Numerical Modeling of the Snowmass Creek Paleoglacier, Colorado: Implications for Middle and Late Pleistocene climate in the Rocky Mountains
Abstract
Well-preserved moraines from the last two glaciations of the Snowmass Creek valley in the Elk Range of Colorado present an opportunity to examine the character of the high-altitude climate in the Rocky Mountains during marine isotope stages 6 and 2. This study employs a 2-D coupled energy/mass balance and flow model (Plummer and Phillips, 2003) to assess the magnitudes of temperature and precipitation change that could have sustained the glacier in mass-balance equilibrium at its maximum extents during the penultimate (MIS 6 or Bull Lake) glaciation and the last glacial maximum (MIS 2 or Pinedale). Variable substrate effects on glacier flow and ice thickness make the modeling somewhat more complex than in geologically simpler settings. Model results indicate that a temperature depression of about 6.4°C compared to the modern (1971-2000AD) would have been necessary to sustain the 26 km-long Snowmass Creek glacier in mass balance equilibrium during the Bull Lake glaciation, assuming no change from the modern in precipitation amount or seasonality. Uncertainty in the modeling is about 1°C. A 50 percent increase or decrease from modern precipitation would have been coupled with 4.8°C and 8.8°C Bull Lake temperature depressions respectively. The maximum extent of the glacier during MIS 2 or Pinedale glaciation is somewhat less clear. Moraines confidently assigned to the Pinedale glaciation indicate a temperature depression of about 6.1°C, assuming no change in precipitation. An intermediate set of moraines which may be Pinedale in age, would suggest a Pinedale temperature depression very close to that of the Bull Lake glaciation. These Pinedale temperature depression estimates are comparable to those obtained using the same model in three other Colorado ranges (5.5 - 6.8°C with no change in precipitation) and slightly less than those previously obtained using a variety of other paleoglaciological methods (6.4 to 8.5°C with no change in precipitation). The Bull Lake climate estimates are the first we are aware of for the Colorado Rocky Mountains.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.C33A0687L
- Keywords:
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- 0720 CRYOSPHERE Glaciers;
- 0798 CRYOSPHERE Modeling;
- 4926 PALEOCEANOGRAPHY Glacial