River Vanished to Build Grand Canyon

March 6, 2008 -- Before the Colorado River had a chance to carve the Grand Canyon out of the Colorado Plateau, the waterway was swallowed up by the desert and disappeared underground.

A flurry of scientific papers this month have edged closer to providing a clear picture of the complicated series of events that led to the river's disappearance and the formation of what Utah State University geologist Joel Pederson calls "the greatest erosional feature in the solar system."

Pederson's latest contribution to the story appears in the March issue of GSA Today, in which he eliminates one popular theory about the location of the ancient Colorado River. For some time geologists had suspected that in times before the western half of today's Grand Canyon existed, the river there flowed northwest and ended at a basin in Nevada's southern tip.

But Pederson found the sediments that now exist along this supposed course, called the Muddy Creek Formation, have all the geological call signs not of the Colorado River but of a different river entirely.

"This (Muddy Creek) deposit had been the primary option," Pederson told Discovery News.

Without that option, the debate grows a bit louder. One possibility doesn't even look for deposits on the surface; it suggests that the river once flowed underground, diverted to several springs that leaked out of the sides of the plateau.

In the drier times prior to 6 million years ago, a lesser Colorado River might have gotten lost in the cavernous limestone under the Colorado Plateau.

"There are huge spring deposits right off the Colorado Plateau," said Pederson.

Bottoms-Up Canyon

Pederson's explanation jives, in a way, with what might be considered a radical new idea suggesting the river carved the Grand Canyon from the bottom up. The theory is presented in a paper in the March 15 issue of the journal Geomorphology.

Carol Hill of the University of New Mexico believes that the river sneaks through the region's subterranean plumbing -- the cave-riddled karst formations created by soluble limestone -- avoiding some otherwise very problematic high ground along the river's present course.

"If you don't understand the plumbing system, then you don't understand the system," Hill told Discovery News.

Her take on the Grand Canyon is that it's not so different from some other steep terrains that have been created by rivers flowing underground and eroding larger and larger caverns until their roofs eventually collapse. When the river carries away the debris, what's left are gigantic, steep-sided sinkholes, much like the bizarre "tiankeng" formations of southern China.

Connect these sinkholes and you have a deep, narrow canyon just like those seen in the Grand Canyon.

"Why couldn't the Grand Canyon form like this?" Hill asks. The main reason the idea hasn't been studied in the past, she said, is that few geologists are familiar with the details of karsts.