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Weather maps circa 2000 B.C.

By sifting through riverbank deposits in the southwestern United States, a team of geologists has uncovered clues about global weather patterns thousands of years ago. The climate information comes from records of extreme floods, which have left lasting marks along the major rivers in the region.

Geologist Lisa L. Ely of Pennsylvania State University in University Park and her colleagues studied 19 rivers in Arizona and southern Utah and detected evidence of 251 floods during the last 5,800 years. They dated the floods through carbon-14 analysis of organic material and archaeological artifacts preserved in the deposited sediments. Although researchers have traditionally thought that large floods occur at random times, Ely's group found a distinct pattern. The rivers record numerous inundations between 3800 B.C. and 2200 B.C. but none during the next 1,800 years, they report in the Oct. 15 SCIENCE.

The geologists can infer ancient weather patterns from the flooding history because the southwestern United States typically receives its most severe rainfall during years when the tropical Pacific Ocean grows warm, an event called El Nino. The geologic record of floods therefore offers a means of charting the frequency of El Ninos, suggests Ely. She and her colleagues think that researchers could reconstruct broad-scale atmospheric circulation patterns by studying the flooding history of rivers at various points around the globe.
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Title Annotation:global weather patterns inferred from study of ancient floods
Publication:Science News
Article Type:Brief Article
Date:Oct 23, 1993
Words:224
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