Geological analysis has revealed more details about the cause of last week’s spectacular eruption at Yellowstone National Park. It’s still unclear whether the incident has permanently altered the national park’s underground composition, but experts say a newly formed geyser is a distinct possibility.
Video of the July 23 explosion showed chunks of rock, along with clouds of water and steam, being thrown up to 600 feet (183 meters) into the air as park visitors ran for cover. Portions of the nearby boardwalk were severely damaged and the area of the park where the incident occurred, Biscuit Basin, remains closed.
Some of the rocks measured several feet across and weighed hundreds of pounds, according to Michael Poland, a geophysicist with the United States Geological Survey (USGS). Luckily, the debris was blown away from the boardwalk and there were no reports of injuries.
Geologists concluded that the rocks were composed of glacial materials, sandstone, siltstone, and gravel. All of these materials are found relatively close to the surface. As Poland points out, none of the rock samples were rhyolite bedrock, which lies 175 feet (50 meters) below the area’s surface.
“This indicates that the explosion was generated at a depth much shallower than that to have not disturbed the bedrock,” Poland explained. “This is not surprising, because hydrothermal conduits mostly exist at shallow levels beneath the surface in Yellowstone.”
The analysis confirms the USGS’s initial conclusion that the blast was caused by an accumulation of hot water and steam in underground conduits that had gotten clogged by a buildup of silica. It’s a similar process to what occurs in geysers like Old Faithful, but unlike geysers, there is no well-worn path for the steam and water to travel to the surface. Instead, the pressure built up until it was stronger than the rock above it. Then, kaboom!
The explosion’s aftermath “clearly changed the shallow hydrothermal flow paths in the area,” Poland said, but exactly how still needs to be studied. Among the possibilities is that the burst cleared the way for a new geyser to form. Or, now that the pressure has dissipated, a return to the status quo could be in order.
Explosions of this sort aren’t unusual in Yellowstone. In 2018, a similar, albeit far smaller, explosion occurred near the famous Old Faithful geyser. The park is also home to a crater in Mary Bay that dates back 13,800 years and, at 1.5 miles (2.5 kilometers) across, is the largest known hydrothermal crater in the world.
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