Chapter 17 - Late Pleistocene Mountain Glaciation in the Lake Bonneville Basin

Abstract

Abstract The record of the last Pleistocene glaciation in the Lake Bonneville basin has been known for decades and has improved significantly due to expanded mapping and geologic dating efforts. Although ice occupied only a small portion of the basin and constituted a small component of the lake water budget, the pattern of glaciation in space and time can be combined with the stratigraphic record from Lake Bonneville to improve the understanding of regional climate change during and after the last glaciation. Mountain glaciers were most abundant in the eastern/Rocky Mountain sector of the basin, with the vast majority of ice volume concentrated in the Wasatch and Uinta Mountains. Here, the geomorphic record of the last glaciation is well preserved, stratigraphic observations of sediments of Lake Bonneville and valley glaciers are documented, and cosmogenic 10 Be exposure ages of several moraines based on new production models of in situ 10 Be are reported. Terminal moraines here, and in the western sector of the basin, were occupied near the time of the Bonneville highstand at 18 ka and subsequently abandoned while the lake continued to overflow. This constitutes a significant revision to initial reports of 10 Be exposure ages based on earlier production rate models, which suggest that ice retreat corresponded to the fall of Lake Bonneville from the Provo shoreline. Still, temporal correspondence of the Lake Bonneville highstand and glacier maxima support the previously proposed model that climate during the lake highstand was favorable for maxima of both glaciers and lakes. The onset of ice retreat while the lake overflowed, however, suggests warming in the basin at c.18 ka but with sufficient precipitation to sustain a positive water budget of Lake Bonneville.