Washington Oregon
The Columbia River Gorge was a channel to the Pacific Ocean for massive floodwaters at the end of the last ice age. Three peaks can be seen in this photo: Mount Rainier on the right, Mount Adams to its left, and Mount Hood barely visible just left of Adams, to the distant south.
For centuries, travelers via land and river have followed this eighty-mile-long canyon that makes up much of the border between Oregon and Washington. Today, air passengers flying into Portland, Oregon, or Seattle, Washington, get an especially telling view of the enormous conduit that is the Columbia River Gorge. But while the gorge has transported people and goods for centuries and is today home to a major interstate, thousands of years ago this canyon was an expressway for superfloods.
The gorge began forming during the Miocene Epoch, between 17 and 12 million years ago, not long after widespread volcanic eruptions covered this part of North America with thick layers of basalt. Around 7 million years ago, the formation of the Cascade Range volcanoes in Oregon and Washington increased rainfall in the region, further chiseling the canyon system into the underlying volcanic rock.
But the most significant carving of the Columbia River Gorge came later, toward the end of the last ice age, when a series of catastrophic floods released near what is now Missoula, Montana, swept across eastern Washington, through the Columbia River Gorge, to the Pacific Ocean. These flooding events, the Glacial Lake Missoula floods, were triggered by periodic ruptures of an ice dam on the Clark Fork River in Montana. When intact, the ice dam held back the waters of Glacial Lake Missoula. Melting at the end of the last ice age led to cataclysmic ruptures at least several times between 15,000 and 13,000 years ago.
The Glacial Lake Missoula floods drastically altered the landscape across four states and through the Columbia River Gorge, in some places creating a scoured, barren landscape known as the Channeled Scablands.
The largest of these floods discharged more than twenty times the amount of water that flows in the Amazon River—all at once. At times, flow rates were as high as a hundred miles per hour, with enough force to carry house-sized boulders for many miles downstream. Geologists are unsure how many of these floods occurred, but evidence for as many as sixty separate flooding events has been uncovered in eastern Washington.
The impact of these floods on the Columbia River Gorge is hard to fathom. Before the floods, the now 4000-foot-deep canyon would have been less of a gorge and more of a river valley. By some estimates, more than fifty cubic miles of rock was carried downriver. Piles of loose rock topping 400 feet, carried by the floods, still sit on the banks of the river. Submerged debris fields from the floods can be seen on the seafloor of the Pacific Ocean, extending hundreds of miles offshore from the mouth of the Columbia.
As evidenced by numerous feeder canyons, a huge network of rivers and streams drains into the Columbia River.
Look for a deep gorge and a wide river running east and west before it turns sharply north near Portland, Oregon, and west again near Longview, Washington, on flights to and from Portland, Oregon.
