Jeff Wilson / Aerial view of Broad Peak in the Concordia confluence, Karakoram Mountains, Himalayas, Pakistan. From Pakistani military helicopter for BBC series Planet Earth 2005

Jeff Vanuga / Old Faithful Geyser erupting, Upper Geyser Basin, Yellowstone NP, Wyoming, USA

Michael Hutchinson / Strokkur geyser erupting, Geysir, Iceland

Michael Hutchinson / People watching Strokkur geyser erupting, Geysir, Iceland

Pete Cairns / Bison foraging in snow beside Old Faithful geyser, Yellowstone, Wyoming, USA

RHONDA KLEVANSKY / Sol de manana geysers, Altiplano, Bolivia

Tim Fitzharris / Norris Geyser basin with steam plumes from geysers, Yellowstone National Park, Wyoming

Tui De Roy / Steam spews from erupting geysers, geyser geothermal field, Iceland

Jim Brandenburg / Erupting geysers, Yellowstone National Park, Wyoming

Tui De Roy / Geysers in extensive geothermal field in Andean foothills, Atacama Desert, Andes Mountains, Chile

Jose B. Ruiz / Geyser, Lake Bogoria NP, Kenya

Jose B. Ruiz / Geyser, Lake Bogoria NP, Kenya

Jose B. Ruiz / Lake Bogoria NP with geothermal activity, Kenya

Jose B. Ruiz / Geyser, Lake Bogoria NP, Kenya

Pete Oxford / Valley of geysers and fumaroles, Kamchatka, Russia

Pete Oxford / People watch thermal vents, Valley of geysers, Kamchatka, Russia

Nigel Marven / Geysers in Geyser Valley, Kamchatka, Russia

Doug Allan / Geysers and boiling mud of Sol de Manana geyser field, Andes, Bolivia

Nigel Marven / Active geyser, Kamchatka, Russia

Nigel Marven / Active geysers, Kamchatka, Russia

Mark Taylor / Steaming hot springs at sunset, Yellowstone National Park, Wyoming, USA

Bryan and Cherry Alexander / Tourists watching the Fountain Paint Pot Geyser erupt. Yellowstone National Park, USA.

Igor Shpilenok / Igor Shpilenok on the telephone, photographing in Valley of the geysers, Kamchatka, Far East Russia, June 2007, photograph by Dmitry Shpilenok

Igor Shpilenok / Igor Shpilenok photographing in Valley of the geysers, Kamchatka, Far East Russia, June 2007, photograph by Dmitry Shpilenok

Tui De Roy / Geysers in extensive geothermal field in Andean foothills, Atacama Desert, Andes Mountains, Chile

Tui De Roy / Geysers in extensive geothermal field in Andean foothills, Atacama Desert, Andes Mountains, Chile

Jose B. Ruiz / Geyser, Lake Bogoria National Park, Kenya

Pete Oxford / Thermal vents Valley of the Geysers Kamchatka Peninsula Eastern Russia

Pete Oxford / Boiling mud holes Valley of the Geysers Kamchatka Peninsula Eastern Russia