GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 81-15
Presentation Time: 9:00 AM-5:30 PM


ZENG, Xinyi, Environmental Studies, College of the Holy Cross, 1 College Street, Worcester, MA 01610 and MITCHELL, Sara Gran, Department of Biology, College of the Holy Cross, PO Box B, 1 College St, Worcester, MA 01610,

While the significance of alpine glacial erosion in limiting mountain altitudes worldwide appears to be robust, questions remain about the erosional mechanisms involved and how the creation of erosional glacial landforms (such as cirques) contribute to this process. Previous work has shown a correspondence between glacial cirque and adjacent peak altitudes and local and global trends in “Quaternary average” equilibrium line altitudes (ELAs), suggesting that the formation of cirques plays a role in the hypothesized “glacial buzzsaw” process. However, the global study was performed on mountains that are now mostly or entirely ice-free, raising the possibility that cirque altitude distributions in these regions are simply a result of being on mountains high enough to have been glaciated but not so high as to be ice covered today. We are testing these competing models by determining the relationships between floor height, relief, and ELAs for valley head overdeepenings in mountain ranges that extend well above local ELAs and are therefore currently ice-covered, such as the Aletsch Glacier valley of the Swiss Alps. Our goal is to test a method for determining whether cirques form a certain distance below adjacent peaks, suggesting that peak altitude controls the altitude of cirque formation, or if cirques form at the elevation of the regional Quaternary average ELA, which would suggest that the ELA controls the altitude of cirque formation. We develop and evaluate a GIS-based method for locating potential sub-ice “cirques” by measuring ice surface topographic profiles and modeling the corresponding sub-ice bedrock topographic profiles in the study area. We then use these modeled profiles to determine the presence of flat or overdeepened areas, and finally estimate the location and altitude of any “potential cirque” floors. We compare the spatial and altitudinal distribution and relief of these ice covered overdeepenings with those in nearby, ice-free drainage basins, and with the regional ELA.