Rock Glacier Movement and Debris Transport over Annual to Multi-Millennial Timescales

Rock glaciers are common in alpine landscapes, but their evolution over time and their significance as agents of debris transport are not well-understood. Here we assess the movement of an ice-cemented rock glacier over a range of timescales with GPS surveying, satellite-based radar, and cosmogenic 10Be surface-exposure dating. GPS and InSAR measurements indicate that the rock glacier displaced at an average rate of ~3-10 cm yr-1 in recent years. Sampled boulders on the rock glacier have cosmogenic exposure ages from 1.2 to 10 ka, indicating that it has existed since the beginning of the Holocene. Ages increase linearly with distance downslope, constraining a long-term flow rate of 3 cm yr-1. Our findings suggest that the behavior of this rock glacier may be dominated by episodes of dormancy punctuated by short-lived intervals of relatively rapid 23 movement over short and long timescales. The volume of the rock glacier corresponds to ~10 m of material stripped from the headwall during the Holocene. These are the first cosmogenic surface-exposure ages to constrain movement of a North American rock glacier, and together with the GPS and radar measurements, they reveal that rock glaciers are effective geomorphic agents with dynamic multi-millennial histories.