GLACIAL SEDIMENTATION IN FISH LAKE, UTAH: EVOLUTION OF BASIN MORPHOMETRY AND IMPLICATIONS FOR PALEOHYDROLOGY

The Fish Lake tectonic basin, located in central Utah on the eastern margins of the Fish Lake Plateau, includes sediments deposited by ice cap outlet type glaciers and cirque constrained glaciers dating to the Last Glacial Maximum. Older moraines also exist, extending beyond LGM ice limits into the margin of the modern lake, but ages have yet to be determined. The older moraines form prominent features along the outflow end of the lake’s shoreline where a single small stream provides an outlet from the lake to the upper reaches of the Fremont River. The purpose of this study is to explore the influence of glacial sedimentation on basin morphology, lake volume, and paleohydrology to inform the interpretation of paleohydrologic proxy data from the ~60,000-year sediment record. The question for the paleorecord is if the Holocene lake’s configuration is an appropriate analogue to apply across glacial-interglacial cycles. An analysis of modern Fish Lake hydrology based on water isotope tracers indicates negligible lake contributions to the surface outflow stream. Rather the outflow stream is dominated by creeks running off adjacent slopes that are re-routed away from the lake by glacial sediment infill. Instead, substantial water loss by evaporation from the lake surface occurs due to long lake water residence times of multiple decades. To investigate pre-glacial basin morphology and former surface outflow configurations, estimates of glacial sediment volumes using GIS tools and seismic information are used to derive possible paleohydrologic scenarios for further testing by lake proxy system models.