New Constraints on Rock Glacier Geometry and Kinematics in the Western USA from Airborne- and Satellite-based Synthetic Aperture Radar

Rock glaciers occur in high numbers in alpine landscapes around the world. These mixtures of ice and rock move downslope at rates from mm/yr to m/yr and can remain active for decades to millennial timescales. Here, we use airborne and satellite interferometric synthetic aperture radar (InSAR) to track the motion of more than 300 rock glaciers in Colorado and Utah, USA. We present a first-of-its-kind inventory of rock glaciers measured with the NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) for our field site in Colorado. UAVSAR provides high resolution (0.6 x 1.6 m pixel spacing) measurements of surface motion along multiple viewing geometries, which allows us to accurately delineate rock glacier boundaries and invert for true 3D surface motion (as opposed to the typical 1D line-of-sight InSAR measurement). We collected UAVSAR data two months apart (July and September) on 8 different flight paths during the summer of 2023. We found that the rock glaciers are moving at rates up to 50 cm/yr during the summer period. We also apply volume conservation techniques to infer the subsurface geometry of multiple rock glaciers and better constrain rock glacier sediment flux. To gain a broader perspective of rock glacier motion over longer time periods (i.e., yearly to near-decadal), we also processed and analyzed satellite InSAR data from the ESA Sentinel-1 A/B satellites between 2015-2024 in Colorado and Utah. The satellite data showed that rock glaciers display seasonal and annual velocity changes, which we infer are driven by liquid water availability (i.e., snowmelt and rainfall). Our findings illustrate that rock glaciers exhibit complex kinematic patterns and geometries. Our new UAVSAR measurements provide key information for constraining rock glacier volume and sediment flux, particularly when combined with field- (e.g., GPS) and lab-measurements (¹⁰Be surface-exposure dating).