On clear nights a red glow radiates from the top of Mount Nyiragongo in the Democratic Republic of the Congo. On the mountain’s summit the source of the light thrashes and boils: the largest and most active lava lake in the world.
Among volcanoes, Nyiragongo stands out. The magma that fuels its violent eruptions is incredibly fluid, capable of racing down the mountainside at highway speeds. The volcano would be a hotbed of research activity — if it weren’t in the crossroads of war.
More than a million people live in the volcano’s shadow, many of them refugees from years of civil war and the 1994 genocide in neighboring Rwanda. Eruptions in 1977 and 2002 poured fast-flowing lava into the booming city of Goma, killing hundreds and blackening the landscape. Yet after both eruptions, people returned to Goma before the lava hardened, and many others have found their way to its fertile land on the shore of Lake Kivu. The city’s population has tripled since 2002.
“Nyiragongo is a humanitarian crisis waiting to happen,” says Kenneth Sims, a geochemist at the University of Wyoming in Laramie.
The white gas that constantly billows from the volcano’s crater is a reminder that the question isn’t if, but when, the volcano will kill again.
Despite Nyiragongo’s deadly potential, scientists know almost nothing about the volcano’s eruptive history. Without knowledge of past eruptions as a guide, forecasting and preparing for the volcano’s next violent outburst has become a dangerous game of assumptions and uncertainty.
The Congolese volcanologists who monitor the mountain struggle with insufficient funding and outdated equipment. Most foreign scientists are scared off by the conflicts that have rattled the region. Just a handful of researchers, including Sims, are braving the volcano’s blistering heat and risking encounters with armed bandits to grab lava rock samples so they can study the isotopes of radioactive elements within. Such information should help in deciphering Nyiragongo’s powerful past to offer at least a glimpse of its future. The results so far suggest that Goma’s residents may be in more danger than once thought.
Rivers of fire
Nyiragongo rises more than 3 kilometers from the East African rift, a seam where tectonic forces slowly rip the African Plate apart. Molten rock from Earth’s mantle wells up through the cracked crust, feeding chains of restless volcanoes and siring what will one day be new seafloor (SN: 7/2/11, p. 22).
Lava from eruptions in 1977 and 2002 flowed from the volcano toward Lake Kivu. Goma’s population has expanded to within 13 kilometers of the crater. Nearly 100 inactive minivolcanoes, called parasitic cones, dot the area, hinting that new ones may form in the future.
Credit: Eric Augenstein, adapted by M. Atarod
Unlike explosive volcanoes such as Mount St. Helens, Nyiragongo doesn’t erupt with a bang. Instead, outward pressure from a magma blob rising from Earth’s mantle can cause stockpiled lava to burst out of fractures in the mountainside or to overflow from the summit. Nyiragongo’s core is a vertical magma-filled vent that fills the 260-meter-wide lava lake in the volcano’s crater. That lava lake contains 9 billion liters of molten rock, volcanologists estimated in the Journal of Geophysical Research: Solid Earth in May. Offshoots of the main magma channel connect to the fractures as well as to defunct minivolcanoes referred to as parasitic cones.
The lava moves fast, “like water over honey,” says Sims, because of the unusually low amount of lava-thickening silica found within this volcano. During the 1977 eruption, lava flows reached speeds of 100 kilometers per hour, the fastest recorded for any volcano.
The next eruption, in 2002, struck without warning. More than 14 million cubic meters of lava gushed down the volcano’s southern flank toward nearby Goma. Two rivers of fast-flowing molten rock flooded into the city, cutting through the middle of the town. The eruption killed at least 170 people, destroyed about 15 percent of Goma and left 120,000 people homeless. The chaos ignited an exodus across the nearby Rwandan border as 300,000 people fled the destruction. A few days later, dozens more died when lingering lava triggered an explosion at a local gas station.
Despite the devastation, the eruption was relatively small and lasted only 12 hours, says volcanologist Dario Tedesco of the Second University of Naples in Italy. With no warning, however, the evacuation didn’t start until after the eruption had already begun, says Tedesco, who spends half of each year working in Goma. Researchers in Goma noticed Nyiragongo belching gas and shaking the ground more than usual beforehand, but they didn’t have the tools or data to confidently predict an eruption.
At the center of local volcanologists’ work is the Goma Volcano Observatory. The small one-story building sits near a dirt soccer field on a hill-sized parasitic cone called Mount Goma, overlooking downtown. Around 14 researchers make do with old equipment and a limited budget. Since grants from European groups dried up a year and a half ago, the observatory has received no external funding. The Congolese government provides monthly salaries of $200 to $350 per person. Tedesco says those salaries are enough for a single person or a couple to eat for only 10 to 15 days, yet many of the researchers have large families.“We’re working at 25 percent capability,” says observatory director general Katcho Karume. “We don’t have enough, but we do what we can.” Without funding and equipment, Karume says, properly monitoring Nyiragongo for potential eruptions is nearly impossible. Well-observed volcanoes elsewhere in the world are covered in a network of sensors, such as GPS trackers used to measure bulges on the mountainside caused by pent-up magma. In Goma, the researchers rely on about half a dozen remote posts that monitor the volcano’s seismic rumblings, but those posts are often out of commission — their valuable batteries stolen.
