ROCK GLACIERS IN CENTRAL COLORADO AS INDICATORS OF LATE-HOLOCENE CLIMATE CHANGE

Kurt A. Refsnider and Keith A. Brugger, 2005 GSA Abstracts with Programs, v. 37.

We used measurements of the lichen Rhizocarpon subgenus Rhizocarpon to date the deposition of 48 individual lobes of 18 rock glaciers or rock glacier complexes in the Elk Mountains and Sawatch Range of central Colorado. Cumulative probability distribution and K-means clustering analyses were used to separate lichen thalli measurements into separate groups, each representing a discrete interval of debris deposition on the rock glaciers. Using a growth curve developed in the nearby Front Range for Rhizocarpon geographicum, these depositional events have mean ages of approximately 3100, 2100, and 1200 calendar years before present. These events generally correspond to periods of climatic deterioration and other Holocene glacial and periglacial activity in the region. Deposits in the eastern part of the study area are older than those in the western part. No trends exist between either elevation or slope aspect and the timing of rock glacier deposition.