This nearly constant performer splashes from several vents and its steam can be seen throughout the Lower Geyser Basin. Its name is Greek for water clock, and was given because the geyser used to erupt regularly every three minutes. Since the 1959 Hebgen Lae Earthquake, however, Clepsydra erupts almost without pause. Sometimes it quits during Fountain Geyser's eruption.

Geysers

Geysers have constrictions in their plumbing systems that prevent water from moving freely to the surface where heat would escape. Water beneath the constrictions creates a buildup of steam. Eventually the steam pushes water past the constrictions and the geyser erupts.

Fountain Paint Pot Area

Hydrothermal features can be grouped into two general categories: those with a great deal of water (hot springs and geysers) and those with limited water (mudpots and fumaroles). Despite their structural similarities, no two features are exactly alike. All of these features occur in the Fountain Paint Pot area.

Thermus aquaticus, the thermophile that revolutionized DNA replication processes, was discovered in this area.

Lower Geyser Basin

The Lower Geyser Basin sits on unstable glacial gravel on top of solid rock. The jarring energy of an earthquake can make the gravel vibrate and shift position, and compact or fracture.

All these changes affect water supplies to hot springs. They might force muddy water to the surface, clouding existing pools or creating new ones. They might divert water from a pool, causing it to dry up. Water temperatures might also increase or decrease due to these subsurface changes.

In the days after the Hebgen Lake earthquake of 1959, all of these changes were observed in various springs of the Firehole River geyser basins. The epicenter (point of origin) of the quake was determined to be about 31 air miles (50 km) northwest of the Fountain Paint Pots area.

Great Fountain Geyser, on the Firehole Lake Drive, is the only geyser outside of the Old Faithful area with eruption forecasts.

Use Caution in Hydrothermal Areas

• Stay on boardwalks and designated trails.
• Hydrothermal water can severely burn you.
• Never run, push, or shove.
• Supervise children at all times.
• Do not scratch hydrothermal mats.

You are responsible for your safety.

Think safety, act safely. Yellowstone is a dangerous place.