大渡河上游鸡心堡滑坡形成的古堰塞湖及其环境效应

THE PALEO-DAMMED LAKE FORMED BY JIXINBAO LANDSLIDE IN THE UPSTREAM REACHES OF THE DADUHE RIVER AND ITS ENVIRONMENTAL EFFECTS

堰塞湖及其溃决洪水对山地地表过程具有强烈影响,严重危害山地区域的安全,对堰塞湖开展相关研究,可为区域现代堵江风险分析提供参考。以青藏高原东缘大渡河上游支流小金川鸡心堡古滑坡堰塞湖为研究对象,采用单片再生剂量法与标准生长曲线法相结合的方法对深度约12.5 m的湖相沉积剖面上的7个光释光样品测试年代,并进行了详细的地层学与年代学研究,恢复该堰塞湖的年代和范围,重建该古滑坡的规模,讨论了该古堰塞湖的成因及其环境效应。研究结果表明:1)研究区在距今约2~3 ka发生过一次滑坡堵江事件,形成鸡心堡古滑坡堰塞湖,持续一段时间后,形成最大流量约为2.70×10^(3) m^(3)/s的洪水溃决过程;2)该古堰塞湖的堵江残留滑坡坝高约150 m,滑坡坝面积约1.41×10^(5) m^(2),体积约4.19×10^(6) m^(3),堰塞湖的面积约1.84×10^(6) m^(2),库容水量约6.10×10^(7) m^(3);3)依据现有地质证据以及文献记载初步推测鸡心堡古滑坡是由地震引起的;4)滑坡坝对现代河道的地貌形态仍然存在影响,在滑坡坝上游形成较宽的现代河道且河道纵剖面的坡度较小,滑坡坝后的河道陡峭指数(k)较高。通过研究,对大渡河流域的古堰塞湖有更全面、科学的认识,为古地质灾害领域提供了一个研究实例。

Dammed lakes and outburst floods have a strong influence on the surface process of mountainous areas and seriously pose threats to human lives and property. Related research on dammed lakes can provide a reference for regional modern rivers damming risks analysis. The Jixinbao paleo-landslide-dammed lake in Xiaojinchuan River,a tributary of the upper reaches of the Dadu River on the eastern margin of the Tibetan Plateau,located between Minjiang fault zone,Xianshuihe fault zone and Longmenshan fault zone. 7 optical luminescence samples on the 12. 5 m deep lacustrine sedimentary section( 31° 01’9. 31″N,102° 17’54. 97″E) were determined Deby the method of single aliquot regeneration combined with standard growth curve( SAR-SGC). The age and extent of the paleolandslide-dammed lake、the scale of the paleo-landslide dam,the causes of the paleo-landslide-dammed lake and its environmental effects are investigated in the present paper. The research results show that a river blocking event occurred about 2 ~ 3 ka ago,forming Jixinbao paleo-landslide-dammed lake. After a period of time,the maximum flow is about 2. 70×10^(3)m^(3)/s flood burst process. The area of the dammed lake is about 1. 84×10^(6)m^(2),the volume is about 6. 10×10^(7)m^(3)、the area of the landslide dam is about 1. 41×10^(5)m^(2),the volume is about 4. 19×10^(6)m^(3),the height is about 150 m. Preliminary speculation that the landslide was triggered by an earthquake. A wide modern river channel is formed in the upstream of the landslide dam,and the slope of the longitudinal river profile is small,the steepness index( ksn) behind the landslide dam is high. Through this study,we have a more comprehensive and scientific understanding of the paleo-dammed lake in the Dadu River Basin,providing a research example for the field of paleo-geological disaster.