Dec. 9, 1998 CHAPEL HILL - Scientists have known for decades that large erupting volcanoes such as Mt. St. Helens in Washington and Mt. Pinatubo in the Philippines can alter climate by spewing smoke, gases and ash into the atmosphere.
Now new evidence indicates that the opposite also occurs - that environmental change can trigger volcanic eruptions. Over the past 800,000 years, a new study shows, glaciers prompted eruptions after they retreated north.
Dr. Allen F. Glazner, professor of geological sciences at the University of North Carolina at Chapel Hill, reported results of field and laboratory research at the American Geophysical Union's fall meeting in San Francisco Tuesday (Dec. 8).
"When we looked at almost the last million years of geologic activity in eastern California, we found that volcanoes tended to erupt between glacial cycles," Glazner said. "When the glaciers were present, the volcanoes were pretty much subdued. When the glaciers retreated, volcanoes became much more active."
Earlier research had shown a similar pattern around islands and along coastlines, but the new study is the first to show it happens far inland as well, he said.
How glaciers suppress eruptions is not known, Glazner said.
"One possibility is that all the extra weight of the glacial ice holds the magma, or molten rock, in place," he said. "Then when the ice melts and the water evaporates, less weight on the Earth's crust triggers volcanoes to erupt."
The UNC-CH scientist, who has been studying California geology for many years, said the newest work involved three years of chipping samples from volcanoes east of the Sierra Nevada and both dating the lava specimens and analyzing them chemically. He and his colleagues also analyzed previously gathered data.
"We are interested in the connection between a natural process - volcanism - and climate, in part because we want to know how much of the recent global warming is due to people burning fossil fuels and how much is just natural," Glazner said. "This past year, for example, has been the warmest on record, and some people are concerned about it."
Others involved in the study were Drs. Curtis R. Manley of geological sciences and Steve Marron of statistics, both at UNC-CH, Lang Farmer of the University of Colorado and Stuart Rojstaczer of Duke University.
The National Science Foundation and the Geothermal Program Office of the China Lake Naval Weapons Center supported the research. The U.S. Navy funds Glazner's work because the China Lake center lies near several young volcanoes that the federal government taps for geothermal energy. It also tests missiles there.
"Data indicate a lot of volcanic activity since the glaciers last retreated about 10,000 years ago, and recent increasing earthquake activity raises the possibility of eruptions in the Mammoth Lakes area of eastern California in the not-too-distant future," Glazner said. "Many people have moved there for skiing, mountain biking and the dry climate."
In the past million years in the Northern Hemisphere, glaciers have moved south about 10 times, he said.
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