Is Yellowstone waking up? October brought only small quakes, no significant uplift and a green alert

Sixty-six earthquakes were located in the Yellowstone National Park region during October, and the strongest was a magnitude 2.0 micro earthquake on Oct. 4. The Yellowstone Volcano Observatory filed that tally in its monthly update on Nov. 2, alongside an unchanged volcano alert level of NORMAL and an aviation color code of GREEN.

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Anyone who has read online that the caldera is stirring can check the observatory’s own numbers for the month, and they point the other way: a modest count of small events, ground measurements that are mostly flat, and no change to any alert label.

Sixty-six quakes, no swarms and one magnitude 2.0

The University of Utah Seismograph Stations located the 66 earthquakes, according to the observatory’s monthly update. The largest struck at 5:32 p.m. MDT on Oct. 4, about 15 miles south of West Thumb, and the report states that no swarms were identified during the month. Seismicity stayed at background levels.

A column by Jamie Farrell, the observatory’s chief seismologist and a University of Utah research professor, sets the long-run baseline at about 1,500 to 2,500 earthquakes a year for the region. Spread across twelve months, that is roughly 125 to 208 a month, which puts October’s 66 below the usual pace. Farrell’s column also recalls what a genuinely restless stretch looks like: the 2013-2014 Norris uplift peaked with a magnitude 4.8 quake on March 30, 2014, the largest in Yellowstone since 1975. October’s biggest event sat 2.8 magnitude units under that one.

Farrell’s column also describes a different kind of event, the swarm that began in late December 2008 under Stevenson Island in Yellowstone Lake and migrated about 10 days north toward Fishing Bridge. As it passed, a GPS station called LKWY slid about 7 millimeters west, and the column attributes the motion to pressurized fluids moving north through the crust. Swarms of that sort are what the observatory’s phrase “no swarms identified” rules out for October, and the contrast shows why the absence of swarms matters as much as the raw count.

Flat GPS lines, and the Norris north-rim rise behind them

Continuous GPS stations show little net deformation of the caldera or the north caldera region over the past several months. The update attributes the small month-to-month wiggles mostly to seasonal groundwater changes, and it reports no significant uplift or subsidence.

The word “significant” matters, because a slow rise has been underway on the caldera’s north rim. The USGS Norris Uplift Anomaly page says a small area just south of Norris Geyser Basin began rising in July 2025. A semipermanent GPS station near the center, BRYL, gained about 2 centimeters (0.8 inch) from July to late September 2025, and satellite radar data from October 2024 to October 2025 also show about 2 centimeters. For scale, the same spot rose about 12 centimeters (4.7 inches) between 1996 and 2004 and then sank about 7 centimeters.

The USGS places the likely cause in magma accumulating about 14 kilometers (9 miles) down, too deep for hydrothermal fluids, and states that the uplift does not indicate an increased chance of eruption. The top of the magma chamber sits near 3.8 kilometers (2.4 miles). Before an eruption, the page says, scientists would expect faster deformation, a shallower source, a major jump in earthquakes and changes in gas and heat output. Michael Poland, the observatory’s Scientist-in-Charge, is the named scientist on that page, which describes an eruption as unlikely anytime soon and calls strong earthquakes and hydrothermal explosions the likelier hazards on human timescales. Seismicity near the uplift center ticked up from September through December 2025, with more than 200 earthquakes and a largest event of magnitude 2.7, and Farrell’s column adds a November 2025 swarm directly over the center of uplift.

NORMAL, GREEN and the hydrothermal events that did occur

The observatory’s Hazard Notification System entry lists Yellowstone at NORMAL for volcano alert level and GREEN for aviation color code, the same pairing it carried in the Oct. 1 update. Neither label changed with the Nov. 2 report.

The activity that did register in October was hydrothermal. A small pool at Biscuit Basin, formed by collapse after the June 13, 2026 hydrothermal explosion, erupted at least twice in small fashion, and Steamboat Geyser produced only minor eruptions; the NPS eruption table shows one major Steamboat eruption in 2026, on Feb. 27. The observatory added a sensor station near Geyser Hill in early September, described in a column by Poland and Farrell, to catch exactly this kind of change, since Biscuit Basin has been closed to visitors since the July 2024 explosion.

The next monthly update will cover November. Farrell’s column calls the outcome of the Norris north-rim episode uncertain, with more or larger earthquakes possible, so the GPS lines near BRYL are the thing to watch. Whether the quiet October reading marks a pause in that rise or only a seasonal lull in the data is a question the monthly updates will have to answer over the winter.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.