Erupting lakes recharge r The Associated Press ' There's new evidence that two Cameroon killer lakes Nyos and Mpnoun are being recharged with deadly carbon dioxide. In August 1986, Nyos, a jewel-like crater lake, erupted with a burst of deadly carbon-dioxide gas that killed 1,700 people. Smaller Monoun, 59 miles to the south, had already stunned the West African nation two years earlier with an outburst that left 37 dead. Probes of Lake Nyos's bottom waters by a team of U.S. scientists show a 26-percent buildup of carbon dioxide since May 1987. "It's a stick of TNT waiting to go off," concludes research scientist George W. Kling, who recently finished his analysis of Lake Nyos water samples at the Marine Biological Laboratory in Woods Hole, Mass. "Our data is still incomplete but we think Monoun is recharging too," says Michele L. Turtle, a U.S. Geological Survey research chemist and a member of the scientific team that is studying the lakes. Some scientists have argued that the 1986 release of gas from Lake Nyos was caused by a volcanic eruption. - Kling and his colleagues are now convinced that carbon dioxide, formed deep inside the earth, feeds into the lake from one or more underground springs. But differences in water temperature and mineral concentrations keep the gas near the bottom of the lake. ' The lake's waters form two layers. The weight of the upper layer acts as a lid and holds the gas on the bottom until a violent event such as a landslide, an earth tremor, or a volcanic eruption stirs the supercharged bottom waters upward. The result is n (hi . Associated Press Lake Nyos looks tranquil but is a menace, scientists say. a violent, foaming eruption much like the uncorking of a warm bottle of champagne. A dense, colorless gas, carbon dioxide weighs one and a half times as much as air. A concentrated form is used in fire extinguishers because it pushes air aside and robs fire of the oxygen needed for burning. These consequences were "evident at Lake Nyos. The eruption of lake gas formed a ground-hugging cloud that, as it moved, pushed aside breathable air. A similar thing happened at Lake Monoun. In both cases, the victims were robbed of oxygen and asphyxiated. A shallower and smaller lake than Nyos, Monoun doesn't have the capacity to release as much gas as its neighbor. Yet, a future eruption could be just as deadly as the last, depending on wind direction. "If another event occurs and the wind is blowing south, it would carry the gas right into a small village," says Kling, whose work in Cameroon has been supported by the National Geographic Society. So far, the Lake Nyos and Lake Monoun tragedies are the only recorded events in which gas released from lakes has caused the loss of human lives. Even without the gas, Lake Nyos's waters are a threat Any fu-' ture disaster at the lake might undermine a natural dam of soft volcanic rock that holds the lake within the crater. "The dam has been steadily eroding since its formation about 400 years ago," says John Lockwood, a volcanologist at the U.S. Geological Survey's Hawaiian Volcano Observatory. "Its collapse would be like letting the Mississippi River rampage for a half hour or so. Flood waters from Lake Nyos would probably reach Nigeria, 65 miles away." Lockwood advocates installing a pipe on one side of the lake that would carry out water, lowering the level enough to prevent a flash flood if the fragile spillway collapses. An even bigger time bomb may be ticking miles away in a larger lake that stores a lot more carbon dioxide than its counterparts in Cameroon. Nearly 50 miles wide, Lake Kivu fills the rift between Zaire and Rwanda and the area around it is heavily populated. Bacterial action converts much of Kivu's carbon dioxide to methane, which can be burned as fuel. A Rwandan brewery already fuels its boilers on lake methane. "I'm most concerned about the possibility of a volcanic eruption below this lake," says Lockwood. "That could trigger both carbon dioxide and a deadly fire storm from burning methane." The resulting fireball would devastate the densely populated lake basin.