A scuba diver ascends into the light emanating above through the sink hole into the clear freshwaters of Devil's Den cave near Williston, Florida.

A small flooded sink hole in the Salar de Atacama, Los Flamencos National Reserve, Chile, South America

Meltwater on the Langjokull ice cap in Iceland disappearing into a moulin, Iceland, Polar Regions

Snorkelers on the surface of a blue hole. Virgin Blue Hole dive site, Palau, Micronesia, Pacific Ocean. More info: Blue holes such as this are submerged limestone sink holes.

Meltwater on the Langjokull ice cap in Iceland disappearing into a moulin, Iceland, Polar Regions

A twenty ton ice explorer truck owned and run by Arngrimur Hermannsson ( Arni), next to a sink hole for meltwater (moulin), Langjokull ice cap, Iceland, Polar Regions

A twenty ton ice explorer truck owned and run by Arngrimur Hermannsson (Arni), taking tourists onto the Langjokull ice cap, Iceland, Polar Regions

A moulin (meltwater sink hole) on the Langjokull glacier, Iceland, Polar Regions

A twenty ton ice explorer truck owned and run by Arngrimur Hermannsson ( Arni), next to a sink hole for meltwater (moulin), Langjokull ice cap, Iceland, Polar Regions