Saturday, March 11, 2017

Formed by Megafloods, This Place Fooled Scientists for Decades



[National Geographic] In the middle of eastern Washington, in a desert that gets less than eight inches of rain a year, stands what was once the largest waterfall in the world. It is three miles wide and 400 feet high—ten times the size of Niagara Falls—with plunge pools at its base suggesting the erosive power of an immense flow of water. Today there is not so much as a trickle running over the cataract’s lip. It is completely dry.
Dry Falls is not the only curiosity in what geologists call the Columbia Plateau. Spread over 16,000 square miles are hundreds of other dry waterfalls, canyons without rivers that might have carved them (called “coulees”), mounds of gravel as tall as skyscrapers, deep holes in the bedrock that would swallow entire city blocks, and countless oddly placed boulders. All across southeast Washington, fertile rolling hills border eroded tracts of volcanic basalt, as if Kansas farmland and Utah canyon land had been chopped up and sewed together into a topographic Frankenstein.
The first farmers in the region named the rocky parts “scablands” and dismissed them as useless as they planted their wheat on the silt-rich hills. But geologists were not so dismissive; to them, the scablands were an enigma. What could have caused this landscape? It was a question hotly debated for several decades, and the answer was as surprising and dramatic as Dry Falls itself.
For that matter, so was the source of that answer: a high school science teacher named Harley Bretz. In 1909, the Seattle teacher visited the University of Washington to see the U.S. Geological Survey’s new topographic map of the Quincy Basin, a large area on the west side of the Columbia Plateau. He was 27, with no formal training in geology, but when he looked at the map, he noticed a striking feature: a huge cataract (much like Dry Falls) on the western edge of the basin, a place where water appeared to spill out of the basin and into the Columbia River, gouging a canyon several hundred feet deep. The falls would have been bigger than Niagara, but there was no apparent source of water for them—no signs whatsoever of a river leading to the cataract.
Bretz asked faculty in the department about the feature, called Potholes Coulee, but they had no answers for him. Nor could they explain many of the other unusual features of the region. That’s when, as legend has it, Bretz decided to become a geologist. He earned his Ph.D. in geology from the University of Chicago four years later, changed his professional name from Harley to “J Harlen” to sound more respectable, and in 1922 returned to eastern Washington to take a closer look at the plateau and its scablands. And after two seasons in the field, his conclusions shocked even himself: The only possible explanation for the all the region’s features was a massive flood, perhaps the largest in the Earth’s history—“a debacle which swept the Columbia Plateau,” ripping soil and rock from the landscape, carving canyons and cataracts in a matter of days. “All other hypotheses meet fatal objections,” he wrote in a 1923 paper. Read More