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Aiming at the rate and causes of the incision variations in the upper Himalaya Orogenic belt of Tibet, a new method of incision rate estimation based on the analysis of the evolution of Zhangmu landslide and its spatial and temporal relationship with the surrounding gullies is applied. The research results are: (1) The Zhangmu landslide was an ancient huge landslide, occurred at 24.2 ± 2.4 ka BP, consisting of an ancient bedrock landslide and subsequent deposit landslides, with an area of 1.23 km2, and remaining volume of 23.4 × 106 m3. (2) The fluvial incision rate shows variations in Poiqu and its branch, which may be controlled by the discharge and decreases from the Poiqu (11.5 ± 1.2 mm/a) to the tributaries, from 4.8 ± 0.5 mm/a in the Bangcundong gully to 2.4 ± 0.2 mm/a in Zhangmu gully. (3) The fluvial incision rate also shows temporal variations in the Poiqu. There are two periods of low rate and high rate incision processes in the Poiqu, while the section shape transforms from a gentle slope to a cliff. In the low rate period from 24.2 ka BP to 10.0 ka BP in the Poiqu valley, the incision rate was 10.4 ± 1.0 mm/a, while the high fluvial incision rate since 10.0 ka BP was 13.0 ± 1.3 mm/a; (4) The fluvial incision promotes the landscape evolution and triggers the potential landslide in thousands of years. |
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