Warm rock keeps North America from drowning, geologists say
Jun 29,2007 00:00 by Bend_Weekly_News_Sources

Much of North Amer­i­ca would be un­der­wa­ter were it not for heat that makes rock buoy­ant, new re­search in­di­cates. Sci­en­tists list­ed var­i­ous parts of the con­ti­nent that stay afloat thanks to heat with­in Earth’s rocky crust, and how far those re­gions would sink be­neath sea lev­el if they lacked that heat-in­duced lift.

On the coast, New York City would sit 1,427 feet (435 me­ters) be­low the At­lan­tic; New Or­leans 2,416 feet (736 me­ters) un­der­wa­ter and Los An­ge­les 3,756 feet (1,145 me­ters) be­neath the Pa­cif­ic, re­search­ers said. 

Rath­er than perched a mile high (1.6 kilome­ters), Den­ver would be 727 feet (222 me­ters) be­low sea lev­el.

“If you sub­tracted the heat that keeps North Amer­i­can eleva­t­ions high, most of the con­ti­nent would be be­low sea lev­el, ex­cept the high Rocky Moun­tains, the Si­er­ra Ne­vada, and the Pa­cif­ic North­west west of the Cas­cade Range,” said Der­rick Has­terok of the Un­ivers­ity of Utah in Salt Lake City, a re­searcher on the stu­dy.

Typ­ic­ally, ge­ol­o­gists at­trib­ute dif­fer­ences in eleva­t­ion to move­ments of sec­tions of the Earth’s crust called tec­ton­ic plates, mountain-building col­li­sions, and sink­ing or “sub­duc­tion” of old seafloor. But Has­terok and his Un­ivers­ity of Utah co­au­thor Da­vid S. Chap­man say tec­ton­ic forc­es con­trib­ute to eleva­t­ion by af­fect­ing the com­po­si­tion and tem­per­a­ture of rock that they move. For ex­am­ple, as crus­tal plates col­lide to form moun­tains like the Him­a­la­yas, the moun­tains rise be­cause the col­li­sion makes lighter crus­tal rock get thicker and warm­er, thus more buoy­ant.

“We have shown for the first time that tem­per­a­ture dif­fer­ences with­in the Earth’s crust and up­per man­tle ex­plain about half of the eleva­t­ion of any giv­en place in North Amer­i­ca,” with most of the rest due to dif­fer­ences in what the rocks are made of, Chap­man said. The find­ings were pub­lished on June 23 as two re­ports in the Jour­nal of Geo­phys­i­cal Research-Solid Earth.

Courtesy American Geophysical Union and World Science staff