Doublet Pool

Doublet Pool, located in Yellowstone National Park’s Upper Geyser Basin, is one of the most captivating thermal features in the area, known for its twin blue pools connected by a narrow channel. These two circular pools sit side by side, giving the feature its name “Doublet,” a reference to their paired, mirror-like appearance. The water shimmers with rich shades of blue and turquoise, surrounded by delicate sinter rims that contrast beautifully against the surrounding geyserite crust.

Doublet Pool

Quick Reference: Doublet Pool

Feature	Details
Name	Doublet Pool
Location	Upper Geyser Basin, Yellowstone National Park, Wyoming, USA
Type	Hot Spring / Hydrothermal Pool
Formation	Two connected circular pools linked by a narrow channel
Water Temperature	Average 187.8°F (86.5°C)
pH Level	Around 8.9 (slightly alkaline)
Conductivity	1992 µS/cm (high mineral content)
Depth	Approximately 4–6 feet (1.2–1.8 meters)
Activity Pattern	Rhythmic pulsing and bubbling caused by underground steam collapse
Eruptive History	Rare; one recorded eruption after the 1959 Hebgen Lake earthquake
Water Color	Deep blue center with orange and yellow edges from thermophiles
Surrounding Surface	White sinter crust with delicate mineral patterns
Elevation	Approximately 7,350 feet (2,240 meters)
Nearby Features	Castle Geyser, Grotto Geyser, and Crested Pool
Accessibility	Easily accessible via Upper Geyser Basin boardwalk
Best Viewing Time	Early morning or cool weather for visible steam and vibrant colors
Safety Note	Stay on boardwalks; water is near boiling and ground is fragile
Fun Fact	Doublet Pool’s rhythmic “thumping” is caused by steam bubble collapses underground — often audible and even felt through the boardwalk.

The rhythmic activity of Doublet Pool has made it a favorite among geologists and visitors alike. Its surface often trembles, creating small, wave-like motions accompanied by gentle thumping or drumming sounds. These vibrations are caused by trapped steam bubbles that suddenly collapse in the superheated water below, a phenomenon sometimes referred to as “bubble collapse activity.” This rhythmic pulsing can be felt even through the boardwalk, and depending on underground pressure and temperature changes, it may vary in intensity. The captivating display offers a reminder that Yellowstone’s hydrothermal system is in constant motion, alive with heat and unseen forces.

Doublet Pool is also notable for its rare but documented eruptions. Although it primarily bubbles and steams, there have been instances where the pool erupted briefly, most notably after the powerful 1959 Hebgen Lake earthquake that affected much of Yellowstone’s hydrothermal system. Since then, its activity has remained mostly limited to gentle boiling, steaming, and pulsing behavior. The pool has an average temperature of 187.8°F (86.5°C), an average pH of 8.9, and an average conductivity of 1992 µS/cm, reflecting its high mineral content and near-boiling conditions.

The colors surrounding Doublet Pool add to its beauty and scientific intrigue. The central water appears a deep blue due to its high temperature and clarity, which allow only blue wavelengths of light to scatter back to the surface. Around the edges, cooler temperatures support the growth of heat-loving microorganisms known as thermophiles, which create subtle orange and yellow bands that accentuate the pool’s contrast with the white sinter crust. This combination of colors, shapes, and textures gives Doublet Pool a painterly quality, as though nature itself crafted it with an artist’s precision.

Doublet Pool lies along the main boardwalk between the Castle Geyser and Grotto Geyser areas, making it one of the most accessible and photogenic hot springs in the Upper Geyser Basin. Visitors walking past often pause to admire its surreal beauty, especially on cool mornings when steam gently rises from its surface and dances in the crisp air. The serenity of the setting, combined with the soft, rhythmic thumping, creates an almost meditative experience for those who linger nearby.