NEW PERSPECTIVES ON THE HISTORY AND DYNAMICS OF LATE PLEISTOCENE GLACIATION IN GREATER YELLOWSTONE AND THE TETON RANGE (Invited Presentation)

The Greater Yellowstone Glacial System (GYGS) covered about 20,000 km² at its Pleistocene maximum. The initiation, culmination, and ultimate decay of the GYGS involved complex interactions between several coalescent ice masses sourced from glacial source areas adjoining and including the Yellowstone Plateau. Here, we present an updated review of the history and dynamics of the GYGS during the last (Pinedale) glaciation, drawing upon an integration of previous glacial-geologic mapping with >170 cosmogenic ¹⁰Be and ³He exposure ages amassed in prior and ongoing research.

In earlier Pinedale time (~21-18 ka), glaciers from the Beartooth Uplift advanced onto the northeastern Yellowstone Plateau, where they dammed a lake in Hayden Valley. Glaciers from the High Absaroka Range advanced northward onto the eastern Yellowstone Plateau and westward into Jackson Hole. Valley glaciers culminated in the Teton Range as evidenced by high lateral moraines dating to this interval; notably, these moraines are offset by the Teton fault, providing a rare opportunity to directly constrain time-integrated slip rates.

By middle Pinedale time (~18-16 ka), the ice surface on the northern and eastern Yellowstone Plateau had risen above the equilibrium-line altitude, stimulating orographic glacial buildup nourished by storms funneled eastward through the Snake River Plain. The nascent Yellowstone Plateau ice cap eventually thickened to >1000 meters and joined glaciers from the Beartooth Uplift and Gallatin Range to form the northern Yellowstone outlet glacier. Terrain to the east of the ice cap was placed in a precipitation shadow, resulting in glacial recession in this region. The glacier flowing into Jackson Hole from the High Absarokas also receded dramatically.

During later Pinedale time (~16-13 ka), the Yellowstone ice cap continued to prograde southwestward, leading to an advance into Jackson Hole and the deposition of voluminous outwash, as well as an advance to terminal moraines near Ashton, Idaho. The northern sector of the ice cap appears to have been nearly stagnant at this time, while ice flowing from the Beartooth Uplift and Gallatin Range stabilized near Deckard Flats. Ages of end moraines and bedrock in the Teton Range along with outwash relationships indicate glacier culminations followed by rapid retreat ca. 15-13 ka.