phys.org)
