Seasonal and annual kinematics of active rock glaciers under different climate regimes in the Western USA

Abstract

<p>Rock glaciers are common landforms in many alpine permaforst landscapes that play an important role in alpine hydrology and landscape evolution, principally through the release of seasonal meltwater and the downslope transport of coarse material. Here, we use satellite-based interferometric synthetic aperture radar (InSAR) to identify and monitor rock glaciers in the Western USA. We focus on the movement of active and transitional rock glaciers in Utah (Uinta, Wasatch, and La Sal Mountains), and Wyoming (Wind River Mountains) between 2015 and 2022. Using the new framework established by the International Permafrost Association (IPA) Action Group, we identified 255 active and transitional rock glaciers in the ~3500 km<sup>2</sup> Uinta Mountains, 45 rock glaciers in the ~200 km<sup>2</sup> La Sal Mountains, 55 rock glaciers in the ~135 km<sup>2</sup> Wasatch Mountains, and 120 rock glaciers in the ~3000 km<sup>2</sup> Wind River Mountains. These rock glaciers currently occur under different climatic regimes based on data from the 30 year (1991-2020) normal Parameter-elevation Relationships on Independent Slopes Model (PRISM). The La Sals and Wasatch are warmer and wetter with a mean annual air temperature (MAAT) of ~3.0± 1.9 ˚C and  2.7 ± 1.1 ˚C and a mean annual precipitation (MAP) of ~92 ± 13 cm and ~130 ± 17 cm, respectively, whereas the Uintas and Wind Rivers are cooler and drier with a MAAT of ~0.24 ± 1.4 ˚C and  -0.87 ± 1.4 ˚C and a MAP of ~87 ± 11 cm and ~81 ± 10 cm. The mean line-of-sight (LOS) velocities for individual rock glaciers range from ~1 to 10 cm/yr. We also examined the time-dependent relationship between the motion of the rock glaciers and local climatic drivers such as temperature and precipitation. We found that rock glaciers exhibit seasonal and annual velocity changes, likely driven by liquid water availability (from snowmelt and rainfall), with accelerated motion during summers and during wetter years. Our findings demonstrate the ability to use satellite InSAR to monitor rock glaciers over large areas and provide insight into the environmental factors that control their kinematics.</p>