Cordilleran Ice Sheet During the late Pleistocene

7 11 2012

The Cordilleran Ice Sheet during the Pleistocene reached down into the Northern parts of Washington and Montana over 20,000 years ago, but started to retreat near the end of the Pleistocene era. During the late Pleistocene (approximately 16,000 – 11,700 years ago) the climate of the region started to see fluctuations, causing the Cordilleran Ice Sheet to began its retreat in some areas while other areas were still advancing. The Ice Sheet during this time frame covers all of a high alpine environment that is exposed today.

Figure 1. The image above shows the direction of ice flow on the Cordilleran Ice Sheet during the Pleistocene era. The portion of ice that reaches the southern most point in this image is known as the Puget Lobe.

Roughly 17 thousand to 16.5 thousand years ago what is known as the Puget Lobe had reached its southern most point in what is now Olympia, Washington. Lasting for roughly 500 years the ice began to retreat North. It wasn’t until about 14.5 thousand years ago that this retreat came to a halt and glacier advance began to take course again. Scientists have suggested that this glacial advance begun the process of morainal deposition  around 13.5 thousand years ago, however no absolute dating methods have been done to prove this.



Figure 1 –


Menounos, Brian, Gerald Osborn, John J. Clague, and Brian H. Luckman. “Latest Pleistocene and Holocene Glacier Fluctuations in Western Canada.” Quaternary Science Reviews 28.21-22 (2009): 2049-074. Science Direct. Web. 10 Nov. 2012. <;.




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