A vast, city-scale rise in the ground along the north rim of Yellowstone’s volcanic system has quietly grown to the size of Chicago, and instruments show it is still lifting. The swelling is subtle to the naked eye, measured in inches rather than feet, but it signals that the restless supervolcano beneath Yellowstone National Park is once again on the move. Scientists are tracking the deformation in real time, parsing whether it reflects a routine pulse of magma and gas or the early stages of something more consequential.
What they see so far is a familiar pattern of uplift that has appeared and faded before, driven by changes more than 8 miles below the surface. The current bulge, which has risen about an inch since midsummer, fits into a long history of Yellowstone breathing in and out, yet its Chicago-scale footprint and location along the park’s volatile north rim have sharpened the focus of researchers who monitor every millimeter of motion.
The Chicago-size bulge taking shape under Yellowstone
Ground sensors and satellite data show that a broad patch of terrain along the volcano’s northern edge has heaved upward over the past several months, forming what scientists describe as a Chicago-sized bulge. The uplifted area, centered near the north rim of the caldera in Yellowstone National Park, has climbed roughly an inch since July, a small vertical change spread across a footprint comparable to one of the largest cities in the United States. According to scientists who specialize in Yellowstone’s behavior, that rise is concentrated along a stretch of the north rim that has a track record of dramatic thermal and seismic activity.
Researchers say the bulge is not a single dome but a broad, gentle warp in the landscape, extending for many miles and affecting everything from forested hillsides to hydrothermal basins. The deformation is large enough to register clearly on GPS stations and radar satellites, yet subtle enough that a hiker might never notice it underfoot. Jan, one of the experts cited in recent reporting, has emphasized that the uplift is part of a complex pattern of inflation and deflation that Yellowstone has displayed for decades, even as the current Chicago-scale feature continues to grow.
A deeper pattern of uplift tied to magma and gas
The new bulge is not an isolated quirk but the latest expression of a deeper cycle that has been documented across the Yellowstone system. Earlier this year, geophysicists confirmed that the ground at Yellowstone is rising again after a lull that lasted several years, and they note that the current pattern mirrors past episodes linked to magma accumulation more than 8 miles, or 14 kilometers, beneath the surface. That depth estimate comes from seismic imaging and deformation modeling, which together suggest that fresh molten rock and pressurized gas are intruding into the crust, pushing the overlying rock upward in a slow, steady swell that matches the recent rising ground signal.
Jan and other researchers stress that such uplift is a hallmark of active caldera systems and does not automatically point to an imminent eruption. Instead, it reflects the constant recharging and degassing of the magma reservoir that has powered Yellowstone’s geysers and hot springs for hundreds of thousands of years. The current Chicago-scale swelling fits that pattern, with the inch of rise since July lining up with a broader regional trend of inflation that has been observed in multiple uplift centers across the park, including the Norris region and the central caldera floor.
The Norris Uplift Anomaly and the north rim hot zone
The location of the new bulge near the north rim is especially notable because that sector of the park has produced some of Yellowstone’s most dramatic ground changes. Scientists first identified a feature in this area known as the Norris Uplift Anomaly when a large patch of terrain near the Norris Geyser Basin began to rise rapidly, a process often driven by the movement of magma or gas underground. The current Chicago-scale swelling appears to overlap with that history, and recent reports describe a gigantic bulge along the volcano’s north rim that is large enough to be mapped from space yet difficult to see from the ground, a description that matches the earlier city-sized bulge labeled Dubbed the Norris Uplift Anomaly.
That anomaly, which was Dubbed the Norris Uplift Anomaly when it first appeared, has become a focal point for understanding how fluids move through Yellowstone’s upper crust. Seismic swarms, changes in geyser behavior, and shifts in hydrothermal discharge have all been documented in the Norris region, suggesting that it acts as a pressure valve for deeper magmatic processes. The fact that the current Chicago-scale uplift is concentrated along this same north rim corridor reinforces the idea that the Norris Uplift Anomaly is not a one-off event but part of a recurring pattern in which magma and gas periodically accumulate, deform the surface, and then either stall or migrate, leaving behind a record etched in the rising and falling ground.
What official monitors are seeing beneath the caldera
While the Chicago-sized bulge has captured public attention, the scientists tasked with watching Yellowstone are focused on a broader suite of measurements that frame the risk. The official monitoring network, which includes the Yellowstone Volcano Observatory and its partners, tracks seismicity, ground tilt, gas emissions, and thermal output across the caldera. In its latest notice for YELLOWSTONE, identified by VNUM #325010 and located at 44°25’48” N and 110°40’12” W, the observatory reported that activity remains within the long-term background range, even as uplift continues. That update, issued on a Friday at 2:30 PM MST (21:30 UTC), underscores that the current deformation is being watched closely but has not yet triggered any change in alert level for the YELLOWSTONE system.
In practical terms, that means seismometers are not recording the kind of intense, sustained earthquake swarms that would typically accompany magma moving rapidly toward the surface, and gas sensors have not detected a surge in emissions that would signal a major shift in the plumbing. Instead, the data point to a slow, deep pressurization that is consistent with the magma reservoir gradually recharging. The coordinates 44°25’48” N and 110°40’12” W, cited in the official notice, place the monitored center squarely within the caldera complex, tying the Chicago-scale bulge into a larger, carefully watched system rather than an isolated curiosity.
How worried should we be about “The Next Big Eruption”?
Any mention of Yellowstone swelling inevitably revives public anxiety about a catastrophic supereruption, but the scientists closest to the data are far more cautious in their language. Long-term studies of the caldera’s history show that the intervals between its largest explosive events are highly variable, and current evidence does not point to an imminent repeat. In fact, experts emphasize that the most recent period of dormancy has already lasted 70,000 years, a span that highlights how slowly these systems typically evolve. In a detailed overview of the volcano’s behavior, researchers discussing The Next Big Eruption note that they do not expect an eruption soon and instead focus on incremental changes in seismicity, tilt, temperature, and geothermal discharge as the key indicators to watch for any shift in status, a perspective laid out in analyses of Next Big Eruption.
From my vantage point, the Chicago-sized bulge is best understood as a vivid reminder that Yellowstone is a living volcanic system, not a dormant relic frozen in time. The inch of uplift since July, the deep magma more than 8 miles down, the recurring behavior of the Norris Uplift Anomaly, and the steady stream of official notices all point to a caldera that is active but not on the brink. The real story is not a looming doomsday scenario, but the quiet, relentless work of scientists who read tiny shifts in elevation and subtle tremors as clues to processes unfolding far below our feet, turning a swelling patch of ground the size of Chicago into a window on one of Earth’s most powerful engines.
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