If you see a crowd at Grand Geyser and the pool looks full, wait a while. You might get to see the tallest predictable geyser in the world erupt. A classic fountain geyser, Grand Geyser erupts with powerful bursts rather than a steady column like Old Faithful. An average eruption lasts 9-12 minutes and consists of 1 to 4 bursts, sometimes reaching 200 feet (60 m).

Grand Geyser has an average temperate of 163°F (72.8°C), an average pH of 8.8, and an average conductivity of 2200 uS/cm.

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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.

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.