Glaciers Can Suppress Eruptions.

• Position: Brief Article

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. Newly discovered evidence indicates that the opposite also occurs--that environmental change is able to trigger volcanic eruptions. Over the past 800,000 years, glaciers prompted volcanic eruptions after they retreated north, indicates Allen F. Glazner, professor of geological sciences, University of North Carolina at Chapel Hill.

"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. When the glaciers were present, the volcanoes were pretty much subdued. When the glaciers retreated, volcanoes became much more active." Earlier research had found a similar pattern around islands and along coastlines, but the new study is the first to show how it happens far inland as well.

How glaciers suppress eruptions is not known, Glazner admits. "One possibility is that all the extra weight of the glacial ice holds the magma, or molten rock, in place. Then, when the...