North-Central Section - 50th Annual Meeting - 2016

Paper No. 6-5
Presentation Time: 9:25 AM


SOCKNESS, Brian, HEADLEY, Rachel and BORCHARDT, Scott, Department of Geosciences, University of Wisconsin-Parkside, 900 Wood Road, P.O. Box 2000, Kenosha, WI 53141,

The Alaska Range is a region of extreme and stunning topography in central Alaska, incorporating high peaks, active faults, glaciers, and large rivers. The highest mountain, Denali (Mt. McKinley), is comprised of a large granitic massif, which is surrounded by sedimentary and meta-sedimentary rocks, and has been eroded by many large glaciers over the Holocene. Muldrow Glacier flows from the eastern side of Denali, is joined by tributary glaciers, turns to the north, and forms its terminal moraines and till plain, before it culminates in the headwaters of the McKinley River. The moraines of the Muldrow Glacier have been previously dated and mapped, with ages ranging from before the Last Glacial Maxima (LGM) in Alaska to more recent Holocene and modern deposits, providing a natural laboratory for studying the connections between erosion and deposition from Holocene warming. Because less erosion likely occurred at high elevations during colder periods, we predict that moraines from these periods should have more local material whereas younger moraines should contain material eroded at higher elevations by the warmer and wetter glacier. We investigate changes in regions of erosion over time using studies of rock type and provenance based on the distinctive geology of the region. A total of 12 samples were collected from lateral moraines, terminal moraines, and the active Muldrow Glacier. The lithology of the sample material greater than 5mm in size was analyzed to determine the abundance of igneous, metamorphic, and sedimentary rocks. Meta-sedimentary rocks of slate and other minor constituents comprised over 80% of 9 sample locations. The terminal moraines displayed a notable quantity of igneous rocks relative to the other sample locations with a generally increasing proportion in successively younger moraines. These preliminary results could indicate that, as expected, a warming climate has caused greater erosion of the granitic massif and is reflected in the composition of the younger terminal moraines. Additionally, the profusion of meta-sedimentary rocks in the samples from the active Muldrow Glaciers likely reflects landslides that have occurred in the surrounding hillslopes.