Extent of the last glacial maximum in the Green Lakes Valley

10Be exposure dating of glacially polished bedrock (from Ward et al., 2009; ages are in thousands of years).

Green Lake 4, 10-20-08

Green Lake 4, 10-24-08

 

About 20,000 years ago, in the last glacial maximum, or LGM, the glaciers in the Colorado Front Range extended much farther downstream of their present-day position (see figure left).

Dating of boulders from moraines deposited during the LGM (using cosmogenic radionuclides), we can establish the timing of the maximum glacier extent. Dating glacial polish on bedrock knobs between the moraines and the present glacier allows us to reconstruct the history of the glacier retreat from 20,000 ago to its present-day position (see second figure).

Ward et al. (2009) show an example of such a reconstruction of the glacial retreat history in the Middle Boulder Creek Valley, also called 4th of July Valley, located just to the south of the CZO. The ages shown, given in thousands of years before present (ka), are from bedrock knobs in the valley. They reveal that the glacier reached its maximum extent near Nederland at about 20 ka and retreated slowly from this position until the valley was completely deglaciated at around 13 ka.

 

 

 

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Every 24 hours, a time-lapse camera above Green Lake 4 captures an image of Green Lakes Valley in the direction of the continental divide.  These photos depict daily changes in snow cover and allow us to reconstruct the histories of snow accumulation and melt.  We also capture the spatial and temporal pattern of lake ice formation and thaw (see photos left).  These can then be used to test models of snowmelt generation in the valley, an all-important aspect of the hydrology, geomorphology and ecology of this valley.

 

Written by Miriam Dühnforth