For example, the most dangerous volcano in Africa could surprise everyone and erupt completely unexpectedly

No one had foreseen the eruption, which killed nearly 1,000 people. But now scientists better understand how this merciless eruption managed to stay under the radar.

It will be May 22, 2021 when the Nyiragongo volcano, located in the Democratic Republic of the Congo, erupts. Lava flows are destroying parts of the nearby city of Goma and thousands of people are displaced. Some too late. For example, the eruption of Mount Nyiragongo, which lasted about six hours, left 220 people missing and 750 injured.

The eruption of the Nyiragongo volcano came as a big surprise to everyone. Just shortly before, residents of the city of Goma sounded the alarm. They witnessed the appearance of a lava flow from a fissure on the side of the volcano. The confusion and lack of preparation made management difficult in the early hours of the crisis. While the lava flow devastated a densely populated area, intense seismicity continued for several days, causing damage in Goma and the Rwandan border town of Gisenyi. This increased the panic and resulted in the spontaneous evacuation of part of the population.

Warning Signs
Researchers have thoroughly analyzed the eruption of Africa’s most dangerous volcano in a new study. Because how could the eruption stay under the radar for so long? In many cases, a volcano that is about to erupt gives some hints. “Volcanic eruptions are usually preceded by a pressure rise in the magma supply system, which is characterized by seismicity, an increase in gas emissions and a swelling of the volcanic structure,” said Delphine Smittarello, a researcher at the European Center for Geodynamics and Seismology in Luxembourg. . “To warn of an impending eruption, volcanology observatories monitor seismicity, soil deformation and gas emissions that reflect the movement of magma in the Earth’s crust.”

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Atypical eruption
Basically, volcanic eruptions are usually caused by magma rising to the surface, which is accompanied by increased pressure. These signals can be detected using instruments. However, there were no such signals in the case of the Nyiragongo eruption. “Despite continuous monitoring by a network of ground-based instruments and satellite sensors, none of the usual signals were observed prior to the Nyiragongo eruption,” Smittarello said. This behavior of the volcano was all the more unexpected because the only two known historical eruptions, in 1977 and 2002, had been preceded by strong earthquakes felt several weeks to several days in advance. And so the researchers come to a clear conclusion: The eruption of the Nyiragongo volcano could not possibly have been predicted, they write.

So how could Nyiragongo volcano erupt without obvious warning signs? According to the researchers, the devastating eruption was probably caused by a fracture in the cone-shaped structure of the volcano. This may have been caused by built-up tension or the result of high temperatures. But more importantly, such a rupture would have meant the magma was already close to the surface. “In retrospect, seismic records show that the first events indicating unusual activity appeared just 40 minutes before the first lava flows began,” said Smittarello. “This very short time lag between the first earthquakes and the eruption tells us that the magma took very little time to reach the surface because it was stored at a shallow depth.” What’s more, this means there was limited time to pick up on and respond to these modest signals.

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New danger
In their study, the researchers also warn of new danger. It appears that a large amount of magma (about 243 million m³) has accumulated under the city of Goma. “The magma quickly spread at a shallow depth (less than 500 meters from the surface) from the volcano to the south, flowing under Goma and finally coming to a halt under Lake Kivu,” explains Benoît Smets, researcher at the University of Groningen. Royal Museum for Central Africa and Nyiragongo Specialist, from. This accumulated magma could pose a new threat. “Our results suggest that there is a risk of lava outflow in the middle of the city,” Smets continues. “Such an event could potentially be much more dangerous than the three known eruptions so far.”

The study’s findings highlight the value of volcano monitoring, which can provide clues as to how to predict eruptions without the usual precursor signals. Certainly with a view to future threats, researchers are keeping a close eye on Nyiragongo volcano. And hopefully a possible next eruption will be noticed in time.

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