Yellowstone Pool Accompanies Temperature Changes with Thumps

According to the National Park Service, national park visits hit about 312 million, an increase of 15 million over 2021 and only 6% below the record visits of 2016. More than 3,290,000 people visited Yellowstone in 2022.

Many swarm to Old Faithful, the Grand Prismatic Spring, or the Grand Canyon of the Yellowstone River. But it was the lesser-known Doublet Pool that attracted a team of scientists for a research study led by the University of Utah.

Doublet Pool is a pair of hydrothermal pools connected by a neck and is small enough to fit into one half of a tennis court. It’s situated on Geyser Hill across the Firehole River from the hotels, visitor centers, and parking lots surrounding Old Faithful. But what is it that makes Doublet Pool so interesting?

Doublet Pool begins thumping every 20-30 minutes, sending the water at its surface dancing and the earth shaking. The team of researchers discovered that the interval between thumps reflects the amount of energy heating the pool at the bottom and indicates how much heat is lost at the surface. Doublet Pool is Yellowstone’s thermometer.

The team set up geophones around Doublet Pool and lowered temperature and water-level sensors into the pool’s depths from 2015 through 2022. They studied the silence interval between the thumps.

The thumping lasts about 10 minutes, caused by bubbles in the plumbing system, which brings water from the magma beneath Yellowstone to the pool. The bubbles collapse when they reach the cooler, upper reaches of the hydrothermal conduit, causing a thump.

Yellowstone’s hydrothermal system is like an Instant Pot, building up heat and pressure, which causes geysers to erupt, among other phenomena. In November 2016, the silence interval between the thumps was about 30 minutes. But by September 2018, that interval was half that, around 13 minutes, and by November 2021, the interval was back up to around 20 minutes.

What else was happening on Geyser Hill during that time? On September 15, 2018, Ear Spring, 200 feet (60 m) northwest of Doublet Pool, erupted for the first time since 1957. After the eruption, the water in Doublet Pool boiled. The unusual behavior of Ear Spring, Doublet Pool, and other features suggests that in 2018 the heat under Geyser Hill was hotter than usual. By 2021 that heat and pressure had subsided, and the silence interval at Doublet Pool had recovered.

“By studying Doublet Pool, we are hoping to gain knowledge on the dynamic hydrothermal processes that can potentially be applied to understand what controls geyser eruptions,” said Fan-Chi Lin, an associate professor in the department of geology and geophysics and a study co-author, “and also less predictable and more hazardous hydrothermal explosions.”

The study is published in Geophysical Research Letters.