Stop 3

Debra Moore, Leah Potter, Rob Sauer, and Susan Sharp

As you look at these pictures, what observations can you make? What forces of nature could have caused these formations?

Markel Pass
Picture 1

prairie
Picture 2

debris field and rolling mounds
Picture 3

Our observations:
As we looked southward from Markel Pass (Picture 1), we observed a gentle slope from the rock wall toward the prairie (Picture 2), a debris field and giant rolling mounds (Picture 3) that varied in heights and stretched across the entire Camas Prairie. The rocks in the debris field were about the size of a shoe box and were in large piles directly below the openings of the passes. The walls and floors of Markel Pass were made up of rock. This rock wall faced North with a gentle slope pointing into the prairie. As we approached Markel Pass, we observed Willis Pass to the right of the sloping hill. Looking southward, we saw debris fields at the mouth of Markel Pass and Willis Pass. These giant rolling mounds began immediately after the debris fields.

Our interpretations:
These giant mounds and debris fields of the Camas Prairie are believed to be the result of a rapid draining of Glacial Lake Missoula about 12,000 to 15,000 years ago. It is hypothesized that these mounds are giant ripple marks formed when the rushing waters of Glacial Lake Missoula plowed through Markel Pass, Willis Creek Pass, and Big Creek Pass. Because this floodwater was forced to squeeze through the narrow passes in its path, it increased in velocity. This increase of velocity resulted in the scouring of the passes as the water plucked rock debris from the rock walls and floors. As the turbulent, or churning, waters moved across the Camas Prairie, it tumbled the sediments on the prairie floor into giant ripples. These ripples are similar to those you might see on the sandy floor of a fast moving creek. The extreme size of these ripples are an indication of the tremendous volume and velocity of water passing over the prairie creating one of the most unique landforms on Earth!