Lava flows in Yellowstone! (Yellowstone Monthly Update September 2025)

Picture a Yellowstone eruption. What comes to mind? It’s a huge explosion, right? Like the one that formed the caldera about 631,000 years ago. But the most common form of eruption in Yellowstone isn’t a huge explosion, it’s a lava flow.

Yellowstone’s most recent lava flow occurred about 70,000 years ago. The type of lava that erupted is not what you might see in Hawaii with its fountains of molten rock and fast-flowing channels of basalt. In Yellowstone, we're talking about thick, viscous flows of rhyolite lava that slowly move across the landscape like a massive wall of rock.

These rhyolite lava flows erupted after the formation of Yellowstone Caldera. What we have found from mapping and studying lava flows is that the rhyolite lava flows are not evenly spaced over time. Eruptions seem to come in clusters. There are several lava flows and then tens of thousands of years of nothing, and then several lava flows, and tens of thousands of years of nothing. Right now? We're in one of those periods of tens of thousands of years of nothing.

The most likely form of any future eruptive activity at Yellowstone is a lava flow. But it's not something we're worried about in the near-term. We have found from seismic imaging that the Yellowstone magma chamber is mostly solid. But if it were to heat up, the most likely future event would be a lava flow, similar to those shown in this video.

During the month of August 2025, the University of Utah Seismograph Stations, which monitors and operates the Yellowstone seismic network, located 94 earthquakes. Deformation trends (subsidence) continue. Steamboat Geyser had minor activity but no major water eruption. Yellowstone Volcano remains at normal, background levels of activity.