GLACIOLOGY IN THE CHUGACH RANGE OF SOUTH CENTRAL ALASKA

Studying the glacial history and limits in the Chugach Mountains provides a proxy for climate history that can be compared globally such as to the marine isotope stages and ice core records. We have investigated glacial deposits and landscapes produced by Holocene and Pleistocene glacial activity in the south central Chugach Mountains using ¹⁰Be and ³⁶Cl terrestrial cosmogenic nuclide dating. We have mapped and dated eight moraines and established the age of ancient preserved penultimate glacial surfaces high across the range. We have also mapped the resulting glacial landscape and quantified provenance and sedimentary characteristics of glacial deposits. Our new geomorphic observations and quantitative age constraints build on prior mapping and relative age dating in the Williwaw Lakes Valley, Crow Pass, Thompson Pass, and surrounding areas. Prior work has been unsuccessful at precise correlation of glacial deposits across the Chugach and Kenai ranges due to the complexity of the glacial history. So far we have completed thirty-six cosmogenic exposure ages on polished bedrock and boulders on moraines and old glaciated surfaces, although more analyses are to be completed. The preliminary results show surprisingly old ages (>50 ka) which predate the last glacial maximum and imply that ice limits were deeper and more extensive during the Pleistocene. Elsewhere, we have obtained neoglacial (<20 ka) ages from polished benches and boulders that are consistent with reconstructions for the last glacial maximum. The new age constraints, mapping, and provenance will be used to reconstruct past glacial equilibrium line altitudes, measure retreat rates, and measure flow directions and drainage, providing a more complete understanding to the glacial history of south central Alaska. In addition, other ongoing work quantifying inheritance on glacial landforms and measuring short-term basinwide erosion rates will help test hypothesis for the erosivity of the glaciers in the region.