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Dissolving salts lower Dead Sea

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LOS ANGELES — The Dead Sea, already the lowest point on Earth, is sinking even lower.

Areas along the shores of the Dead Sea subsided by as much as 2.5 inches a year between 1992 and 1999, according to a new study. The region on the Israeli-Jordanian border lies about 1,360 feet below sea level.

The subsidence followed a drop in the water table around the Dead Sea, allowing the ground to settle and compact, according to scientists who published their findings in the January issue of the Geological Society of America Bulletin.

Water that would normally flow into the Dead Sea has steadily been siphoned off for agricultural and other uses in the thirsty region. As a consequence, the level of the body of water, among the world's saltiest, has fallen by about 20 feet over the past decade.

The study used seven years' worth of data from a pair of European radar satellites to examine changes in the level of the ground along the southern and western shores of the Dead Sea.

By comparing high-resolution radar images of the same area taken at varying intervals, scientists could pinpoint movements of the Earth that otherwise would be nearly imperceptible, unless the area was peppered with expensive global positioning system receivers that can track the minute changes.

"You wouldn't be able to detect these things any other way," said David Sandwell, a co-author of the paper and a professor of geophysics at the Scripps Institution of Oceanography in La Jolla.

The subsidence may be related, but only circumstantially, to the gigantic sinkholes that have begun to appear along the shores of the Dead Sea, a popular tourist destination, scientists said.

As the salt water of the Dead Sea recedes, in some cases by hundreds of yards, fresh ground water replaces it. That water then dissolves buried salt deposits, causing the ground to collapse and threatening the stability of resort hotels.

Scientists believe a different mechanism explains the larger-scale subsidence. They suspect that when the water table drops in the area, the matrix of soils, sands and gravels that held the water collapses behind it.

Gerald Bawden, a research geophysicist with the U.S. Geological Survey in Menlo Park who was not connected with the study, said the drop was hardly unusual given the dramatic drawdown of the water table.

However, the areas seen to subside in the radar images were just a mile or so in length, or smaller than he would have expected, Bawden said.