Years of mining for zinc and lead has left Picher, Oklahoma, near the border with Kansas, literally full of holes-including this sinkhole seen in 2008. Some mines were dug too close to the surface, and the roofs were unable to support the weight of earth on top, leading to collapses.
"It has happened in Missouri and in western Pennsylvania from coal mining," Missouri State's Gouzie said. "We've gotten better with buidlng mines so the roofs can support the weight over top of them."

7. Iceland Sinkhole

Swimmers float in the saphirre waters of the Ik-Kil cenote, near the Maya site of Chichén Itzá in Mexico's Yucatán Peninsula. Cenote means "natural well" in Spanish. Sinkholes occurring at sea level will fill up as high as the water table, creating the famous clear blue pools, used by the Maya royalty for both relaxation and ritual sacrifices.

9. Neversink Pit, Alabama



Neversink Pit, a wet limestone sinkhole in Alabama seen above in 1998, is about 50 feet (15 meters) deep and houses a rare species of fern. The sinkhole was bought in the 1990s by a group of cavers to preserve it for future generations.
Karst is the geologic term for landscapes formed mainly by the dissolving of limestone or dolomite bedrock. In the United States, karst underlies parts of Missouri, Arkansas, Kentucky, Tennessee, northern Alabama, Texas, and most of Florida. Such areas are marked by sinking streams, subterranean drainage, large springs, caves-and, of course, sinkholes.