Thermal and hydrologic attributes of rock glaciers and periglacial talus landforms: Sierra Nevada, California, USA

摘要

To explore thermal regimes and hydrologic capacity of rock glaciers and related periglacial talus land-forms, mini-thermochrons were deployed in and around potentially ice-embedded features of the Sierra Nevada. Results from pilot studies at 13 rock glaciers and 7 taluses indicate that outlet springs from these landforms generally do not desiccate but persist year-round as ice (frozen) in winter and flowing water in the warm season. Temperatures of water (liquid and ice) in rock-glacier outlet springs had an annual mean of -0.2 ℃ and mean of 0.6 ℃ during the warm season with very low diurnal fluctuation. These and other attributes suggest the existence of internal ice and/or permafrost supplying the springs. Air temperatures of rock-glacier matrices (1 m below the surface) versus surface air corroborate the periglacial nature of internal environments: annual air temperatures of matrices were below freezing (mean, -0.8 ℃). Compared to surface air, especially during the warm season, matrix air temperatures were significantly colder and fluctuated less. Talus landforms followed a similar pattern, although water- and matrix air temperatures were warmer, and contrasts with surface air were not as strong as for rock glaciers. For rock glaciers and talus slopes, matrix air temperatures showed resistance (buffering) to changes in external air temperatures. Unique geomorphic conditions of rock glaciers and periglacial taluses in the Sierra Nevada appear to maintain cool-buffered thermal regimes at least partly decoupled from external air. Springs support persistent wetlands and lakes at their snouts, retaining water in otherwise semi-arid high cirques, and contribute as hydrologic reserves and critical habitat for alpine biota. Daily and seasonal lags and buffering effects suggest that ice within these landforms might resist surface warming on the longer term, which could make these landforms increasingly important as regional climates change.