After teaching geology at the University of Washington for a decade, I had become embarrassed that I hadn’t yet seen the deep canyons where tremendous Ice Age floods scoured down into solid rock to sculpt the scablands. So I decided to help lead a field trip for students to see the giant erosion scars on the local landforms.
We drove across the Columbia River and continued eastward, dropping into Moses Coulee, a canyon with vertical walls of layered basalt. We gathered the students on a small rise and asked them how the canyon had formed. They immediately ruled out wind and glaciers. The valley was not U-shaped like a typical glacial valley, and none of us could imagine how wind might gouge a canyon out of hard basalt. But neither were there rivers or streams. After a while I pointed out that we were standing on a pile of gravel. I asked how the rounded granite pebbles came to be there when the closest source of granite lay over the horizon. Silence.
Hiking through eastern Washington canyons littered with exotic boulders is a standard field trip for beginning geologists. It takes a while to register what you see. A dry waterfall hundreds of feet high in the middle of the desert. Giant potholes where no river flows today. Granite boulders parked in a basalt canyon. Gradually the contradictions fall into place and a story unfolds. Where did wayward boulders the size of a car or house come from? What was the source of the water that moved them around and carved the falls? Today, even novice geologists can conjure up eastern Washington’s giant floods.
Long before the discovery of the scablands, geologists dismissed the role of catastrophic floods in interpreting European geology. By the end of the 19th century such ideas not only were out of fashion but were geological heresy. When J. Harlen Bretz uncovered evidence of giant floods in eastern Washington in the 1920s, it took most of the 20th century for other geologists to believe him. Geologists had so thoroughly vilified the concept of great floods that they could not believe it when somebody actually found evidence of one.
Bretz was a classic field geologist and a controversial figure throughout his career. In 1925 he presented the story of the region’s giant floods, seeing what others at first could not — and then would not — see. He spent his lifetime piecing together the story of how a raging wall of water hundreds of feet high roared across eastern Washington, carving deep channels before cascading down the Columbia River Gorge as a wall of water high enough to turn Oregon’s Willamette Valley into a vast backwater lake.
