Sunday, March 31, 2013

Tracks of the Bull Lake and Pinedale Glaciations

I did learn a little about the glacial history of the Rockies from my recent trip. After the views of glacial moraines and alluvial fans on the east side of the Lemhi Range in Idaho alluvial-fans-and-glacial-moraines, I had a great view of the upper Green River Valley. With the snow cover and just right sun angle, I had good view of the topography.
Upper Green River Valley. Note the lumpy glacial recession deposits.
The Green River is on the lower left. 
A bit further on I had a great view of the a series of glacial moraine lakes on the west side of the Wind River Range with obvious multiple terminal moraines including moraines that cross the lakes.  
New Forks Lakes

Fremont Lake and Willow Lake

Soda, Boulder, Burnt, and Half Moon Lakes along with a few others

The Wind River Range developed a full ice cap during glacial periods. The moraine lakes formed when the ice flowed out from the ice cap. There are still glaciers in the Wind River Range. The well preserved moraines are the type localities of the two latest ice ages in the Rockies. The Pinedale Glaciation is named for a town a bit west of Fremont Lake. The Bull Lake Glaciation in named for Bull Lake, a glacial moraine lake on the east side of the range. The extensive recessional deposits in the first picture in the upper Green River Valley were deposited during the older Bull Lake Glaciation.

The Pinedale Glaciation correlates with the Fraser Glaciation in Washington State. The Fraser was a continental glaciation between 20,000 and 13,000 years ago saw glacial ice flow out of ice caps in the Canadian Coast Range down through what is now Puget Sound and out the Strait of Juan de Fuca. This same glacial period had continental ice covering the entire northern tier of Washington State.

The Bull Lake Glaciation may correlate with older continental glaciations by figuring out the dates is troublesome both in the Wind River Range and in the Puget Sound.  

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