title: Thermal and hydrological conditions of the Goethe rock glacier, Central Sierra Nevada, California
Creators: name: Beaulieu, Jezra
Publisher: name: Western Washington University
Year: 2013

description: <p>The potential of rock glaciers in the Sierra Nevada to provide critical hydrological reservoirs and ecological habitats in a changing climate remains largely untested. In an effort to constrain the microclimatic contributions of buried ice, continuous temperatures were recorded in the near-surface debris of a variety of ice-cored and associated landforms in the Goethe cirque from August 2011 and July 2012 (Goethe rock glacier=GRG, valley-wall rock glaciers=VRG, Recess Peak debris=RPD, talus=TAL, ranging from most ice to least ice). In addition, continuous meteorological conditions on the rock glacier and stage of the main meltwater outwash stream were recorded to assess temporal and spatial responses of hydrologic inputs and outputs to the rock glacier. The mean annual surface temperature (MAST) of the GRG is -2°C and the mean annual temperature at depth (MADT) is -2.5°C. The GRG has the steepest average annual temperature gradient of all the landforms with 0.44°C/m, indicating the presence of a large ice core. The MAST for RPD, VRG, and TAL are -0.5°C, -2°C, and -2.5°C, respectively, and their MADTs are -1°C, -3°C, and -3°C respectively. The mean annual air temperature (MAAT) from the on-site weather station in the cirque was -1.5°C, and the total cumulative precipitation was 552 mm. The modeled discharge varies from 0-1.6 cms, averaging 0.35 cms, and the stream temperatures vary from 0-3.85°C, averaging 0.53°C. According to Tritium signatures of stream water samples, the percent of ice-core melt versus snowmelt in the stream was 0% for the mid-summer of 2011, 5% for fall of 2011, and 13% for the early summer of 2012. The thermal and hydrological conditions in the Goethe cirque indicate a large sensitivity to meteorological conditions that is seasonally moderated by cold internal temperatures within the ice and debris of the landforms. The two contrasting summers during the yearlong study period exhibited different characteristics, particularly in discharge, stream temperature, and relative contribution of runoff source. The summer of 2011 was largely affected by exceptional snowpack from the previous winter, which was expressed by lower mean debris matrix temperatures, strong correlations between discharge and air temperature, and tritium signals that indicate a nearly pure snow-melt source for the outlet stream. The summer of 2012 was characterized by an exceptionally low snowpack compared to the winter of 2010-2011, which was expressed by higher mean matrix temperatures, strong correlations between stream temperature and matrix temperatures, and a tritium signal that indicated a modest amount of ice melt contribution to discharge in the outlet stream. Projected decreases in snow-cover and earlier onset of spring snowmelt for the region will likely change the timing of peak runoff in alpine basins, as well as increase the duration that rock glacier debris matrix is open to warm air temperatures, thereby inducing more melt of internal ice and greater contribution of ice melt to stream runoff. With continued warming, even these insulated ice bodies will degrade unless the climate returns to cooler and wetter conditions.</p>