YELLOWSTONE NATIONAL PARK, Wyoming – On July 23, 2024, a large hydrothermal explosion rocked Biscuit Basin in Yellowstone National Park. The explosion came from the Black Diamond Pool, launching rock fragments and water 400-600 feet into the air. There was no precursor detected by monitoring instruments, and Biscuit Basin will remain closed as geologists assess the situation. The Yellowstone Volcano Observatory released a new update on the explosion on July 29.
Based on geologist examinations, the debris from the explosion consisted mostly of glacial materials, sandstones and siltstones, and gravels. No rhyolite bedrock, which sits about 175 feet under the surface, was present, indicating that the explosion originated from a much shallower depth than that. The press release explains that this is not a surprise, as hydrothermal conduits in Yellowstone mostly sit at shallow levels.
It’s still unclear how much change Biscuit Basin will see following the explosion. Shallow hydrothermal flow paths were clearly changed due to the explosion, but how the thermal features will respond is unknown. It’s possible that a placid hot spring will reform, but it’s also possible that a new geyser could form. Further data will help explain the future of the basin.
Yellowstone Volcano Observatory on the July 23 Explosion:
“The explosion was largely directed to the northeast toward the Firehole River (away from the boardwalk), and the largest boulders—some measuring several feet across and weighing hundreds of pounds!—fell in that direction. This fortuitous directionality was probably the reason that no one standing on the boardwalk at the time of the event was injured.“
Hydrothermal explosions occur when liquid water boils and converts to steam in the shallow subsurface. This sort of transition happens all the time in established geyser systems, like Old Faithful or Steamboat Geyser, where well-defined conduit systems allow that steam and hot liquid water to take an unobstructed path to the surface, resulting in a geyser eruption. But when the liquid-steam mixture is within a confined space that has become sealed and without that well-defined conduit system, pressure due to the expansion of steam bubbles eventually overcomes the strength of the rock, and an explosion occurs.
In the case of Black Diamond Pool, the July 23 explosion was probably caused by a change in the hot-water reservoir in the shallow subsurface. Silica precipitation can clog conduits or “pipes” in the reservoir leading to accumulation of steam and a pressure buildup. The data that geologists are collecting from the explosion debris will provide even more detail on the exact conditions at the time of the event.“