Quenched fire found in Greenland ice.

More than 7,000 years ago, Mount Mazama in Oregon exploded out of existence. In the largest known eruption in the Cascades mountain range, this 12,000-foot peak blew its top--and much of its torso--into the sky, leaving behind Crater Lake, the deepest lake in North America. Researchers have now turned up shards from this eruption deep within the Greenland ice cap, providing clues to how the blast affected the globe.

From past studies of Mount Mazama ash found in western North America, geologists have dated the eruption to within a decade of 7,680 years ago. Christian M. Zdanowicz of the University of New Hampshire in Durham and his colleagues found volcanic debris of just that age in a core of ice extracted from the Greenland's ice sheet in the early 1990s.

The distinct band of volcanic chemicals and ash particles was discovered in a layer of ice dated to 7,676 years ago. Moreover, analysis of the ash shards indicates that they are chemical cousins of volcanic samples taken near Crater Lake, the team reports in the July GEOLOGY.

From the amount of sulfuric acid found in the ice, the researchers estimate that the eruption filled the stratosphere with 88 million to 224 million tons of sulfuric acid droplets. By blocking sunlight, the droplets would have lowered Earth's temperature by 0.6 [degrees] C. The blast also shot up 8.1 million tons of chlorine that would have chewed away part of the protective ozone layer.

"It gives us an idea of what could be expected from a very large eruption along the Pacific Rim of the U.S.," says Zdanowicz.

Geologists have previously tried to estimate the atmospheric effects of the eruption, but the Greenland ice provides a direct measurement of the chemicals that drifted around the globe. "It's probably the best place to learn about that stuff," says Charles R. Bacon, a volcanologist with the U.S. Geological Survey in Menlo Park, Calif., who has studied the Mount Mazama eruption.

While the ancient blast dwarfs the 1980 shot from Mount St. Helens, Mazama doesn't hold a candle to truly giant eruptions. When Bacon compares Mount Mazama to the volume of a half-gallon milk carton, the Mount St. Helens blast would fill half of a small espresso cup and the 1991 eruption of Mount Pinatubo would equal a 6-ounce coffee cup. A giant eruption, like one that occurred in Yellowstone National Park 600,000 years ago, would stuff a 30-gallon garbage can.