OSL dating of the massive landslide-damming event in the Jishixia Gorge,on the upper Yellow River,NE Tibetan Plateau

Abstract

Frequent natural hazards cause huge damage to human life and society in the mountainous regions along the eastern rim of the Tibetan Plateau. A massive landslide damming event has been reported in the Jishixia Gorge on the upper Yellow River as it emerges from the NE Tibetan Plateau. It was speculated that a breach of the dammed lake might have resulted in a super flood disaster that ruined the major Neolithic settlement at Lajia (4.20–3.95 ka BP) within the Guanting Basin that is located in the downstream. However, our detailed investigations along the Jishixia Gorge and Guanting Basin indicate that the dammed lake became shallower and desiccated gradually rather than breaching suddenly. The Yellow River has cut into the dammed lake deposits forming well-exposed profiles on the riverbanks. The dammed lake deposits are considered to provide an accurate natural record of the life-span of the dammed lake. Optically Stimulated Luminescence (OSL) dating was carried out on a series of eight samples taken from the profile. The OSL ages of the dammed lake deposits fall within the range of 8.25 ± 0.39 to 5.65 ± 0.21 ka at the Yisiri site about 2.5 km upstream of the landslide dam. These results indicate that the massive landslide damming event and the corresponding dammed lake occurred at 8.25 ka in the early Holocene. The dammed lake existed for about 2600 years and desiccated gradually and disappeared at 5.65 ka because the landslide dam was dissected slowly by the Yellow River. This means that the landslide dammed lake on the Yellow River disappeared about 1700 years before the Neolithic settlement at Lajia became ruins. The landslide damming event in the Jishixia Gorge is not related to the prehistorical catastrophic disasters that overcame the Lajia settlement within the Guanting Basin.