Sinkholes are the result of water eating away bedrock and soil underground, causing the earth to drop out from under itself in vast depressions or gaping chasms.

They can form gradually (like that of Berezniki, Russia) or very suddenly (last year in Guatemala City). It's unclear why there aren't more apocalyptic horror films about this sort of event. As evidenced by this collection of images of 13 of the most intense sinkholes on earth, they're terrifying and strange enough in real life.

Photo: Sinkhole in Florida

Via Neatorama