Abstract. The geologic record of mountain glaciations is a robust indicator of terrestrial paleoclimate change. During the last glaciation, mountain ranges across the western US hosted glaciers while the Cordilleran and Laurentide
ice sheets flowed to the west and east of the continental divide,
respectively. Records detailing the chronologies and paleoclimate
significance of these ice advances have been developed for many sites across
North America. However, relatively few glacial records have been developed
for mountain glaciers in the northern Rocky Mountains near former ice sheet
margins. Here, we report cosmogenic beryllium-10 surface exposure ages and
numerical glacier modeling results, which show that mountain glaciers in the
northern Rockies abandoned terminal moraines after the end of the global
Last Glacial Maximum around 17–18 ka and could have been sustained by −10 to −8.5 ∘C temperature depressions relative to modern assuming
similar or less than modern precipitation. Additionally, we present a
deglacial chronology from the northern Rocky Mountains that indicates while
there is considerable variability in initial moraine abandonment ages across the Rocky Mountains, the pace of subsequent ice retreat through the
late glacial exhibits some regional coherence. Our results provide insight on potential regional mechanisms driving the initiation of and sustained
deglaciation in the western US, including rising atmospheric CO2 and
ice sheet collapse.
