http://www.washingtonpost.com/wp-srv/WPlate/2000-01/31/100l-013100-idx.html

Pipes Will Help Volatile 'Killer Lakes' Vent

By David Brown Washington Post Staff Writer Monday, January 31, 2000; Page A09

Lakes are not the kind of things one normally thinks of as explosive. But we live in a strange and wondrous world, and in the fullness of time nearly everything happens. At 9:30 p.m. on Aug. 1, 1986, Lake Nyos, in northwest Cameroon, exploded, killing 1,700 people and 3,000 cattle.

Although nobody witnessed the event, survivors in the valley below recalled hearing a rumble that lasted about 20 seconds. Evidence gathered several days later strongly suggested that a fountain of water and foam rose about 300 feet above the lake's surface. At one end, a wave of water at least 80 feet tall scoured the rocky shore.

The explosion wasn't triggered by a volcanic eruption or, directly at least, any other incendiary force. Instead, it was the result of the upwelling of water laden with carbon dioxide gas from deep in the lake. Freed of the pressure keeping it in solution, immense quantities of the gas simply bubbled out, dragging water with it.

The effect was similar to what occurs when an agitated bottle of beer is rapidly uncorked. Only in this case, the bottle was a mile and a quarter long, three quarters of a mile wide and 610 feet deep--and had five times as much carbonation.

It was not the explosive force, however, that was responsible for the fatalities. It was the carbon dioxide itself. Heavier than air, it poured over the lip of rock surrounding the lake and slithered down the valley like a serpent emerging from its burrow. Carbon dioxide normally makes up 0.03 percent of air, and concentrations of 10 percent or more can be fatal. People and animals up to 16 miles away were simply asphyxiated in their tracks.

The explosion of Lake Nyos is one of the strangest natural disasters in recorded history. Curiously, however, it isn't unique. Two years earlier, Lake Monoun, 60 miles to the southeast, exploded, killing 37 people. Geologic evidence from the shores of Nyos suggests that it, too, had exploded at least once before 1986.

Nor has the danger passed. Carbon dioxide, vaporizing from melted magma 50 miles below the lakes' bottoms, is seeping back into their water. Research done in 1994 found that the gas is accumulating at a rate that makes an explosion at Monoun likely in less than 10 years, and at Nyos in less than 30.

Now, however, an international team of scientists is trying to prevent the inevitable. Later this year, it will install two startlingly low-tech devices intended to defuse what have become known as the "killer lakes of Cameroon."

On each lake, they will place a floating platform holding a pipe 5.5 inches in diameter, one end of which will be lowered to the lake depths. Bottom water, loaded with dissolved carbon dioxide, will then be drawn up the pipe. As it gets near the surface it will effervesce, creating a self-powering fountain. The biggest cash contributor to the project is the U.S. Agency for International Development, whose Office of Foreign Disaster Assistance will provide $433,000. The governments of Cameroon and Japan will also provide services.

This strategy to vent off the lakes' gas in a controlled way won't immediately make them safe. With a single pipe, it will take five years to "degas" Monoun. Nyos, which is much larger, will need two or three pipes to reduce its gas content. A single vent--which is all the project's current budget permits--will do little more than keep up with Nyos's annual carbon dioxide accumulation.

Nevertheless, the project is a rare preemptive strike at natural disaster.

"With hurricanes, tidal waves and earthquakes, we are essentially limited to going in after and picking up the pieces. With this, we have the opportunity to mitigate the hazard before there is a loss of life," said George W. Kling, professor of biology at the University of Michigan, who is the head of the scientific team.

As their bizarre behavior attests, Nyos and Monoun are highly unusual bodies of water. They are two of only three lakes in the world known to store dangerous concentrations of gas in their deep water. The third is Lake Kivu, on the Congo-Rwanda border in Central Africa. In addition to carbon dioxide, it contains vast quantities of methane, the flammable hydrocarbon known as "natural gas." Kivu contains so much methane, in fact, that the gas is vented from the depths, captured and sold.

