Group explores scablands from Crab Creek to Moses Lake
Last updated 10/9/2020 at 2:09pm
The Palouse Falls Chapter of the Ice Age Floods Institute hosted their annual Fall tour Saturday, Oct. 26. This is the fifth tour since their formation in 2015. The previous tours were by bus but due to Covid-19, it was decided to hold this tour by car caravan.
The tour was led by Chapter President Lloyd Stoess, Vice-President Jacqui Hair, and Chad Pritchard, a professor of geology at EWU. Seventeen people checked in at the Ritzville City Park for introductions and instructions. Not only was there local participation, but guests from as far as Seattle, Lewiston, Idaho, and Bozeman, Mont. came to learn more about our incredible flood story.
The first stop was at the Marcellus elevator north of Ritzville on the eastern edge of the Telford/Crab Creek Scabland Tract. This minor coulee was formed when spillover from Crab Creek flooded though it during one or two of the first larger floods from Glacial Lake Missoula.
Glacial Lake Missoula formed when an ice lobe from the Cordilleran Ice Sheet dammed the Clark Fork River at present day Lake Pend Oreille about 18,000 years ago. In about 120 years, this lake increased to over 100 cubic miles with a depth of 2,000 feet. The ice dam catastrophically failed and in about two days all the water was released with the flow rate equivalent to 10 times all the rivers of the world today. The ice would advance and the cycle repeated. Field evidence now suggests that this cycle occurred 89 times during the last Ice Age. These floods carved the Channeled Scablands of eastern Washington.
The caravan continued for a stop at Crab Creek on Rocky Ford Road. This creek originating near Reardan is longest in the state and one of the longest in country. Then on to the Lomana Rock Shelter across Highway 28 from the Lamona Elevators. Pritchard explained that unlike most of the rock shelters in the area that are formed by the plucking of the fractured basalt by huge floodwaters, this one developed because the lava, million of years ago, flowed over wetlands. Clay lenses can be seen in the basalt.
The next stop was north of Odessa to hike around three of the Odessa Craters. The formation of these circular features is still being debated with several hypothesis presented. Then it was a trip across the back roads through the Telford/Crab Creek Scablands to Dry Falls in the Grand Coulee for lunch. In addition to the Missoula Floods carving out this coulee, it was also the route of the diverted Columbia River between about 14,000 and 18.000 years ago. It is quite the contrast to the first stop of the day at Marcellus Coulee.
The first two stops in the lower Grand Coulee were to look at the Coulee Monocline, a flexure in the basalt and an exposure of unusual horizontal basalt columns. Pritchard explained that most likely, a basalt flow filled an existing canyon and the lava cooled from the sides rather than the bottom and top which caused the horizontal columns.
Another hike was taken at the Lenore Caves above Lake Lenore. Four rock shelters were visited which were formed from the flood waters plucking out the basalt columns.
Continuing south, the caravan arrived on the Ephrata Fan south of Soap Lake. This deposit of huge boulders, rocks and gravel was left as the flood waters left the confines of the Grand Coulee and spread out onto the Quincy Basin. The larger "Sediments" were dropped first with the finer ones deposited further south in the Moses Lake area. The group stopped at the largest of the boulders on the fan called monster rock which weighs an estimated 1,500 tons.
The final stop was above Moses Lake which occupies the last channel of the diverted Columbia River from the time of the floods.
The Ice Age Floods Institute is a non-profit educational organization that focuses on the incredible story of the Missoula Floods. It also includes education about local geology, geomorphology, and human history that was affected by our natural history. Last spring, a lecture on Mount St. Helens in Ritzville was postponed due to Covid-19. This is planned to be presented this fall via Zoom. The date is still to be determined.
The local Palouse Falls Chapter is one of eleven in the Northwest that focuses on their immediate area. With over eighty members, it has grown to be one of the four largest chapters. More information can be found at http://www.iafi.org.
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