Geothermal activity

Other sources of internal heating can be gravitational differentiation of substances, tidal friction, metamorphism, or phase transitions.

Fumaroles tend to form concentrated deposits of sulfuric minerals, which fall out of suspension when the volcanic gases cool to the air.

These range from a smooth dent in the ice cap to deep holes with very steep walls formed by concentric rings of crevasses.

[citation needed] They occur when groundwater in underground cavities becomes superheated under a lid of colder surface water.

[8] The behaviour of these mud pots can vary on a seasonal cycle based on variations in the amount of rainfall and the level of the water table.

A rocky surface with a mound centrally in the image. The mound has holes in the top. Surrounding rocks have been stained orange and yellow. There is smoke or steam rising from the top.
A fumarole in the Solfatra crater, the orange and yellow colouration is from minerals that are deposited by the superheated fumes as they cool to ambient temperature .
A pool of greyish-blue bubbling sludge surrounded by rocks and steam
Mud pots in the Sol de Mañana Hydrothermal field, Bolivia . The yellow coloring in the soil derives from deposits of sulfur
A green landscape with a platform of grey rock. steam is rising from a pool or hole in the middle of the platform
Geysir , a geyser in Iceland, after which the phenomenon is named. [ 5 ]
A crystal-clear pool with a bright yellow bottom. Where the water is deeper the bottom seems more green or blue. In the background, where the water of the first pool turns red, there is a raised rim surrounding a smaller bright-blue pool, which steams heavily. The pools have white beaches and are surrounded by a pine forest
Two Hot springs in Waiotapu , New Zealand, with Artist's Palette in the foreground, and Champagne Pool directly behind it in the background.