Lobby > Exhibits > Why Geysers Erupt > Underlying Geology > Branded by a Volcano

Beginning a little more than two million years ago, three enormous volcanic eruptions have occurred in the Yellowstone area.

The first created a 2,400 square mile (3,862 sq. km) hole known as the Huckleberry Ridge Caldera. This crater extended from outside present-day Yellowstone National Park into the central area of the park.

The second eruption took place about 1.3 million years ago, just southwest of Yellowstone National Park. The Henry’s Fork Caldera covered approximately 15 square miles (24 sq. km).

Then 640,000 years ago, a third eruption created the Yellowstone Caldera in what is now the central part of the park. It extended about 1,000 square miles (1,609 sq. km)—just a little smaller than the state of Rhode Island. Approximately 80 smaller eruptions and lava flows followed the third major eruption. The most recent volcanic eruption at Yellowstone, a lava flow, occurred 70,000 years ago.

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