Killer Lakes: II
In 1986, a huge carbon dioxide explosion triggered one of the world's most devastating natural disasters at Lake Nyos, West of Cameroon.
Part 1 * 2 * 3
The explosion killed more than 1700 people and reduced livestock herds up to 25 kilometers (15 miles) away. Many understood the disaster as something akin to shaking a carbonated bottle of water and then popping the shaken soda's cap. Dissolved carbon dioxide in Lake Nyos had become trapped in deep water because the lake bottom extended so far beneath the surface. Given the weight of water, the lake had to blow; its high hydrostatic pressure had capped this relentless buildup of carbonated water. But over time, bubbles started to appear until eventually the soda lake erupted, literally turning itself upside down in a few days of devastation.
To astrobiologists, the story of Lake Nyos offers a fascinating and modern look into a field called paleogeology--the combined records of climate with geology and their mutual influences on the history of Earth's life. A few theories have extended what happened in 1986 to our distant past, when global catastrophes altered the entire course of evolution. For instance, over two hundred million years ago, nearly 70 percent of land life and 95 percent of marine organisms suddenly and mysteriously disappeared. Did an asteroid strike? Did an ice age begin? Some suppose this event known as "The Great Dying" may share similarities to what happened on a much smaller scale at Lake Nyos. Was the Great Dying precipitated by dissolved gases such as poisonous methane building up in the world's oceans, only later to be released as explosive clouds of acid rain?
In this way, the modern soda fountain at Lake Nyos provides a case study for evaluating how biologically important theories in paleogeology might have worked. Astrobiology Magazine had the opportunity to sample ground truth about what happened at Lake Nyos from someone who visited the devastation afterwards. Cameroon became the destination for award-winning science journalist, Kevin Krajick.
Krajick's article, "Defusing Africa's Killer Lakes", first appeared in the September 2003 issue Smithsonian Magazine, and was subsequently honored by receiving the Walter Sullivan Award for Excellence in Science Journalism. His articles have appeared in National Geographic, Newsweek, The New York Times, Science, Discover, Audubon, Natural History, Smithsonian and many other publications. Krajick also authored "Barren Lands: An Epic Search for Diamonds in the North American Arctic". All publication rights and copyright remain with K. Krajick. This second installment is reprinted for the NASA-sponsored Astrobiology Magazine with author permission.
|Author Kevin Krajick went places in Cameroon many scientific groups and journalists alike have had difficulty getting to. Shown here in northern Canada from his book "Barren Lands"
Image Credit: Krajick
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'e'tat, 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 Lake Monoun had reactivated.
The U.S. embassy in Yaounde' 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.
|The planet Venus is thought to have been altered by the build-up of greenhouse gases like carbon dioxide. Its current surface temperatures are hot enough to melt lead. Ultraviolet image of Venus obtained by Pioneer-1.
Image Credit: BNSC
That curious finding prompted Sigurdsson's recognition that, indeed, the deaths around Lake Monoun 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. A 10 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 Yellowstone National 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 Lake Monoun 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.Then Lake 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 Okayama University 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."
|The atmosphere viewed from a high altitude balloon. The edge between bright haze and the darker blue is the top of the troposphere at 12 km and the beginning of the stratosphere. Water vapor is transported upwards to the top of the atmosphere where it is split to oxygen that stays and hydrogen that is lost to space.
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."
The scientists motored out onto Nyos in inflatable dinghies to take water samples and look for clues. Once again, some assumed that an underwater volcano had erupted. But others immediately grasped that the villagers around Nyos had perished under the same conditions previously documented at Monoun--that Sigurdsson's "unknown natural hazard" was real.
Over ensuing weeks and months, scientists would piece together the Nyos story. The crater lake is extraordinarily deep (682 feet) and rests atop a porous, carrot-shaped deposit of volcanic rubble--a subaqueous pile of boulders and ash left from old eruptions. Carbon dioxide may remain from this old activity; or it could be forming now, in magma far below. Wherever it comes from, underwater springs apparently transport the gas upward and into the deep lake-bottom water. There, under pressure from the lake water above, the gas accumulates; pressure keeps the CO2 from coalescing into bubbles, exactly as the cap on a seltzer bottle keeps soda from fizzing.
If the lake were farther north or south, seasonal temperature swings would mix the waters, preventing carbon dioxide buildup. Cold weather causes surface waters to become dense and sink, displacing lower layers upward; in spring, the process reverses. But in equatorial lakes like Nyos and Monoun, the deep layers seldom mix with top layers; indeed, the deepest layers may stagnate for centuries.
But something must have detonated the built-up carbon dioxide that August night 17 years ago. One theory is that boulders crashing into the lake (perhaps the rockslide Ephriam Che heard) set it off; the scientists at Nyos noted that an adjacent cliff face bore signs of a fresh rockslide. Or a fluky drop in air temperature, causing surface water to cool and abruptly sink, might have been the trigger, or a strong wind that set off a wave and mixed the layers. Whatever the cause, water saturated with carbon dioxide was displaced upward from the depths; as it rose and pressure lessened, dissolved carbon dioxide bubbled out of solution, and the bubbles drew more gasladen water in their wake, and so on, until the lake exploded like a huge shaken seltzer bottle. (The explosion, they determined, had also brought up iron-rich water, which oxidized at the surface and turned the lake red.)
