hydrothermal

/ˌhɑɪdrəˈθɜrməl/

The adjective hydrothermal is used to describe hot water, particularly water that's heated underground. If you visit Yellowstone, you'll probably see hydrothermal attractions like geysers and hot springs.

Hydrothermal derives from Greek roots hydor, "water," and therme, "heat." It's been used by geologists since the 1850s to describe underground hot water. Hydrothermal activity occurs all over the planet, and it's especially common around active volcanoes. As well as steamy hot springs and dramatic geysers shooting hot water into the air, smaller mud pots and hydrothermal vents in the ocean floor are also evidence of water heating up beneath the earth's surface.

Definitions of hydrothermal

1. adjective

   relating to the effects of heated water on the earth's crust