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Currently, the theory and methodology of digital terrain analysis (DTA) has been well developed. However, this technique has not been widely applied in the research of loess landslides in China. This study investigated the application of DTA on loess landslides with the high-resolution terrain data obtained from low-cost unmanned aerial vehicles (UAVs). Taking a high-speed and long-runout landslide occurring on the Bailu Loess Tableland, a typical landform type on the Loess Plateau, as an example, we illustrated the fundamental characteristics and spatial patterns of the landslide from various perspectives and performed hydrology analysis, geomorphic change detection, hypsometric integral (HI) and stability analysis, morphology analysis, and structure analysis. The results prove that the DTA methodology cannot only advance understanding of the geomorphology and structure of landslides and detect geomorphic change but also reveal the evolution principles of landforms and demonstrate unique advantages in the prediction of the internal stability of landslides. In conclusion, the DTA methods adopted in this paper are useful to better understand loess landslide and its relationship with geomorphologic evolution. [ABSTRACT FROM AUTHOR]

The Wenchuan earthquake has caused abundance of loose materials supplies for debris flows. Many debris flows have occurred in watersheds in area beyond 20 km, presenting characteristics differing from those in small watersheds. The debris flows yearly frequency decreases exponentially, and the average debris flow magnitude increases linearly with watershed size. The rainfall thresholds for debris flows in large watersheds were expressed as I = 14.7 D (2 h < D < 56 h), which is considerably higher than those in small watersheds as I = 4.4 D (2 h < D < 37 h). A case study is conducted in Ergou, 39.4 km in area, to illustrate the formation and development processes of debris flows in large watersheds. A debris flow develops in a large watershed only when the rainfall was high enough to trigger the wide-spread failures and erosions on slope and realize the confluence in the watershed. The debris flow was supplied by the widely distributed failures dominated by rill erosions (14 in 22 sources in this case). The intermittent supplying increased the size and duration of debris flow. While the landslide dam failures provided most amounts for debris flows (57 % of the total amount), and amplified the discharge suddenly. During these processes, the debris flow velocity and density increased as well. The similar processes were observed in other large watersheds, indicating this case is representative. [ABSTRACT FROM AUTHOR]