Tracking the Ice Age Floods...again

On Monday I traveled south thru Central Washington, following the Ice Age Floods. This massive glacial erratic lies in a field 30-40 miles southwest of Grand Coulee Dam. It was deposited by a huge ice sheet, thousands of feet thick, that dammed the Columbia River and diverted it from its historic (and present) course past Wenatchee. Instead, the river flowed through the Grand Coulee, dozens of miles...and over 500 feet higher! to the east. The ice sheet created Glacial Lake Columbia, which lasted for a couple thousand years and was occasionally inundated itself by the Missoula Floods.

The diverted Columbia flowed over Dry Falls, at the southern end of Grand Coulee. During normal river flow, the river would have cruised over the cliffs on a front perhaps a mile wide and maybe 50 feet deep...impressive enough, probably about like Iguazu Falls in Brazil and Argentina today. But during the Missoula Floods...the scene was tremendous! Imagine a torrent of water at least 300 feet deep, roaring at 60 mph, dropping over the 400 foot precipice with such speed and volume to render the falls a megarapids rather than a cataract! Nothing like it has been seen anywhere in the world since. Between the ordinary flow of the diverted Columbia and several dozen Missoula Floods, each lasting several days, the basalt cliffs in the coulee were eroded about 20 miles back in just a couple thousand years!

On this trip I acquired a new book titled "On the Trail of the Ice Age Floods" One of the highlights of the book was this area called the West Bar, on the Columbia River near Quincy Washington. What this picture shows, incredibly, are flood current ripples. You can see ripples like these in any creek with a sandy bottom...I see them at the beach in Monterey during the winter when little streams...mostly rainfall drainage...run into the ocean. Of course, such ripples are maybe an inch high and a few inches apart. These ripples in the picture average 24 FEET high and 360 feet apart! The flow of water that created these ripples is estimated to have been as much as 650 feet deep. Interestingly, the book theorizes that the ripple flood was not one of those associated with the emptying of Glacial Lake Missoula, but was probably the result of a huge flood on the Columbia River when the Cordilleran Ice Sheet broke and Glacial Lake Columbia emptied at the end of the Ice Age. Blow up the pic for more ripple detail.

These are basalt columns in Potholes Coulee, a few miles south of the West Bar. Water from the Missoula Floods roared westward across the prairie around present day Ephrata and Quincy, and then flowed over a cliff down almost a thousand feet to the Columbia River basin. With the huge volumes of water and the speeds of flow involved, the floodwaters carved the basalt back from the cliffs a good mile in this area. The waterfalls involved, while not as spectacular as at Dry Falls, must have been really massive for a few days during each flood. Just south of this locale is the Gorge Amphitheatre, a famous concert venue located in an area where the highest floods eroded a small canyon in which the Amphitheatre sits. I'd love to go to a show there sometime...Coldplay was there last month just before I saw them near Sacramento.