There was no immediate word on any casualties, but witnesses said that lava already had engulfed one highway that connects Goma with the city of Beni in North Kivu province.
Mount Nyiragongo's last eruption, in 2002, left hundreds dead and coated airport runways in lava. More than 100,000 people were left homeless in the aftermath, adding to the fear in Goma on Saturday night.
"We are already in a total psychosis," resident Zacharie Paluku told The Associated Press. "Everyone is afraid; people are running away. We really don't know what to do."
Congolese President Felix Tshisekedi said he would be returning home on Sunday from Europe earlier than planned in order to help coordinate relief efforts.
The government said an evacuation plan was being activated, but the official announcement came several hours after the sky turned a fiery red, and many already had fled on foot in hopes of crossing the Rwandan border post just outside town. Car horns honked and motorcycle taxis weaved as people attempted to escape in panic.
Rwandan immigration authorities reported that some 3,000 people already had officially crossed over from Congo to escape the volcano's eruption, according to the national broadcaster.
The U.N. peacekeeping mission known as MONUSCO tweeted dramatic footage of the city alit, saying it was conducting reconnaissance flights over Goma where it maintains a large base.
"The lava doesn't seem to be headed toward the city of Goma. We remain on alert," it said.
Some sought refuge aboard boats on Lake Kivu, while others fled to Mount Goma, the highest point in the metropolitan area. Dorcas Mbulayi left her home about an hour after the volcano first showed signs of erupting.
"We were eating when a friend of dad's called him on the phone and told him to go and look outside," said Mbulayi, who was still a child the last time the volcano erupted. "Dad told us that the volcano was erupting and that we were going to go to Mount Goma to escape the lava of the volcano."
She also blamed authorities "for not informing us in time about the possible volcanic eruption."
The lack of immediate announcements from authorities and conflicting accounts circulating on social media only added to the sense of chaos in Goma.
Authorities at the Goma Volcano Observatory initially said it was the nearby Nyamulagira volcano that had erupted. The two volcanos are located about 13 kilometers apart.
Volcanologist Charles Balagizi said the observatory's report was based on the direction in which the lava appeared to be flowing, which was toward Rwanda rather than Goma.
Goma sits along the border between Congo and neighboring Rwanda, and is a regional hub for many humanitarian agencies in the region, as well as the U.N. peacekeeping mission known as MONUSCO.
The volcano erupting is also close the Virunga National Park, home to some of the last mountain gorillas in the world. While Goma is home to many U.N. peacekeepers and aid workers, much of the surrounding eastern Congo is also under threat from a myriad of armed groups vying for control of the region's mineral resources.
In 2002, the last time Nyiragongo volcano erupted, lava raced down its flanks into the crowded city of Goma, on the border between the Democratic Republic of the Congo and Rwanda. About 250 people died, 20% of the city was destroyed, and hundreds of thousands fled. Since then, the at-risk population living in the shadow of the 3470-meter-tall volcano has more than doubled to 1.5 million.
Now, conditions are ripe for another disaster, says Dario Tedesco, a volcanologist at the Luigi Vanvitelli University of Campania, who earlier this year led a campaign into the volcano's roiling crater. He and his colleagues found the lava lake there filling at an alarming rate, raising the risk that the molten rock could burst through the crater walls once again. Their analysis suggests peak hazard will arrive in 4 years, although they believe an earthquake could trigger a crisis earlier. Adding to the concerns, the Goma Volcano Observatory , the only monitoring station in the region, is losing its financial support from the World Bank. Tedesco's assessment is blunt. "This is the most dangerous volcano in the world!"
Tedesco began to watch the volcano in the mid-1990s, when refugees, fleeing the genocide in nearby Rwanda, swelled Goma's population. The United Nations sought his advice on the dangers of the volcano, so he monitored Nyiragongo's moods in the years before the 2002 eruption. He is alarmed by parallels to today.
The 2002 eruption began after an earthquake opened up fissures in the southern flank of the volcano. The 200-meter-wide lava lake, the largest in the world, drained in a matter of hours, releasing low-silica, runny lava that flowed as fast as 60 kilometers per hour. The lava piled up in layers up to 2 meters deep in Goma and created a new delta 800 meters wide in nearby Lake Kivu.
