AEG OR Chapter December 14, 2021 Meeting
The Missoula Floods and Channeled Scabland
PURCHASE OF TICKETS USING BROWN PAPER TICKETS: Ticket sales stops by Noon on Monday December 13th.
(At the door payments in Cash or Checks only.)
6:00 Social Hour and Dinner*
*Please contact the Board if you have any specific dietary restrictions.
Speaker: Dr Jim O'Connor
The U.S. Pacific Northwest has been fertile ground for understanding ice-age megafloods, including observations by Thomas Condon himself. Floods from a variety of sources affected the Columbia River and its tributaries but the largest, best known, and perhaps most spectacular were the Missoula floods. At the close of the last ice age, 15,000-20,000 years ago, a lobe of ice flowing south from Canada blocked the Clark Fork River in northern Idaho and western Montana. The resulting ice-dammed lake, known to geologists as Glacial Lake Missoula, was at times more than 2000 feet deep and contained 500 cubic miles of water20 times the size of Puget Sound. The ice dam ruptured and reformed dozens of times, each break-out sending torrents of water across eastern Washington and down the Columbia River. The flood waters were in places 1000 feet deep and flowing at 30 or 40 miles per hour, lifting boulders the size of automobiles and tumbling them downstream. With such force, these humongous floods
instantaneously shaped the landscape of the Pacific Northwest by carving the Channeled Scablands,shaping the Columbia River Gorge, depositing bars of sand and gravel 100s of feet high, and backfilling broad valleys with silt and clay. But the floods also shaped the science of geology. When these floods were first proposed by early geologist J Harlen Bretz, such catastrophes were loathed by geologists confined by an intellectual framework of slow gradual processes shaping the planet over millions of years. The debate raged for decades, with many twists and turns. In the end Bretz prevailed, but surprising findings continue to emerge, challenging our understanding of one of the greatest natural events in earth history.
Jim OConnor is a Pacific Northwest native long interested in the processes and events that shape the remarkable and diverse landscapes of the region. Following this interest with a Geological Science major at University of Washington and M.S. and Ph.D. degrees at University of Arizona, he has spent the last 30 years, mostly with the U.S. Geological Survey, focused on understanding the geology of the U.S. Pacific Northwest.
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