Boiling water and steam can erupt skyward at irregular or regular intervals. A geyser is a hot spring that periodically ejects a column of water and steam. The behavior requires a plumbing system that allows pressure to build before sudden release.

Most geysers occur in volcanic regions where magma heats groundwater. Constrictions in the conduit prevent free boiling until the temperature and pressure reach a critical point. Flash boiling then expels the water, after which the system slowly recharges. Yellowstone’s Old Faithful is the most famous example.

Geysers are sensitive to changes in the subsurface and can be altered or extinguished by nearby drilling or earthquakes. Their spectacular eruptions attract visitors, yet the underlying hydrothermal systems also deposit mineral sinter and support specialized microbial communities. Few places on Earth combine the necessary heat, water, and plumbing.

• Hot spring that intermittently erupts
• Requires heated groundwater and constricted conduit
• Found mainly in volcanic areas
• Sensitive to subsurface changes