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Much of what we now understand about the region’s basalt is
the work of geochemist Peter Hooper, who recently retired from WSU.
He and Don Swanson ’60, a former student who moved on to the
U.S. Geological Survey, mapped the basalts.
Webster’s expertise is the Cenozoic, that relatively brief
geologic period that, beginning about 65 million years ago, overlaps
with the existence of mammals and seed-bearing plants on Earth. Webster,
with colleagues from Yakima, Eastern Washington University, and University
of Washington, mapped the interstitial deposits, the gravels and
soils, that cover the basalt of the Columbia Plateau. He drove virtually
every road in this area, he says.
As fundamental and permanent as the basalt would now seem, Webster
points out the cracks in the opposite canyon walls, the very existence
of the canyon itself. We are deep within otherwise solid rock. What
possibly could have carved this canyon?
It’s only recently that geologists broke out of the intellectual
prison of uniformitarianism, the notion that geologic phenomena can
always be explained by gradual, calmly fathomable events.
J Harlen Bretz started out within that camp. But years of contemplating
the Channeled Scablands transformed him and Cenozoic geology.
A University of Chicago geologist who had become fascinated with
Pacific Northwest geology as a high school biology teacher in Seattle,
Bretz finally understood that the only thing that could have created
the scablands was an unimaginably massive flood.
But the idea of a flood so cataclysmic that it ripped a scar down
eastern Washington, scouring out the Grand Coulee, ripping through
solid basalt to create the Palouse River canyon, was simply unfathomable
to anyone who had not contemplated the scablands as Bretz had, particularly
anyone comfortably ensconced in the sureness of uniformitarianism.
Webster recounts the story told him by former Geology chair Charles
Campbell, who was at the American Association for the Advancement
of Science meeting in 1940 that was the turning point in the debate
over the scablands’ origin. Sure as he was about the giant
ripple marks and clearly defined channels, Bretz was plagued by a
lingering question: What was the source of the water?
Then Joseph Pardee got up to talk about giant ripple marks in the
bed of Glacial Lake Missoula—which could only have been created
by a sudden outrush of water.
As soon as Pardee finished, Bretz leaped up. “There’s
my water!” he said.
No one knows, says Webster, why Bretz had not yet connected his
theory to Pardee’s work. Pardee had first published his observations
more than 20 years earlier. Regardless, Bretz finally had his water,
and the reluctant uniformitarians gradually gave in.
What Bretz had understood about the strange and beautiful scablands
is what we now understand. Fifteen thousand years ago, chunks of
glacial ice had formed a dam above Clark Fork, Idaho, backing up
a 180-mile-long lake that contained as much water as today’s
lakes Erie and Ontario combined.
When the dam collapsed, the water rushed westward at 45 miles per
hour, scouring the landscape down to basalt, a flood so powerful
it chewed into the volcanic basalt, following existing drainages
as it could, then creating its own drainages when it overwhelmed
them. One flow swept westward from Spokane, then down through the
Quincy Basin, another down the Crab Creek drainage near Odessa. A
third swept down through present-day Cheney, through Washtucna and
Pasco. Near Pasco, the flows recombined at Wallula Gap, along the
present-day course of the Columbia. Formed by bluffs only a mile
apart, the Wallula Gap constricted the flow, forcing the water to
back up behind it.
From there, it surged down the Columbia, still powerful enough when
it reached the coast that it deposited huge granite boulders in the
Willamette Valley it had carried, probably in chunks of ice, all
the way from Idaho.
But this happened not just once, says Webster. It may have happened
as many as 105 times.
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