Meeting

(This will be the same presentation as June 27.) Giant Current Dunes or MegaRipple Marks – One of the most important pieces of evidence for catastrophic flooding was the “giant current dunes.” These large-scale bedforms appeared as patterns of parallel ridges and swales on many aerial photographs in the flood channels in the scabland of Washington, but had escaped recognition from the ground because of their size.  Giant Current Dunes are visible west of Clark Fork near Castle Rock; however, the most prominent and visible Giant Current Dunes are located several miles east of Spirit Lake along Hwy 54 where the highway cuts through the dunes showing their undulating profile. The location of many of the telephone poles on the crest of these dunes accentuates these landforms. The dunes form transverse to the current direction, and form cusps that are convex upstream, with arms that point downstream. Furthermore, the size of the cusps appears to decrease in the direction of lower velocity. Internally, the dunes consist of gravel and pebble foresets. Giant current dunes exhibit an asymmetrical profile with the downstream (lee) slope steeper than the upstream slope. Crests range from 20 to 200m apart and heights range from 1 to 15m (Baker and Nummedal, 1978) and are among the largest measured throughout the Floods area. The Spirit Lake current dunes can also be easily recognized from the air by their characteristic pattern, accentuated by vegetation. This dune field is immediately in the path of the breakout from Lake Pend Oreille, and experienced some of the highest energy flows. Presented by Dr. Linda McCollum, president of the Ice Age Floods Institute (IAFI), Cheney-Spokane Chapter No registration required. Call Librarian Nicole Ferris with any questions at 208-623-5353. PDF Resource Materials Waitt, R.B. 2016 Megafloods and Clovis cache at Wenatchee, Washington Baker, V.R. 2023 J Harlen Bretz & the cataclysmic Late Pleistocene mega-flooding origin of the Channeled Scabland Romano, M. 2015 Reviewing the term uniformitarianism in modern Earth sciences Baker, V.R. Sept. 1995 Joseph Thomas Pardee and the Spokane Flood Controversy