Massive Gorge Geology

I think the Columbia Gorge is one of the most fascinating places in the world. I have believed this for close to 50 years, since I started exploring it with my parents as an ankle biter. The gorge, of course, is spectacularly beautiful; a major mountain range, the Cascades, is cut almost to sea level by the mighty Columbia River. It features majestic palisades and graceful waterfalls. The gorge is harsh; as you can tell from the trees in this picture, it's a windy place. The winds usually come from the west, which is the side of these trees with no branches. The winds are strong and frequent, especially in the summer, making the gorge a global windsurfing mecca. But the really hostile weather comes when the winds shift to the east; searing heat in the summer, blizzards and ice storms in the winter. Enormous volcanic forces have been at work here, too. Check out the huge, sloping slab of basalt in the background, on the Washington side of the river. Vast areas of eastern Oregon and Washington were overrun with basalt flows 20-30 million years ago. Here, near The Dalles in the dry end of the gorge, these natural processes are easy to see.

OK, here's a scenario for you. Imagine a day fifteen thousand years ago. You're at this spot, looking east toward The Dalles. First, a cold blast of air hits you. And then, following the icy onslaught, you see a THOUSAND FOOT HIGH WALL OF WATER comin' at y'all's head!!! As high as you're sitting here above the river, you're toast. You have just been caught in one of the first of dozens of Missoula Floods. Far upstream, in the Idaho panhandle, a glacial ice dam has given way, and a lake half the size of Lake Michigan...glacial Lake Missoula...has emptied in two days and is headin' for the ocean wikiwiki. This happened several dozen times at the end of the last ice age, 15 to 12 thousand years ago. (See June 07 posts for more flood talk and pics...good article on Wikipedia too). Before the floods, the Columbia Gorge was a large valley; the floods scoured away the lower slopes of the valley and made it into a chasm. Blow up this picture and check out the gorge walls on the upper left side. Notice how the lower walls are almost sheer cliffs, bare of vegetation, while higher up, the slope is more gentle and the terrain is covered with brown grass. From what I've read, I'm pretty sure that all the bare lower spots were scoured by the Missoula Floods, while the upper slopes...waaaay up there...escaped the water. Simply amazing.

This is Lyle, Washington. The entire town sits on a gravel bar composed of debris left by the Missoula Floods.