Mount Nyiragongo just erupted—here's why it's one of Africa's most dangerous volcanoes

Lava from the recent eruption stopped just short of the city of Goma in the Democratic Republic of the Congo. But geologic factors and inconsistent monitoring make the volcano a perpetual threat.

Mount Nyiragongo is rarely calm. The mountainous volcano in the east of the Democratic Republic of the Congo (DRC) is one of the few places in the world to feature a persistent lake of lava bubbling within its summit crater.

And late on May 22, local time, things abruptly escalated: Fractures opened up in the volcano’s rocky sides, spilling fast-moving lava down its slopes. Some of it headed toward the city of Goma, a metropolis just six miles away that’s home to around 1.5 million people. The night sky shimmered with a crimson hue as lava, sometimes piling up to three stories high, speedily invaded the streets of several villages surrounding Goma and swallowed any buildings it encountered, setting them ablaze. As of this writing, there have been 15 confirmed casualties, a number expected to rise in the coming days.

Two of Nyiragongo’s recent eruptions, in 1977 and 2002, were full-blown disasters. In 1977, estimates suggest somewhere between 600 and 2,000 people were killed by lava flows. In 2002, molten rock destroyed up to a fifth of Goma, leaving 120,000 people homeless and killing around 250 people through carbon dioxide asphyxiation, burns, and the lava-triggered explosion of a gas station.

These past disasters have left volcanologists nervous every time Nyiragongo shows signs of life. “It’s one of the most dangerous volcanoes in Africa,” says Benoît Smets, a geohazards expert at the Royal Museum for Central Africa in Tervuren, Belgium.

Nyiragongo’s deadly reputation is due to a perfect storm of factors. Because of the geologic complexities of the region, its lava is remarkably fluid, able to move at up to 40 miles an hour. Eruptions can also send large amounts of lethal carbon dioxide gas to the surface. That’s extremely worrying, since millions of people live in the volcano’s shadow.

Add in the region’s political instability and bouts of conflict, and Nyiragongo is a profoundly difficult volcano to monitor. Despite the best efforts of the Goma Volcano Observatory—set up in the eponymous city in 1986—no clear warning signals were detected prior to its latest eruption.

With all these factors in play, the fiery mountain is capable of producing “the kind of eruptions you really fear,” says Corentin Caudron, a volcanologist at the Institute of Earth Sciences in Grenoble, France.

A tectonic rift 

Nyiragongo, whose peak stands 11,400 feet above the DRC’s Virunga National Park, owes its existence to two things. One is the leisurely geologic fragmentation of Eastern Africa. A strip of land from the Red Sea down to Mozambique is being pulled asunder, with the Nubian plate to the northwest and the Somalian plate to the southeast moving in opposite directions by a few inches every decade. This tectonic divide is known as the East African Rift.

Among other things, this rifting action makes pathways for magma to rise and create volcanoes. What’s more, a plume of superheated but solid mantle material is rising from considerable depth to interact with the underbellies of the tectonic plates. This combination of rifting and pluming creates some strange magmatic concoctions, says Christopher Jackson, a geologist at the University of Manchester in the U.K.

Most magma has a decent amount of silica in it, a compound that acts as a sort of skeleton in molten rock. The less silica you have, the less viscous or goopy the lava is once it erupts. Basaltic magma, the stuff erupting out of Iceland’s Reykjanes Peninsula right now, has a low proportion of silica in it, making it fairly runny, but on a flat surface it can easily be outwalked.

Not so for Nyiragongo’s molten matter: Its lava has such a deficit of silica that it zips across the ground, especially if the lava is erupting at a high rate. If the lava erupts from a high elevation, the volcano’s steep slope may give it an additional speed boost.

The volcano’s magma is also particularly rich in carbon dioxide, an invisible, odorless gas. This gas often quietly exudes to the surface via aquifers above deep-seated bodies of degassing magma. Being denser than air, the gas gathers unnoticed in low-lying areas. Locals refer to it as mazuku, or “evil wind.”

“We have many people die because of mazuku every year in the area,” Smets says. If carbon dioxide-rich magma is tapped by Nyiragongo, dangerous volumes of the gas may also gush out of fissures and flood areas rather suddenly.

