Five others in the house escaped without injury, including Jeremy Bush, who tried in vain to save his brother. With Jeff Bush now presumed dead and the search for his body called off, demolition crews have begun taking down his four-bedroom home, which sits astride the fissure.

The tragedy has left the community shaken and full of questions. To find out more about how and why sinkholes happen, National Geographic sat down today with Randall Orndorff of the U.S. Geological Survey.

A sinkhole is basically any collapsed or bowl-shaped feature that's formed when a void under the ground creates a depression into which everything around it drains. (Gallery: Sinkholes from around the world.)

There are two basic kinds. One is