GOMA, Democratic Republic of Congo — Tens of thousands of people jammed highways, crowded boats and set off on foot to flee this major African city on Thursday, seeking an escape from the rumbling threat of Mount Nyiragongo, one of the world’s most active and dangerous volcanoes.
After a fiery fissure ripped open on Saturday, sending a stream of lava rushing down the mountain’s rocky slopes toward Goma and killing more than two dozen people, scientists and local authorities warned that the danger had not passed.
Overnight, they ordered as many as one million people to evacuate, even as a steady series of tremors and minor earthquakes rocked the city.
Just 2.5 miles beneath the unsteady ground, scientists detected a flow of magma, a lake of fire just beneath the city, and the fear was that the tectonic activity could trigger a new eruption.
A new fissure could rip open at any moment, said Benoît Smets, a geological hazards expert at the Royal Museum for Central Africa in Tervuren, Belgium, who is part of an international team working to assist the Goma Volcano Observatory, the only monitoring station in the region.
“We have a very active volcano with a very dense and populated city at the foot of the volcano, so there is a huge risk of a disaster,” he said in a telephone interview.
What made Saturday’s eruption different from two past eruptions, the most recent in 2002, was that it came without warning, he said.
By the time the people living in Goma and the surrounding towns and villages knew they were in danger, the sky was already ablaze. For more than five hours, the night sky burned crimson red as lava poured out of the flanks of Mount Nyiragongo.
By morning, the lava flow had destroyed 17 communities in its path, according to relief agencies.
The U.N. refugee agency, citing local authorities, said 32 people had died in incidents related to the eruption, including seven people killed by lava flow and five asphyxiated by gases.
The lava stopped just short of the city center and nearly reached the airport.
Since the eruption, the lava basin in the volcano has rapidly filled back up and scientists have been racing to understand what is happening under the earth’s surface.
The 2002 eruption destroyed about 20 percent of Goma, burying it under molten rock, leaving 120,000 people homeless and killing around 250 people through carbon dioxide asphyxiation, burns and the lava-triggered explosion of a gas station.
Since then, the number of people living in the shadow of the 11,385-foot-high volcano has more than doubled, to an estimated 1.5 million to two million.
The unstable political situation in the country, wracked for decades by civil wars, ethnic conflicts and systemic corruption, has complicated efforts to study the volcano. The World Bank withdrew its funding for the Goma research facility over concerns that the money was being embezzled.
In 2020, a team of volcanologists had to be flown into the area by United Nations peacekeepers who protected the scientists from armed rebels in the area.
Dario Tedesco, a volcanologist at the Luigi Vanvitelli University of Campania, in Sicily, was on that mission and he told Science magazine that he and his colleagues found the lava lake there filling at an alarming rate.
“This is the most dangerous volcano in the world,” he said shortly after that trip.
Located on the tectonic divide known as the East African Rift, on the eastern edge of the Democratic Republic of Congo near the border with Rwanda, it is less than eight miles from the center of Goma, which sits on the shore of Lake Kivu.
While it is not clear if the latest eruption and seismic activity will trigger a more deadly disaster, officials in the central African country decided that the risk was too great not to take action.
“The situation can change quickly,” the military governor of the province, Lt. Gen. Constant Ndima, told the public. “In anticipation of this possible disaster and in agreement with scientists and volcanologists, we have taken the decision to relocate the population” from 10 of the city’s 18 districts.
As many as one million people reside in those districts, but it was hard to know how many heeded the government warning.
Adolphe Basengezi, a taxi driver who lives in Goma, said there were not many people left in his part of town.
“Most have run away,” he said. “I was driving and people in the road were panicking and trying to save their lives.”
Many of the wealthier people in the city, those who can afford cars, sped to the east and into Rwanda. More than 3,000 had crossed the border by 9:30 a.m., according to an official at the checkpoint.
Others flocked to the port located on Lake Kivu, hoping to escape by ferry. Witnesses reported seeing at least two boats so overwhelmed by people that they were broken and had to be abandoned.
The lake itself, however, presented another threat.
Covering more than 1,000 square miles, and around 1,500 feet deep in parts, the lake has been shaped by the same geological forces that gave birth to Mount Nyiragongo and seven other volcanoes known as the Virunga chain.
Over the years, the volcanic activity has led to a steady buildup of carbon dioxide and methane at the bottom reaches of the lake.
“As this lake is very deep, that layer does not mix with the rest,” Mr. Smets said. The fear is that if the lake bed is destabilized by something like an earthquake and then exposed to superheated lava, it could cause the gas to be released — with deadly consequences for anyone caught in the suffocating cloud.
“For the moment,” Mr. Smets said, “what is reassuring is there is no sign of perturbation in the lake.”
The danger of the magma moving under the ground and building up in the volcano was the most pressing concern.
Patrick Muyaya, the country’s minister of communication, said that at the moment, “scientists do not have a clear answer to what is going on.”
“Goma faces four types of risks: accentuation of earthquakes, a new volcanic eruption, explosion of gas pockets under the lake, and the toxicity of the ambient environment,” he said at a news conference on Wednesday.
“Faced with this specter of dangers and, while awaiting the results of the surveillance and the global analysis of the situation, the only option has been that of protecting human lives and putting the population away from harm.”
With the decree to evacuate issued in the middle of the night, many of those who took to the road to escape also expressed confusion.
The largest crowds of people fled on foot — carrying their prized possessions slung over their shoulders and mattresses tied to their back. All morning and afternoon, a mass of humanity marched west toward the town of Sake more than 12 miles away.
“All roads out of town are full completely,” Mr. Basengezi, the taxi driver, said. “People don’t have clear information.”
He said all the hotels in Sake were full by late afternoon and people kept arriving.
But not everyone left. Some, like Albert Muihigi, 28, could not. His mother is diabetic and he needed to stay and care for her.
“Most of those who left are women and children,” he said. “Many of the young men stayed back to look after our homes because there are no police around.”
He said he was not scared but there was an atmosphere of fear in the air.
“We are young enough that if anything happens we can make a run for it,” he said.
Finbarr O’Reilly reported from Goma and Marc Santora from London. Steve Wembi contributed reporting from Kinshasa, Democratic Republic of Congo.