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Defusing Africa's Killer Lakes

In a remote region of Cameroon, an international team of scientists takes extraordinary steps to prevent the recurrence of a deadly natural disaster

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Che, an energetic man who never seems to stop smiling, walked with me around Nyos' rim, telling a story he had learned from his grandfather. Long ago, the story went, a group of villagers decided to cross LakeNyos. One man parted the waters, much as God parted the Red Sea for the Israelites, but a mosquito bit the man on a testicle; when he swatted the insect, he lost his grip on the waters and every villager was drowned. Che pointed toward the lake with the homemade spear he often carries. "They're between those two rocks," he said, referring matter-of-factly to the ghosts of that catastrophe. "You hear them talking sometimes, but you do not see them."

The story falls under the rubric of what anthropologist Shanklin calls "geomythology"—in this case, an account of an actual disaster that would become more fantastic as it passed down the generations, eventually fading into legend. "Details shift over time, but these stories probably preserve real events," Shanklin says.

On August 15, 1984, two years before the catastrophe at Nyos, a strangely similar incident, albeit on a smaller scale, took place at Monoun, a bone-shaped crater lake about 60 miles south of Nyos. Monoun is located in a populous area, surrounded by farms and bordered in part by a road. Just before dawn, Abdo Nkanjouone, now 72, was biking northward to the village of Njindoun when he descended into a dip in the road. Parked along the road was a pickup truck belonging to a local Catholic priest, Louis Kureayap; Nkanjouone found the priest's dead body next to the truck. Moving on, he found another corpse, a man's body still astride a stalled motorcycle. "Some terrible accident has happened," thought Nkanjouone. Sinking into a kind of trance, he became too weak to bike and continued on foot. He passed a herd of dead sheep and other stalled vehicles whose occupants were dead. Beginning to climb uphill now, he encountered a friend, Adamou, walking toward him. He says he wanted to warn Adamou to turn back, but Nkanjouone had lost the capacity to speak. As though in a dream, he shook Adamou's hand silently, and the two continued in opposite directions. Nkanjouone made it into Njindoun alive. "God must have protected me," he says. Adamou and 36 others traveling that low stretch of road at the time did not survive.

Rumors about the disaster arose instantaneously. Some said that plotters attempting to mount a coup d'état, or perhaps the government itself, had carried out a chemical attack. Conspiracy theories abound in Cameroon, where unexplained events are often attributed to political intrigues. But a few officials looked to the local geology, theorizing that the long-dormant volcano under LakeMonoun had reactivated.

The U.S. embassy in Yaoundé called on Haraldur Sigurdsson, a volcanologist from the University of Rhode Island, to travel to Cameroon to investigate. Venturing out to the lake several months after the incident, Sigurdsson performed an array of analyses and found no signs of a volcanic eruption. He detected no indication of temperature increase in the water, no disturbance of the lake bed, no sulfur compounds. But a strange thing happened when he hauled a water-sample bottle from the lake depths: the lid popped off. The water, as it turned out, was loaded with carbon dioxide.

That curious finding prompted Sigurdsson's recognition that, indeed, the deaths around LakeMonoun appeared to be consistent with carbon dioxide asphyxiation. Carbon dioxide is a colorless, odorless gas heavier than air. It is the normal by-product of human respiration and the burning of fossil fuels—probably the main culprit in global warming. But at high concentrations, CO2 displaces oxygen. Air that is 5 percent carbon dioxide snuffs candles and car engines. A10 percent carbon dioxide level causes people to hyperventilate, grow dizzy and eventually lapse into a coma. At 30 percent, people gasp and drop dead.

Carbon dioxide is also a natural by-product of geologic processes, the melting and cooling of rock. Most of the time it's harmless, surfacing and dispersing quickly from vents in the earth or from carbonated springs—think San Pellegrino water. Still, CO2 poisonings have occurred in nature. Since Roman times, vented carbon dioxide in volcanic central Italy occasionally has killed animals or people who have wandered into topographic depressions where the heavy gas pools. At YellowstoneNational Park, grizzly bears have met the same fate in a ravine known as Death Gulch.

Sigurdsson, after a few weeks, began to conclude that carbon dioxide from magma degassing deep under LakeMonoun had percolated up into the lake's bottom layers of water for years or centuries, creating a giant, hidden time bomb. The pent-up gas dissolved in the water, he believed, suddenly had exploded, releasing a wave of concentrated carbon dioxide. He wrote up his findings, calling the phenomenon "a hitherto unknown natural hazard" that could wipe out entire towns, and in 1986, a few months before the Nyos disaster, he submitted his study to Science, the prestigious U.S. journal. Science rejected the paper as far-fetched, and the theory remained unknown except to a few specialists.ThenLake Nyos blew up, killing 50 times more people than at Monoun.

word of the nyos disaster spread quickly around the world. In Japan, a government official awakened Minoru Kusakabe of OkayamaUniversity at 1 a.m., inquiring if the geochemist would be willing to go at once to Cameroon. Kusakabe did not even know where the country was. French volcanologists; German, Italian, Swiss and British scientists; U.S. pathologists, geologists and chemists—all would converge on Nyos. Many departed from home so precipitously that they carried little more than a briefcase, a change of clothes and whatever scientific instruments they could grab. Among the Americans was limnologist (lake scientist) George Kling of the University of Michigan, who, as it happens, was making his second visit to the remote location. While studying the chemistry of Cameroonian lakes for his doctoral thesis the year before, he had sampled Nyos' waters from the shore because he didn't have access to a boat. The shallow water had yielded no hints of the dangerous gas in the depths. Now, a year later, the local boy who had guided him along the lake was dead, along with nearly everyone else he had met. "I was numb," recalls Kling. "I had always dreamed of going back there, but not like this."

Arriving within days of the disaster, the scientists themselves were fearful; no one was sure what had just happened—or if it was about to happen again. The Cameroon military had buried human victims in mass graves. Thousands of cattle lay dead, their carcasses bloated and decomposing. Heavy rains fell. Only the survivors' hospitality alleviated the grimness. They took the researchers into their houses and cooked meals of corn mush over open fires. "Can you imagine that?" says Kling's research partner, geochemist Bill Evans of the U.S. Geological Survey. "These people had just lost everything, and they were worried about us."

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