DATING OF GLACIAL LANDFORMS USING LICHENOMETRY, MATANUSKA GLACIER, ALASKA

Lichenometric analysis was used to constrain ages of glacial landforms near the terminus of the Mantanuska Glacier, Alaska. Two growth curves for Rhizocarpon geographicum were created for the Matanuska Valley. One growth curve was established using lichen measurements on a 1950 gravestone in Palmer, which is located ~80 km from the present ice margin at the mouth of the valley. It yielded a growth rate of 0.12 mm y-1. The second curve used diameters of lichens growing on a piece of heavy equipment that had not been moved or operated for 30 years and was located within 2 km of the present ice margin. It yielded a growth rate of 0.14 mm y-1. Local climatic differences are hypothesized to account for the different growth rates. Mantanuska Glacier is located in the South Central region of Alaska, between the Chugach and Talkeetna mountain ranges. Lichen diameters were measured at eight locations on and around the glacier using sample populations of 100 lichens. Surfaces on which sampling was conducted include debris-covered glacier ice, an outwash plain, moraine with medium vegetation cover and moraine with heavy vegetation cover. To determine the minimum age of the landform surfaces, the five largest lichens from each site were averaged and compared to the local lichen growth curve developed in this study. Results provide minimum ages for the glacial landforms at each site. However, ages of boulders on the debris-covered ice suggest that inheritance may be a problem when dating moraines composed primarily of medial moraine debris.