Slide Planes, Mud Squirts, and a Diamict, Upper Grand Coulee
Brian Atwater always makes you feel like a million bucks. He invited me to join a group of geologists meeting in the Upper Grand Coulee in July to plan an October field trip for the Geological Society of America. The group made several discoveries related to various aspects of megaflooding over the course of several enjoyable days. In this video, I describe curved shear planes exposed in shoreline bluffs of Banks Lake south of Steamboat Rock. The concave features look like simple channel forms incised into the silt-clay deposits of Glacial Lake Columbia (Pardee's "Nespelem Silt"), but show clear indications of sliding, possibly caused by ice loading. Bouldery glacial till that grades to diamict and flood-related soft sediment deformation features are also described. Video shot in September 2021.