Figure 9. Histograms of the landform aspects for (a) all RGs, (b) DMS-RGs, (c) G-RGs, (d) GF-RGs, and (e) T-RGs.
4.3 Surface kinematics of the mapped active rock glaciers
Among the 290 active rock glaciers mapped based on InSAR, we obtained the surface velocities of 256 rock glaciers in total, including 115 DMS-RGs, 97 G-RGs, 21 GF-RGs, and 23 T-RGs (Figure 10). We lacked high-quality InSAR data over the rest of the mapped rock glaciers. Each velocity result was presented in the format of apparent annual velocity (unit: cm yr-1) while the observation period was labelled in the dataset. Figure 11 gives examples of the velocity distributions of the four categories of rock glaciers. The spatial average velocities of the four rock glaciers are 79±6 cm yr-1 (Figure 11a), 44±1 cm yr-1(Figure 11b), 32±1 cm yr-1 (Figure 11c), and 24±1 cm yr-1 (Figure 11d), respectively. The movement rates usually decrease towards the terminus with the highest values occurring in the upper and middle parts of the landforms.
Table 3 presents the general statistics of the documented rock glacier velocities. Most (90%) RGs move towards the downslope direction at a rate lower than 50 cm yr-1, with a mean velocity of 24 cm yr-1. The G-RGs and GF-RGs have faster mean velocities of 31 cm yr-1 and 35 cm yr-1, respectively, whereas the DMS-RGs and T-RGs creep at a relatively lower rate of 17 cm yr-1. The median velocities of the mapped rock glaciers are all smaller than the corresponding mean velocities, indicating most of the kinematic data are distributed near the lower end, as shown in Figure 12. Among all the mapped rock glaciers, a DMS-RG has the largest mean velocity of 127±7 cm yr-1.