Rock Glaciers in Utah Scott Hotaling,1,2 Kendall Becker,1,2 and Matthew Morriss3 1
Department of Watershed Sciences, Utah State University (USU) 2 USU Climate Resiliency Extension 3 Utah Geological Survey
Utah’s primary water supply––winter snowpack––is in decline due to climate warming coupled with more precipitation falling as rain instead of snow. As snowpack dwindles, other sources of cold stream water, such as rock glaciers, will become more important. Rock glaciers contain significant volumes of internal ice covered by debris. This internal ice provides cold meltwater to mountain streams, sustaining flows in summer and supporting biodiversity. Rock glaciers are common in Utah’s mountains and are projected to be more stable under climate change than Utah’s snowpack. Thus, rock glaciers are likely to persist in their current form even as snowpack volumes continue to decrease. Because rock glaciers may provide a critical, climate-resilient water source for Utah, more research is needed to quantify their relevance for present and future water availability and ecosystems.
What Are Rock Glaciers? Rock glaciers are large masses of talus and debris that “flow” downhill due to the deformation of substantial internal ice. Rock glaciers accumulate new ice in their higher elevation portions, typically when rockfall covers seasonal snowpack and insulates it. Rock glaciers can also accumulate new ice when rain or meltwater percolate into their interior and freeze. The internal ice of rock glaciers flows downhill through a mix of internal deformation and basal sliding, forming distinctive lobes (Figures 1 and 2). Pressure from the weight of the ice and debris paired with warmer conditions at the lower-elevation “toe” of the rock glacier causes internal ice to melt, which feeds streams and lakes (Figure 1, right). If the cycles of ice addition and loss are equal, the rock glacier is stable (i.e., not growing or receding). But any alterations to the balance, such as more melt than accumulation, drive directional change. At present, surface ice glaciers in the western United States are in the midst of a long-term trend of melt exceeding accumulation, causing them to broadly recede. Rock glaciers, in contrast, appear to be near a state of equilibrium, though more data are needed to confirm their slow rates of change.
Figure 1. A rock glacier—outlined in red—in the Gad Valley area of Little Cottonwood Canyon, UT. The “toe” of the rock glacier is the lower-elevation, rounded part in the bottom left of the image (left). A stream emanating from the terminus of the Gad Valley rock glacier (right). Photo credits: (left) Adam Hiscock and (right) Matthew Morriss, both from Utah Geological Survey. 1