Scientists with the Yellowstone Volcano Observatory are tracking a broad, slowly rising section of ground along the northern rim of the Yellowstone Caldera—an area roughly comparable in size to the city of Chicago. Instruments first detected the change in July 2025, and by January 2026 the region had risen about an inch. While the scale of the uplift has captured public attention, researchers emphasize that this behavior is neither unprecedented nor indicative of an impending eruption. Instead, it reflects the caldera’s long‑established pattern of gradual inflation and deflation driven by deep magmatic and hydrothermal processes.

The uplift is centered south of Norris Geyser Basin, near Gibbon Falls, in a zone the USGS refers to as the Norris Uplift Anomaly. This area last experienced a significant deformation cycle between 1996 and 2004, when the ground rose several inches before subsiding again. After that episode, the region remained mostly quiet for nearly two decades. The current rise appears to be a renewed pulse of the same long‑term pattern, likely caused by the movement of magma or hot fluids about nine miles beneath the surface. These deep intrusions do not necessarily migrate upward toward the surface; instead, they can spread laterally, pressurizing the overlying rock and causing broad, gentle uplift detectable only through sensitive GPS and InSAR measurements.

Although the phrase “Chicago‑sized bulge” suggests something dramatic, the deformation is extremely subtle on the ground. Visitors would not notice any change in the landscape, and the uplift is occurring far more slowly than the seasonal swelling and shrinking of the park’s hydrothermal systems. What makes it scientifically important is not the visual impact but the insight it provides into the caldera’s internal plumbing. Yellowstone’s crust is riddled with fractures, conduits, and reservoirs of hot water and partially molten rock. When pressure shifts within these systems, the surface responds. Tracking these movements helps scientists understand how heat and fluids circulate beneath one of the most active volcanic regions on Earth.

The current uplift also fits within a broader context of Yellowstone’s “breathing” cycles. Over the past century, the caldera floor has alternately risen and fallen by several feet, sometimes switching direction within a single year. These changes are not signs of instability but rather the natural rhythm of a large, living volcanic system. The USGS notes that uplift episodes like the one underway now have occurred many times without leading to eruptions or even significant seismic crises. In fact, Yellowstone’s last major eruption occurred 640,000 years ago, and its most recent lava flow was more than 70,000 years ago. Today, the most common signs of unrest are earthquake swarms and hydrothermal disturbances, neither of which has shown unusual activity associated with the current uplift.

Scientists continue to monitor the region closely, not because they expect an eruption, but because Yellowstone is one of the most instrumented volcanic systems in the world. Every shift in the ground, every change in gas chemistry, and every cluster of small quakes adds to a long‑term dataset that helps researchers refine their models of how large calderas behave. The present uplift is a reminder that Yellowstone remains dynamic, but it is also a testament to how well‑understood and carefully watched the system has become. For now, the Chicago‑sized rise is a geological curiosity—important to scientists, but not a threat to the public.