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. Within the next few decades, large and moderate earthquakes and hydrothermal explosions are certain to occur. Volcanic eruptions are less likely, but are ultimately inevitable in this active volcanic region.
Over the past 2.1 million years Yellowstone volcano has had three immense explosive volcanic eruptions that blanketed parts of the North American continent with ash and debris. Each of these eruptions created sizable calderas: basins formed by collapse of the ground after evacuation of subsurface magma reservoirs. The Yellowstone Caldera, which comprises nearly one-third of the land area in the park, formed 0.64 million years ago and was followed by dozens of less explosive but large lava flows, the last of which erupted 70,000 years ago. Basin and Range extension of the western U.S. has created a series of regional faults that are responsible for large and devastating earthquakes in the Yellowstone region along the Teton and Hebgen Lake Faults; most recently a devastating Ms 7.5 earthquake in 1959 killed 28 people. Yellowstone’s famous geothermal waters create fabulous hot springs and geysers but occasionally explode catastrophically to create hydrothermal explosion craters found throughout the park.