Ash/Tephra Fall

The Yellowstone Plateau in the northern Rocky Mountains in Wyoming, Montana, and Idaho is centered on a youthful, active volcanic system with subterranean magma (molten rock), boiling, pressurized waters, and a variety of active faults with significant earthquake hazard.

The Yellowstone Plateau Volcanic Field forms the high continental divide between the northern and middle Rocky Mountains.

Yellowstone's volcanism is the most recent in a 17 million-year history of volcanic activity that progressed from southwest to northeast along the Snake River Plain.

The most likely type of volcanic eruption at Yellowstone would produce lava flows of either rhyolite or basalt.

Volcanic rock deposits from eruptions in the Yellowstone Plateau Volcanic Field reveal that a typical sequence occurs as the magma storage region evolves.

Ash and tephra fall are the most widespread volcanic hazard. Even lava-flow eruptions could include explosive phases that might produce significant volumes of volcanic ash and pumice. The least-likely scenario is another caldera-forming eruption, in which case much of the United States, southern Canada, and northern Mexico would experience some ashfall.

Decades of geologic work in Yellowstone has led scientists to understanding how and when eruptions took place from the Plateau.