Close to the Firehole River, Oblong Geyser is a deep blue pool with a raised sinter rim and geyserite. Sawtooth-textured geyserite surrounds part of the main pool, but also forms small, shallow pools in the overflow of the main pool. Oblong Geyser is unique in that while its eruptions aren't as dramatic as other features, the volume of water flowing into the Firehole River has been estimated to be at least 10,000 gallons! Eruptions occur every 2.5–11 hours. Some yellow and orange thermophile line the edge of the hillside where the overflow from Oblong reaches the river.

Oblong Geyser has an average temperate of 185.1°F (85°C), an average pH of 7.6, and an average conductivity of 2025 uS/cm.

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.