MODELING ROCK GLACIER GENESIS BASED ON OBSERVATIONS FROM THE WASATCH RANGE, UTAH

Over the last century, the process by which ice is incorporated into rock glaciers has been hotly debated. Hypotheses include 1) the percolation and freezing of water in talus cones; 2) the en-mass covering of glaciers by debris from hillslopes; 3) the movement of ice-cored moraines downslope; and 4) the covering of avalanched snow by rockfall from hillslopes. Here, we present a numerical model inspired by the observations of Potter (1972) who suggested that Galena Creek Rock Glacier in Wyoming formed from the accumulation of wind and avalanche-loaded snow at the base of mountain headwalls. We explore how rock glaciers can gain ice and rock mass even in the modern alpine climate of the Wasatch Mountains of Utah. Even if most years there is no evidence of mass addition to a rock glacier, it can still be maintained because ice melt rates are low or zero beneath the debris mantle. We simulate how the stochastic behavior of snow, melt, and rockfall interact to add mass to rock glaciers in pulses. Winter snow and summer melt totals vary from year-to-year due to natural climate variability (i.e., weather) and can be represented as normal distributions. The frequency and magnitude of rock falls in the rooting zone also varies from year-to-year following a power law function. Our model combines these processes using parameters extracted from the Timpanogos massif, Wasatch Mountains, Utah. It is able to reproduce modern observations of the interior of Timpanogos Rock Glacier. A moulin high on this rock glacier reveals that it is predominantly composed of ice with layers of ~10 cm of debris alternating with several meters of ice. Further down glacier, electrical resistivity data reveal that the interior is largely ice below a thick surface debris mantle. Additional observations from rock glacier rooting zones support this model of rock glacier genesis. We found examples of loose rock deposited on snow from the previous winter on two rock glaciers in the Wasatch Range. Using our model, we also explore the effect of climate change on mass addition to rock glaciers. A 1-degree increase (or decrease) in the mean summer temperature can stop ice accumulation (or send the system towards a more typical glacial snow accumulation regime). This work reveals how rock glaciers can still gain ice mass even in the modern climate of the arid western US.