A volcanic ambush

Eruptions at Nyiragongo generally transpire when the pressure of accumulating magma or an earthquake forces open fissures in the sides of the mountain, leading to the catastrophic draining of the lava lake or the eruption of magma stored deeper down.

But like the volcanoes that make them, individual eruptions have their own unique behaviors and properties, and no two are identical. Monitoring volcanoes for signs of upcoming paroxysms is therefore fraught with difficulties, and Nyiragongo’s latest flare-up is a perfect example of these challenges.

Between eruptions, Nyiragongo’s summit crater tends to fill up with magma, and it has been doing just that since the 2002 eruption. In 2016, a second vent opened at the summit. In 2020, volcanologists flown in by UN peacekeepers, who shielded the scientists from armed rebels in the area, noticed the lava lake was filling up faster than ever. A worrying sight, but scientists can’t be sure whether the height of the lava lake is an indicator of the volcano’s readiness to erupt.

On May 10, 2021, the Goma Volcano Observatory detected an uptick in seismic activity at the summit. This was perhaps suggestive of magma moving about at shallow depths, but it was not a surefire harbinger of an upcoming eruption.

The observatory’s efforts to keep an eye on Nyiragongo have been somewhat stymied as of late. Some of its seismic stations had been subjected to theft and vandalism, with the risk of violence leaving many of them unrepaired. The observatory also lost financial support from the World Bank last year amid allegations of embezzlement.

Consequently, for several months, remote sensors lacked an internet connection, and regular on-site measurements of the volcano were not possible. Despite these ongoing issues, the observatory, with a small budget from the DRC government, and in cooperation with other international partners, kept up its efforts to monitor Nyiragongo.

But in the end, the volcano erupted unexpectedly, providing no clear geologic hints that it was about to blow. “There was absolutely no precursor for this eruption,” Smets says. “Nobody could have detected this eruption” in advance.

This weekend’s eruption surprised a city haunted by Nyiragongo’s past infernos. Down to luck alone, the lava missed Goma. By Sunday morning, the eruption had lost its intensity. The lava stopped less than 1,000 feet from Goma’s edge, leaving behind a frozen, hissing river of volcanic rock.

Even so, tragedy struck 17 nearby villages, which suffered incursions of lava, leading to the loss of hundreds of houses, a school, three health-care centers, and a water pipeline. As of this writing, two people burned to death, nine died in a traffic collision during the chaotic evacuation, and four prisoners were killed as they attempted to escape their cells.

A future of fire 

Nyiragongo is still making a lot of seismic noise, and some significant earthquakes are shaking the region, hinting at turbulence below. But scientists don’t know whether another eruption could happen soon.

This past weekend is the first time that an expansive suite of monitoring equipment—as opposed to the small assortment of seismic stations in the past—has been up and running during a Nyiragongo eruption. That’s great news for those wishing to study the current geologic activity, but without older data to compare it with,  the recent volcanic activity is difficult to interpret. But, Caudron says, these records will be invaluable to scientists working to understand the churnings of the volcano in the run up to the next eruption.

Nyiragongo will certainly erupt again, eventually. Lava could tear through Goma next time. If the area’s Lake Kivu is disturbed by major underwater volcanic activity, significant quantities of carbon dioxide may flood its shores. And if the magma moves elsewhere below ground, a new volcanic vent could open up in the middle of the city.

The hazards are plentiful and omnipresent around this hyperactive volcano. Goma, along with Gisenyi—a Rwandan city contiguous with Goma—are in near-perpetual peril.

But work is continuously being done to bolster scientists’ understanding, from determining how often it erupts to mapping out the likely future paths of lava flows, says Matthieu Kervyn, a natural hazards expert at the Free University of Brussels in Belgium.

Whatever the science reveals, many of the city’s residents likely can’t or won’t move to somewhere safer, even those who live in the eventual paths of the volcano’s future flows. Should lava once again slither through the streets of Goma, it could inflict great harm and lasting trauma on millions of people.

But perhaps the recent close encounter with widespread destruction will spark a renewed mitigation effort, leading to more robust scientific work on the ground, more active monitoring, and renewed city planning in the most at-risk areas.

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