Killer Belching Lakes in Cameroon Poised to Erupt With Lethal Gas
10.43 a.m. ET (1443 GMT) September 14, 1999 By Amanda Onion NEW YORK
It emerged like a giant phantom from the lake, slinked down the valley for 13 miles and killed almost every living creature in its path, including 1,746 people and thousands of cattle.
When the gas cloud struck at about 9 p.m., livestock and people laid down and died by asphyxiation
The eruption of lethal mist at Cameroon's Lake Nyos in 1986 was so sudden and mysterious that many attributed it to a spiritual disturbance. Villagers offered sacrifices of young fowl to an angry Mammy Water, a spirit woman in local folklore who inhabits lakes and rivers.
Scientists puzzled for weeks before attributing the devastation to a massive burst of carbon dioxide. They found carbon dioxide levels had accumulated at the lake's bottom to such a degree that it exploded up through the lake and into the air.
Now, 13 years later, scientists fear it may happen again.
"These lakes are just time bombs waiting to go off," said George Kling, a limnologist at the University of Michigan who was one of the first scientists at the scene in 1986. "They could go off tomorrow, they may go off next year, they may have gone off yesterday and we just haven't heard yet."
Measurements show the amount of carbon dioxide at the bottom of the 700-foot deep Lake Nyos is even higher than what exploded from the waters in 1986. And one month ago, a small earthquake triggered a mini-release of gas that left scores of fish floating dead at the water's surface. Kling worries there's more to come.
Not far away, carbon dioxide levels at Lake Monoun are also reaching volatile levels. Lake Monoun exploded in 1984 in the only other recorded CO2 burst in history, killing 37 people.
"If a volcano erupts everybody knows it and runs away from it," said Jack Lockwood, a volcanologist who has inspected all three lakes for the United States Geological Survey. "When a lake de-gasses, people may be having dinner and they just fall asleep and never wake up. It's insidious."
Sudden gas bursts are as rare as they are mysterious. Only one other lake, Lake Kivu in East Africa, holds the potential for a similar disaster. The natural disaster is so unusual because several factors are required to create a CO2-volatile lake.
The first is a stable climate. Lakes in any temperate region mix twice a year in fall and spring when water temperatures at the top and bottom of the lake equalize. As top and bottom waters mix, gasses dissolved in the colder bottom waters are released gradually and harmlessly into the air.
In regions where temperatures remain steady, however, lakes can become heavily stratified divided by temperature differences in the water. Since cold water is denser than warm water, it remains at the bottom while the upper layers remain warm. In deeper lakes, mixing is further reduced since more energy is required to bring denser, colder water up to the surface.
Lakes Nyos, Monoun and Kivu are all deep lakes in nontemperate regions that are also located near active volcanoes. Even when a volcano is not erupting, it constantly releases gases from its steamy plumbing underneath. CO2 from the volcano's inner magma dissolves into stream water, which then feeds directly into the bottom of the lakes. Here, the pressure of waters above keep the CO2 captured in the bottom waters the way carbon dioxide is contained in bottled soda and beer.
Shake up a can of soda and fast-escaping gas can make a mess. That's because once CO2 is released from solution, it rises. As it moves upward, pressure above decreases, it gains speed and more gas is released, causing it to rise even faster.
When Lake Nyos degassed 13 years ago, fast escaping carbon dioxide from the lake's bottom created a fountain that rose nearly half a mile above the surface of the lake. That fountain then produced an 80-foot surface wave.
Kling believes there were two explosions at Nyos. The first released a steamy cloud of CO2 into the lake's basin that spilled down into the valleys below. Then a second, more powerful burst occurred when even more gas-heavy water was disturbed at the lake's bottom. Eyewitnesses reported hearing a giant rumbling from the lake at the second explosion.
But most never heard a thing.
Carbon dioxide is harmless at moderate levels. Mammals exhale the gas, and it gives beverages their fizzle. It's also commonly used in fire extinguishers since it is denser than air and smothers a fire by pushing away oxygen as it spreads.
But it can be very deadly. When it emerged from Lake Nyos in 1986, the immense cloud of carbon dioxide killed its victims as it pushed away oxygen. Survivors recalled only falling asleep as the CO2 cloud passed by.
In October, a team of researchers, including Kling, plan to travel back to Lake Nyos and Lake Monoun to try and effectively "burp" the lakes of their excess CO2. Using $400,000 from the U.S. Department of Foreign Disaster Assistance, the team will install pipes at both lakes. Each pipe will provide a passageway from the lakes' bottoms, where gas has accumulated, to the surface. Once a pump starts the system flowing, the force of escaping gas should provide enough boost to keep it flowing from the bottom continuously.
Kling estimates one pipe will be enough to drain Lake Monoun of its excess CO2 in five years. But one pipe may not be sufficient to drain Lake Nyos. Calculations show that at least 10 pipes will be needed to drain that lake within 20 years.
Until then, some 3,500 villagers from the Lake Nyos region remain refugees, banished from their homes in case the lake explodes again. Some, especially near Lake Monoun, have disregarded the warnings and moved back into their lakeside homes. And since many attribute such hazards to spirits, there is little officials can do to convince them to leave.
"One man at Lake Monoun told us his father was a fisherman on this lake and his father's father was a fisherman," Kling recalled. "He said he had no choice but to fish the lake too."
One can only hope that Mammy Water isn't angered again soon.
Ah, Africa. The land of dangerous carnivores, rampant disease and famine, and now giant killer belching lakes.
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