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Volcanic history in the Aleutian arc.

Volcanic history in the Aleutian arc

Benjamin Franklin was probably thefirst to suggest a correlation between volcanic eruptions and changes in the global climate when he proposed that a 1783 volcanic eruption on Iceland had induced abnormally cold temperatures later that year. More recently, scientists have accused volcanic eruptions of causing the yearly depletions of polar ozone and even the extinction of the dinosaurs. However, to support volcano-climate theories, scientists must rely on an incomplete and often sketchy list of the major eruptions in the earth's history, says Thomas P. Miller of the U.S. Geological Survey (USGS) in Anchorage, Alaska.

In the May GEOLOGY, Miller and RobertL. Smith, a USGS colleague from Sacramento, Calif., report results that fill in some of the gaps in the eruption chronology. Their study will help climatologists confirm or deny that volcanoes had caused certain prehistoric climate changes, says Miller. He and Smith have identified and dated 12 large eruptions--11 of them previously undated or poorly documented--in the eastern Aleutian arc, a volcanically active boundary between the Pacific plate and the North American plate.

Using carbon-14 dating, the researcherspinpointed the age of organic material either charred by the eruptions or buried under the debris. From these dates, they determined that most of these eruptions occurred relatively recently, within the last 10,000 years. Eight of those eruptions and two earlier ones were large enough "that they must be considered in hypotheses linking large eruptions and climate changes in the late Quaternary [last 100,000 years] time,' write the USGS researchers.

Volcanic eruptions influence global climateby ejecting sulfur dioxide into the stratosphere. When this combines with water, it forms small, stable droplets of sulfuric acid, which interact with solar radiation and raditation from the earth, thereby affecting global temperatures.

This study of the Aleutian volcanichistory, says Thomas Simkin, a geologist with the Smithsonian Institution in Washington, D.C., will also aid those who assess the potential hazard from future volcanic eruptions.

Photo: View of Alaska's Aniakchak caldera,formed by the collapse of a volcanic cone during an eruption about 3,400 years ago.
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Author:Monastersky, Richard
Publication:Science News
Date:Jun 6, 1987
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