Abstract

During the Pinedale Glaciation (~32-15 kya) alpine glaciers filled cirques and valleys extending from the crest of the Colorado Front Range These glaciers are small remnants today, but their erosion over time dominates the landscape. Using field evidence, modeling techniques based on glacial flow rules, and Lidar imagery, I determined glacier size and local ice-flow direction, and estimated volumes of sediment deposited during late Pinedale time. The volume estimates help constrain how rapidly those glaciers cut their cirques and valleys.
At glacial maximum, ice flowing out of the Green Lakes and Arapaho valleys joined and covered 22.3 km², but was only 83 m thick on average. Between 21 and about 15 kya, the glacier deposited morainal debris with a volume between 67 and 90 x10⁶m³, which equates to a bed-lowering rate between 0.5 and 1.35 mm yr^-1. Moraine volumes suggest that cutting the Arapaho and Green Lakes Valleys required as few as 11 glacial events of size similar to the late Pinedale. Results from the Horseshoe and Rainbow Cirques to the south suggest respective bed-lowering rates of 0.25 to 2.98 mm yr^-1 and 0.15 to 1.37 mm yr^-1. Calculated erosion rates are similar to those measured for glaciers in the Swiss Alps. Late Pinedale cirque glaciers in the Front Range eroded at a moderate rate- far greater than polar ice sheets (0.01 mm yr^-1), but well below rates of glaciers in southeastern Alaska that lower their beds on the order of 1to 10 cm yr^-1.

Citation

Kantack, Keith McBride. (2011): Reconstructing Pinedale (latest Pleistocene) ice in the Green Lakes Valley and adjacent areas, Colorado. Thesis submitted in partial fulfillment of the requirements for the Degree of Bachelor of Arts With Honors in Geosciences(Williams College).