Friday, March 4, 2011

The Puget Ice Lobe Turns West

Blue arrows indicate glacial ice movement, red line marks approximate ice margin (click image to enlarge)

As glacial ice retreated from the Puget Sound the retreat stopped for a period when the ice had retreated back to approximately Coupeville on Whidbey Island. The direction of ice flow changed at that point from a north to south flow to a northeast to southwest flow towards the Strait of Juan de Fuca. The last ice flow direction can be seen in LiDAR image. South of the ice margin near Coupeville the land is streaked by the ice in a series of gentle north-south ridges. North of the ice margin near Coupeville the ridges are oriented toward the southwest marking the last glacial movement direction prior to the ice melting even further back.

The glacial lobe likely hung up at this location for a time after the ice spanning the entrance of Puget Sound collapsed when the lake that had formed south of the ice lobe in what is now Puget Sound drained out to the west. A lumpy area of kettles and moraine material can be seen in the LiDAR image immediately north of the text block indicating the glacial margin.  

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