Imagine that you are in a glider, soaring over the Grand Canyon. You see layers of rock, red and yellow, brown and black. You see a deep gorge, as if someone has cut a trench a mile deep out of the layers of rock. Some places the cut is narrow, the walls steep, and some places the canyon widens out so that the walls stretch wide apart. And at the bottom, through the 277 miles of the canyon, runs the Colorado River.
Mostly, the river looks rather calm and quiet from above, oozing along the bottom of the great channel. But it's not quite right to think of the canyon as being the route that the river follows. In fact, the river is what carved the canyon.
Hundreds of millions of years ago, changes in the earth's climate brought changes to the environment where the Grand Canyon is now. At different times, deserts, swamps, and inland seas covered the area, alternately, for hundreds of thousands, if not millions, of years apiece.
With each new environment a new layer of sediment was deposited on top of the previous one. The weight from each new layer pressed and compacted the ones below, cementing each layer into rock.
Tectonic plates, blocks of the Earth's crust, shifted these layers of rock around. When the Kula and Farallon plates slid under the North American plate 75 million years ago the movement forced the land to push up, creating the mountains we now call the Rocky Mountain range. A similar movement 60 million years later formed the flat rise of land we call the Colorado Plateau.
The first uplift created the path of the Colorado River. And as the river ran through the layered rock, the water began to erode the relatively soft sandstone. As the river flowed along, bits of rock moved along with it, carried to the river's end at the Gulf of Mexico. The second uplift increased the Colorado's already steep slope, causing the river to flow faster and erode the rock more quickly. But it wasn't until the Ice Ages, a little more than 2 million years ago, that the Colorado River did most of its work. During this period of the Earth's history the Colorado ran high from snow and rain, carrying more rock and soil than ever before. Boulders as big as trucks went crashing down the river's length, as the power of the water cut the canyon deeper and deeper.
There's a dam across the Colorado River now, and the river flows more slowly. But still, gradually, the Grand Canyon continues to be carved deeper and deeper. So you might want to ask yourself this: Which is stronger, rock or water? If you pour water on a rock, the water will flow away, while the rock stands firm. But given enough time (lots and lots of time!) it is the power of water that carved the Grand Canyon out of the rock.
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Last updated on Tuesday, August 21, 2012.
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