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

There are several lines of evidence that the dams failed, including bits of volcanic glass found embedded in the canyon walls. When the lava hit the river, the cold water was "hydro-explosive," she says, cooling the basaltic lava so quickly that it formed glass that in turn exploded into fragments.

More lava poured on top of the fragments until the dam was formed, sometimes spanning the entire canyon. But glass, of course, isn't the best building material for a dam.

"That isn't a dam that's constructed by people," Fenton says. "It's a natural dam. There's been no engineering behind it."

As she searched through the canyon, she found glass deposits of the type that were formed when the hot lava hit the cold water, and the deposits were scattered everywhere. That suggests, quite strongly, that the dams failed from the bottom up.

"We think there's evidence in our flood deposits that suggest the dams actually failed near the base," she says.

"These were high dams," adds hydrologist Robert H. Webb of the Geological Survey. "We estimate some were more than 1,500 feet tall."

When a dam fails, the water doesn't all come out in a steady stream. The water level is much higher near the dam than farther downstream, resulting in something called an "exponential decay curve." Evidence of that curve was found in the canyon walls, and the record there is almost a perfect match with the record left behind when Idaho's Teton Dam failed in 1976.

"We have that curve preserved from a lava dam that failed in the Grand Canyon 165,000 years ago," Webb says.

Big and Getting Bigger

Webb, by the way, is a leading proponent of the idea that the canyon was formed somewhat intermittently, rather than at a steady pace. The end of a glacial period would send higher amounts of water down from the Rocky Mountains, for example, allowing the river to carve much more rapidly than during drier periods.

But that doesn't mean the river is through with its work. Geologist Joel Pederson of Utah State University, Logan, argues in the August issue of the journal Geology that scientists were wrong in thinking that the Grand Canyon was "largely finished" about 1.2 million years ago.

Pederson says his research shows the erosion is continuing at "healthy" rates, even today.

Various scientists are now concluding that some of the canyon's most famous features, including the colorful Marble Canyon are much younger than the earlier estimates of 3 million to 5 million years old. They may be as young as 600,000 years old, based on newer dating techniques.

That's a mere child, as geological features go.

Now we know it's had more than a few temper tantrums. Some years have been harder than others. And it still has some growing to do.

But it's hard to imagine that it could get any better.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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