Newspaper article The Christian Science Monitor

Glaciers, Known for Erosion, Can Help Mountains Grow

Newspaper article The Christian Science Monitor

Glaciers, Known for Erosion, Can Help Mountains Grow

Article excerpt

Glaciers' 'buzz-saw effect' can level mountains. But at high altitudes, glaciers can freeze to mountains and shield against erosion, new research suggests.

Mountain glaciers have long been recognized as powerful agents grinding down the craggy landscapes they occupy.

But new research suggests that under the right conditions, long- lived mountain glaciers and ice caps also can facilitate the growth of mountains - highlighting the role global climate change on multi- million-year time scales can have on the tectonic processes that stretch, knead, and fracture Earth's fragile crust.

In short, if conditions are cold enough, large-scale glaciers freeze to the land beneath them, significantly slowing the glaciers' movement downslope and substantially reducing the amount of erosion the mountain might otherwise experience. They protect the mountain as it grows, rather than scrape away at it.

That leaves the forces driving the growth of a mountain range free to build the peaks at a faster rate than glaciers whittle away at the summits.

Scientists have observed frozen-base glaciers in mountains in Antarctica and northern Canada. But these mountains are no longer are rising. The new study, published in the latest issue of the journal Nature, represents the first time scientists have been able to document the influence such glaciers have on mountains that are still rising at a geologically speedy clip.

The results "were quite surprising," says Stuart Thomson, a geologist at the University of Arizona in Tucson who led the team of US and Chilean scientists exploring the role of the effect of long- lived mountain glaciers on the evolution of mountain ranges.

The team was gathering data to test an idea dubbed the glacial buzz saw. In effect, the notion holds that glaciers limit the height mountain ranges can achieve. As the crust buckles under the inexorable force of crustal plates colliding, mountains build, finally reaching altitudes where they can sustain a long-lived snow and ice pack. Over time, that frigid caps thickens and form glaciers that flow down the mountainsides carrying large amounts of crushed rock and boulders with them.

The overall effect is to lower the mountain range's average height and narrow its base relative to the surrounding landscape.

The team selected as its laboratory the Andes in Patagonia, a region that arguably helped give rise to modern geology and geophysics through Charles Darwin's first studies of the region in the mid 1830s. …

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