Gigantic Sinkhole in Guatemala City

Heavy rains from tropical storm Agatha likely triggered the collapse of a huge sinkhole in Guatemala on Sunday, seen above a few days afterward.

In the strictly geologic use of the word, a sinkhole happens when water erodes solid bedrock, carving an underground cavity that can then collapse. Many parts of the United States are at risk for that type of event.

The Guatemala sinkhole fits into a broader use of the term, which refers to any sudden slump of the ground's surface. Instead of solid bedrock, much of Guatemala City rests atop a layer of loose, gravelly volcanic pumice that is hundreds of feet thick.