Catastrophic Ice-Age Floods
Formation of the Scablands of Washington and Scouring of the Columbia River Gorge
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Dry Falls in the scablands of eastern Washington.

One of the greatest torrents of water to ever flow across the Earth's surface flowed across eastern Washington and into the Columbia River Gorge and to the sea. Known as the Missoula Floods, the source of the water was a large lake (Lake Missoula) that formed over western Montana. It was held back by a lobe of ice that acted as a dam. At one point the dam rose as a wall of ice more than two thousand feet high.

At the end of the most recent ice age, as the planet warmed and the ice sheet that covered northern North America retreated, the lobe of ice failed. That sent the waters of Lake Missoula pouring across the landscape.

It scoured the land of eastern Washington, leaving an area of deep erosional features known today as the scablands. One of these is Dry Falls, 400 feet high and more than three miles wide—five times the width of Niagara Falls.

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Crown Point at the western end of the Columbia River Gorge. Beacon Rock can be seen in the background.

About two hundred miles from the ruptured ice dam, the torrent of water encountered a bottleneck at a place along the Columbia River known as Wallula Gap. It took about two weeks for the water to drain through the gap and through the Columbia River Gorge and for the water level to recede.

The rapidly flowing water scoured the walls of the gorge, leaving, among other features, a series of high waterfalls, such as Multnomah Falls in Oregon. To gauge the depth of the water, stand at Crown Point, also in Oregon. The water reached almost up to—or may have overtopped—this site. Several miles upriver is Beacon Rock, the remnant of a large cinder cone. The depth of the water almost overtopped this tall rock—there are still patches of cinders atop Beacon Rock that indicate the floodwater did not quite reach the top.

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Beacon Rock in Washington.