Grotto Geyser

Steam emerges from travertine arches

Quick Facts
Old Faithful

Historical/Interpretive Information/Exhibits

A popular performer, Grotto Geyser splashes 15 feet (5 m) from 1.5 hours to a day. The weirdly shaped cone may have resulted from siliceous sinter covering trees. Situated on the bank of the Firehole River, Riverside Geyser is one of the most picturesque and predictable geysers in the park.

During its 20-minute eruptions, a 75-foot (23 m) column of water arches gracefully over the river. Eruptions are about six hours apart. Watch for water flowing over the edge of the cone beginning 90-120 minutes before an eruption. Grotto Geyser has an average temperate of 200.1°F (93.4°C), an average pH of 9.1, and an average conductivity of 2300 uS/cm.


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.

Upper Geyser Basin

The majority of world’s active geysers are in the Upper Geyser Basin, including Old Faithful. Only four other places in the world have large concentrations of hydrothermal features: Russia (Kamchatka), Chile, New Zealand, and Iceland.

The heat for the hydrothermal features comes from Yellowstone’s volcano. Molten rock or magma may be as close as 3-8 miles (5-13 km) underground. Rain and snow supply water that seeps down several thousand feet (more than a kilometer) below the surface where it is heated.

Underground cracks form a natural plumbing system. Hot water rises through the plumbing to produce hot springs and geysers.

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.

Yellowstone National Park

Last updated: April 5, 2024