Why and how these lakes store gas is a fascinating lesson in elementary physical chemistry.

Carbon dioxide reaches the earth's surface in many places, seeping upward through fissures from Earth's mantle layer, where it is formed. When the gas is discharged in shallow groundwater, it's called "soda springs." Nyos, Monoun and Kivu happen to be places where carbon dioxide reaches the "surface" not on land, but at the bottom of a lake.

Why the gas stays in the water is a little more complicated.

The amount of gas that can be dissolved in water without forming bubbles depends on two things, the water's temperature and pressure. The colder the water, the more gas can dissolve in it. But pressure is the bigger determinant.

A column of water 10 meters high (about 32 feet) exerts pressure equivalent to that of the entire atmosphere above Earth's surface. At the bottom of Lake Nyos, there are about 22 atmospheres of pressure--21 of water and one of the atmosphere itself. Consequently, far more carbon dioxide can dissolve in a gallon of bottom water than in a gallon of surface water.

That wouldn't be a problem if the bottom water occasionally got to the surface, where it could release the gas. Like many tropical lakes, however, Nyos never experiences the seasonal "turnover" seen in temperate regions. In that process, winter cools a lake's surface water, which then becomes more dense and drops to the bottom, forcing bottom water to the top.

"Lake Nyos is virtually a layer cake," said William C. Evans, a research chemist with the U.S. Geological Survey in Menlo Park, Calif., who is also on the international scientific team. "You have horizontal mixing within layers, but you don't have much vertical mixing."

As it happens, the more carbon dioxide that is dissolved in Nyos's deep water, the more "stably stratified" the lake becomes. That's because a small proportion of the gas reacts with water to create a weak acid, which in turn reacts with minerals in the lake bottom to form salts. It's so dense that even though the bottom water is about 2 degrees warmer than the surface, that water never rises.

The bottom water of Nyos is now 60 percent saturated with carbon dioxide gas, and the bottom water of Monoun about 83 percent. When they reach 100 percent saturation, gas will bubble out spontaneously, making an explosion inevitable. Even before then, however, they could explode. A rock slide or earth tremor that disturbs the water layers could trigger one. What triggered the 1984 and 1986 eruptions is unknown. What is certain is that a stupendous amount of potential energy is stored in the lakes' depths.

The scientists estimate that the water-and-gas mixture will exit the pipes at a velocity of about 200 miles per hour. The fountain will rise about 80 feet in the air.

"If you put generators on the surface, you could produce megawatts of energy," Kling said recently. "You could rim the lake with lights so you could see it from space."

-- Homer Beanfang (Bats@inbellfry.com), January 31, 2000

Answers

Thank you Homer,
Just when you thought it was safe to go back in the water. BLAM!!!

I vote this best off-topic post of the day.

-- Possible Impact (posim@hotmail.com), January 31, 2000.

Thank You.,Homer.Learn somethin'every Day.Just amazing Story.

-- Liberator (Feeding@the Trough.com), January 31, 2000.

Interesting article. But I am confused about the statement that CO2 makes up 0.03 percent of the atmosphere. Three hundredths of a percent? I am almost sure it is considerably more than that. Don't plants need it for photosynthesis (or whatever it is they do most of the time)? And aren't we constantly exhaling it?

Maybe some of the more scientific among us can give an authoritative answer.

regards,

gene

-- gene (ekbaker@essex1.com), January 31, 2000.

i wonder if this is a similar phenomenon (only on a much larger scale) we witnessed in maine when we noticed a lake "turning over". it was very strange. all of a sudden the lake started steaming and bubbling and then the whole lake sort of flipped over--the contents of the bottom of the lake all ended up on top. i guess it happens when the decaying matter on the bottom of the lake gets warmer than the top of the lake/also possibly creating co2?

i know, i know. right up there with aliens and contrails.

-- tt (cuddluppy@aol.com), January 31, 2000.

I second the motion for best OT topic - Fascinating - Thanks, Homer

-- Guy Daley (guydaley@bwn.net), January 31, 2000.