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Prehistoric Cameroon-style lake events.

Prehistoric Cameroon-style lake events

In 1986, a large cloud of carbon dioxide burst out of Lake Nyos in Cameroon and swept down a hillside into a populated valley, killing 1,746 people (SN: 6/20/87, p.388). Two years earlier, a similar but less damaging event had occurred at another crater lake in Cameroon. In the earth's 4 1/2-billion-year history, is it possible that the Cameroon disasters are the only examples of this type of phenomenon?

Geologists don't think so. In fact, James D. White and Richard Fisher of the University of California at Santa Barbara report that an ancient crater lake in northeast Arizona may have behaved in a fashion similar to the Cameroonian lakes. Most scientists believe that carbon dioxide enters these crater lakes from volcanic chambers of molten rock, located far below the lake bottoms. Over thousands of quiescent years, the gas concentrations increase in the bottom of the lakes. Finally, a rock slide or some other disrupting event overturns the stratified sections of the lake, releasing the dissolved gas.

A cloud will dissipate without leaving any permanent marks in the rock record. But at the Arizona lake, White and Fisher think they have discovered evidence of the huge waves that would accompany a gas release. They found large dunes of coarse-grained sediment, 5 million to 6 million years old, near the sides of the dry lakebed; preserved in the dunes are patterns of strong water currents that flowed in many directions. Flash floods or waves generated by earthquakes could not account for such strong waves, says White. These formations do not on their own prove that a Cameroon-style overturn occurred in the lake, but such evidence will help scientists identify other possible sites of previous lake overturn.
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Author:Monastersky, Richard
Publication:Science News
Date:Nov 21, 1987
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