| 摘 要： |
Reconstructing the ages and magnitudes of prehistoric extreme events that are recorded in landforms and sediments allows us to capture the full range of frequency-magnitudes and estimate the expected time for the repetition of a catastrophic event. The Eastern Himalayan Syntaxis and its surrounding areas are highly prone to the occurrence of river blocking. Previous studies have re-established three glacier-dammed lakes in the valley of Yurlung Tsangpo, namely, Gaga Lake, Dazhuka-Yueju Lake and Jiedexiu Lake. Here, we identified a series of sedimentary evidence containing offshore clay or silt varve, nearshore vaguely stratified silty sand and subaqueous foresets, which are associated with five landslide-dammed lakes in the lower reach of Purlung Tsangpo, including Lulang (LLDL), Dongjiu (DJDL), 102 (102DL), Jialong (JLDL) and Zedang (ZDDL). By assuming an initial catastrophic drainage, the highest elevation of exposures and original dam heights derived from dam morphology were used to represent the minimum and maximum estimates of lake levels of individual lakes. The maximum estimate of lake volume ranges from 4.3 x 10(9) m(3) (LLDL) to 1.1 x 10(8) m(3) (ZDDL). The C-14 dating results provide the chronology of the LLDL from 24.2 ka BP to 15.4 ka BP. DJDL from 11.5 ka cal. BP to 7.0 ka cal. BP, JLDL from 4.9 ka cal. BP to 2.7 ka cal. BP. ZDDL from early Holocene to 5.8 cal. BP. Most of them occurred during deglaciation. We further used low-temperature thermochronological data to illustrate the spatial pattern of fluvial incision rates. Overall, climate-driving factors, such as rainfall intensity along with enhanced river incision post LLGM, preconditioned the occurrence of the abovementioned landslides. |
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