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Rocks' heat buoys the U.S.

June 30, 2007|Thomas H. Maugh II | Times Staff Writer

If the rocks under Los Angeles were not unusually warm, the city would rest 3,756 feet beneath the Pacific Ocean, according to Utah geologists.

In fact, without the rocks the only parts of the U.S. that would be above sea level would be the Pacific Northwest and the upper Rockies, they reported Monday in the Journal of Geophysical Research-Solid Earth.

Previously, researchers believed that the inherent density of rocks floating on the earth's molten core was the primary factor in determining the elevation of landmasses.

But new calculations show that temperature is responsible for about half the elevation of land areas, according to University of Utah geologist David Chapman and graduate student Derrick Hasterok .

"Researchers have failed to appreciate how heat makes rock in the continental crust and upper mantle expand to become less dense and more buoyant," like ice floating on water, Hasterok said.

Researchers measured the temperatures at various depths by charting the speed of sound waves, which move faster through cold, dense rock.

The pair based their calculations compared to the relatively cold -- 750 degrees -- crustal rock of the Canadian shield, which underlies most of Canada. Rock under the U.S., in contrast, is 200 to 300 degrees hotter.

If the U.S. rock were the same temperature as the Canadian rock, the Mile High City, Denver, would be 727 feet below sea level; New York would be 1,427 feet below the Atlantic; and Miami would be 2,410 feet underwater. New Orleans would not have to worry about hurricanes; it would be submerged 2,416 feet.

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