Last year a volcano erupted in the Congo. But before that, he had given no sign to prevent disaster. In other words, the eruption was very sudden. A phenomenon that, according to a recent study, would be as unusual as it is dangerous.
A disturbing absence of signs
Nyiragongo is a stratovolcano that culminates at an altitude of 3,470 m and is located to the east of the Democratic Republic of the Congo, in the Great Rift Valley. In May 2021 there was an eruption that generated lava flows that surprised the inhabitants from the town of Goma, located 20 km. If the eruption lasted only a few hours and the city was finally spared, several towns were affected and the human toll is still 13 dead.
Delphine Smittarello, a researcher at the European Center for Geodynamics and Seismology in Luxembourg, is the lead author of a study published in the journal Nature August 31, 2022. The interested party and other researchers explain why the latest eruption of Nyiragongo is worrying. despite a continuous monitoring by instrument arrays ground and satellite sensors, none of the usual signals were present.
In other words, the eruption could not have been foreseen. The study indicates in particular that the seismic records showed that the first events that marked unusual activity began only 40 minutes before the first lava flows. However, this is very surprising, especially when we consider the only two documented historical eruptions, in 1977 and 2002, each preceded by strong earthquakes a few weeks to a few days earlier.
A volcano already “ready” for a long time
In addition to earthquakes, there may be other warning signs such as the swelling of the slopes of the volcano or gas leaks and fumaroles. These signs indicate a filling the magma chamber as well as a strong increase in pressure. However, if these details do not make it possible to accurately predict the date of the eruption, they still provide an opportunity to warn populations and, if necessary, carry out evacuations. And yet the Nyiragongo gave no sign, which surprised everyone. For the leaders of the study, the behavior of the volcano could be explained by the fact that it was already ready to erupt for a long time. The recharge of magma and the increase in pressure would have been gradual, which made it difficult for the instruments to detect it.
Finally, the study also noted the displacement of 243 million cubic meters of lava under the city of Goma. Therefore, this testifies to new threats related to this volcano. In particular, it may be a matter of risk of lava spill in the middle of the city or phreatomagmatic eruption (if the lava comes into contact with cold water). Mention should also be made of the risk of a limnic eruption in Lake Kivu, whose deep waters contain a large amount of CO2 and dissolved methane.