Abstract. Spatio-temporal patterns related to the viscous creep in
perennially frozen sediments of rock glaciers in cold mountains have rarely
been studied outside the densely populated European Alps. This study
investigates the spatial and temporal variability of rock glacier movement
in the Ile Alatau and Kungöy Ala-Too mountain ranges, northern Tien
Shan, a region with particularly large and fast rock glaciers. Over the
study region of more than 3000 km2, an inventory of slope movements was
constructed using a large number of radar interferograms and high-resolution
optical imagery. The inventory includes more than 900 landforms, of which
around 550 were interpreted as rock glaciers. Out of the active rock
glaciers inventoried, 45 are characterized by a rate of motion exceeding
100 cm/a. From these fast rock glaciers we selected six (Gorodetzky,
Morenny, Archaly, Ordzhonikidze, Karakoram, and Kugalan Tash) and studied
them in more detail using offset tracking between repeat aerial images and
historical and modern high-resolution optical satellite data. Two of these
rock glaciers showed a steady increase in decadal surface velocities from
the 1950s onwards, with speeds being roughly 2 to 4 times higher in
recent years compared to the 1950s and 1960s. Three rock glaciers showed
similar accelerations over the last 1 to 2 decades but also phases of
increased speeds in the 1960s. This development indicates a possible
significant increase in current sediment and ice fluxes through rock
glaciers and implies that their material transport in the region might gain
geomorphodynamic importance relative to material transport by glaciers,
assuming the latter decreases together with the regional glacier shrinkage.
The study demonstrates how air and satellite image archives are exploited to
construct one of the longest decennial times series of rock glacier speeds
currently available. Our results are in line with findings from Europe about
rock glacier speeds increasing with atmospheric warming and underline local
variability of such an overall response.