Goma’s strategic importance on the Rwandan border and along the shores of Lake Kivu makes it a prime target for rebels. In November 2012, the M23 rebel group took control of the city, forcing out the Congolese army. The rebels withdrew from the city days later, but hung around in nearby Virunga National Park. For the last two years the group’s movements around Nyiragongo put a stop to direct monitoring by scientists. Expeditions to the summit finally resumed in October.
As the observatory scientists struggle to keep tabs on the volcano, more is at stake today than in 2002, Karume says. Goma’s population has boomed from 400,000 then to more than 1.1 million in 2013, nearly three times the population of Miami. Many of the new residents come from the war-torn countryside or neighboring Rwanda, seeking safety and opportunity in Goma, which is home to the United Nations regional headquarters. The sprawling city’s edge now stretches to just 13 kilometers from the volcano’s crater.
“If there is an eruption, it is going to come out quickly and people won’t have enough time to escape,” Karume warns.
Assessing the risk
Karume is revising the Nyiragongo hazard map, a report designed to help officials prepare for potential volcanic events. The work is problematic, he says, because scientists know for certain only about past eruptions in 2002, 1977 and another in 1300, dated by carbon-14 measurements. Many unmapped cooled lava flows stretch down the mountain. Since they have no vegetation, they appear at most a few centuries old. But those flows have never been dated. The nearly 100 parasitic cones that surround Nyiragongo seem young as well but lack specific age estimates. With so little to go on, Sims says, researchers can’t tell if existing parasitic cones are centuries old — from a previous stage in Nyiragongo’s evolution — or if new minivolcanoes may emerge in busy, downtown Goma.
Having a complete eruptive history is like having a career criminal’s record, he says. You might not know exactly when he’ll strike next, but you at least have an idea of what to expect.But the three dated eruptions simply aren’t enough, says Mark Bebbington, a geostatistician at Massey University in Palmerston North, New Zealand. “A rule of thumb would be 20 to 30 dated eruptions to really get anywhere,” he says.
Bebbington applies statistical analysis to volcanic histories to uncover patterns, such as how often a volcano erupts, what size outpouring it’s capable of or whether it’s becoming increasingly restless. In June, he reported in Geophysical Journal International the possibility of predicting the intensity of a volcano’s next explosive eruption using volcanic histories.
These calculations can’t predict exactly when an eruption will happen, he says, but they can help cities create evacuation plans and guide the placement of infrastructure. This would be particularly important in Goma, where the limited number of roads leading away from town could create a bottleneck during a disaster.
Volcanoes near large populations elsewhere in the world have much more complete histories than this mysterious volcano, Bebbington says. For example, written accounts chronicle the eruptions of Italy’s Mount Vesuvius for thousands of years. But because Goma is a young city, established about 75 years ago, no such accounts exist for Nyiragongo’s ancient eruptions.
For volcanoes without extensive eyewitness histories, researchers rely on several techniques, some more direct than others. With carbon-14 dating, scientists look for a plant or animal killed by the eruption. By measuring the levels of radioactive carbon in the fossilized remains, researchers can estimate how long ago the eruption responsible for its demise happened. This technique requires luck, however, because fossils buried under volcanic debris must first be found.
A new technique called cosmogenic dating uses rocks perched in plain sight. As cosmic rays bombard Earth, they can trigger formation of isotopes such as helium-3 in outer rock layers. Scientists can measure ratios of these isotopes to determine how long a rock has been exposed. Unfortunately, the method can’t be applied to Nyiragongo because the weather causes too much erosion, making all the lava flows seem much younger than they actually are.
For Nyiragongo, Sims studies the radioactive elements locked inside the volcano’s ancient lava flows. Over time, unstable thorium, potassium and uranium atoms in the rocks decay into other elements. By measuring the relative amounts of these daughter products — such as radium and lead — he can estimate how long ago the lava hardened.
To begin his dating project, Sims needed a baseline to compare his results against— zero-age lava fresh from the edge of the volcano’s lava lake. He got his chance during a 2010 expedition.
Dollars and guns
Sims’ mission for a fresh lava sample, his second since he began studying Nyiragongo in 2004, took more effort than a typical volcano ascent.Goma has no ATMs and most shopkeepers won’t accept African currency. To buy the climbing equipment, camping gear and food for the weeklong stay, Sims carries $5,000 to $6,000 in U.S. bills with him every time he prepares an expedition. The locals are picky even when it comes to U.S. currency, Sims says. They accept only pristine bills printed after 2006 — no cuts, marks or too many folds. Carrying that amount of money, Sims says, makes him feel like “a walking target.”
He recalls one year having a drink with a fellow scientist in a bar in Goma. “I had one drink and both of us were totally trashed, and we both think we got mickied [drugged].” They were lucky to stagger back to their hotel unharmed.
The 2010 trip required 150 porters — locals paid a month’s wage for hauling equipment and supplies up the volcano. Ten scientists accompanied Sims, including Tedesco and researchers from the volcano observatory. Five armed park rangers came along for protection. On a previous expedition, Tedesco says, crooked soldiers robbed some of his friends, even taking their shoes, before a firefight broke out between the rangers and the robbers. “There are guns everywhere,” Sims says. “It’s always in the background.”
