The Volcano Next Door

Scientists descend to a fiery lava lake to protect a Congolese city in its path.

This story appears in the April 2011 issue of National Geographic magazine.

When? This is the question that has brought two of the world's leading volcano scientists to the center of Africa; it's the question that haunts a team of Congolese seismologists; it's the question that may determine the fate of close to one million people. When will Nyiragongo erupt?

Nyiragongo is a two-mile-high volcano towering over the eastern edge of the Democratic Republic of the Congo (DRC)—one of the most active volcanoes on the planet and also one of the least studied. The chief reason for the lack of research is that for the past 20 years the eastern DRC has seen nearly constant warfare, including a spillover of the massacres in neighboring Rwanda. One of the largest United Nations forces in the world, some 20,000 troops, currently maintains a fragile, and often broken, peace.

At the base of the volcano sprawls the city of Goma, growing by the day as villagers from the countryside seek refuge from rebel and government forces. An estimated million people are now crammed into Goma. Twice in recent years Nyiragongo's eruptions have sent molten rock flowing toward the city. In 1977 lava raced down the mountain at more than 60 miles an hour, the fastest ever observed. Several hundred people died, even though the flow had hardened before it reached the main part of the city. In 2002 the volcano shot more than 15 million cubic yards of lava into downtown Goma, destroying 14,000 homes, burying buildings to the top of the first floor, and forcing 350,000 citizens to flee. Both eruptions were mere grumbles, though, compared with the fury Nyiragongo is thought capable of unleashing.

Part of Dario Tedesco's job is to envision that possibility. For much of the past 15 years, with funding from the European Union, the Italian volcanologist has struggled to focus the scientific community's attention on Nyiragongo. According to Tedesco, there is no question the volcano will erupt again, potentially transforming Goma into a modern Pompeii.

"Goma," he says, "is the most dangerous city in the world."

Last July, Tedesco headed to Nyiragongo with U.S. volcanologist Ken Sims, a team of younger scientists, and a support crew, including six Kalashnikov-toting guards. Their three-week mission was akin to that of a doctor giving a patient a long-overdue physical exam. They wanted to take the measure of the mountain, to study its rocks and sample its gases, to decipher its methods and moods. They hoped to transform the question of when into the beginnings of an answer.

Reaching the summit rim of Nyiragongo was straightforward: Sims and Tedesco followed the lava. The recent eruptions hadn't been classic, spouting-out-the-top types, so-called Plinian eruptions, but rather fissure eruptions, like bursting pipes. In 2002 the rupture happened a few hundred feet below the 11,385-foot peak. Nyiragongo has an intricate plumbing system, widespread as the roots of a tree, and once the initial seam opened, the pressure blew open vents systemwide, shooting out fountains of molten rock, including in the very center of town. The risk, it turns out, is not just near the city of Goma, but directly beneath it.

The lava had steamrolled through forests and neighborhoods. It looked as if a ten-lane highway had been dropped down the mountain's flanks, right across the city. Though the next eruption will likely follow a similar path, thousands of homes, shacks of hand-hewn eucalyptus boards and sheet-metal roofs, have been built directly atop the old flow. Real estate brokers sell tiny lots consisting of nothing but lava rocks enclosed by lava walls for as much as $1,500. And if Goma doesn't have enough to worry about, the thousand-square-mile Lake Kivu conceals an enormous underwater concentration of carbon dioxide and methane. The theory is that a major eruption could release it, spreading a lethal cloud across the city that would spare no one.

After a full day of hiking, Sims and Tedesco reached the barren, wind-wracked summit rim. A long line of porters hauled camping gear, climbing equipment, scientific instruments, food, and water. From here, the scientists looked into the mouth of the volcano. Crumbly sheer walls ringed by ledges dropped a quarter mile down to a vast, flat floor, black with hardened lava. In the middle, contained in a giant soup-bowl-shaped spatter cone, was a stunning sight: a lake of lava.

