75 Outline of Last Ice Age Glaciers in Central-Western Wyoming

Faculty Mentor: Dr. Leif Anderson (Geology and Geophysics, University of Utah)

During the last Ice Age, many of the mountain ranges in the western United States were covered with glacial ice in the form of glaciers and ice caps. These glaciers grew because, (probably put climate cooled first here) as the climate cooled, the elevation above which snow accumulation exceeds ablation, or the Equilibrium Line Altitude (ELA), dropped below the topography as the climate cooled. When the climate warmed at the start of the current interglacial period, these glaciers began to retreat and eventually disappear because the ELA rose above the landscape and annual snow accumulation could no longer overcome the increasing ablation rate. The evidence of these glaciers’ presence remains in the depositional and erosional landforms they left behind, the most notable of which are loose deposits of rock called moraines and “U-shaped” valleys. This study aims to find these features in the mountains of central-western Wyoming and use them to create outlines of glaciers as they appeared during the last Ice Age. Specifically, our region of interest (ROI) includes the full extents of the Wyoming and Salt River Ranges, as well as portions of the Salt River Range, the Tetons, and the Gros Ventre Range. These outlines are given a confidence rating based on how much evidence the glacier left behind, and the highest confidence outlines are used to create estimates for local ELAs using an assumed Accumulation Area Ratio of 60/40. Determining past glacial extent allows for more accurate estimates of paleoclimate during the last ice age based on glacier modeling. These models will provide a better understanding of how glaciers react to warming climates over longer timescales and more diverse ELA conditions than we can infer from the active glaciers of today. We observed evidence for 329 distinct paleoglaciers with a total area of 1387.96 km2, including indications of a previously undocumented ice cap across parts of the Wyoming Range. We also observed a preference for larger glaciers across ranges with more high-elevation topography. Studying where these glaciers were and what they left behind will allow for more accurate predictions of how modern glaciers and the landscapes they inhabit might evolve in the face of ongoing anthropogenic climate change. These outlines will also be added to a living database that tracks glaciation from the last Ice Age across the western United States and will be used in future research to further investigate how different landscapes changed during the last glacial period and how they continue to evolve during the present interglacial period.