While most people think of Yellowstone National Park as being a collection of small geothermal features, the geological reality is that the majority of the park is located within a huge caldera: the collapsed dome of a volcano. Geologists have determined that over the last few million years, there have been multiple enormous eruptions of the entire Yellowstone area; these were cataclysmic events that would, for example, make the 1980 eruption of Mount St. Helens look like a child's science experiment by comparison.

This image shows in the distance part of the rim of the Yellowstone Caldera. It was taken near the top of Dunraven Pass, which at 8859 feet, is the highest roadside elevation in Yellowstone National Park.