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Glacial Lake Missoula Megaflood

Glacial Lake Missoula and the Ice Age Floods There have been at least five major ice ages in the past one billion years. The most recent, the Pleistocene Ice Age, began about 2 million years ago. Glaciers did not continually cover the earth during this time; there have been interglacial periods where temperatures warm slightly and the glaciers melt and retreat. In the most recent advance, glaciers reached their maximum extent 15,000 years ago and had almost completely melted by 10,000 years ago. It was during this glacial advance that a finger from the glacial ice sheet moved south through the Purcell Trench in northern Idaho, near present day Lake Pend Oreille, damming the Clark Fork River creating Glacial Lake Missoula. The water began to build up behind the 2,500-foot ice dam filled the valleys to the east with water, creating a glacial lake the size of Lake Erie and Lake Ontario combined. The water continued to rise until it reached its maximum height at an elevation of 4,200 feet. As the water rose, the pressure against the ice dam increased, ultimately, causing the dam to fail catastrophically. The failure occurred when the water reached a depth of 2000 feet. The water pressure caused the glacier to become buoyant, and water began to escape beneath the ice dam by carving sub-glacial tunnels at an exponential rate. It is estimated that the maximum rate of flow was equal to 9.46 cubic miles per hour (386 million cubic feet per second). This rate is 60 times the flow of the Amazon River, the largest river in the world today. At this rate, the lake probably drained in a few days to a week. Water moving at speeds between 30 and 50 miles per hour raced across eastern Washington. The floodwaters from Glacial Lake Missoula moved through eastern Washington on a 430-mile journey to the Pacific Ocean, forever changing the landscape by stripping away topsoil, and picking apart the bedrock. The floodwater carved an immense channel system across eastern Washington. In 1928, geologist J. Harlen Bretz poetically described the scene: "No one with an eye for land forms can cross eastern Washington in daylight without encountering and being impressed by the 'scabland.' Like great scars marring the otherwise fair face of the plateau are these elongated tracts of bare, or nearly bare, black rock carved into mazes of buttes and canyons. Everyone on the plateau knows scabland. It interrupts the wheatlands, parceling them out into hill tracts less than forty acres to more than forty square miles in extent. One can neither reach them nor depart from them without crossing some part of the ramifying scabland. Aside from affording a scanty pasturage, scabland is almost without value. The popular name is an expressive metaphor. The scablands are wounds only partially healed great wound in the epidermis of soil with which Nature protects the underlying rock." Massive Cordilleran ice sheet blocked the mouth of the Clark Fork River and caused the water to backup and submerge the city of Missoula. One day, the massive Ice Dam broke. Imagine a highlander, running atop the highest peak of a mountain. With bated breath, he watched the breaking of the ice dam, unleashing a megafood of biblical proportions. The Megaflood plowed ahead and created havoc in the Columbia River Gorge in no time. The highlander, who watched massive waves, towering thousands of feet high moving at great speeds with a deafening noise and approaching him, he stood thunderstruck. The giant waves scoured and stripped the topsoil, cut deep canyons and coulees in no time, randomly depositing hulking boulders at different places. The gargantuan water then turned into a colossal vortex, spiraling with tremendous velocity. It drilled the hard rock and sunk into the belly of the earth. One vortex followed another. The water poured in from three-mile high cliff into deep gorges. It was the greatest show by the Geological Force ever happened in human history.