Denotes
thermal activity that is a result of the interaction of
water with naturally occuring
subterranean hotspots. Such hotspots typically occur along the boundaries of
tectonic plates, such as the
Ring of Fire, however they are also known to occur in isolation from volcanic activity. Geothermal activity typically occurs when water is able to seep through a cracks in the
strata to reach heated underground rock or
magma. The water is
superheated, and returns under pressure to the surface, where it may rise as
steam, or appear as a
geyser or
mud pool.
Examples of geothermal activity around the world include Old Faithful in Yellowstone National Park and Rotorua in New Zealand. In New Zealand, geothermal activity has been sufficient to be harnessed as a power source: Water is pumped at pressure into the ground, where it is heated and returns at high pressure as steam, and is used to drive turbines.