Planetary Geology
Cryovolcano
A cryovolcano is a volcano that erupts volatile substances such as water, ammonia, methane, and brines instead of molten silicate rock. Cryovolcanism shapes the geology of many outer Solar System bodies, with confirmed activity on Enceladus and Triton and strong evidence on Europa, Ceres, and Pluto.
Geyser
A geyser is a rare type of hot spring that intermittently ejects boiling water and steam through a surface vent. Geysers form where abundant groundwater, a strong heat source, and a constricted subsurface plumbing system coincide, conditions that exist in only a few regions worldwide, notably Yellowstone in the United States, Kamchatka in Russia, Iceland, New Zealand, and northern Chile. Their eruptions, mineral deposits, and associated microbial ecosystems make them important subjects in geology, hydrology, and astrobiology.