Along the shores of the Dead Sea, the solidity of the ground underfoot cannot be taken for granted. In recent years sinkholes, up to 20 meters in depth, have been cropping up at a rapid clip. The collapses have rendered a recreation area unusable and have reportedly trapped a handful of people who required rescue. To get ahead of the problem, a team of scientists identified the signs of an emerging sinkhole from subtle elevation changes in soil. Now they are using those indicators to predict collapses ahead of time.
The sinkhole problem stems from the shrinking of the saline Dead Sea, which thousands of years ago deposited thick layers of salt in the soil. Now fresh groundwater has infiltrated areas left dry by the Dead Sea's retreat, dissolving the ancient salt layers and weakening the ground under former lake bed and shoreline.
To spot developing sinkholes, the scientists monitored the region with radar-equipped satellites and laser-ranging aircraft. Meanwhile one researcher paid regular visits to the study area to spot recent sinkholes.
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Once new basins opened up, the scientists returned to their data bank to identify subsidence—on the scale of millimeters—in the months leading up to the collapse. The team is using those patterns of emergence to sound the alarm about future collapses. “In one case, we alerted the government, and they designed a road that bypasses the sinkhole area,” says study co-author Ran N. Nof, a geophysicist at Tel Aviv University.
It remains to be seen whether the approach would work in Florida and other sinkhole-plagued regions. University of South Florida geologist Timothy Dixon notes that Florida's moist air interferes with radar imagery and encourages vegetation, “which makes it hard to compare one radar image with the next.”
