Dating the Ice Age Floods
Cosmic rays and the dating of ice age floods was the topic of the annual Spring Fling meeting of the Glacial Lake Missoula Chapter on May 30th. Jorie Clark recently co-authored a paper on the dating of the different flood paths across eastern Washington by examining boulders deposited by floods along the routes. The methodology involves pulverizing samples of the rock surface and using an enormous mass spectrometer to measure the amount of a nuclide (10Be) produced through exposure of certain minerals to cosmic rays over time. This time consuming and expensive process yielded 45 new ages for boulders located in Wenatchee, Wallula Gap, Withrow Moraine, Ephrata Fan, and Pend Oreille.
The conclusion was that of the 90-100 floods between 21,000 and 14,000 years ago, the biggest dated in this study travelled through the NW Columbia River 18,000 years ago, those that were forced through the Scablands by the advance of the Okanagan Lobe of the continental ice sheet were dated at 18,000–15,500 years ago, and those that returned to the NW Columbia River Valley after the subsequent retreat of ice lobe were dated at 15,500-14,000 years ago, all ages variable within ±500-800 years. The largest of these floods are estimated at 100-200 times the size of the current Amazon River.
This methodology could be applied to boulders in the Glacial Lake Missoula area if rocks with the appropriate minerals could be identified, they are correctly sampled, and adequate funding secured.
The Spring Fling was also celebrated by a special cake designed with the Glacial Lake Missoula logo.