Yellowstone National Park guide · 1 min read
Living Atop the Yellowstone Supervolcano Caldera
Most of Yellowstone rests on a supervolcano, a volcanic field capable of an enormous eruption.
The Yellowstone Caldera is the largest volcanic system in North America, and worldwide only the Lake Toba Caldera on Sumatra compares. The park marks the active end of a hotspot that the North American Plate has drifted across, leaving the Snake River Plain curving roughly 400 miles toward the Idaho-Oregon border.
Huge eruptions have struck here about every 600,000 years. The latest, around 631,000 years ago, burst from two vents, one near Old Faithful and another just north of Fishing Bridge. That blast was about 1,000 times the size of Mount St. Helens, and its ash has turned up across the continent. Afterward the emptied magma chamber caved in, leaving a basin 30 by 45 miles wide that later lava flows partly filled.
Yellowstone Lake fills part of that collapsed ground, in a basin covering 136 square miles. The early lake stood 200 feet above today's shoreline and stretched north across Hayden Valley to the foot of Mount Washburn. Look south across the water and you can pick out the caldera rim on the horizon.
The heat behind those ancient eruptions still drives more than 10,000 hydrothermal features: geysers, hot springs, fumaroles and mudpots. Over 500 geysers are active, more than half of all the geysers on Earth, with Old Faithful the best known. The ground stays restless too, with 1,000 to 3,000 earthquakes shaking the area each year.
For a look at the volcano's earlier chapters, stop at the columnar basalt near Tower Fall. Floods of basalt and other lava came before the great explosions of superheated ash and pumice, and these tall columns hold a record of that older activity in solid rock.
