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March 4, 2008 – Original Source: ScienceDaily

The West Antarctic rift is a region of volcanic activity and crustal stretching that is roughly the size of the western United States (from Salt Lake City to the Pacific Ocean).

About 98 percent of it is buried beneath glacial ice, up to 2.5 miles thick, and bedrock beneath the ice is 2000–3000 feet below sea level over large areas. All of this makes it a difficult region to study.

It is interesting nevertheless, because volcanic eruptions beneath the ice could destabilize the ice sheet, leading to as much as 25 feet of sea-level rise. How likely is it that this could happen is a question scientists have debated for over a decade. LeMasurier addresses the question by comparing the West Antarctic rift with similar areas of crustal stretching elsewhere in the world.

The comparison shows that volcanic activity in rifts is most common where the land is a mile or more above sea level, and rising, which can readily be seen in Antarctica along the Transantarctic Mountains, and in the Pacific coast mountains of Marie Byrd Land. The large sub-sea-level interior of the rift does not, therefore, seem to be a likely place for present-day volcanic activity.

This is good news, because the sub-sea-level base of the West Antarctic ice sheet is already especially vulnerable to warming of the atmosphere and surrounding seas. However, this study also shows that the land in West Antarctica has been rising beneath the ice sheet in some areas and subsiding beneath it in others, over roughly the past 25 million years.

Some areas have subsided to as much as 8500 feet below sea level.

This tectonic restlessness contrasts markedly with the stability of the regions that lay beneath the northern hemisphere ice sheets of the recent geologic past, and its affect on the history of the West Antarctic ice sheet has not yet been evaluated.

The article “Neogene extension and basin deepening in the West Antarctic rift inferred from comparisons with the East African rift and other analogs” by Wesley LeMasurier, Institute of Arctic and Alpine Research, University of Colorado at Boulder, was published in the March issue of Geology ,Pages 247-250.

Adapted from materials provided by Geological Society of America, via EurekAlert!, a service of AAAS.

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