英语听力：自然百科 死海岸边的致命沙洞

The Dead Sea is the lowest point on earth and runs more than 50 miles in length and stretches 11 miles across its wildest point, bordering Israel, The West Bank and Jordan. Large sections of the coast are fenced off and sign posted in Hebrew and English: Warning of sinkholes.

The sea's dropping water levels is leading to dangerous consequences. In April, an Israeli hiker wandered into an area that had no warning signs and was critically injured when he fell into a sinkhole.

"Due to the rapid drop, the ground water are now facing with the salt rock and the salt rock is undergoing a very rapid dissolution. Cavities(空腔) are formed inside and eventually the surfacecollapses down to these cavities and these are therefore the sinkholes."

Geologist Eli Raz himself became the victim of a sinkhole several years ago.

"(I) just remembered that I was busy by documenting a new sinkhole, and then suddenly I found myself covered by a pile of avalanche on the bottom of a sinkhole."

He spent 14 hours at the bottom before his rescue, and even wrote his will, not knowing he would be saved.

"I just can tell you that it was terrible, very frightened and in the first place, in the beginning, I started to write my will without knowing that somebody will find it of course."

Now Raz is working to save others from the similar fate, leading an effort to map the sinkholes that are spreading on the banks of the saltwater lake.

The formation of the Dead Sea sinkholes are caused by a drop in the sea’s water level due to limited rainfall, the diversion of much needed water from its upstream sources, pollution, and industrialevaporation of water by the Dead Sea mineral industry. As the sea levels drop, high levels of salt are left behind in the soil. When fresh water washes in and dissolves the salts, cavities are created, causing sinkholes.

Detecting potential sinkholes is crucial because they not only damage the environment, but pose a direct threat to the tourist industry and agriculture.

These underground pits can now be better detected by a new monitoring system. The Geophysical Institute(地球物理研究所) of Israel, along with the Geological Survey of Israel, has been trying to locate sinkholes when they are being created and to follow them. The monitoring can help reveal dangerous sinkhole zones in their early stages.

"We developed a methodology of combining geophysical prediction of sinkholes appearing at the Dead Sea costal plane. What we have (as) a problem now is we need to create at least (a) few geophysical teams with the aim of the constant geophysical monitoring of the dangerous area."

When a sinkhole is deemed dangerous, reportedly, crews can fill it in with cement or initiate itscollapse before it would happen naturally.

In the 80 years that records have been kept, the water level in the Dead Sea has dropped by over 65 feet. The sea has shrunk by more than a third. And in the absence of any expensive water replenishment(补充，补给) plan, the sea is expected to shrink to about two thirds of its current size over roughly the next century.