Washington state is famous for its dramatic landscapes, many carved by the immense power of the Ice Age Floods. We know the stories of the Grand Coulee, Palouse Canyon, and the Potholes. But tucked away in north-central Washington, cutting a path from northeast to southwest across the Okanagan Plateau, lies Moses Coulee – perhaps the most mysterious of them all. Unlike its famous cousins, Moses Coulee doesn’t quite fit the standard narrative. Its head seemingly emerges from beneath the Wisconsin Withrow Moraine, and its very formation presents a fascinating puzzle for geologists.
Flood Theories and Questions: An Enigma
The Grand Coulees (Upper and Lower) are widely believed to have been carved by the spectacular Missoula Floods. These colossal deluges were unleashed when the Okanagan Lobe of the Cordilleran Ice Sheet blocked the Columbia River, redirecting massive amounts of water southward. For Moses Coulee, it’s not so clear-cut. While cataract retreat due to massive floodwaters is generally assumed, most theories suggest the Okanagan Lobe effectively blocked the Missoula Floods from entering Moses Coulee. So, what carved this impressive landscape?
Enter J. Harlan Bretz, the pioneering geologist who first championed the idea of colossal floods shaping the Pacific Northwest. Bretz observed a distinct wide bench within Moses Coulee, high above its floor. This led him to speculate about two distinct periods of glacial floods:
- An older, pre-Wisconsin “Spokane Flood” that initially carved Moses Coulee.
- A later Wisconsin period flood (what we now call the Missoula Floods) that deepened the coulee floor.
Interestingly, current speculation suggests the Upper Grand Coulee might also owe its primary formation to these earlier “Spokane Floods,” with the Lower Grand Coulee being a product of the later Missoula Floods. It seems the story of Washington’s coulees is far more layered than once thought!
Beyond Glacial Lakes: A Subglacial Hypothesis
But wait, there’s another fascinating idea. Some investigators propose that Moses Coulee wasn’t carved by the well-known Missoula or Columbia glacial lake outbursts at all. Instead, they suggest outbreak floods from under the ice sheet itself. Joel Gombiner and Jerome Lesemann have explored this idea, suggesting that the immense pressure of the overlying ice lobe could have forced subglacial meltwater to flow uphill over topographic highs. This water would then have exited from under the ice, becoming the powerful floodwaters that sculpted Moses Coulee. Imagine that — floods erupting from beneath a massive glacier!
Explore the Mystery Yourself
The interplay between the Withrow Moraine and the unique features of Moses Coulee makes this a truly captivating area for exploration, especially for those intrigued by the raw power of ancient ice and water. To truly enhance your visit to this less-traveled gem, we highly recommend:
- Watching several of Nick Zentner’s insightful videos where he dives deep into these Moses Coulee questions. His engaging explanations bring the geology to life!
- Examining J. Harlan Bretz’s original field notes, meticulously organized in geolocated Google Maps by Glenn Cruickshank. It’s like stepping back in time with the pioneering geologist himself.
Moses Coulee is more than just a landscape; it’s an ongoing geological debate etched into the earth. Are you ready to explore this remarkable natural mystery?
AI-assisted article by Lloyd DeKay – Columbia River Gorge Chapter