Sawmill Geyser is an example of the dynamic nature of these hydrothermal systems. While previously an active geyser, Sawmill Geyser stopped erupting in 2017 with no noticeable change at the surface. The pool is surrounded in geyserite from the previous high levels of geyser activity, with a dry outwash channel indicating a previously higher water level. Thermophiles are visible in the vent at the bottom of the clear pool. Part of the Sawmill Complex, Sawmill activity follows periods of 'Sawmill mode' and grows quiet during the less common 'Penta-Churn mode'.

Sawmill Geyser has an average temperate of 138°F (58.9°C), an average pH of 7.5, and an average conductivity of 2157 uS/cm.

Sawmill Geyser's eruptions were highly variable, some lasting only 9 minutes while others may last over 4 hours. Sawmill received its name because water spins in its crater as it erupts looking somewhat like the rotating circular blade of a lumber mill.

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.