Active rock glaciers of the contiguous United States: geographic information system inventory and spatial distribution patterns

Abstract. In this study we present the Portland State University Active Rock Glacier Inventory ( n=10  332) for the contiguous United States, derived from the manual classification of remote sensing imagery (Johnson, 2020; https://doi.org/10.1594/PANGAEA.918585 ). Individually, these active rock glaciers are found across widely disparate montane environments, but their overall distribution unambiguously favors relatively high, arid mountain ranges with sparse vegetation. While at least one active rock glacier is identified in each of the 11 westernmost states, nearly 88 % are found in just five states: Colorado ( n=3889 ), Montana ( n=1813 ), Idaho ( n=1689 ), Wyoming ( n=839 ), and Utah ( n=834 ). Mean active rock glacier area is estimated at 0.10 km 2 , with cumulative active rock glacier area totaling 1004.05 km 2 . Active rock glaciers are assigned to a three-tier classification system based on area thresholds and surface characteristics known to correlate with downslope movement. Class 1 features ( n=7042 , average area = 0.12 km 2 ) appear to be highly active, Class 2 features ( n=2415 , average area = 0.05 km 2 ) appear to be intermediately active, and Class 3 features ( n=875 , average area = 0.04 km 2 ) appear to be minimally active. This geospatial inventory will allow past active rock glacier research findings to be spatially extrapolated, help facilitate further active rock glacier research by identifying field study sites, and serve as a valuable training set for the development of automated rock glacier identification and classification methods applicable to other large regional studies.