Abstract
Abstract. Rock glaciers are widespread in the Tien Shan. However, rock glaciers in the Chinese part of the Tien Shan have not been systematically investigated for more than 2 decades. In this study, we propose a new method that combines SAR interferometry and optical images from Google Earth to map active rock glaciers (ARGs) in the northern Tien Shan (NTS) of China. We compiled an inventory that includes 261 ARGs and quantitative information about their locations, geomorphic parameters, and downslope velocities. Our inventory shows that most of the ARGs are moraine-derived (69 %) and facing northeast (56 %). The altitude distribution of ARGs in the western NTS is significantly different from those located in the eastern part. The downslope velocities of the ARGs vary significantly in space, with a maximum of about 114 cm yr−1 and a mean of about 37 cm yr−1. Using the ARG locations as a proxy for the extent of alpine permafrost, our inventory suggests that the lowest altitudinal limit for the presence of permafrost in the NTS is about 2500–2800 m, a range determined by the lowest ARG in the entire inventory and by a statistics-based estimation. The successful application of the proposed method would facilitate effective and robust efforts to map rock glaciers over mountain ranges globally. This study provides an important dataset to improve mapping and modeling permafrost occurrence in vast western China.
Highlights
Rock glaciers are lobate or tongue-shaped landforms consisting of mixtures of unconsolidated rock debris and ice in an alpine environment
We visually examined the landforms in the Google Earth images that correspond to the moving targets in the interferograms and identified the Active rock glaciers (ARGs)
We identified and mapped a total of 261 ARGs across the northern Tien Shan (NTS)
Summary
Rock glaciers are lobate or tongue-shaped landforms consisting of mixtures of unconsolidated rock debris and ice in an alpine environment They are commonly regarded as visible expressions of permafrost presence in periglacial areas (Barsch, 1996; Humlum, 2000; Haeberli et al, 2006; Brenning et al, 2007; Boeckli et al, 2012). Due to the potential melting of internal ice in the runoff season, rock glaciers serve as important freshwater reserves for the downstream water use in semiarid regions (Brenning, 2005; Janke et al, 2015). According to their kinematic status and the presence of internal ice, rock glaciers can be classified into three groups: active, inactive, and relict. The downslope movement of ARGs may cause mass waste hazards on steep slopes, threatening the sensible infrastructures in some downhill areas (e.g., Schoeneich et al, 2015)
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