Dry Falls and Bretz's Flood

Dry Falls in the scablands of Eastern Washington.  Photo: B. Perry

N 47° 36.432’    W 119° 21.859’

The scablands of Eastern Washington State are well-named.  Much of the region from Spokane to the Oregon border is exposed basalt, laid down millions of years ago during the area’s volcanic past.  But where is the gentle wooded forest and loamy soil that covers other parts of the region?  It’s as if it has been stripped off, exposing the black volcanic bedrock below.  Braided channels with enormous vertical walls, called “coulees” by the locals, carve through the scablands.  The Grand Coulee, for instance, is a 50 mile long ancient river bed, one to five miles wide with walls over 1000 feet.  Though recently filled for irrigation use, the Grand Coulee has been dry for many millennia.  Halfway down the canyon is Dry Falls, the remains of an ancient scalloped-shaped waterfall 3.5 miles long and 400 feet high.  It would have dwarfed Niagara Falls which is only one mile wide and 165 feet high.  Though Dry Falls is, well, dry, it is easy to imagine the enormous amount of water that must have spilled over its lip to carve the gaping canyon below.   And this is just one spectacular example of the many scabland features in which the basalt bedrock appears to have been carved away by enormous amounts of water.  Throughout the region are dozens of other deep trenches and potholes that could only have been made by far greater volumes of water than the little creeks that run through them today.  What happened here?  Where did the water come from? Where did it go? And just how much water are we talking about?

Drumheller Channels  Photo: Tom Foster

Geologist J Harlen Bretz
(Credit: Geological Society of America)

In the early 1920’s, J Harlen Bretz, a geologist from the University of Chicago, toured the scablands with a handful of grad students, mapping the terrain and examining the wondrous features.  Bretz was puzzled, though.  The system of channels didn’t look like normal river systems which are tree-like with smaller tributaries running into larger rivers.  Instead, scabland channels crossed back and forth in a braided fashion.  Furthermore, river valleys eroded over millions of years tend to be V-shaped whereas the channels of the scablands were U-shaped.  He found house-sized rocks that didn’t belong there, called “erratics”, dumped willy-nilly throughout the region.  He realized that these coulees, dry falls, potholes, and erratics could only have been the work of an enormous flood of biblical proportions.  The flood that carved the scablands would have been hundreds of feet deep and swept across much of the region.  It would have been the biggest flood the world had ever known!

The present day Palouse Falls is too small to have cut
the surrounding gorge

When Bretz published his catastrophic flood hypothesis, the reaction was at first dismissive and later abusive.  Geologists in his day were quite comfortable with the tenet of uniformitarianism, that geologic features on earth are created by natural forces over millions of years.  In fact, it had taken geology one hundred years to get away from the biblical view of earth’s creation.  Now, here was a brash upstart proposing that a colossal flood had carved the scablands in a matter of weeks.  Undaunted, Bretz returned to the scablands again and again to gather more evidence.  At Quincy Basin, he found three exit points miles apart at the same elevation.  The water must have filled the entire basin like a bathtub until it poured over the lip at all three exit points.  He found the flood had given the Palouse River a 90 degree turn into an enormous gorge; it had reversed the flow of the Snake River for a hundred miles; and left sandbars hundreds of feet above the Columbia River.  Bretz continued throughout the 20’s to publish his evidence for the flood with detailed maps and complex calculations of water volumes.  Unfortunately, his argument had one gaping hole:  where did the flood come from?  He suspected that the glaciers of the last ice age, which reached its maximum extent about 15,000 years ago, were probably involved – but he didn’t know how.   Detractors continued to be loud and many (although some of them had never even been to the scablands).  After defending his flood for over a decade, J Harlen Bretz left the scablands behind and moved on to other geological pursuits.

Giant current ripples on Camas Prairie.  Photo: Tom Foster

Years earlier, a U.S. Geological Survey geologist named J.T. Pardee had noticed old shorelines high on the hills around Missoula, Montana and in the Bitterroot Valleys, evidence of a Glacial Lake Missoula.  He followed the shorelines down the Clark Fork River into the Idaho panhandle where they disappear.  He knew that the Ice Age ice fields that covered most of Canada extended into the northern valleys of Washington, Idaho, and northeastern Montana.  Pardee hypothesized that if a glacier filled the valley of the Clark Fork River, a 30-mile-long mass of ice would dam the Clark Fork River, creating Glacial Lake Missoula.  This inland sea would have been 2000 feet deep at the dam and 950 feet deep at Missoula.  Pardee estimated that the lake held 500 cubic miles of water – about half the volume of Lake Michigan.  As Bretz defended his catastrophic flood, Pardee speculated: what if the ice dam had failed?  The entire volume of Glacial Lake Missoula, all 500 cubic miles of it, would have crashed across eastern Washington.  In the 1930’s, Pardee searched for evidence of this catastrophic ice dam failure.  On Camas Prairie, he found strange ridges as much as 35 feet high that cross the plain at regular intervals.  Using aerial photography, Pardee identified these ridges to be giant ripples left behind by enormous quantities of water rushing out of the valley.   In his 1942 paper, he hypothesized a catastrophic failure of the ice dam and the rapid drainage of Glacial Lake Missoula.  Although Pardee never mentions it in his paper, it seems he had found the source of Bretz’s flood.

Touchet Formation near Lowden, Washington

It took forty years for Bretz’s catastrophic flood hypothesis to be fully accepted by the geological field.  As the old guard retired, a new generation of geologists returned to the scablands.  Examination of the Touchet Formation in the Walla Walla Valley revealed layer upon layer of basalt debris separated by soils blown in on the wind.  Apparently, there wasn’t just one flood but dozens.  The current theory is that when the lake reached a certain level the ice dam would float, fracture, and fall apart.  After each flood, the glacier closed off the Clark Fork River Valley once again and Glacial Lake Missoula would refill.  This cycle went on for thousands of years.  Finally, the ice retreated for good and the floods stopped.  Only the battered landscape was left to tell the tale.

Alt, David.  Glacial Lake Missoula and its Humongous Floods. Mountain Press Publishing Co., Missoula, MT, 2001.

Soennichsen, John, Bretz’s Flood: The Remarkable Story of a Rebel Geologist and the World’s Greatest Flood.  Sasquatch Books, 2008.

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