Native Americans knew Yellowstone for thousands of years - the Shoshone, Crow, and Blackfeet hunted in the region and used obsidian from its volcanic flows for tools. European trappers heard stories of 'boiling rivers' and 'smoking mountains' that they dismissed as tall tales.

In 1870, the Washburn-Langford-Doane Expedition documented the geothermal wonders. Their reports led to the creation of Yellowstone National Park in 1872 - the world's first national park, set aside 'for the benefit and enjoyment of the people.' They had no idea what lay beneath.

A volcanic hotspot sits beneath Yellowstone - a plume of magma rising from deep in the Earth's mantle. The hotspot is stationary, but the North American plate drifts over it, leaving a trail of volcanic calderas across Idaho. Yellowstone is the current position.

The magma chamber beneath the park is approximately 40 by 50 miles and 3-10 miles deep - enough molten rock to fill the Grand Canyon several times over. Three supereruptions have occurred: 2.1 million years ago, 1.3 million years ago, and 640,000 years ago. The average interval suggests another is statistically due.

Yellowstone contains over 10,000 geothermal features - more than anywhere else on Earth. Old Faithful erupts every 60-90 minutes, sending 8,400 gallons of boiling water 130 feet into the air. Grand Prismatic Spring, the largest hot spring in the US, displays rainbow colors from thermophilic bacteria. Mammoth Hot Springs builds terraces of travertine.

The geothermal activity is beautiful but deadly. Over 20 people have died falling into hot springs since records began. Pets have leaped into scalding pools. The ground itself is unstable - trails are closed when new thermal features emerge. Beauty and danger are inseparable at Yellowstone.

A full supereruption would be catastrophic. Pyroclastic flows would incinerate everything within 100 miles. Ash would bury states under feet of debris. The ash cloud would circle the globe, blocking sunlight and dropping temperatures for years - a volcanic winter.

Geologists estimate the annual probability of eruption at about 1 in 730,000 - low, but not zero. Yellowstone is constantly monitored: seismographs detect earthquakes (1,500-2,000 annually), GPS measures ground deformation, satellites track thermal output. So far, nothing suggests imminent eruption. But 'so far' covers a tiny fraction of geological time.

Four million visitors come to Yellowstone annually, walking boardwalks over thermal basins, watching geysers erupt, spotting bison and bears. Most have no idea they're walking on a supervolcano. The park doesn't hide the geology, but it doesn't emphasize it either.

Yellowstone represents something rare: a landscape so valuable that humanity set it aside before development could destroy it. The supervolcano beneath will do what it does regardless of human wishes. Until then, the geysers will spout, the springs will shimmer, and visitors will marvel at forces they can barely comprehend.