Visitors to Yellowstone National Park experienced a shocking hydrothermal explosion last month when underground hot water erupted violently, sending steam, boiling water, mud, and large rocks soaring hundreds of feet into the air.

Thankfully, there were no injuries. The incident, which occurred on July 23 in the Biscuit Basin region, about 2 miles north of the iconic Old Faithful geyser, caused damage to a boardwalk and nearby thermal pools. The park authorities have since closed off Biscuit Basin for inspection and assessment.

While many tourists are drawn to Yellowstone for its stunning landscapes, the park is also known for its geysers, earthquakes, and hydrothermal explosions, all of which illustrate the volcanic activity lying beneath its surface.

What triggered the hydrothermal explosion in Yellowstone?

The Yellowstone Plateau Volcanic Field, which includes the caldera, is part of an active volcanic region that extends through northern Nevada, Idaho, and Wyoming. This caldera is responsible for the geysers that erupt in the area.

According to the U.S. Geological Survey, while the geological activity in Yellowstone can sometimes seem alarming, the explosion at Biscuit Basin does not indicate a forthcoming volcanic eruption. Most hydrothermal explosions tend to be small and go unnoticed, as explained by Michael Poland, the lead scientist at the Yellowstone Volcano Observatory.

Understanding Yellowstone’s hydrothermal systems

Yellowstone is home to over 10,000 thermal features, including hot springs, mudpots, and steam vents, as reported by the National Park Service. The park also experiences significant seismic activity, typically witnessing between 1,500 to 2,500 earthquakes each year. In 2023, for example, there were 1,623 recorded earthquakes, which is considered an average year. The most intense earthquake last year had a magnitude of 3.7, according to the Yellowstone Volcano Observatory.

Explosions can occur wherever there is hydrothermal activity, as explained by Poland. (“Hydrothermal” refers to heated water found in the Earth’s crust.)

In the past month, Yellowstone experienced 64 earthquakes, as reported by the University of Utah Seismograph Stations. Frequent clusters of earthquakes contribute to roughly half of the seismic activity observed in the Yellowstone area.

How large is the magma chamber under Yellowstone?

The Yellowstone Caldera measures about 55 miles in length and nearly 25 miles across. The term “caldera” describes a massive crater and signifies the largest volcanic vent in North America.

Consequences of the Biscuit Basin eruption

What triggers hydrothermal explosions?

The USGS states that hydrothermal explosions occur when water trapped underground is heated by magma. This causes the water to quickly turn into steam, resulting in an explosion. If a conduit links the underground chamber to the surface, a geyser can form to release the built-up pressure.

Typically, geyser water is heated to around 200 degrees Fahrenheit, while hot springs can reach temperatures between 200 and 459 degrees Fahrenheit.

In Yellowstone’s Upper Geyser Basin, Old Faithful Geyser erupts, on average, every 90 minutes, discharging between 3,700 and 8,400 gallons of boiling water during eruptions that last from 1.5 to 5 minutes and can reach heights of 106 to 184 feet.

Historical volcanic eruptions at Yellowstone

The last significant volcanic eruption at Yellowstone occurred approximately 640,000 years ago.

This eruption was the most cataclysmic of the three major eruptions in the park’s history, spewing over 20 feet of lava, ash, and rock across an area larger than California. Even the smallest eruption from Yellowstone was vastly larger than the infamous 1980 eruption of Mount St. Helens, having a volume 280 times greater.

Each of these eruptions released vast amounts of volcanic ash, gas, and magma into the atmosphere, covering most of the continental United States with debris.

Is Yellowstone’s supervolcano overdue for an eruption?

In short, No. There is no immediate concern.

Hydrothermal explosions are not indications of an impending volcanic eruption, as confirmed by the USGS. Researchers are actively investigating methods to predict these events.

“We are still uncertain if these phenomena can be predicted,” stated Poland. “It’s a question that remains open.”

While signs of an impending eruption may take decades to manifest, possible indicators could include numerous significant earthquakes, alterations in the chemical makeup of hot springs, increases in temperature, and ground movement of several feet along with gas releases.