EXPERIENCING THE ICE AGE FLOODS,PART III

After about an hour of flying north, we passed Ephrata and nearby Soap Lake and entered the southern end of Grand Coulee. It is fascinating to see this deep watercut which resulted not from ages of river-type erosion but from gigantic flash floods tearing across surface of the land, trying to bypass the southern edge of the glacial icecap and follow the ever so slight drop in elevation. A river would have left a wide wandering route, but in this region the tremendous volume and pressures of raging flood waters gouged deep trenches, called coulees, which feature,among other characteristics, remarkably vertical walls and distinctive scouring of the bottom surfaces. In the picture below, taken just above Dry Falls, the scree at the bottom has been formed and accumulated by more recent erosion of the loose lava walls and is much younger than the floods.

The Dry Falls segment separates Upper and Lower Grand Coulee. In the photo below, the falls portion is in the top center of the picture. For a close and sharp picture check out David's recent post at http://www.pirep.blogspot.com/ and take a moment to read his text. At this point in its southwestward rush, water hurled itself off the these cliffs to the bottom over 350 feet below. The total width of this massive cataract measured along the ragged edge may have been as much as five or six miles along a irregular and sinuous route. The sound of so much water hundreds of feet deep falling so far must have made a thunderous and continuous roar that would have been heard for scores of miles. A few days after each flood passed - silence again, for the falls were dry again! Notice in the picture and closer to the foreground, evidence of brading channels, and on both sides a few lakes which remain today.
After whatever accumulated topsoils had been flushed away in the earlier floods, what remained was layer upon layer of ancient lava flows which covered large portions of these eastern Washington basins. Much of this igneous material was deposited like the various layers of a cake and was composed mostly of basalt. In many places, the hot basalt, after being put in place, solidified into separate, loose, interlocking columns or rods of rock. (Think of pillars of landscaping rock popular in many shopping complexes.) As the deep coulees formed under the rushing flood, massive and unbelievably powerful underwater "tornados" sucked great holes in the layers of basalt and lava. The result was many places where deep cavities were formed - gigantic potholes - which are additional evidence of the scale of the floods which formed them. Other huge potholes formed at the base of many of the falls along the route.
The final picture shows a "hanging valley", a common sight all along the coulee walls. These were formed when the newly torn coulees slashed across the path of existing watersheds completely separating the source from the destination in countless small streams and rivers. In these cases, the flowing water had no option by to hurl itself into the abyss and begin eroding the vertical coulee walls. Here we see how a small waterflow which had been gently dropping across the landscape was interrupted by the abrupt flood-formed gash and was radically altered from that point the the coulee floor.
All along our flight route one phenomenon after another testified to the cataclysms and changes the Ice Age Floods caused in thoussssssssands of square miles of varying terrain across parts of four states! [Note: I thought I would just leave that last typo; it seems so appropriate here!] We averaged perhaps a little over 100 MPH overall as we flew over all these sights and did not linger long in any one location. Consequently we were able to see dozens of features which spoke of the size and power of rushing water which rearranged the surface, marking it and molding it and moving it in curious and stunning ways. In fact, in viewing so much so quickly, some of the sights were so amazing and challenging to grasp that I simply forgot to take pictures as a witness to what chaos can accomplish.

In the final blog on this topic, I'll show a few flood caused features we saw on the return leg which basically followed the present day Columbia River back to the Tri-cities area. Come on back in a few days.