Hot bubbling mud pool at Orakei Korako Thermal Park, The Hidden Valley, North Island, New Zealand, Pacific

Hot springs and mud pools, Aguas Calientes, Southwest Highlands, Bolivia, South America

Boiling mud pool, Namafjall geothermal area, near Lake Myvatn, northeast area, Iceland, Polar Regions

Bathers enjoying the therapeutic benefits of the volcanic mud in the hot spring pool, Vulcano Island, Aeolian Islands, UNESCO World Heritage Site, north of Sicily, Italy, Mediterranean, Europe

African elephant (Loxodonta africana) at sunset, Nxai Pan National Park, Botswana, Africa

Furnas Valley, a site of bubbling hot springs and fumaroles on the Azorean capital island of Sao Miguel, Azores, Portugal, Europe

Tourists around the hot mud pools at Namaskard thermal area, Hverarond, near Lake Myvatn, North area, Iceland, Polar Regions

Bubbling mud pools and geothermal ground on Krafla mountain near Myvatn, Iceland, Polar Regions

Bubbling mud pools in the geothermal area of Hverir near Myvatn, Northern Iceland, Polar Regions

Bubbling mud pools in the geothermal area of Hverir near Myvatn, Northern Iceland, Polar Regions

Bubbling mud pools in the geothermal area of Hverir near Myvatn, Northern Iceland, Polar Regions

Bubbling mud pools in the geothermal area of Hverir near Myvatn, Northern Iceland, Polar Regions

Hot, bubbling mud in a pool in the Gunnuhver geothermal area, Iceland, Europe

Mud pool in the Namafjall geothermal area at Lake Myvatn in Iceland, Europe

A blue coloured boiling hot mud pool emanates steam as the sunset colours the sky orange, in Hveraröndor Hverir Geothermal Area at Namaskard Pass, North Iceland.