Thankfully, the team ascended the mountain without any run-ins, hiking through sweltering jungle and carefully traversing steep slopes leading to Nyiragongo’s high, windy and frigid summit.
Hell on Earth
About a kilometer across, Nyiragongo’s crater opens into a supersized natural amphitheater deeper than the Empire State Building. At center stage, the huge lava lake burns bright red and breathes a plume of sulfur dioxide into the sky at a rate of more than 1,300 kilotons per day, Tedesco and colleagues reported in November in the Journal of Geophysical Research: Atmospheres. “When you’re up on the rim, it’s like you’re looking down into hell,” Sims says.The crater descends in three gigantic steps like tiers on an inverted wedding cake. Dead bugs scatter the ground, drawn in by the glowing light and killed by the blistering temperatures and noxious gases. Sims’ experience as a mountain climber and wilderness guide came in handy in 2010 as the team rappelled down the unstable slope wearing gas masks.
Along the descent, Sims chiseled away layers of weather-beaten old lava flows with a sledgehammer to reach the rock’s untarnished inner layers. Weathering alters the chemistry of the lava and makes the outer layer useless for analysis. The testing Sims does in his Wyoming lab requires only tiny fragments, but he broke off chunks the size of shopping bags. With so much effort needed to collect the samples, he didn’t want to risk running out.
To get a fresh sample, Sims descended alone to the lowest tier, Nyiragongo’s heart. The lava lake rises 15 meters above the crater bottom, encased in a bowl-shaped spatter cone built by overflows and spray from popped lava bubbles.
Donning a silver-colored, heat-resistant suit, Sims quickly scaled the steep spatter cone, making his way to the freshly deposited lava rocks along the lake’s edge that had been molten just 30 minutes earlier. After breaking away a lava rock with his fist, he sprinted back to safer ground, his boots melting underfoot and the precious sample burning through his oven mitt–like gloves. At last Sims had a rock that he hoped would help pin down Nyiragongo’s eruptive timetable.
Rock of ages
Back in his University of Wyoming lab, Sims and geologist Erin Phillips examine the lava samples freighted back from Nyiragongo in labeled cloth sacks. Each rock contains a geological birth certificate encoded in its chemistry. By measuring the ratios of radioactive elements in the rock, Sims and Phillips can estimate how long ago it spewed from the volcano.The rocks that melt to form Nyiragongo’s magma innards contain uranium-238 atoms. Over time uranium decays into radioactive thorium-234, which eventually decays into unstable protactinium-234 and so on. In total, the decay chain bridges 19 isotopes and culminates in a stable lead-206 atom. Scientists can approximate the age of a rock by comparing the relative number of atoms of each isotope embedded within.
If the rock remains solid, uranium’s offspring stay trapped. However, when rock melts under the extreme temperatures and pressures inside Earth’s mantle, much of the radioactive isotopes wash away or bubble up to the surface as gas. When the liquid rock solidifies as a lava flow on the surface, any new decay products are once again confined. The melting essentially resets the rock’s age.
This rock reboot allows scientists to determine the ages of ancient lava flows, Phillips says. “We’re putting it all together to get a story about the volcano.”
Phillips crushes rock chips from an undated lava flow near Nyiragongo’s summit that is not from the 1977 or 2002 eruptions. She drops the pulverized rock into a swirling mix of water, hydrogen peroxide and hydrochloric acid. This acid bath breaks down rock and makes the isotopes entombed inside easier to find. After a long soak, she puts the processed sample inside a mass spectrometer to measure the types and quantities of atoms inside.
Sims and Phillips compare the levels of a pair of uranium decay products: lead-210 and radium-226. This isotopic duo is important, Sims says, because scientists know how long into a rock’s life it takes for the elements to reach a stable ratio. Lead-210 and radium-226 take around 100 years to reach this equilibrium.
Using the newborn lava samples he collected in 2010 for calibration, Sims and Phillips discover that the undated sample contains more radium-226 than lead-210. The flow, it seems, formed less than 100 years ago. This unpublished finding is the first significant evidence of a third Nyiragongo eruption within the last century, Sims says. “It looks like Nyiragongo has been more active recently than had previously been known.”
A more active Nyiragongo is bad news for the people of Goma, Sims says. The newly dated eruption suggests the volcano’s magma refills more quickly after each outburst than once thought. Still, four known eruptions aren’t enough to fully understand a volcano’s personality, he says. He plans to return in 2015 to date more lava flows around the mountain so he can establish a comprehensive eruptive history and help the city better prepare for the next big one.
Tedesco doesn’t think that the news of increased danger will cause people to leave Goma. For many residents, he explains, Goma is their first real home after spending years as refugees.
For now, Tedesco says, he’s staying too. “After so many years I think I belong more to Goma than to Italy,” he says. “I love that place [Goma], although I also hate that place. Nothing changes, it’s very difficult to work, there’s too much corruption sometimes — but we have to work with what we have and believe we can make the difference.”