Ice Age Flood

Driving through central Washington, one can��t help but notice an extraordinary geological panorama unfolding along the roadways. What most people fail to realize is that the entire terrain��hillsides, cliffs, valleys, and canyons��created over millions of years, was dramatically reshaped by an unusual series of events, which took place during the end of the last Ice-Age.

Approximately 17,000 years ago near the end of the Pleistocene Epoch enormous glaciers covered nearly one third of North America. The western portion of the glacial ice was known as the Cordilleran Ice Sheet and the eastern portion as the Laurentide Ice Sheet. East of the Cascade Mountains, the Okanogan lobe of the Cordilleran Ice extended south on a line between what is now Chelan and Coulee City.

Farther east a lobe of advancing ice blocked the Clark Fork River at the point where the river passed through the Bitterroot Mountains. This buildup of ice blocked the drainage of a large portion of what is now northwestern Montana. The subsequent backup of water from the melting glaciers formed an enormous lake known today as Glacial Lake Missoula. Although we don��t know the eventual height reached by the ice dam, high water marks on the mountainside indicate a depth of approximately 2000 feet.

Exactly what happened next is still open to speculation; however, evidence shows the ice dam was eventually breached. When the dam collapsed it permitted catastrophic flooding of the landscape to the west. With incredible force, approximately 500 cubic miles of water and glacial ice burst through the channel gap, sweeping all before it, as it roared westward.
This massive flow of water scoured the soil from the landscape, breaking loose enormous chunks of rock, which it rolled and tumbled along for miles. Iceburgs with incorporated large boulders or ��erratics�� floated on the muddy turbulent flood-waters until finding a quiet resting place sometimes hundreds of miles from their ice dam origin.

It is believed the force of the rushing water was so great a mere four days were required to drain the entire lake. Today, we can see evidence of how the floods carved out more than 50 cubic miles of earth, deposited mountains of gravel, and scattered 200 ton boulders across the landscape. This astounding process is believed to have happened not once, not twice, but again and again, possibly as many as 100 or more times.