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.