IMPACTS OF HOLOCENE WARMING ON PATTERNS OF EROSION AND MORAINE DEPOSITION FOR THE MULDROW GLACIER IN DENALI NATIONAL PARK

At high latitude and altitude, the Alaska Range has experienced considerable warming over the Holocene, with major impacts on some of the largest mountain glaciers in North America. This warming has made its mark on glacial and progracial regions not only through direct melting but also by changing where and how fast the glaciers erode their beds and deposit their moraines. In colder periods, because less erosion likely occurred at high elevations, we speculate that moraines would be sourced from more local and lower-elevation bedrock whereas moraines formed when a glacier was warmer and wetter would generally contain increasing amounts of material eroded at higher elevations. The highest mountain in North America, Denali (Mt. McKinley), and its surrounding landscape are comprised of distinctive geology: granitic massifs surrounded by sedimentary flysch deposits. One of many glaciers draining this peak, Muldrow Glacier flows from the eastern side of Denali, turns to the north, and forms its terminal moraines and till plain, before it culminates in the headwaters of the McKinley River. Capitalizing on the previously mapped and dated moraines, from pre-LGM to modern deposits, along with the easily identifiable underlying lithologies, we used the Muldrow glacier’s deposits to track changes to its erosional signature. We investigated changes in regions of erosion over time using studies of rock type and provenance for a total of 12 samples, which were collected from lateral moraines, terminal moraines, and on top of the active Muldrow Glacier. The lithology of deposits greater than 5 mm in size was analyzed to determine the relative abundance of igneous and sedimentary rocks, and sedimentary rocks comprised over 80% of 9 sample locations. Relative to the lateral and supraglacial deposits, which might also reflect many other geomorphic processes, the terminal moraines displayed increasing proportions of igneous material in successively younger moraines. Our results indicate that, as expected, a warming Holocene climate led to greater erosion of the high-elevation granitic massif as reflected in the composition of the younger terminal moraines. These climate-related changes have implications for modern warming impacts on the Muldrow’s erosion and deposition.