As soon as the fissures healed, however, fresh lava began to bubble up and refill the crater lake. Activity accelerated in 2016 when a second vent began to fountain within the crater. In February, on their most recent inspection, Tedesco and his colleagues—flown in by U.N. peacekeepers to avoid the rebels active in the area—found the lake rising faster than ever. The second vent was gushing an estimated 4 cubic meters of lava per second, enough to fill an Olympic swimming pool every 10 minutes. "As long as the volume is increasing, it increases the chances of a volcanic eruption onto Goma," says GVO Director General Katcho Karume, who also took part in the campaign.
Pierre-Yves Burgi, a geophysical modeler at the University of Geneva, says the lava lake level is effectively a pressure gauge for the volcano's internal plumbing, like mercury in a barometer. His model suggests the internal pressure is 20 atmospheres, well beyond the mechanical strength of the volcano's rocky flanks, Burgi and colleagues reported in August in Geophysical Research Letters. "This situation is unstable," he says. "The danger is of a tremor opening up a new fissure."
They believe the system may be reaching a critical point, as it did before the 2002 eruption and an earlier one in 1977. In both cases lava lake levels stabilized several years before the eruption, they argue, as the mass of molten rock weighed down on the magma below. The eruptions lagged because magma takes time to force open existing fractures, explains Andrew Bell, an expert on rock mechanics at the University of Edinburgh who developed a model to explain the collapse of Mount St. Helens in 1982. Burgi expects the lava lake to stop rising soon, in which case the period of peak danger for Goma would be from 2024 to 2027.
Nyiragongo's 2002 eruption covered Goma, Democratic Republic of the Congo, in lava up to 2 meters deep. Karel Prinsloo/AP PHOTO
"They are right to be concerned," Bell says. "Nyiragongo is dangerous in a way a lot of volcanoes aren't." He adds, however, that the behavior of the lava lake doesn't say much about the immediate risk of eruption. Swarms of small earthquakes or ground deformation are clearer warning signs of restless magma, he says. Cynthia Ebinger, an expert on Rift Valley geology at Tulane University, also has issues with Burgi's model, which assumes the magma plumbing feeding Nyiragongo's lava lake is the main factor controlling an eruption. She says the stretching of tectonic plates in the region leads to earthquakes and fresh intrusions of magma that can also trigger eruptions.
A network of seismometers around the volcano, operated by GVO and installed in recent years with assistance from researchers in Belgium and Luxembourg, shows high earthquake activity and several deep swarms, says François Kervyn, director of the natural hazards division at the Royal Museum for Central Africa in Belgium. He doesn't know how unusual the activity is because his team lacks comparable, older data. But he says sustained, rumbling tremors were recorded months before the 2002 eruption. "Nothing like that is detected for the moment," he wrote in an email.
Kervyn says the network requires constant maintenance, because of vandalism, theft, and lightning damage. Several seismometers are currently out of action. But the civil unrest in the area makes repairs dangerous. Earlier this year 13 park rangers were killed in an ambush in the surrounding Virunga National Volcano Park.
The threat of violence is only one of GVO's problems. Established in 1986, the observatory is set to lose the funding it has relied on for the past 5 years. With a staff of about 40, the observatory maintains the seismic stations and monitors the lake and the potentially deadly gases emitted by the volcano. It also plans for Goma's evacuation, and will issue the alarm if an eruption occurs.
Since 2015, the World Bank has given the observatory $2.3 million, as part of an aid package primarily intended to rebuild and protect the city airport, which was seriously damaged in the 2002 eruption. But that project has ended. In an email, a spokesperson for the World Bank Group confirmed that "no follow-up activities are envisioned by the WBG so far."
The U.N. peacekeeping force is concerned. At the end of September, it flew Tedesco back to the city for more talks with the World Bank and other development agencies. A U.N. spokesperson says the peacekeepers are considering supporting GVO in the short term. "We are conscious of the importance of keeping the volcanoes monitored as a way to protect civilians and save lives."
