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September 2000 Ice Age Floods - President's Field Trip Review

• Date: September 2-9, 2000
• Location: Columbia River Gorge, eastern Washington State, Idaho, Montana
• GSOC President: Ray Crowe
• GSOC Field Trip Director: Taylor Hunt
• Guides: Richard B. Waitt, USGS

Eugene P. Kiver and Dale F. Stradling, Eastern Washington University
John H. Whitmer
• Reviewer: various
• Objective: View Ice Age Floods and related features

ICE AGE FLOODS FIELD TRIP: Day 1
Evelyn Pratt

One thing we'll remember about this field trip is that Dr.Waitt took us to a lot of bars - gravel bars, that is. In all the years we've seen Vancouver's high straight riverbank, I never knew we were looking at a huge gravel bar. When 500-foot high floods roared through the narrow Gorge and passed Washington's Prune Hill and Oregon's Chamberlain Hill just east of Sandy River, the water would then spread out on flat ground. Boulders and gravel were dropped in long pendant bars just west of the two hills. It's no wonder that gardeners on Alameda Ridge, part of Portland's bar, rake up a lot of rocks!

I-84 runs through Sullivan's Gulch from Rocky Butte to downtown. The Gulch is just one of several flood channels in east Portland. We've got a lot more channels than Vancouver does. Did water swirling around all those Boring lava vents do this?

Back to the bars. Just east of The Dalles, nearly a thousand feet above the Columbia, we stopped and studied a cliff cut into a giant bar. The direction the floodwaters came from was obvious from the bar's cross-bedding. We were to see similar patterns time and again as we stopped at other bars farther upriver.

Another pattern that became very familiar was that of the scablands. Over the millions of years since Columbia River Basalt lavas stopped flowing, soil had built up on top of their wavy surfaces. The floods scoured off these soils. Left behind were scablands - low mounds of bare basalt separated from each other by thin grass-covered dirt. Probably the best example was beside the highway driving into The Dalles. Scablands showed how high the floods went. Above that level the hills were smooth and rolling. We passed isolated buttes capped by Columbia River Basalt all the way from Horsethief Butte opposite The Dalles to Hat Rock and Twin Sisters east of Umatilla. These picturesque landforms were created by floods which stripped away soil and tore through and opened up joints and faults in the underlying basalt. To do this the water had to have been 125 to 275 meters deep, traveling anywhere from 5 to 22 meters per second. (If you don't like meters, multiplying by 3 gives you a very rough estimate in feet.) The result was what is known as butte-and-basin scablands.

This kind of topography was evident from Wishram to the John Day Dam. As we stood at Celilo Overlook Dr.Waitt told us about the now-covered Celilo Falls. The Columbia River here consisted of a couple of miles of narrow chutes, in some places less than 150 feet wide, separated by large holes. At Big Eddy and the head of Five Mile Rapids the holes are more than 130 feet deep, their bottoms 100 feet below sea level!

The amount of water that the floods carried is mind-boggling. Wallula Gap upriver from Umatilla is about a mile wide. During the largest floods so much water came down that the thousand-foot-high walls of the Gap formed a hydraulic dam - all the water couldn't get through at once, and backed north into the Pasco Basin for many days. The last stop involved some rebellious mutterings beforehand. It turned out to be, for amateur archeologists and many of the rest of us, one of the day's high points. Dr. Jim Chatters, the forensic expert who identified Kennewick Man, talked with us on the banks of Columbia Park, the place where the skeleton was discovered. He feels, of course, that it is very important to be able to get all the information we can from it. Few human bones of this age have been found. The skull measurements and characteristics are more similar to Pacific Islanders and the Ainu of Japan than they are to Native Americans. Further study could give us much better insights into who was here when. But shortly after we returned from the field trip the skeleton was declared off-limits to scientists. He and many others must be deeply disappointed.

Here are some photos of the trip from Duane Diller:
 
 

GSOC Missoula Floods Tour 2000, arm-wavers and detailers	"Fresh salmon, two dollars a pound."

Sleep hard tonight with a basalt pillow	"Note the layering, this is water borne deposit, not wind blown, right?" photo of Taylor and Don inspecting sediment near Ellensburg

"There's a thrust and the top folds over." photo of John explaining to Elaine	Stream Bed Sediments Aren't we all getting tired with these beds and pillows?