February 29, 2012 at 9:08 pm

The Legacy of the Megaflood



The Legacy of the Megaflood

Via Nasa.gov

A river runs through it

To the trained eye, the terraced profile of Grand Coulee’s cliffs says, “Water was here.” So do the crisscrossing, stream-like paths carved into the floors of many of the lesser coulees. It’s no surprise, then, that geologists in the early 1900s concluded Grand Coulee had been carved by a river, probably the Columbia, slowly etching its way down through layer upon layer of dirt and rock.

That was the mainstream view when Bretz went to the Channeled Scablands in 1922 to do field studies. And his first impression of the terrain was consistent with that thinking. When he came across hills of gravel 10 stories tall, for example, he considered them terrace remnants—the remains of a riverbank that had been slowly worn away.

But the more Bretz investigated the region, the more unusual landforms he found: winding channels that split off into smaller and smaller branches, crisscrossed each other, and sometimes joined together again; here and there inside the canyons, peculiar hills shaped like the prow of a boat; fan-shaped fields of debris on the canyon floors; and more.

He began to realize that slow-acting erosion by a river could not adequately explain it all. Something sudden and much more violent was required. And the massive proportions of the scabland features, often measuring hundreds of feet, meant that whatever had formed them happened on such a gigantic scale, nothing like it had ever been seen.

The best fit for all the evidence, Bretz concluded, was a catastrophic flood. This hypothesis was so contrary to the collective wisdom of hundreds of years of geology, however, that even Bretz doubted it at first.

Read more at Nasa.gov

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