The lake was 700 feet across—one of the largest in the world—with a mesmerizing kaleidoscopic surface. Black plates were cut by jagged cracks of orange, violently shifting and roiling. One moment the crust took the form of a shattered windshield, then it coalesced into a jigsaw puzzle, then a ragged map of the world. The lake roared like a jet plane taking off and emitted a thick white plume of dozens of deadly gases. "The whole periodic table is churning in there," Sims said.

Even from the rim the scientists could feel the heat. The 1800°F lava exploded from the lake in electric orange geysers, several every minute—25 feet high, 50 feet, 100 feet, bursting into evanescent arches of liquid rock morphing from orange to black in midair as they cooled. The lake seemed to breathe, expanding and contracting, rising and falling, its surface level changing several feet in a matter of minutes, spectacular and terrifying at once.

Sims was awestruck. "There," he said after a long silence, pointing down at the lake, "is where I'd really love to get a sample."

Sims is 50 years old, an avid rock climber and former professional mountain guide. He doesn't like cities; he's allergic to crowds. He dresses as if life were one long camping trip. A professor at the University of Wyoming, he lives in Laramie with his wife and two young children. He hasn't owned a TV set in 25 years. Volcano science has never been a safe occupation—more than 20 scientists have died on volcanoes in the past 30 years. Sims carries a scar on his right arm from Sicily's Mount Etna, where his shirt melted into his skin. He's even-tempered and analytical and seemingly never off duty. He once wrote a paper on a restaurant tablecloth, scribbling until 3 a.m. Then he took the tablecloth home.

Tedesco, 51, is fiery and fashion conscious, an inexperienced alpinist and an unrepentant epicure. On the Nyiragongo expedition, where every ounce hauled up the mountain was carefully considered, Tedesco brought a large glass bottle of extra virgin olive oil. He lives with his wife, teenage daughter, five cats, and three dogs just outside Rome and is a professor at the Second University of Naples. When he speaks of Nyiragongo, he drops all pretense of scholarly dispassion. "It's no secret that I love Goma," he says. "My greatest fear is to make a big mistake—not to predict an eruption."

Sims led the descent into the crater, anchoring ropes and spidering down walls. The rest of the party followed. Nyiragongo is in the Great Rift Valley, where the African continental plate is being wrenched apart, and microquakes constantly shake the volcano. Pebbles clattered down walls. Town-house-size rocks wobbled like loose teeth. The mountain seemed ready to collapse.

The team set up camp on a wide ledge 800 feet below the rim, a few hundred feet above the thundering lake. The ledge was covered with heavy ash, called tephra, and speckled with droplets of volcanic glass and delicate lava threads known as Pele's hair. The surface was warm; hiking pants left on a tent floor had a fresh-from-the-dryer feel in the morning.

Every day the lava lake emits around 7,000 tons of sulfur dioxide, the chief element in acid rain. This is more than the total from every car and factory in the United States. "Basically, it's one big chimney," Tedesco said. The environment was noxious, the air full of acid and metallic aerosol particles. Raindrops sizzled as they landed in fumaroles. Gas masks were worn. Within days, zipper pulls corroded; camera lenses began disintegrating. Sims handed out throat lozenges.

Here on this ledge Tedesco and Sims began working with the field lab they'd brought. A blue padded case held what Tedesco called a "gas sniffer" to measure carbon dioxide, carbon monoxide, and methane. A shoe-box-size RAD7 tested for radon. A vacuum pump, housed in a rusty ammo box, captured a fumarole's plume.

Why measure gas? Because volcanoes are gas-driven machines. An eruption is often preceded by an increase in discharged gas and by variations in its chemical composition. The rise of magma, its accumulation in chambers, its propulsion into fractures—these events produce chemical signals that reach the surface well ahead of the magma itself.

Sims uses radioactive clocks to decipher volcanic processes, measuring and comparing two isotopes of radon. By tracking this ratio over time, he can determine how long gas has taken to reach the surface and gain clues to the chemical, thermal, and mechanical state of the rocks the gas is passing through. But few conclusions can be derived from a single expedition. Only long-term studies can determine which type of gas fluctuations are cause for alarm and which are part of the volcano's normal cycles. Until top scientists make regular visits—something Tedesco has been desperately urging—the best that can be done is to maintain a precise record of Nyiragongo's every move.

