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Unearthing early El Ninos.

Unearthing early El Ninos

Scientists know that an El Nino upsets world weather patterns every seven years or so as the warm equatorial waters of the Pacific Ocean are directed toward the Americas. But they haven't been able to predict the exact timing or severity of El Ninos with any great success, largely because detailed meteorologic records have been kept only for a few decades. So a number of scientists are turning to the geologic record for traces of El Ninos that occurred in the more distant past.

One such study is being conducted at a site on the coast of northern Peru by Lisa E. Wells of Stanford University. Wells has examined the sheets of mud that were deposited by swollen rivers during the last El Nino, in 1982 and 1983; that El Nino and all others are thought to be the only causes of flooding along the normally arid Peruvian coast, she says. By noting the characteristics of these sheets, Wells learned to recognize the flood deposits left by major El Ninos in the past. At one study site, she has identified at least 11 large events that occurred in the last 10,000 years.

"I think there are significant events on a 100-year interval that come through this site, but events that actually flood the entire floodplain occur roughly every 1,000 years," she says.

Wells notes that rivers to the north of her study site usually flood more often during El Ninos. She thinks that a record of smaller, more frequent events may be preserved in these areas. Other researchers are searching for geologic traces of El Ninos in Australia and the Galapagos. These types of studies, she says, may help scientists understand the conditions that foster El Ninos and help address questions such as whether El Ninos occurred during periods of glaciation.
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Author:Weisburd, Stefi
Publication:Science News
Date:Nov 29, 1986
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