Reconstructing the Glacial History of Green Lakes Valley, North Boulder Creek, Colorado Front Range

We document the post Last Glacial Maximum (LGM) deglaciation history of a small catchment in Colorado's Front Range and model the glacial history responsible. We combine cosmogenic exposure dating of moraine boulders and glacial polish from 10 sites down the valley axis with a set of 1-D and 2-D numerical glacier models in which climate is represented by prescribed winter and summer mass balance profiles. Moraine ages of 24-18 ka constrain the LGM maximum glacial extent at 15 km downvalley from the range crest. Glacial polish sites decline in age along the center portion of the valley, dropping to roughly 12 ka by 5 km from the crest. This supports a monotonic but non-steady decline in glacier length. Modeling of the deglaciation history reveals that the equilibrium line altitude (ELA) rise from similar to 18 ka to similar to 14 ka was between 250 and 350 m, and that from similar to 14 ka to similar to 12 ka was between 100 and 150 m. Complete deglaciation requires at least another 250-300 m of ELA rise. A transient model run employing this ELA history can both reproduce the spatio-temporal pattern of glacial polish ages, and honor the constraints on maximum glacial extent. The full deglaciation between 18 ka and 10 ka can be modeled successfully with a 4.5-6 degrees C temperature rise and little to no change in precipitation.