What causes sinkholes?

It’s the stuff of nightmares: last week, the ground opened up and swallowed a Florida man as he lay sleeping in his home. But why do these sinkholes occur and how widespread are they?

Photos: 1. Three buildings collapsed after a huge hole appeared in, Guangzhou, Guangdong province, China on 28 Jan 2013. There are no casualties from the incident, which was near a metro tunnel construction site. Imaginechina/Rex Features. 2. Guatemala city, 2007 Photograph: Ulises Rodriguez/EPA/Corbis