Doublet Pool is actually two clear pools connected in the middle, allowing water to flow between. Deep vents exist in the center of the pools with shallow shelves at the edges of the pools. Raised, sawtooth-textured sinter outlines the edge of the pools and lines areas of the outwash channel. Some water spills out of the sawtooth textures around the pools, resulting in starburst-like trails of orange thermophiles, as well as the saw colors lining the outwash channel. Only rarely has Doublet Pool actually erupted, once after the 1959 earthquake, but most of its activity is bubbling and steaming.

Doublet Pool has an average temperate of 187.8°F (86.5°C), an average pH of 8.9, and an average conductivity of 1992 uS/cm.

Hot Springs

Hot springs are the most common hydrothermal features in Yellowstone. Their plumbing has no constrictions.

Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below.

This circulation prevents water from reaching the temperature needed to set off an eruption.

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.