In addition, the scientists observed that a lakeside promontory had been stripped of vegetation to a height of 262 feet, presumably by a carbon dioxide-driven waterspout rocketing into the air. The explosion released a cloud of carbon dioxide--perhaps as much as a billion cubic yards, scientists estimate--that thundered over the lake's rim, hit Suley's family first and poured downhill at 45 miles per hour through two valleys and into the villages of Lower Nyos, Cha, Fang, Subum and, finally, Mashi, which is 14 miles from the lake.
|Self-sustained soda fountain (21 m height), Lake Nyos, Cameroon, Africa, is part of a project to degas gradually soda lakes.
Credit: Bernard Canet
Those on high ground survived. A few individuals at lower elevations, like Suley, were spared for no apparent reason. The only other survivor in her family was her husband, Abdoul Ahmadou. He had been away on business in Wum that night. When he returned, it was to join his wife in burying their dead, then to flee to a refugee camp near Wum. Amid fears that the lake could erupt again, the military ordered out most of the region's survivors, around 4,000 in all.
The scientists began making frequent return trips to Cameroon, not only to study both Nyos and Monoun but also to make the region safe for people wishing to return. Testing of the lake depths showed that the explosions had not cleared all the pent-up carbon dioxide; indeed, the gas was accumulating at alarming rates. The researchers speculated that certain layers of Monoun, if left untouched, could become saturated with carbon dioxide by this year, and Nyos, sometime after. But either lake, even short of saturation, could explode at any moment.
The researchers considered various measures, such as blowing out the carbon dioxide by dropping bombs (too dangerous); dumping in massive quantities of lime in order to neutralize the gas (too expensive); or digging tunnels in the lake bed to drain the gas-laden bottom waters (way too expensive). In the end, they settled on a low-tech approach: running a pipe from the lake's deepest water layer to the surface, gradually releasing the gas to disperse quickly and harmlessly in the air. In theory, such a pipe, once primed, would carry the pressurized water from the depths and shoot it into the air like a natural geyser--a controlled explosion that could be sustained for years.
But not all researchers agreed that vent pipes would work.
Geologist Samuel Freeth of the University of Wales, among others, speculated the process might set off a new explosion by spurting cold, dense bottom water onto the surface of the lake; the water would sink and create turbulence below. Even the researchers who advocated venting were worried, says Michel Halbwachs, an engineer from France's University of Savoy, who would design and install most of the equipment: "We were in an area [of science] little known and dangerous."
Using seed money from the European Union and private sources, a team headed by Halbwachs tested garden-hose-diameter pipes in Nyos and Monoun in 1990, then progressively larger pipes in 1992 and 1995. The experiment worked: the gas began venting. Halbwachs and coworkers were jubilant. Then the money ran out. The Cameroon government said it could not afford the $2 million to $3 million for permanent degassing installations. International aid agencies-- more used to reacting to natural disasters than preventing them--did not grasp the concept. Kling, Kusakabe and others lobbied oil companies, governments and other organizations to pay for venting. Finally, in 1999, the U.S. Office of Foreign Disaster Assistance (OFDA) came up with $433,000 for a permanent pipe to be installed at Nyos.
By January 2001, the researchers had assembled rafts and piping at the site. Attached to a raft in the middle of the lake, a 5.7-inch-diameter pipe reached 666 feet to the deepest water layer. The Cameroon military provided emergency oxygen tanks for all workers in case of a rogue carbon dioxide release. After everyone retreated to distant high ground, Halbwachs pushed a remote-control button to activate a pump that primed the pipe. Within seconds a 148-foot spray shot into the sunlight at 100 miles per hour, and the small crowd let out a cheer. The degassing of Lake Nyos had begun.
But with 5,500 tons of carbon dioxide still pouring into the lake annually, one pipe barely keeps up; Kling and Evans estimate it may take more than 30 years before enough dissolved carbon dioxide can be vented to make the lake safe. Five pipes, the researchers say, might do the job within five or six years--but so far funding has not materialized. The venting of the lake cannot happen too quickly, as far as locals are concerned. Families have begun drifting back into nearby hills, siting their compounds in high passes but venturing down to the forbidden zone by day. "You can't keep people out forever," says Greg Tanyileke of Cameroon's Institute for Geological and Mining Research. "We need to go faster."
Related Web Pages
Methane: The Great Dying
Great Impact: Part I
Impact Hazards Website
NASA/JPL Near Earth Object Program
Do We Know What Killed the Dinosaurs?
Massive Volcanic Eruptions in Siberia Linked with Mass Extinction
Theories of Causes of the PT extinction