Get to know Doublet Pool

BASICS

• 8 to 12 feet deep
• Has rare eruptions of up to 2-3 feet.
• Thumps can be felt and heard, usually about every 30 minutes.

WHERE IT’S LOCATED

Doublet Pool is located on the upper boardwalk on Geyser Hill, a short walk from Old Faithful. Near the sign for Doublet Pool are what I call “Doublet’s Bubblers” – a group of small thermal features that are more active some years than others.

ABOUT

Doublet Pool is one of the prettiest pools in the Upper Geyser Basin. With its lacy, scalloped edge, and blue water, it’s a favorite of photographers and worthy in itself to take the short walk around the Geyser Hill loop.

About two feet down is another ledge. These ledges (also seen at Blue Star Spring and Heart Spring as well as others in the park) form from water gently overflowing at the same level for a very long time. The mineral in the water (silica) forms a hard water deposit (deposition) a little bit at a time. This is similar to the hard water deposits that can form on shower heads in your home. This lower ledge in Doublet Pool (as well as similar ledges in another pool we no longer have any safe access to) gives us a hint of what a younger Geyser Hill may have looked like.

The thickness of ledges lets us know how much the water level varied. Very thin ledges mean there’s not much variation. Here at Doublet Pool, the ledge is two to three inches thick, telling us that the water regularly cycles from the top of the ledge to the bottom of it. This is a key to knowing if you’re close to the time when you have the opportunity to feel, see and hear thumps.

THUMPS AND ERUPTIONS

About every 30 minutes, the water in Doublet Pool rises to the top of the scalloped edge. While at a “full pool” you’ll start to see bubbles rise and waves on the surface of the water. Then the thumps begin, lifting the water in the pool as a whole. This lifting times with the thumps you can hear and feel if there’s nobody walking on the boardwalk or talking too loudly. If you sit down on the bench or put your hand on the boardwalk, you can feel the thumps better. These thumps last about five minutes.

Eruptions of Doublet Pool are incredibly rare and have only been recorded as seen only four times. Two of these times were in conjunction with Giantess Geyser, one was after the Hebgen Lake earthquake, and during unusual behavior in this section of Geyser Hill in the fall of 2018.

IN CONCLUSION

If you are in the Old Faithful area and don’t have time to see lots of the thermal areas on your visit, taking a walk around Geyser Hill will let you see this gorgeous hot spring as well as other thermal features. Bonus points if you sit and wait for the thumps.