One More Glacial Lake and Megafloods


Glacial Lake Ahtna dominated Alaska’s southcentral region during the Ice Age. Utah’s massive Lake Bonneville triggered the Bonneville Flood. But both Lake Ahtna and Lake Bonneville, stupdendous flood events themselves, were mere pikeminnows in comparison to the sturgeon that was Glacial Lake Missoula, which was not only a bigger flood event but happened as many as 80 times, scouring Eastern Washington to such an extent that even 14,000 years later the flooding damage is readily visible.

The Missoula Floods were important in another way: they changed geology science in profound ways, almost as dramatically as they changed the physical landscape.

Lake Missoula happened when the North American Pleistoscene glacial ice sheet moved south through the Purcell Trench in northern Idaho, near present day Lake Pend Oreille, damming the Clark Fork River. The ice dam created a 4,200 foot deep lake, Glacial Lake Missoula, with an estimated reservoir greater than Lakes Erie and Ontario combined. When the ice dam failed under the pressure of all that water, Lake Missoula drained at a stupendous 9.46 cubic miles per hour (386 million cubic feet per second). That’s 60 times the flow of the Amazon River, the largest river in the world today. At that rate, the entire lake probably drained in a few days to a week.

Blue-gray areas were flooded during one or more of the Missoula Floods

Blue-gray areas were flooded during one or more of the Missoula Floods

Those staggeringly immense amounts of water raced across southeastern Washington, scouring down to bedrock, creating immense waterfalls and erosion basins. In narrower parts of the Columbia River Canyon, where flow was constricted, the floodwaters backed up. In the case of the Willamette Valley, all the way south to Eugene. The floods would have submerged most of Portland’s skyline.

And this happened multiple times, perhaps as many as forty, maybe even eighty times, depending on who is counting the ash and sediment layers.

Why did the Missoula Floods come as such a massive shock to the new science of geology?

Geology grew out of a rebellion against the Biblical timeline and, especially, the Noachian Flood. Late Nineteenth Century geology was the the triumph of Uniformitarianism, Charles Lyell’s thesis articulated in his 1830 text Principles of Geology . That thesis was that geological change was gradual and uniform – always the product of, as Lyell put it, “causes now in operation.” Catastrophic, epic flood events smacked of Biblical events, everything Lyell and his successors sought to put behind the science of geology.

Uniformitarianism triumphed. In fact, it became dogma, and when a former high school science teacher and geologist named Harley Bretz published a paper in 1923 describing the scablands and erosional features of the Columbia Valley as the product of a flood, Bretz’s meticulous documentation was greeted with hoots of derision. Mainstream (sorry) geologists said Bretz’s hypothesis was not just “wholly inadequate,” in the words of one critic, but “preposterous” and “incompetent.” Mind you, none of those mainstream geologists has gone to southeast Washington themselves and seen with their own eyes what Bretz was describing. Vic Baker, a geologist with the University of Arizona, who became the pre-eminent scablands expert after Bretz’s death, tells this story:

Sometime in the late 1950s or early ’60s, a geologist named Aaron Waters brought one of Bretz’s most vocal critics—James Gilluly, the one who’d called his ideas “preposterous” and “incompetent”—to the scablands for a first-hand look. As they took in the sight of the falls and the canyon, Gilluly was dumbfounded by their scale. “Gilluly was just quiet the whole time,” Baker said, “and as they were leaving, he broke out into this immense laugh and said, ‘How could anybody be so wrong?’” After resisting Bretz’s theory for decades, simply seeing the landscape with his own eyes had changed his mind.

Palouse Falls, Washington: This little river did not create this giant bowl

Palouse Falls, Washington: This little river did not create this giant bowl

The story of the Missoula Floods not only teaches a lesson in geology; it teaches a lesson in science. Facts matter. Nature has the answers. Scientists have theories. If the facts don’t match the theories, it’s probably not the facts that are wrong.

Uniformitarianism was a theory. The scablands are a fact.

More on the Missoula Floods and Harley Bretz: Formed by Megafloods, This Place Fooled Scientists for Decades

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