ROCK GLACIERS IN SOUTHWESTERN COLORADO AS INDICATORS OF LATE-HOLOCENE CLIMATE CHANGE: A LICHENOMETRIC STUDY USING RHIZOCARPON SUBGENUS RHIZOCARPON

Lichenometry was used to date the stabilization of 75 individual lobes on 18 rock glaciers in the Elk Mountains and Sawatch Range of southwestern Colorado. A K-means clustering analysis was used to separate lichen thalli measurements into four groups, each representing a discrete interval of rock glacier stabilization. A one-way ANOVA test confirmed the groups are significant at a 95% confidence level. Using a growth curve developed in the nearby Front Range for Rhizocarpon geographicum, these stabilization events were dated at 3560, 2980, 2170, and 1220 YBP. The event dated at 2980 YBP corresponds with a period of brief climatic warming documented in the adjacent San Juan Mountains. The most recent interval of stabilization may coincide with a period of slightly warmer temperatures lasting from approximately 1100 to 2000 YBP recognized in other paleoclimate studies. Rock glaciers in the eastern portion of the study area stabilized earlier than those in the western portion. No trends were found between either elevation or slope aspect and rock glacier stabilization.