A parked bus was the unfortunate "meal" of a sinkhole that opened up in the streets of Lisbon, Portugal, in 2003. Anything that increases the flow of water into subsurface soil can speed up the formation of sinkholes, Missouri State's Gouzie said.
In many cities, utility infrastructure such as sewer lines and fiber optic cables are buried in troughs filled with loose material, which can wash away over time. In some cases, a stretch of road can essentially become a concrete bridge over mostly empty space. "It's eventually not enough to hold the weight of the next truck over it," Gouzie said.
Guatemala Sinkhole, 2010 (Photograph by Daniel LeClair, Reuters)
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. And at least one geologist says leaking pipes—not nature—created the recent sinkhole. Overall, the risk for repeat sinkholes in Guatemala City is high—but highly unpredictable.