Mud pots, fumaroles and dormant Volcan Santa Clara at the San Jacinto volcanic thermal area north of Leon, Leon, Nicaragua, Central America

Steaming volcanic mud pools, Rincon de la Vieja National Park at foot of Rincon Volcano, Gaunacaste, Costa Rica

Hot pools and boiling mud at Namaskard thermal area, Hverarond, near Lake Myvatn, North 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

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

Steaming volcanic mud pools, Rincon de la Vieja National Park at foot of Rincon Volcano, Gaunacaste, Costa Rica

Steaming volcanic mud pools, Rincon de la Vieja National Park at foot of Rincon Volcano, Guanacaste, Costa Rica, Central America

Blisters measuring about 10 cm across in boiling mud pool, Mud volcano, Yellowstone National Park, UNESCO World Heritage Site, Wyoming, United States of America (U.S.A.), North America

Steaming volcanic mud pools, Rincon de la Vieja National Park, at foot of Rincon Volcano, Guanacaste, Costa Rica, Central America

One of the many bubbling mud pools in a hot spring area on the outskirts of Hveragerdi, a geothermal hot spot, with steam rising from fumeroles right in the middle of town, South West Iceland, Polar Regions

One of the many bubbling mud pools in a hot spring area on the outskirts of Hveragerdi, a geothermal hot spot, with steam rising from fumeroles right in the middle of town, South West Iceland, Polar Regions

One of the many bubbling mud pools in a hot spring area on the outskirts of Hveragerdi, a geothermal hot spot, with steam rising from fumeroles right in the middle of town, South West Iceland, Polar Regions

Solfataras, fumaroles, mud pools, sulfur and other minerals, steam, Hveraroend geothermal area, N√°mafjall mountains, M√Ωvatn area, Nor√∞urland eystra, the north-east region, Iceland, Europe

Solfataras, fumaroles, mud pools, sulfur and other minerals, steam, Hveraroend geothermal area, N√°mafjall mountains, M√Ωvatn area, Nor√∞urland eystra, the north-east region, Iceland, Europe

Solfataras, fumaroles, mud pools, sulfur and other minerals, viewing platform, steam, Hveraroend geothermal area, N√°mafjall mountains, M√Ωvatn area, Nor√∞urland eystra, the north-east region, 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.