What geologists discovered in Yellowstone is as beautiful as it is disturbing

A new milky-blue pool opened at Yellowstone’s Norris Geyser Basin. U.S. Geological Survey (USGS) geologists traced its formation to a window from late December 2024 to early February 2025, using satellite images and field evidence gathered in April.

Michael Poland, a USGS geophysicist and Scientist in Charge of the Yellowstone Volcano Observatory, helped document the discovery.

His team described a 13-foot-wide pool, one foot below the rim, with water near 109°F and a ring of ejected rocks coated in fine gray mud. 

The walls show a thin coating that marks an earlier, higher water level. Nearby rocks up to one foot across point to brief bursts strong enough to toss debris a short distance. 

Silica-rich water scatters light, creating a pale-blue hue typical of hot water that dissolves and carries minerals upward.

Steam bursts, not eruptions

A hydrothermal explosion happens when hot water flashes to steam near the surface and pressure breaks rock. It is not the same as a volcanic eruption, and it does not signal fresh magma movement.  

Events span a wide range, from small pits a few feet across to craters bigger than an acre. Those on the scale of the 1989 Porkchop event tend to occur every several years, according to an analysis. 

Yellowstone holds thousands of hydrothermal features, so occasional small blasts fit the system’s normal rhythm. They still pose hazards in thermal basins – which is why boardwalks and closures exist.  

Watching Yellowstone from all angles

Scientists used high resolution satellites to pin down timing, spotting a depression by January 6, 2025 and a water filled pit by February 13, 2025. Those images complement notes from the April 10, 2025 maintenance trip.  

The Norris basin now has a dedicated monitoring station. It tracks low frequency infrasound, weather, ground deformation, and small quakes to catch short lived activity.  

During the formation window, the array recorded weak acoustic signals from the direction of the pool on December 25, 2024, January 15, 2025, and February 11, 2025.

Seismic instruments did not show matching signals, which points away from one big blast.  

Pool carved by pressure releases

“Clearly, the new thermal feature did not form in a single major explosive event. Rather, it appears to have developed through multiple small events that created a pit later filled with silica-rich water,” said Poland.

That pattern fits the lack of a strong explosion signal on the infrasound system during that time. It also matches the modest scatter of rocks and the skim of fine mud around the rim.  

The simplest view is a sequence of shallow pressure releases that carved the pool, then eased. Satellite and acoustic clues line up with those short bursts.  

Looking back at Porkchop

Porkchop Geyser is one of the more dramatic features in Yellowstone National Park’s Norris Geyser Basin.

For many years, it wasn’t really a geyser at all – it was a hot spring that boiled steadily, shooting a narrow jet of water and steam almost like a pressure cooker with the lid cracked open.

What made Porkchop unusual was that it ran almost continuously, unlike most geysers that erupt in bursts and then rest.

Scientists think the narrow vent of the geyser created high pressure, forcing water to spout out in a steady stream that sometimes reached 20 feet high.

In 1989, Porkchop Geyser in the same basin exploded and left behind a debris apron and a new crater. That well recorded case shows what a larger blast looks like when a vent chokes and pressure spikes.  

The new Tree Island pool is smaller and gentler, showing up as a modest change rather than a dramatic scar. It adds one more data point to a record that ranges from quiet simmering to rare violent bursts.  

Significance for Yellowstone

Norris Geyser Basin ranks among the hottest and most changeable parts of the park. It sits within the Yellowstone Caldera, where hot fluids and gas move through fractured rock at shallow depths.  

Features like this remind us that thermal basins are active geologic neighborhoods, not static attractions. They call for caution and patience from anyone on the boardwalks.  

Teams will keep watching temperature logs, infrasound traces, and aerial imagery through the seasons. Spring snowmelt and summer heat can shift fluid flow, so the pool may change as its plumbing evolves.  

If activity ramps up, instruments will catch it and managers can adjust access to keep people safe. If little changes, the pool will settle into the busy mosaic of Norris, a new face in a familiar crowd.  

The study is published in USGS Caldera Chronicles.

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