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Overview
Doublet Pool is a paired hot spring on Geyser Hill in the Upper Geyser Basin. Known for its vivid blue water, scalloped sinter rim, and starburst-like orange thermophile patterns, it mostly bubbles and steams rather than erupts. Average water temperature sits around 187.8°F (86.5°C) with an alkaline pH near 8.9.
What Makes It Unique
This pool is famous for a subtle, rhythmic "thumping"—pressure pulses from its hydrothermal plumbing that can ripple the surface and sometimes vibrate the boardwalk. The cycle varies over time, so some days you’ll hear frequent thumps, and other visits may be quiet.
Geology in Plain English
Doublet Pool is a hot spring, not a predictable geyser. In hot springs, circulating convection generally keeps water from reaching eruption temperatures. It’s one expression of Yellowstone’s vast hydrothermal system, powered by the underlying volcano; molten rock may lie roughly 3–8 miles underground, heating groundwater that rises through cracks to feed features like this.
Getting There
Reach it via the Upper Geyser Basin/Geyser Hill boardwalk loop from the Old Faithful area. There’s no parking or services at the pool—use the Old Faithful lots and facilities, then walk the short, mostly level boardwalk to Geyser Hill.
How to Experience It
- Pause and listen quietly for a few minutes; the thumps can be subtle and intermittent.
- Watch for surface ripples and the pool’s striking color and sinter rim textures.
- Expect steam and boardwalk traffic during peak hours.
Safety and Wildlife
Stay on the boardwalks—hydrothermal ground is thin and the water is near- or above-boiling. Keep children close, never touch the water, and give any wildlife (often bison or elk in this area) plenty of space.
Best Time to Visit
- Early morning or late afternoon helps avoid boardwalk crowds and offers softer light for photos.
- Calm, cool mornings can make the thumping easier to hear.
- Midday is busiest, especially when nearby Old Faithful draws crowds onto the loop.
Pros
- Occasional rhythmic thumping you can hear or feel
- Quick, easy boardwalk stop near Old Faithful
Cons
- No facilities at the feature itself
- Thumping is intermittent—you might not catch it
Tips
- Stand quietly for a few minutes—thumps can be faint and irregular.
- Visit early or late to dodge the heaviest boardwalk crowds.
- Use restrooms, water, and food in the Old Faithful area before the loop.
- Calm, cool mornings improve your chances of hearing the thumping.
- Park at the Old Faithful lots and follow the Geyser Hill boardwalk.
