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Without Hot Rock, Much Of North America Would Be Underwater


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Kara Sundstrom
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« on: December 20, 2008, 12:09:37 am »

Why it is Important to Know How Heat Affects Elevation

The new study's scientific significance is that by accounting for composition, thickness and, now, temperature of crustal rock in North America, scientists can more easily determine how much elevation is explained by forces such as upwelling plumes of molten rock like the "hotspot" beneath Yellowstone, and places where vast areas of mantle rock "dripped" down, letting mountains like the Sierras rise higher.

The new method also will make it easier to identify areas where crustal rocks are unusually hot due to higher-than-average concentrations of radioactive isotopes.

Chapman says temperatures in Earth's crust and upper mantle often are inferred from measurements in boreholes drilled near the surface, while elevation reflects average rock temperatures down to 125 miles beneath Earth's surface. Inconsistencies in both measurements can be used to reveal the extent to which borehole temperatures are affected by global warming or changes in groundwater flow.

Elevation increases in a given area could provide notice -- tens of millions of years in advance -- of volcanic processes beginning to awake deep in the lithosphere, he adds.

Most Regions Would Sink, but Seattle would Soar

Some locations -- sitting atop rock that is colder than average -- actually would rise without the temperature effect, which in their case means without refrigeration.

Instead of its current perch along saltwater Puget Sound, Seattle would soar to an elevation of 5,949 feet. Seattle sits above a plate of Earth's crust that is diving or "subducting" eastward at an angle. That slab of cold, former seafloor rock insulates the area west of the Cascades from heat deeper beneath the slab. Removing that effect would warm the Earth's crust under Seattle, so it would expand and become more buoyant.

To calculate how elevations of different regions would change if temperature effects were removed, the researchers did not remove all heat, but imagined that region's rock was as cold as some of North America's coldest crustal rock, which still is 750 degrees Fahrenheit at the base of the crust in Canada.


Here are other locations, their elevations and how they would sink if their crust had the same temperature:

Atlanta, 1,000 feet above sea level, 1,416 feet below sea level.
Dallas, 430 feet above sea level, 1,986 feet below sea level.
Chicago, 586 feet above sea level, 2,229 feet below sea level.
St. Louis, 465 feet above sea level, 1,499 feet below sea level.
Las Vegas, 2,001 feet above sea level, 3,512 feet below sea level.
Phoenix, 1,086 feet above sea level, 4,345 feet below sea level.
Albuquerque, 5,312 feet above sea level, 48 feet above sea level.
Mount Whitney, Calif., tallest point in the lower 48 states, 14,496 feet above sea level, 11,877 feet above sea level.
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