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

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

Champagne Pools steaming, Waiotapu thermal reserves, Rotorua, North Island, New Zealand

A thermal mud pool bubbles near to Wai-o-tapu Thermal Wonderland, Rotorua, North Island, New Zealand, Pacific

Steam and bubbling mud pools in thermal area, Rotorua, South Auckland, North Island, New Zealand, Pacific

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

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

Thermal bathers in Copahue, Argentina at the El Chancho (the pig) lagoon. Mud is supposed to be good for bone and arthritis.

Bathers in mud at Las Maquinitas near Copahue, Argentina. Margarita Nievas, 56, blue and Susana Nievas, 48 are sisters. Both are from Neuquen and come here 2 or 3 times a year for one week just for prevention.

Thermal bathers in Copahue, Argentina at the El Chancho (the pig) lagoon. Mud is supposed to be good for bone and arthritis.