A high-resolution rock glacier inventory of South Tyrol: evaluating lithologic, topographic, and climatic controls

In South Tyrol, a comprehensive and homogeneous database of rock glaciers is missing. This is a critical shortcoming for the basic understanding of creeping permafrost in the region, as well as for geohazard assessment and planning, especially in relation to contemporary climate warming. To this purpose, we have: (1) compiled a regional inventory through visual inspection of optical and LiDAR-derived imagery; and (2) analyzed the spatial distribution of rock glaciers in relation to topography, lithology, and climate. Climatic attributes were drawn from regionally interpolated data of the 3PClim project. The inventory tallies 2798 rock glaciers that occupy a surface of 146 km2. Of these, 502 were classified as active rock glaciers, 615 as inactive, and 1681 as relict. Median front elevation of the active landforms (2695 m) is 100 m and 440 m higher than that of the inactive and relict ones. This offset can vary over 200 m as a function of slope aspect. Median MAAT on active and inactive rock glaciers is respectively -2.3 and -1.6 °C, and above the melting point (+0.2 °C) on relict landforms. Despite such differences, we find that median days of snow cover is comparable in active and inactive landforms (310 and 302 respectively) and significantly lower in relict ones (273). Most of the rock glaciers develop(ed) on paragneiss, mica schists and phyllites (83%), followed by orthogneiss (21%), and limestones and dolostones (8%). Lithologic effects, except in calc schists, which score distinctively lower than schists and orthogneiss, are largely masked by interactions between topographic and climatic conditions across physiographic zones.