Kinematic process and mechanism of the two slope failures at Baige Village in the upper reaches of the Jinsha River, China

Abstract

The two landslides are located in the upper reaches of the Jinsha River and both dammed the river. Immediately since the slides, the authors have been working on the slides and help disaster reduction. Based on the data collected by April 2020, this paper is aimed at clarifying the geological condition of the slides and at explaining why the slides occurred and what the whole sliding process was. Conclusions are summarized as follows. First, the two landslides occurred in the suture belt of the Jinsha River and the rocks are composed of tectonic mélange slices of mainly gneiss intermingled with carboniferous slate and marble and with intruded serpentine and granite porphyry. The gneiss generally bears a schistosity plane with an averaged attitude of N47°W/47°, dipping into the slope. Secondly, long-term geomorphological evolution of the bank slope due to river incision contributed to the progressive slope deformation for the development of the "10.10" rockslide. No preferential joints exist in the slope, but alteration and weathering played important roles in its occurrences. Rainfall and earthquakes may also accelerate its deformation. Thirdly, the "10.10" rockslide is of high-speed wedge-like slope failure with a high-position and a high-shear outlet. Its sliding and deposition process demonstrate special features as initial speed, collision between debris, surging waterjet, and second slipping. Fourthly, the whole process of the "10.10" rockslide can be divided into 6 steps, i.e., startup of the major sliding and sliding resistance zones, sliding initiation of the trailing zone, formation of debris-eroded zones, collision of debris and triggering waterjet and mist, secondary slip of the landslide dam, and surface flush in the deposition area. The estimated speed may reach as high as 67 m/s. Fifthly, the "11.3" rockslide follows a different mode, i.e., wedge cleaving effect. And finally, the cracked zones still have the risk to constitute a potential landslide and to dam the river again.

Seismic Monitoring and Geomorphic Impacts of the Catastrophic 2018 Baige Landslide Hazard Cascades in the Tibetan Plateau

“…The failure of the material at about 3,700 m elevation initiated at 22:05:46 October 10 (Beijing time, UTC + 8; all subsequent time are given in Beijing time) for the first event and at 17:21:30 November 3 for the second event, and moved downward rapidly, generating an upward force. As the material on the hillslope is eroded and entrained, the volume of the two landslides gradually increased to approximately 24 million and 8.7 million m 3 (Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021) before entering the Jinsha river at 22:06:21 October 10 (Zhang, He, et al., 2019) and 17:21:53 November 3 respectively, generating the downward subvertical forces with a northeastward component, consistent with the boundary of the impact area. As the first landslide rushed into the river, a landslide dam with a length of ∼1,200 m, width of 143 m, and minimum height of ∼51 m, formed (Chen et al., 2021; Gao et al., 2021).…”

“…Three weeks later at 17:40 CST on 3 November, a second landslide in Baige transported an additional 8.7 × 10 6 m 3 of materials into the Jinsha River. This smaller landslide deposited atop the residual dam from the first landslide and created a higher dam that was at least 96 m high that inundated terrain up to ∼70 km upstream (Figure 1b; Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021; Zhong et al., 2020). To mitigate the potential damage from an unexpected outburst flood, the Yangtze River Flood Control and Drought Relief Headquarters dug a ∼15 m deep drainage trench on the west side of the dam (Zhong et al., 2020).…”

“…On 10 October and 3 November 2018, two successive landslides in the Tibetan plateau (Figure 1a; Zhang, He, et al., 2019; Zhang, Xiao, et al., 2019; Zhong et al., 2020; Fan, Yang, et al., 2020; Gao et al., 2021; Chen et al., 2021) blocked the Jinsha River, which is the upper course of the Yangtze River, and created two LDLs. The subsequent dam breaches resulted in massive outburst floods that caused the immediate evacuation of >120,000 people (NDRCC, 2018b, 2018a) and severe damage/destruction of 27,000 houses, 8 bridges, 4 hydropower plants, and 33,000 ha of farmland up to 670 km downstream (Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021; Zhang, Xiao, et al., 2019; Zhong et al., 2020). The second landslide lake outburst flood (LLOF), with peak discharge of ∼31,000 m 3 /s and volume of 5.8 × 10 8 m 3 (Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021; Zhong et al., 2020), is the largest recorded LLOF of the 21st century to date and provides a unique opportunity to understand such hazard cascades.…”

“…The subsequent dam breaches resulted in massive outburst floods that caused the immediate evacuation of >120,000 people (NDRCC, 2018b, 2018a) and severe damage/destruction of 27,000 houses, 8 bridges, 4 hydropower plants, and 33,000 ha of farmland up to 670 km downstream (Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021; Zhang, Xiao, et al., 2019; Zhong et al., 2020). The second landslide lake outburst flood (LLOF), with peak discharge of ∼31,000 m 3 /s and volume of 5.8 × 10 8 m 3 (Chen et al., 2021; Fan, Yang, et al., 2020; Gao et al., 2021; Zhong et al., 2020), is the largest recorded LLOF of the 21st century to date and provides a unique opportunity to understand such hazard cascades. Here, we integrate seismic observations with hydrological data, videos/photographs, satellite observations, and numerical modeling to study the detailed seismic signatures, evolution, and impact of the hazard cascades.…”

“…On 10 October and 3 November 2018, two successive landslides in the Tibetan plateau (Figure 1a; Zhang, Xiao, et al, 2019;Zhong et al, 2020;Fan, Yang, et al, 2020;Gao et al, 2021;Chen et al, 2021) blocked the Jinsha River, which is the upper course of the Yangtze River, and created two LDLs. The subsequent dam breaches resulted in massive outburst floods that caused the immediate evacuation of >120,000 people (NDRCC, 2018b(NDRCC, , 2018a and severe damage/destruction of 27,000 houses, 8 bridges, 4 hydropower plants, and 33,000 ha of farmland up to 670 km downstream (Chen et al, 2021;Fan, Yang, et al, 2020;Gao et al, 2021;Zhang, Xiao, et al, 2019;Zhong et al, 2020).…”