Photos

This is Yellowstone River, the slow but relentless demolition force that is carving out the brightly colored Grand Canyon of the Yellowstone. Looking down into the earth from the lip of the canyon to the river below is a trip backward in time through successive volcanic eruptions: from 640,000 years ago; 160,000 years ago; and 70,000 years ago. Layers of sulfur-covered lava from those eruptions give the river, the canyon, and the park its name.

Actually, the excavation of the canyon is more complex than just the slow but consistent action of this one river. The majority of the rock was formed during the first eruption, a cataclysmic event that formed the current caldera. Hundreds of cubic miles of pyroclastic material exploded from the supervolcano, and one thousand square miles of earth collapsed two thirds of a mile (one km) deep into a giant crater. This crater filled with lava, and giant lava flows spilled out and over the landscape for thousands of years. The Canyon Rhyolite flow reached the site of the current canyon. Geothermal forces weakened the lava from that flow, and saturated the color. Water flowing out of rivers and lakes that were formed and redirected by other lava flows started the carving. Then, three separate episodes of glaciation followed by massive melts each deepened and cleaned out the canyon. The last glacier, which melted 10,000 years ago, left much of what is seen today.

The Grand Canyon of the Yellowstone, Yellowstone Park, Wyoming, August 8, 2008

Sources:
“Yellowstone National Park.” Wikipedia: The Free Encyclopedia. 24 June 2009
“The Grand Canyon of the Yellowstone Tour.” Yellowstone Online Tours. National Park Service, US Dept. of the Interior. 26 June 2009 < http://mms.nps.gov/yell/features/canyontour/index.htm>