In May last year, plumes of ash launched miles into the air above the city of Goma in the Democratic Republic of Congo (DRC). Cracks dug the ground for hundreds of meters, releasing hot gases or flames. When Mount Nyiragongo, a volcano near the city, erupted, it destroyed around 3,600 homes and buildings, forced the evacuation of 400,000 residents and killed at least 32 people, according to a report of the Smithsonian’s Global Volcanism Program, and injured hundreds of others.
But no one saw this destruction coming – in fact, the eruption took residents and seismologists completely by surprise.
At the time, the nearby Goma Volcano Observatory noticed no warning signs that the volcano was about to spew lava. But now, in a study published last week in the journal Natureresearchers explain how the impending eruption managed to evade detection.
Mount Nyiragongo lies near the DRC’s eastern border with Rwanda. It threatens both the Congolese city of Goma and the Rwandan city of Gisenyi, which are respectively home to around 700,000 and 83,000 people a year. Scientific News‘ Caroline Graming.
“Nyiragongo is unique in that a million people live right at the foot of the volcano,” says Delphine Smittarello, first author of the paper and volcanologist at the European Center for Geodynamics and Seismology. Scientific News. “There are so many people so close to a very dangerous place.”
In 1977 and 2002, eruptions from the mountain killed hundreds of people. But those disasters were preceded by large earthquakes, the eruption of a nearby volcano and other indicators of an impending explosion, according to the New York Times‘ Robin George Andrews. With these events, people in the area felt precursor earthquakes for days in advance, according to Scientific News.
In addition to earthquakes, other signs of an impending eruption include ground deformations and the release of noxious gases, according to the Time. But as researchers sifted through sightings made before Mount Nyiragongo erupted, they couldn’t find any of these warnings. “We could not detect any dramatic change that would tell us that an eruption is going to occur,” Smittarello told the Time.
But the scientists found subtle changes: They report that small earthquakes started 40 minutes before the eruption and some acoustic signals occurred only 10 minutes before. The magma, which had already risen near the surface of the volcano’s crater, probably produced a rupture in the volcanic cone and vomited. Since the magma didn’t have to travel far to erupt, the warning signals came at the last minute, according to Scientific News.
Mount Nyiragongo is a bit unusual in that a lava lake sits at the top and its magma is not tightly trapped inside, writes Alison Snyder for Axios. Thus, there was no pressure buildup which, in another type of volcano, would typically lead to signs of an upcoming eruption.
“It’s a strange volcano,” says Benoît Smets, study co-author and geohazard expert at the Royal Museum for Central Africa in Belgium. Time. “You won’t be able to detect such types of eruptions,” if this volcano is treated as a typical volcano.
Worldwide, there are about 100 observatories monitoring some 1,350 volcanoes, for Axios– which means that there is no detailed data on most of them, and many remain unmonitored. Scientists’ understanding of these volcanoes is based on one of the most studied groups, while many others are still shrouded in unknowns.
Seismologists need to develop a better understanding of Nyiragongo to improve monitoring of its eruptions, says Michael Poland, a geophysicist at the US Geological Survey who did not contribute to the study, for Scientific News. “The traditional approach is less reliable in Nyiragongo,” he told the publication.