WITH a thunderous roar, hundreds of tons of dirt and rock dropped from sight, tossing trees around like matchsticks and leaving the yawning, lunar-like crater shown above. Now, after investigating the massive cave-in, which occurred last December in central Alabama's Shelby County, the U.S. Geological Survey has identified the crater as a "sinkhole." It may be the largest yet (as much as 425 ft. across and 150 ft. deep) in a growing number of such cave-ins that have pockmarked central and northern Alabama in recent years. Sinkholes often occur when the roofs of underground limestone caverns suddenly collapse. Government scientists are...
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