What’s up with Biscuit Basin?

On the morning of July 13^th, 2026, before the rest of the park was awake, another hydrothermal explosion occurred in Biscuit Basin. This basin has been closed for the better part of two years due to changing activity in the area. Unrest here began in dramatic fashion on July 23^rd, 2024, when a nearly 600-foot (180-Meter) explosion sent water, steam, and rock debris into the air. 

With all the news coverage that Biscuit Basin received, you may think this was a one-of-a-kind situation in the park. But unsurprisingly, Yellowstone is much more complex than that. The eruptions at Biscuit Basin give a unique opportunity for park scientists to gain a better understanding of how these explosions work and where they might occur in the future. 

“Aerial view of Biscuit Basin after hydrothermal explosion” by Yellowstone National Park, Public Domain Mark So, what exactly is a hydrothermal explosion? 

Hydrothermal explosions occur when the pressure in a hydrothermal (hot water) system rapidly drops and the water flashes to steam. The water in geyser basins usually sits right around its boiling point at the surface. When it sits contained in chambers under the surface, the water experiences higher pressure. Increased pressure conditions allow the water to reach higher temperatures while remaining a liquid and at equilibrium. Equilibrium—the state of balance in earth systems—is what the thermal system needs to stay stable. 

Think of these thermal fields like pressure cookers. Heat and pressure build up in reservoirs under the surface, putting the water under a tremendous amount of stress. In your pressure cooker at home, a pressure release valve manages the stress. This keeps the pressure in the cooker container at a manageable level. Unfortunately, the Earth does not have the same features, so the surrounding rocks trap water in reservoirs and pressure builds unchecked. Ultimately, this energy has nowhere else to go and results in an explosion.

But how does the pressure drop so suddenly? 

Hydrothermal systems are extremely dynamic, with many distinct factors contributing to their functions. All these factors need to be in balance to ensure equilibrium in the system, with the biggest players being hot water and earthquakes. 

Hydrothermal Fluids 

Hydrothermal fluids are chemically active, meaning the water carries dissolved elements from the rocks around them. As water moves towards the surface, these ions precipitate out of the water and deposit as solid minerals—think stalactites and stalagmites in caves! It’s the same process. 

When these minerals continually deposit in the same location, they can eventually cap the system and cause pressure to build underground. As this pressure reaches a critical level, these caps can crack, allowing the pressure in the system to rapidly dissipate, causing the fluid to flash to steam. 

 Earthquakes 

Seismic events change what’s happening under the surface every time they happen, which in Yellowstone is quite often. But don’t worry! They are extremely small (not noticeable to humans) and completely normal in the park. Small earthquake events help to keep plumbing systems open in these thermal areas, which ensures that conduits do not get clogged with mineral deposits. 

Larger earthquakes, however, can cause major changes in these thermal systems that can ultimately facilitate hydrothermal explosions. The Hebgen Lake earthquake in the summer of 1959 serves as an example of one of these events. This quake caused major changes in and around the park and was attributed to a few small explosions in thermal areas. 

“Sapphire Pool erupting (7 September 1959)” Original photo taken by Lewis; public domain image provided by the American National Park Service View of Hebgen Lake, MT, looking east toward Yellowstone National Park. January 25, 2017 Forest Service Northern Region / Flickr What happens when a liquid flashes into a gas?  

Well, for one, it takes up more space. When water becomes water vapor (steam), it can expand to 1000 times its original volume. Which, on the surface, is not an issue. The issue with this dramatic volume difference in geyser basins is that the gas is contained within the rocks. Rocks cannot move to accommodate the added volume, so they are thrown out of the way in the violent and dramatic manner seen at Biscuit Basin.  

So… these explosions don’t spell doom?  

Nope! They are completely normal and happen multiple times throughout the year in the park and globally. Studies in Yellowstone have shown that explosions like these are not directly related to the magmatic activity of the volcano. They are merely the result of pressure dynamics beneath Earth’s surface. 

Geologists can use Biscuit Basin to learn more about how these processes occur and what signs they might show before they happen. After the eruption in 2024, the United States Geological Survey set up a multitude of instruments to collect data on the basin. Temporary seismic stations, temperature probes, cameras, and much more allow the USGS to receive a near constant stream of data from this area.  

Scientists with the Yellowstone Volcano Observatory are using this data to figure out patterns in hydrothermal explosion activity, allowing them to investigate possibilities for forecasting these events. Looking for temperature fluctuations or seismic activity that coincides with these eruptions gives scientists a more well-rounded picture of what is happening beneath the earth, so they can apply it to other areas in the future.  

Lexi Luft