ROCK GLACIER DISTRIBUTION AND IMPLICATIONS FOR ALPINE HYDROLOGY IN THE NORTHERN ROCKY MOUNTAINS

The meltwaters of annual snowpack and mountain glaciers have been recognized as vital contributors to semi-arid, high mountain water budgets. Yet, until recently the role of rock glaciers as persistent alpine water reservoirs has been largely overlooked. Understanding the hydrologic significance of rock glaciers including flow patterns, annual discharge rates, and the biogeochemical characteristics of the meltwaters is necessary for informing effective water resource management through the coming century. This study seeks to contribute to the greater body of rock glacier hydrology research by developing a regional inventory of rock glaciers and characterizing the hydrology and isotope geochemistry of rock glacier meltwater streams in the central Idaho mountains.

We continuously monitored discharge, water temperature, and ambient air temperature of nine Idaho mountain streams during the 2023 summer melt season, building on limited previous monitoring efforts to develop a hydrologic dataset for meltwater processes. Seven of the streams are fed by rock glaciers and two by seasonal snowpack to provide a comparison of flow patterns. We also characterized the hydrochemistry of selected streams through elemental and isotopic analysis, and by monitoring electrical conductivity (EC). Finally, to understand residence times of possible ancient carbon within the system and its significance to stream biota, we collected biofilm samples for radiocarbon analysis. Preliminary datasets show that 1.) consistent summer stream persistence in discharge (Q) and temperature (T) (Q=~0.3-0.9 m³/s, T=1-2 °C) is a characteristic feature of rock glacier streams that fundamentally contrasts with snowmelt streams (Q drops from ~1.5 to 0.3 m³/sec, T increases from 4 to 12 °C), 2.) rock glacier meltwaters demonstrate seasonally variable hydrochemistry with EC levels slightly increasing through summer, 3.) rock glacier outlet streams are sustained, frigid cold-water habitats that support cold water-obligate invertebrates (such as uncommon Zapada species) and are likely reservoirs of ancient carbon. These results provide initial insight on questions about climate change stream resilience, water storage and hydropower potential, meltwater hydrochemistry, and ancient carbon export generally absent from the literature.