Yellowstone Caldera and Mount St. Helens
The Yellowstone River flowing through Hayden Valley in the northeastern part of the Yellowstone Caldera, Yellowstone National Park, Wyoming, USA. The caldera rim can be seen in the distance.
A magnitude 5.1 earthquake at 8:32 a.m. PDT on May 18, 1980 caused the entire weakened north face of Mount St. Helens to slide away, suddenly exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure and triggering a major pumice and ash eruption.
Yellowstone Caldera: Ed Austin and Herb Jone, National Park Service
Mount St. Helens: Austin Post, USGS
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