A sinkhole swallows three cars during a heavy rainstorm in Chicago, Illinois, in 2013. Aquifers can be weakened when they lose water (due to drought or when well water is removed faster than it is replaced) that supports the open spaces in an aquifer. A heavy rain event may add enough pressure to the overlying ground to cause the aquifer to collapse and open up a sinkhole.
Zbigniew Bzdak/Chicago Tribune/McClatchy-Tribune via Getty Images