The hiss and roar of a fumarole comes from gases—steam, carbon dioxide, and a little hydrogen sulfide—rushing from the ground through the vent. Its plumbing reaches down into the hot rock masses, but contains very little water. When water contacts the hot rock, it flashes into steam, increasing the water's volume 1,500 times and driving the gases from the vent.

Fumaroles

Fumaroles or steam vents, are the hottest hydrothermal features in the park. The limited amount of water flashes into steam before reaching the surface. The result is a loud hissing of steam and gases.

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.