Solfatara

Solfatare, commonly known as "mudpots", are formed in high-temperature geothermal areas where water is in short supply, and the little water that there is becomes mixed with clay and other undissolved materials to form mud. This mud is generally of white to greyish colour, sometimes stained with reddish or pink spots from iron compounds. As the boiling mud is often squirted over the brims of the mudpot, a sort of mini-volcano or "mudvolcano" starts to build up, sometimes to the height of 3-5 feet.

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Solfatara is also the name of a dormant volcano near Naples, part of the Campi Flegrei volcanic area.