SPATIAL VARIATION IN GLACIAL EROSION AND MORAINE DEPOSITION OF THE MULDROW GLACIER THROUGH HOLOCENE WARMING

The Alaska Range has experienced considerable warming over the Holocene, with major impacts on some of the largest Alpine glaciers in North America. This warming and shorter-term glacial dynamics are recorded in the glacial signature on the landscape. Muldrow Glacier (Henteel No' Loo') drains the eastern side of Denali before turning north and forming the McKinley River (Henteel no' Tl'o). Previous research has dated many of the Muldrow’s terminal moraines and deposits from before the Last Glacial Maximum to younger surges. The Muldrow is also well known as a surging glacier, with a surge starting in 2021 overridden some older deposits.

Comprised of distinctive granitic massifs surrounded by sedimentary flysch deposits, the geology of Denali and its surrounding area provides a natural laboratory for linking glacial deposition, transport, and erosion in a warming climate. These lithological variations allow for both qualitative and quantitative differentiation of material from its original erosional source. Over terminal moraines, lateral moraines, and the active glacier toe, 12 detrital samples were collected in summer of 2015. For detrital clasts larger than 5 mm, a simple lithological analysis determined abundance of igneous versus sedimentary rocks, with sedimentary clasts comprising over 80% of 9 lateral and terminal sample locations. Despite this, the terminal moraines still displayed increasing proportions of igneous material in successively younger moraines, likely influenced by changing erosional source.

To more specifically determine provenance of detrital material, we present preliminary results from detrital zircon geochronology. Zircon is a robust and durable mineral that can record age information of crustal units that contribute to sediment deposits. In this study, detrital zircon U/Pb age dating is used to derive depositional provenance for spatially distinct till deposits and moraines. To date, zircon grains have been extracted from bulk sedimentary samples from the 12 locations on lateral and terminal moraines, as well as on the active glacier surface. U/Pb will be measured by LA–ICP–MS, the raw data will be processed using the Glitter software package, and U/Pb age clusters will be determined and compared between the glacial deposits.