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#241655 06/26/07 09:52 PM
Joined: Jan 2003
Posts: 7,479
SimonB Offline OP
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Report: Hot rocks keep N. America afloat By PAUL FOY, Associated Press Writer
Tue Jun 26, 4:26 PM ET

If it weren't for the hot rocks down below Earth's crust, most of North America would be below sea level, report researchers who say the significance of Earth's internal heat has been overlooked.

Without it, mile-high Denver would be 727 feet below sea level, the scientists calculate, and New York City, more than a quarter-mile below. Los Angeles would be almost three-quarters of a mile beneath the Pacific. In fact most of the United States would disappear, except for some major Western mountain ranges, according to research at the University of Utah.

"Researchers have failed to appreciate how heat makes rock in the continental crust and upper mantle expand to become less dense and more buoyant," said Derrick Hasterok, a graduate student in geology and geophysics.

Hasterok and his professor, David Chapman, published their findings in the June online issue of Journal of Geophysical Research-Solid Earth.

In what they said was the first calculation of its kind, the researchers said heat inside the planet accounts for half the reason land rises above sea level or higher to form mountains.

Scientists previously gave other factors greater weight in explaining elevation differences, such as the density and makeup of rocks and tectonic forces.

The Utah team calculated how much of North America would sink if the engine of heat was taken away, leaving regions as relatively cold as the bottom of the vast Canadian shield - bedrock that hasn't changed for billions of years.

They did it by estimating temperatures under the North American plate based on previous experiments that bounced seismic waves deep underground. The waves travel faster through colder, denser rock. That data allowed the researchers to calculate how much of an area's elevation is due to the thickness and composition of its rock and how much is due to the heating and expansion of rock.

Their measurements showed that among coastal cities, New York would drop to 1,427 feet below the Atlantic ocean, Boston and Miami even deeper. Los Angeles would rest 3,756 feet below the surface of the Pacific ocean.

New Orleans, still recovering from Hurricane Katrina's 2005 storm surges, wouldn't have a chance without planetary heat. No levee could protect the city, which would sit 2,426 feet deep in the Gulf of Mexico.

The country's midsection wouldn't be spared, either. Chicago would sink 2,229 feet below sea level. Most of the country, in fact, would disappear, leaving only ridges of the Rocky Mountains and the Sierra-Nevada Range and the western slope of the Cascade Range in the Pacific Northwest.

The Colorado plateau, a major uplift of land driven by 1,200-degree underground heat, consists of much the same layers of rock found deep under the Great Plains, where the base of the Earth's crust is relatively cooler, 930 degrees, the researchers estimated.

Hasterok said the gravitational collapse of the Earth at its formation and radioactive decay drives the engine of heat inside the planet and will stay around for a long time to come.

Even if the planet's interior cooled, it would take billions of years for continents to sink. Coastal areas face a more immediate threat from global warming, which could raise sea levels and flood cities, he said.

SimonB #241661 06/27/07 12:06 AM
Some areas are still rising as they recover from the immense weight of the ice that used to cover them. NW Scotland is a case in point, which is having a fulcrum effect in pushing SE England down.

Plate tectonics is a fascinating and so little understood subject.

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