That task falls to the Goma Volcanic Observatory, located in a dilapidated one-story building in the city center and staffed around the clock. Katcho Karume, 44, the observatory's director general, has a Ph.D. in environmental physics. "Seismology is the heart of what we do," he said. Swarms of tremors are usually, though not always, a sign that an eruption is coming. But many of the observatory's seismic stations on Nyiragongo's slopes were looted during the wars. "For batteries," said Karume, shaking his head at the thought that Goma's population could be decimated for a few dollars' worth of batteries.

"You know, I hardly sleep," said Karume. "One million people depend on us." Without modern equipment, which could cost two million dollars—a daunting sum in one of the poorest nations in the world—an accurate forecast might not be possible. And even if the observatory were able to predict an eruption, then what?

"There is an emergency plan," insisted Feller Lutaichirwa, vice governor of North Kivu Province. Warning flags at stations throughout town, he said, announce the risk level of an eruption, from green, indicating low danger, to red, meaning an eruption is imminent.

Others begged to differ. "There is no plan," said journalist Horeb Bulambo. "And the flags are old." He was right. At most of the stations I saw, every flag had faded to white. Esteban Sacco, who until recently operated Goma's United Nations humanitarian affairs office, mentioned that only one road leads out of the city away from the volcano. "Within a couple of hours the whole town will be stuck," he said. "Imagine the worst."

Meanwhile, people continue to live on top of the lava. "I saw the eruption in 1977 and again in 2002," said Ignace Madingo, administrative secretary of the city district closest to the volcano. Both times he fled with his family, and both times his house disappeared. "Many people from this area died," he said. "The lava turned them into stones. You can't imagine. You never see them again. No trace." Today his land is a pile of jagged volcanic rocks. "We know the mountain will erupt again. Lava will come. Our houses will burn. And after, we will build once more."

To prevent a catastrophe, Sims believes, we must gain a deeper understanding of Nyiragongo. For starters, one crucial source of information is what's known as a zero-age sample: a chunk of lava fresh from the lake. It would be the Rosetta stone of Nyiragongo, the piece that could unlock the mountain's story, allowing every other rock to be accurately dated. "Ultimately it could lead to better eruptive predictions," Sims said.

Sims wanted that lava chunk. But he knew retrieval would be dangerous, and he struggled with the decision. He thought of his family; he fretted over lava bombs and rockfalls. He would never allow one of his own students to risk his or her life for such a sample. Yet he also understood that he was one of only a few people with both the climbing skills and scientific knowledge to get exactly what he wanted.

So he rappelled into the heart of the volcano. Standing on the crater floor, he couldn't see the lake itself, which was above him within the cone of cooled lava. But he could hear its hissing gases and smell its acrid fumes. He pulled on a silver-colored thermal suit, like a full-body oven mitt, so rigid he couldn't bend over to tie his shoes.

As he approached the spatter cone, the lava crunched like eggshells beneath his feet. The rim was 40 feet high, the wall nearly vertical, requiring rock-climbing skills to ascend. He started up, stretching for handholds and foot placements, drenched in sweat inside the suit. When he was ten feet from the top, spotters described to him over the radio the level of the lava, where it was exploding, where it was spilling over. Conditions changed by the minute. He was five feet away. Then three. Suddenly his foot slipped, and he smelled burning rubber. Looking down, he saw his shoe melting out from under him.

But he kept going. He peeked over the top, eye to eye with the boiling lava. This was beyond science. This was personal, the culmination of a lifetime of exploration and adventure and tireless curiosity. Over the radio the emotion in his voice was palpable. "Amazing. Incredible. I'll never see anything like this again."

After a few seconds he backed away. There was still essential work to do. He didn't have a hammer, so with a hard slam of his fist he broke off a piece of fresh lava. It was shiny, iridescent black, and so hot that, even wearing thermal gloves, he juggled it from hand to hand.

But he had it. The zero-age sample. Through a war zone, up a mountain, down a crater, to the edge of a lava lake, he had it. Now the science, at long last, could begin.