Is the Grand Canyon Still Growing?

Perhaps John Muir said it best. If you happened to find yourself unknowingly on the rim of the Grand Canyon, the chasm stretching before you would seem "as novel to you, as unearthly in the color and grandeur and quantity of its architecture, as if you had found it after death, on some other star …"

That incredible site has humbled us all, including scientists who have struggled for decades to understand the mechanisms that gave us this great treasure.

But teams of scientists from across the country are scouring the canyon these days, and they are uncovering enough of the canyon's secrets to render most textbooks obsolete.

The evidence suggests that large sections of the canyon are much younger than had been thought, and some of the most dramatic features may be no more than 600,000 years old, making the canyon a geological infant. And although scientists had thought the cutting of the canyon by the mighty Colorado River was pretty well wrapped up more than a million years ago, the most recent research suggests it is still going on.

So the Grand Canyon appears to be a work in progress, not a fait accompli.

Sudden, Violent Floods

Many scientists have presumed that the canyon was cut gradually and at a steady pace by the flow of the river, but some remarkable research indicates that the cutting has been periodic, punctuated by catastrophic floods so huge they are hard to imagine.

According to research by scientists from the University of Arizona, the U.S. Geological Survey, and the University of Utah, one flood alone was 37 times larger than the largest known flood from the Mississippi River.

Scientists are in general agreement that the birth of the canyon started about 6 million years ago — still just the blinking of an eye in geological time — when the Colorado River formed its present path to the sea. To say that the river created the canyon is a gross oversimplification. But it was the dominant player, carving a trench that exposed layers of rock along its side to wind and water erosion.

The region was quite different in the beginning than it is today, with active volcanoes along the rim, and earthquake faults that to this day remain among the most active in Arizona. From time to time, the volcanoes would erupt, sending lava flowing down the sides of the canyon and into the river.

Scientists have known for more than a century that the lava sometimes formed dams across the river and the dams gradually eroded away by the flowing water. Or so they thought.

As part of her doctoral dissertation at the University of Utah, Cassandra Fenton has spent a lot of time down in the canyon, collecting samples left behind by some of those lava dams. The samples have quite a story to tell. It seems that many of the dams did not erode away slowly, as had been believed. Some of them failed big time, releasing massive floods to scour the canyon for miles downstream.

Fenton and her colleagues have found evidence of at least five major floods resulting from lava dams that failed between 100,000 and 525,000 years ago. And when the dams gave way, they apparently did so quickly.

"As soon as it began to leak, it could have taken less than 10 hours to fail," says Fenton, who is enroute to Tucson to begin a new job with the U.S. Geological Survey.

Glass Lava

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