News: Earth's inner heat keeps cities afloat.

Earth's inner heat keeps cities afloat

http://news.yahoo.com/s/ap/20070627/ap_on_sc/hot_rocks_17;_ylt=AjOegRN7DX6QbphW_MuAvVyFDvII

By PAUL FOY, Associated Press Writer 16 minutes ago

SALT LAKE CITY - 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 the area west 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.

Their scenario actually lifts Seattle and the Pacific Northwest. The
region sits on a cold slab of oceanic crust that is diving under the
continent, insulating the land mass from the Earth's heat. It would
rise if the crust was warmed to a temperature equal to the warmer
bottom of the Canadian shield.

The Seattle scenario is puzzling but emphasizes a region that's on a
different tectonic plate than the rest of the West Coast, said Barbara
EchoHawk of Geological Society of America.

The researchers used the Canadian shield ? "a special, stable and cool
area of rock" ? as their statistical baseline for the effect of
removing heat from under the continent. The slab under Seattle,
however, is colder than the Canadian shield, so it would be the only
U.S. region to rise under this analysis, she said.

Hasterok said heat from Earth's deep interior and from radioactive
decay of uranium, thorium and potassium in Earth's crust 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.

--
Bob.

.

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