Bobbing Boulders
Illhorn and Illgraben valley, Switzerland (credit: Wikipedia)
Geomorphology is the study of landforms and the processes that have created them. Whether mountain building, erosion, drifting continental plates, wind, or random events like earthquakes, floods, and landslides these processes have produced all the Earth's landscapes. One stark result of a geomorphological process was the landscape-scale formation around the Grand Coulee region in eastern Washington State. In this case, the features were formed in the geologic 'blink of an eye'.
According to research investigations, ~18,000 years ago a lobe of the Pleistocene icecap reached into what is now Idaho and blocked present-day Lake Pend O'reille. The ice dam, perhaps 2000 feet tall, cut off drainage of the Clark's Fork River and created a gigantic lake that stretched far into western Montana. As the lake deepened, the ice dam began to float and leaks likely appeared in several locations. In one massive event, the entire dam failed. The volume of water stored behind it was released, and is estimated to have been ~500 cubic miles of water (1 cubic mile=1,101,117,147,352 gallons) and emptied Lake Missoula. The resulting mega-flood may have happened over a period of just two days. A flood of that scale, equivalent to 10X the combined flow of all the world's rivers, would have been powerful beyond imagination. The trillions of gallons of water released across the landscape cut all the sharp canyons visible today.
Two brief videos from Switzerland capture a similar, though much smaller, event when a huge volume of water was released by torrential rains across unstable slopes. The boulders bobbing in the debris flow are the size of mini-vans and illustrate the power of these random events. As the saying goes, geomorphology rules! WHB