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PACIFIC NORTHWEST ARCHAEOLOGICAL SOCIETY

The Late-glacial Tanwax Flood and Debris Flow—An Ice-Age Flood from the Cascade Range into the Puget Lowland and Likely Source of Sediments for the Mima Mounds

9/16/2020

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Hope all going ok in these trying times.  

We are changing our PNWAS format and will have presentations on ZOOM in the future.  Please be sure your membership is current for 2020 so you get to continue to enjoy these talks from home (see attached membership form and you can pay on PayPal).  We are continuing with our theme on the Chehalis River Hypothesis (CRH), proposing the first entrance into the entire American Continent was down the coast until eventually reaching our area and the ice free Chehalis River drainage (I am attaching member Vic Kucera and my publication on this CRH so you can refresh this proposed hypothesis for the talk).  Together we can explore testing this hypothesis with different specialists in our region.  The foremost Geologist in our region is Professor Pat Pringle, who will present the following presentation the evening of Thursday, September 24 at 7pm.  You'll need to provide your own coffee/tea/hot coco/cider (maybe wine/beer) and treats since we sadly will not be at the Mountaineers in Seattle.
If you are an updated member (2020) you will receive an invitation to join us via email in the near future (so signup and help us) and here is a ZOOM tutorial: 

https://www.youtube.com/embed/hIkCmbvAHQQ?rel=0&autoplay=1&cc_load_policy=1
​

Here is our first CRH Program (see attachment with color map and description below):

​
2017 CROES & KUCERA-CHEHALIS RIVER

​Thursday, September 24th, at 7 pm, starting PNWAS Meetings on ZOOM
 
The Late-glacial Tanwax Flood and Debris Flow—An Ice-Age Flood from the Cascade Range into the Puget Lowland and Likely Source of Sediments for the Mima Mounds


By Pat Pringle, Research Geologist,
Professor Emeritus of Earth Sciences, Centralia College
The Puget Lobe of the Vashon Glacier blocked the Carbon River at the time of the last glacial maximum about 17,000 years ago. A large lake filled the Carbon River and adjoining areas of the ice margin. Sometime later the lake level dropped by more than 50 meters as indicated by the levels of existing kame terraces, releasing a large flood of water that carved into sediments of the Puget Lowland creating and deepening the Tanwax, Ohop, and other valleys. The flood also triggered a number of landslides that transformed into debris flows whose equivalent deposits can be traced more than 100 km flow distance to the west.  Equivalent deposits (rich in andesite) can be found in Rocky, Violet, Mima, and Ford Prairies, Tenino, and the Skookumchuck and Chehalis River valleys.
 
The flood merged with outwash from the Puget Lobe in the Black River Valley and continued downstream in the Chehalis River. Both the flood and discharge from the Puget Lobe into the Chehalis River modified the landscape of the southernmost Puget Lowland and Chehalis River. Although the floods of water would have posed a temporary obstacle to movement of people, the prairie landscapes left behind proved favorable for human use and travel.
 
[this is based on work Barry Goldstein of University of Puget Sound (UPS) and I have done over the past 20 years]
TANWAX FLOODS IN CHEHALIS RIVER

​Future programs will present the result of TESC student, Christina (Jellyfish) Gomez, who got a student grant to visit and record mammoth/mastodon and other megafauna remains at regional museums.  Her illustrated presentation will show examples of these megafauna remains in our region.  We also have a PNWAS grant through the Squaxin Island Charitable Fund (1%) to C14 date the mammoth/mastodon bones of interest she finds (hopefully with cut marks!).

So we will send an update, inviting members to begin joining us on  ZOOM to brainstorm these ideas and test our hypotheses through our Society.  Thanks and see you soon [zoom], best to all,  Dale

PS if you are not sure if you are up-to-date on membership, let me know, and thanks for help at this time, Dale
PNWAS MEMBERSHIP FORM 2020

    You can RSVP here to attend the ZOOM meeting!

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