Hot spring

A natural place where groundwater heated by geothermal energy flows or pools at Earth’s surface. Its temperature and chemistry reflect the heat source, water pathways, and surrounding rock.

Geothermal energy: Heat stored within Earth, originating mainly from planetary formation and radioactive decay. This internal heat warms groundwater beneath hot springs.
Geothermal gradient: The rate at which temperature increases with depth inside Earth. It helps determine how deeply water must circulate to become heated.
Balneotherapy: The use of bathing in mineral or thermal waters as a therapeutic practice. Hot spring bathing has long been used for relaxation and perceived health benefits.
Grand Prismatic Spring: A large hot spring in Yellowstone National Park known for its vivid concentric colors. Its colored microbial mats vary with temperature around the spring's margins.
Hydrothermal circulation: The movement of water through heated rock, driven by temperature and pressure differences. Circulating groundwater acquires heat before rising to a spring.
Fault (geology): A fracture in Earth's crust along which blocks of rock have moved. Faults can provide pathways for groundwater to descend and heated water to rise.
Geothermal power: Electricity or useful heat produced by harnessing Earth's internal energy. Hot spring regions can indicate accessible geothermal heat, though springs themselves are not necessarily power sources.
Morning Glory Pool: A deep hot spring in Yellowstone whose color has changed as its vent accumulated debris. It illustrates how altered circulation can change a spring's appearance.
Groundwater: Water held beneath Earth's surface in pores, fractures, and other openings. It supplies most hot springs and carries dissolved minerals to the surface.
Permeability: A material's capacity to transmit fluids through connected pores or fractures. Rock permeability controls how readily water circulates through a geothermal system.

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