八宿巨型滑坡的发现及其意义

Recognition and Implication of Basu Giant Rock Avalanche

巨型滑坡全球不常见,但是破坏性极强,其识别对于加深区域构造背景的认识、防灾减灾和工程建设均有指导意义。基于遥感解译、无人机地形测绘和现场调查,报道了新发现的八宿巨型滑坡及其残留堆积体特征,初步分析了成因机制与演变过程,估算了滑坡方量。主要结论如下:1)八宿滑坡发育于怒江缝合带的夏里—八宿裂谷带内,岩性以古生界嘉玉桥岩群大理岩组和侏罗系马里组变质砂泥岩为主,上部岩层产状为陡倾顺坡向,下部岩层产状为陡倾逆坡向,岸坡结构总体上为上硬下软。2)滑坡区横跨冷曲的左右两岸,长约7200 m,宽约4800 m,面积约22.5 km^(2),估算方量约35×10^(8) m^(3),目前残余方量约14×10^(8) m^(3),是国内已经确认的方量最大的滑坡。3)滑坡极可能属于历史地震诱发的高速堵江滑坡,堰塞坝高度约185 m,堆积体碎裂化严重,且在冷曲右岸爬升超过600 m。滑坡形成后,堆积区历经了堰塞坝溃决、多拉寺次级滑坡、泥石流堆积与冲刷、表面流水冲刷等改造过程,但滑坡地貌特征整体保存良好。由于滑坡和泥石流堵江,冷曲在滑坡区先后两次改道。4)从滑坡与冷曲的演变过程来看,推测滑坡的发生时间应在晚更新世,即八宿滑坡为古滑坡。5)八宿巨型滑坡的发现说明迄今为止对青藏高原地质环境的认知仍然十分有限;川藏铁路等工程建设应加强基础地质与工程地质研究,以及地质灾害风险论证,确保施工与运行期安全。

Giant rock avalanche is uncommon globally,but quite devastative,so its recognition is important both for deepening our understanding of regional tectonic background,and for disaster reduction and engineering safety.Based on remote sensing,UAV surveying and filed reconnaissance,a newly recognized Basu giant rock avalanche is reported,with its deposition features characterized,formation and evolution briefly analyzed and volume calculated.Major conclusions are summarized as follow.1)Basu rock avalanche is developed within the Xiali—Basu rift valley of Bangong—Nujiang suture zone.Bedrocks are mainly marble set of the Paleozoic Jiayuqiao Group and metamorphosed sandstone and mudstone of Jurassic Mali Group.Most of its upper slope is composed of hard rocks dipping down the slope at a steep angle,while the lower slope is mainly of soft rocks dipping steeply into the slope.2)The avalanche is about 7200 m long,4800 m wide,covering both sides of the Lengqu River,and having an area of 22.5×10^(6) m^(2) and an estimated volume of 3.5×10^(9) m^(3).Its reserved volume can still reach about 1.4×10^(9) m^(3),the largest one ever recognized and documented in China.3)The avalanche is most likely triggered by a historical earthquake,as its debris is highly fractured and can climb up the right bank as high as over 600 m.That is,its sliding speed is quite high.The slide dammed the Lengqu River and the height of its landslide dam is about 185 m.The slide experienced a series of geomorphological process,as dam breaching,secondary Dora Kamiyama sliding,debris accumulation and erosion,and runoff-induced surface erosion,but its geomorphological features are still well reserved.Both the slide and the debris led to the route change of the Lengqu River.4)Based on the evolution of both the slide and the Lengqu River,it is inferred that the slide occurred during Late Pleistocene,i.e.it is an ancient slide.5)The recognition of Basu giant avalanche implies that our knowledge on the geological environment of Qinghai-Tibetan plateau is quite limited.For the construction of projects as Sichuan—Tibetan Railway,it is quite necessary to strengthen the investigation of both basic geology and engineering geology,and the evaluation of geo-hazard risk,so as to secure their safety during the construction and operation phases.