ROCK GLACIERS AND ALPINE STREAM RESILIENCE IN THE SEMIARID NORTHERN ROCKY MOUNTAINS

Rock glaciers are important water systems in semiarid mountain ranges. We report a quantitative examination of 2023 rock glacier hydrology, including discharge, temperature, chemistry, and isotopic signatures across several rock glacier sites in the Lost River and Pioneer Ranges of the Northern Rocky Mountains. Multiple patterns emerge: rock glacier streams maintain stable discharge throughout the melt season and exhibit extremely cold temperatures (<5 °C) in comparison with non-rock glacier alpine streams. Isotopic analyses suggest that seasonal precipitation in 2023, a year of 140% normal snowpack, remained a dominant water source across rock glacier springs (d¹⁸O: -19‰ to -17‰), with minimal evidence of meltwater contributions from aged ice. An initial conceptual model explains rock glacier hydrology in terms of short-term hydrologic modification and long-term water storage. Yet, heterogeneities in hydrologic responses from rock glaciers reveal influences of variable morphology and topographic settings between landforms. We use these distinctions to develop a sub-classification of rock glacier springs. We find that rock glacier streams produce early season outflows supported primarily by supraglacial snowmelt and later season outflows influenced by evolving hydraulic conductivity. The hydrologic contributions of rock glaciers are thus crucial, yet non-uniform, and likely of increasing importance in warming alpine climates.