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Sci Tech
Why active mountains don't get taller
The higher and steeper the mountains, the greater the slope and the more material transported away to the oceans.
ACTIVE MOUNTAIN ranges like the Olympic Mountains, Taiwan Central Range or the Southern Alps are still growing, but they are not getting any taller. According to an international team of geoscientists river cutting and erosion keep the heights and widths of uplifted mountain ranges in a steady state. The team reports the results in the journal Science. "These mountains grew to 2.5-3 miles high over the past few million years and then they stopped increasing," says Rudy Slingerland, a geologist at Penn State University.
Mountain ranges form near the border of two tectonic plates, the large moving sheets of rock that cover the earth's surface. When one plate slides beneath the other, or subducts, a veneer of rocks on the subducted plate is scraped off and piles up to form the mountains. Even though tectonic plates subduct for tens of millions of years, mountain ranges usually stay between 2.5 and 3 miles high and about 75-150 miles wide.
This is because the slopes become steeper as the mountains grow in elevation and more material erodes away via landslides, river cutting and other forms of erosion. The higher and steeper the mountains, the greater the slope and the more material transported away to the oceans.
``People inhabit high mountain regions, and understanding unstable landscapes is a key for their survival and for the preservation of fragile mountain ecology,'' says Herman Zimmerman, director of NSF's earth sciences division. ``These earth processes are also critical factors for the water supply of people living in cities and towns many hundred of miles from the mountains.''
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