In Tampa, Florida, in February 2013, a giant hole opened up under the bedroom floor of Jeffrey Bush, swallowing the 36-year-old as he slept. His body was never found. Bush was a victim of a sinkhole – a growing worldwide hazard that lurks wherever limestone and other water-soluble rocks underpin the soil. When carbon dioxide in the air dissolves in rainwater, it forms a weak acid that attacks the soft rocks, riddling them with holes. Sinkholes can occur gradually when the surface subsides into bowl-shaped depressions or suddenly, when the ground gives way – often catastrophically.