Vegetation and Glacial Outwash in Moses Coulee

Mosses Coulee in central Washington was the route of some of the earlier huge ice- age floods. State Highway 2 crosses the Coulee and crosses over one of the huge gravel bars left by the flood on the coulee floor (huge-deflation-bar-at-moses-coulee). 

A couple of miles north of the Highway 2 crossing is another crossing. The Withrow Moraine crosses the coulee.  

As glacier ice advanced from the north the ice blocked the ice age flood path down Moses Coulee. The glacial moraine left by the maximum extend of ice overlies the ice age flood deposits on the coulee floor. A geologic classic case of superpostion meaning the ice-age floods in Moses Coulee are older than the maximum ice advance. The advanced ice blocked the Moses Coulee flood route and diverted the later floods down the Grand Coulee route to the east.

The above summary can readily be seen by taking a trip up the coulee on Jameson lake Road. But of course it can be readily seen on Google earth. But the most striking thing to me is how the melt water routes are enhanced by the vegetation based on the subtle changes in sediment composition. This feature was not noticeable on the ground but with the right season and light stood out sharply in this view.