Teachers' Domain; Earth and Space Science; The Grand Canyon: How It Formed

Scientists argue the details of precisely how and when the Canyon was created. The mystery may never be completely solved because the river like a master criminal carried off the cruise as it carved the canyon. Many geologists now think it happened something like this. All of the Earth's oceans and continents ride upon enormous pieces of the earth's crust called plates which fit together like a restless jigsaw puzzle jostling each other at the edges. Eighteen million years ago two of these plate collided. At North America's West Coast. The Pacific plate slid under the North American plate creating the Rocky Mountains. And ultimately forcing the uplift of the whole Colorado Plateau. The combination of that mighty Colorado River flowing over the already rising plateau created a geological buzz saw a deep

from which the river could not escape. Many scientists now think it took only about four million years for the Colorado River to colonize the canyon compared to the rocks and its walls some nearly two billion years old. The canyon itself is a relative youngster. But the river is bust so all can account for only a narrow gash in the earth and in places the remains of the Grand Canyon are 18 miles apart. How did the canyon get so wide. What's important understand that the river by itself did not carve this canyon. The river did cut down its own channel but basically it's a transportation system it's the freight train that carried all the rest of the rock out and the canyon was widened out by all of the side streams and all the little regulates that are carving into the canyon wall. It's not the river that made the great white canyon that we see but all the tributary

drainage systems that led to the carving of the canyon. Side streams and tributaries flow into the main Colorado River. Gouging out their own side canyons like this one. When there's a violent storm. Truck sized boulders tear loose from the canyon walls and are driven headlong in a terrifying war of mud when Rock cold debris flows. This rare footage of a debris flow sweeping through a dried Valley was shot by scientists in China in 1990. Traveling 20 miles per hour. The flow packs the power of a river of liquid concrete. Here in the canyon. Such debris flows rip out of side cans.

Like this one. Finally emptying into the main stem of the Colorado. Given enough time. All rocks no matter how settled they may appear are subject to change. Now.