Biscuit Basin hydrothermal eruption on July 23, 2024

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The Yellowstone Caldera Chronicle is a weekly column written by scientists and collaborators at the Yellowstone Volcano Observatory. This week’s contributor is Michael Poland, a geophysicist with the U.S. Geological Survey and chief scientist at the Yellowstone Volcano Observatory.

Shortly before 10 a.m. on July 23, 2024, an explosion of hot water, mud, and rock occurred at the Black Diamond Pool in Biscuit Basin in Yellowstone National Park, just about 2 miles northwest of Old Faithful. Monitoring instruments did not detect any precursors to the event. Dramatic videos posted on social media showed a column of water and rock fragments rising into the air, estimated to be 400-600 feet (120-180 meters) based on analysis of photos, and people running in all directions. The explosion severely damaged a nearby boardwalk, and the basin remains closed while geologists assess the activity. Thankfully, no one was injured.

Map of the main geothermal features in Biscuit Basin, Yellowstone National Park. Base map from Google Earth.

Geologists who examined the deposit noted that the rocks thrown out by the explosion consisted of glacial material, sandstone, siltstone and gravel, which were directly located in Siliceous sinter The rhyolite bedrock (based on Drilling in the 1960s) were found. This suggests that the explosion occurred at a much shallower depth than that and therefore did not disturb the bedrock. This is not surprising, as most of Yellowstone’s hydrothermal conduits exist in shallow layers below the surface.

This boulder is the largest confirmed to have emerged from the July 23, 2024, hydrothermal eruption of Black Diamond Pool in Biscuit Basin, Yellowstone National Park. The measuring tape is 50 centimeters (20 inches) long. In the background is Black Diamond Pool and a boardwalk. In the foreground are scattered smaller pieces of rock from the explosion. Photo by Lauren Harrison of Colorado State University, July 25, 2024.

The explosion was primarily directed northeast, toward Firehole River (away from the boardwalk), and the largest boulders—some several feet across and weighing hundreds of pounds!—fell in that direction. This fortuitous directionality may be the reason that no one standing on the boardwalk at the time of the event was injured.

Hydrothermal Eruption This transformation occurs when liquid water boils and turns into steam in shallow underground layers. This transformation occurs all the time in existing geyser systems, such as Old Faithful or Steamboat Geyserwhere a well-defined system of pipes allows steam and hot liquid water to reach the surface through an unobstructed path, resulting in a geyser eruption. However, when the liquid-steam mixture is in a sealed, confined space without a well-defined system of pipes, the pressure from the expanding steam bubbles eventually overcomes the strength of the rock, causing an explosion.

In the case of the Black Diamond Pool incident, the July 23 explosion was likely caused by changes in a shallow underground hot water reservoir. Silica precipitation The data geologists collect from the blast debris will provide more details about the exact circumstances when the explosion occurred.

Aerial view of Biscuit Basin in Yellowstone National Park, showing debris deposited by the Black Diamond Pool hydrothermal eruption on July 23, 2024. Major features are labeled. The main debris field (inside the dashed yellow line) is in gray. Photo by Joe Bueter, Yellowstone National Park, July 23, 2024.

Scientists assess the level of natural hazards by combining knowledge of the frequency and severity of hazardous events. In the Yellowstone region, destructive hydrothermal explosions and earthquakes may occur several times per century. Lava flows and small eruptions are rare—none in the past 70,000 years. Large eruptions, while Yellowstone’s most destructive hazard, are extremely rare—only three times in the past few million years. These events recur at irregular and unpredictable intervals.

Hydrothermal eruptions at Yellowstone National Park are more common than you think. Compared to strong earthquakes, lava flows and dome and volcanic crater eruptions, this is the most common but least destructive hazardOn average, several hydrothermal eruptions of varying sizes occur somewhere in Yellowstone National Park each year, often in remote areas where they may go unnoticed.

Some of the largest hydrothermal eruptions in Yellowstone National Park over the past 150 years occurred in the 1880s at Excelsior Geyser, adjacent to Grand Prismatic Hot Spring Located in Midway Geyser Basin. Pork Chop Fountain Eruption in September 1989This eruption in the Norris Geyser Basin is probably one of the most famous hydrothermal eruptions in this famous area. Several tourists witnessed the eruption, but no one was injured. On April 15, 2024, another small explosion occurred in the Norris Geyser BasinThe event was detected by nearby monitoring instruments designed specifically for this purpose. Without the data from these instruments, this unwitnessed event might never have been identified. Yellowstone Monitoring Plan Released in 2022The Yellowstone Volcano Observatory has specifically targeted expanding hydrothermal monitoring to counter the threat posed by these small but dangerous hydrothermal explosions. To be installed at Norris Geyser Basin in September 2023 is the first step to achieve this goal.

Smaller events are more common, e.g. The rare eruption of Erquan volcano in 2018near Old Faithful. That eruption brought decades of human waste to the surface. But much bigger events could have happened, too. Since the end of the last ice age in the Yellowstone region about 14,000 years ago, there have been more than a dozen hydrothermal explosions that have left craters hundreds of feet wide. The largest such crater—in fact, the largest hydrothermal explosion crater known on Earth!—is about 1.5 miles (2.5 kilometers) wide and formed in Events that took place at Mary Bay approximately 13,000 years agoalong the northern part of Yellowstone Lake.

It’s too early to predict what will happen next in Biscuit Basin. The eruption clearly changed the flow paths of shallow hydrothermal fluids in the area, and it’s unclear how the hydrothermal features will respond. Are we witnessing the birth of new geysers? Will activity return to its previous quiet state? Will quiet hot springs reappear? The data geologists are collecting will help us better understand the July 23 event and how the area may evolve in the future.

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