Lake

Yellowstone Lake

West Thumb, the lake’s round western bay, is itself a volcanic crater — formed by an eruption about 174,000 years ago.

Source: nps.gov

The lake sits inside the Yellowstone Caldera, 30 by 45 miles across, left by an eruption 631,000 years ago. The area still has 700 to 3,000 earthquakes a year.

Source: nps.gov