How Do Sinkholes Form?

In the aftermath of Tropical Storm Agatha, a 330-foot-deep sinkhole opened up in the middle of Guatemala City. Like all sinkholes, the one in Guatamala City formed when a swath of land collapsed, leaving behind a crater-like depression in the ground.

The phenomenon is most common in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee and Pennsylvania, according to the U.S. Geological Survey. The ground beneath these states is rich in easily dissolved rocks such as limestone, carbonates and salt beds. When groundwater flows through these rocks, it eats away at them, leaving behind subterranean holes and caverns. When the roof of one of these caverns collapses, it takes the land above down with it.

The most dangerous sinkholes are those that collapse suddenly. In some cases, the groundwater filling the underground caverns drains away because of drought or because humans divert the flow of groundwater for mining, drinking water or irrigation. Without the water supporting the roof from below, the land above crumbles. In other cases, the roof of the cavern becomes too weak to support the weight of the soil above it.

These sudden sinkholes can swallow cars, houses and even drain entire lakes without warning. In September 1999, Lake Jackson near Tallahassee, Fla., which measured more than 6 square miles (16 square kilometers), disappeared almost completely, drained from below by a 50-foot-deep (15-meter-deep) sinkhole. But don't worry, it'll be back: According to the Florida Geological Survey, the lake drains and refills every 25 years.

Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.