Before the supereruptions: Yellowstone’s ancient volcanoes (Yellowstone monthly update – August 2026)

Long before explosive eruptions formed the Yellowstone Caldera and heat from the magmatic system began feeding a dynamic hydrothermal system, there was the Absaroka volcanic range. Remnants of the rugged terrain are still visible on the east and north sides of Yellowstone National Park.

The Absaroka volcanoes were active from about 43 to 53 million years ago and probably looked a lot like volcanoes of the Cascade Range look today. During their eruptive period, the Absaroka volcanoes fed numerous debris flows and mudflows that buried the surrounding forests. These forests are preserved as petrified wood, and one of the densest concentrations of petrified wood in the world is in Yellowstone—for example, along Specimen Ridge and at the Petrified Tree site. The Absaroka rocks are also home to the largest landslide above water that's known on planet Earth—the Heart Mountain slide just east of Yellowstone National Park. 

During the month of August 2026, the University of Utah Seismograph Stations, which monitors and operates the Yellowstone seismic network, located 61 earthquakes. The largest was a Magnitude 2.0. There has been no significant uplift or subsidence of the caldera since January 2026. Echinus Geyser had an overflow event and there were two water eruptions at Giant Geyser, on August 17 and 30. Yellowstone volcano remains at normal, background levels of activity.

For questions, email yvowebteam@usgs.gov

Read Caldera Chronicles https://www.usgs.gov/volcanoes/yellowstone/caldera-chronicles

Visit Yellowstone Volcano Observatory website https://www.usgs.gov/volcanoes/yellowstone