National Geographic : 2009 Sep
PHOTO: REUTERS The Sinkhole Truth Something was messing with Texas in May 2008. A dip in Daisetta, a tiny town near Houston, became a hole the size of two football fields, sucking trucks, trees, and build- ings into its 250-foot-deep maw. Residents were shaken; scientists were left shaking their heads. "This exceeds anything I've seen or read about," says the U.S. Geological Survey's Mark Kasmarek. Few sinkholes match Daisetta's drama, and the cause of most is debatable. But gradual or sudden, natural or human abetted, sinkholes can occur anywhere rocks can dissolve. Groundwater eating away at soil or bedrock, a cave roof collapsing, a company injecting chemicals into a salt dome---sinkhole recipes all. Some countries, like Italy and Jamaica, are geologically primed for sinkholes. So is about a fifth of the U.S., notably limestone-rich Florida and salty Texas. But knowing where to look isn't the same as knowing when. As geophysicist Carlos Aiken says, "There's no early warning system." Nor is there a typical outcome. While some big holes have been turned into landfills, others, like Daisetta's, become lakes---and possible rest stops for migratory fowl. ---Jeremy Berlin In 2007, a giant sinkhole in Guatemala City claimed three lives and swallowed several houses. SCIENCE HOW HOLES SINK IN Cover-collapse sinkholes occur abruptly, often when an underground cavity gives way and surface clay falls in. Cover-subsidence sinkholes develop gradually as sandy surface sediment falls into cavities in the bedrock below. Dissolution sinkholes are similar to subsidence ones, except exposed bedrock wears away at the surface.