As Science went to press, there was no news of a resolution. Tedesco planned to inspect Nyiragongo's crater again, but bad weather forced the cancellation of a helicopter flight. "If things remain like this, there is little to be optimistic about," he says.
Mount Nyiragongo is an active stratovolcano with an elevation of 3,470 m in the Virunga Mountains associated with the Albertine Rift. It is located inside Virunga National Park, in the Democratic Republic of the Congo, about 20 km north of the town of Goma and Lake Kivu and just west of the border with Rwanda. The main crater is about two kilometres wide and usually contains a lava lake. The crater presently has two distinct cooled lava benches within the crater walls – one at about 3,175 m and a lower one at about 2,975 m . Nyiragongo's lava lake has at times been the most voluminous known lava lake in recent history. The depth of the lava lake varies considerably. A maximum elevation of the lava lake was recorded at about 3,250 m prior to the January 1977 eruption – a lake depth of about 600 m . Following the January 2002 eruption, the lava lake was recorded at a low of about 2,600 m , or 900 m below the rim. The level has gradually risen since then. Nyiragongo and nearby Nyamuragira are together responsible for 40 per cent of Africa's historical volcanic eruptions.
The volcano partly overlaps with two older volcanoes, Baratu and Shaheru, and is also surrounded by hundreds of small volcanic cinder cones from flank eruptions.
Nyiragongo's cone consists of pyroclastics and lava flows. Nyiragongo's lavas are low-silica, alkali-rich, ultramafic extrusive rocks essentially free of feldspars. They range from olivine-rich melilitites through leucites to nephelinites, containing, in various proportions mainly the minerals nepheline, leucite, melilite, kalsilite, and clinopyroxene. This very low silica composition results in eruptions with unusually fluid flows. Whereas most lava flows move rather slowly and rarely pose a danger to human life, Nyiragongo's lava flows may race downhill at up to 100 km/h .
2002 eruptions Satellite image of the eruption plume from Nyiragongo in July 2004
Lava lakes reformed in the crater in eruptions in 1982–1983 and 1994. Another major eruption of the volcano began on 17 January 2002, after several months of increased seismic and fumarolic activity. A 13 kilometres fissure opened in the south flank of the volcano, spreading in a few hours from 2,800 to 1,550 metres elevation and reaching the outskirts of the city of Goma, the provincial capital on the northern shore of Lake Kivu. Lava streamed from three spatter cones at the end of the fissure and flowed in a stream 200 to 1,000 metres wide and up to 2 metres deep through Goma. Warnings had been given and 400,000 people were evacuated from the city across the Rwandan border into neighbouring Gisenyi during the eruption. Lava covered the northern end of the runway at Goma International Airport, leaving the southern two-thirds usable, and reached Lake Kivu. This raised fears that the lava might cause gas-saturated waters deep in the lake to suddenly rise to the surface, releasing lethally large amounts of carbon dioxide and methane – similar to the disaster at Lake Nyos in Cameroon in 1986. This did not happen, but volcanologists continue to monitor the area closely.
About 245 people died in the eruption from asphyxiation by carbon dioxide and buildings collapsing due to the lava and earthquakes. Lava covered 13 per cent of Goma, about 1.8 square miles , and nearly 120,000 people were left homeless.
Immediately after the eruption stopped, a large number of earthquakes were felt around Goma and Gisenyi. This swarm activity continued for about three months and caused the collapse of more buildings.
Six months after the start of the 2002 eruption, Nyiragongo volcano erupted again. Activity at Nyiragongo is ongoing but currently confined to the crater, where another lava lake has formed about 250 metres below the level of the 1994 lava lake. Nyiragongo, 2014 Ongoing threat
Localized carbon dioxide toxicity, known locally as 'mazuku', has killed children even more recently. In locations where the gas seeps from the ground at relatively high levels, without the dispersing effects of wind, its effects can be deadly. On 8 March 2016, Goma Volcano Observatory discovered a new vent that opened in the northeast edge of the crater, following local reports of rumblings coming from the volcano. Some fear that this could lead to a flank eruption. Activity in 2020, including a rise in the lava lake, has led observers to suggest that an eruption is likely by 2024.