December 12, 2001
On occasion, sinkholes can suddenly open up and swallow cars and homes. However, quite often their presence isn't so obvious. On the photograph above, a group of mature trees appear to be growing in a depression, but they're actually sinking into a pit just beneath the surface, which is in the act of collapsing. The photo was taken in southern Missouri and is an example of karst topography. Sinkholes are common where the rock below the surface is limestone - rocks that can naturally be dissolved by ground water circulating through them. As the rock dissolves, small pits or large caverns may form underground. Eventually, when there's insufficient support for the land above the pit, it'll collapse. Sinkholes are commonly found in parts of Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania.