Canyon Virtual Tour


About 640,000 years ago, a huge volcanic eruption occurred in Yellowstone, emptying a large underground chamber of magma (partially molten rock). Volcanic ash spread for thousands of miles in a matter of minutes. The roof of this chamber slowly collapsed, forming a giant caldera 30 miles (45 km) across, 45 miles (75 km) long. The caldera began to fill with lava and sediments. Infilling of lava flows continued for hundreds and thousands of years.

Looking down from the Brink of Lower Falls.
Looking down from the Brink of Lower Falls (NPS/Neal Herbert).

Scientists think the oldest Grand Canyon of the Yellowstone formed in rock and sediments about 160,000 to 140,000 years ago. This paleocanyon was not as deep, wide or long as the canyon visible today.

Past and current hydrothermal activity altered and weakened the rhyolite, making the rocks softer. The Yellowstone River eroded these weakened rocks to deepen and widen the canyon, a process that continues today. The current canyon begins at Lower Falls and ends at Tower Fall.

The 308-foot (93 m) Lower Falls may have formed because the river flows over volcanic rock more resistant to erosion than the downstream rocks, which are hydrothermally altered. The 109-foot (33 m) Upper Falls flows over similar rocks. The large rocks upstream from Upper Falls are remnants of a lava flow resistant to erosion.

The multi-hued rocks of the canyon result from the hydrothermally altered rhyolite and sediments. Look closely at dark orange, brown, and green areas near the river for still-active hydrothermal features. Their activity—and that of water, wind, and earthquakes—continue to sculpt the canyon.

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