There are other supervolcanoes on Earth, some of which erupted in prehistoric times and could erupt again. At least one has had an eruption bigger than Yellowstone's largest and may have played a critical role in shaping human history.

The history — even the location — of others is less certain. Some are identifiable only by the deep layers of ash they left behind, such as the more than 1,000 cubic miles of tuff dumped in eastern Africa and the Red Sea by a mystery eruption somewhere in Ethiopia.

There are also calderas that have just not been well studied, a prime example being Ethiopia's 460-square-mile Awasa caldera and the 1,000-square-mile Pastos Grandes caldera of Bolivia, which rivals the latter, which in turn rivals the largest in the world: Lake Toba, Indonesia.

START THE TOUR OF OTHER SUPERVOLCANOES»