Research On Development Characteristic And Mass Mechanism Of Superlarge Landslide In The Upper Yellow River

This paper mainly discussed the characteristics, cluster mechanism and genetic scheme of the large-scale landslides in the upper Yellow River. Based on the structural evolution, paleoclimate evolution and the formation and evolution of the Yellow River, the absolute age determinations of landslides were dated. And then the research of cluster mechanism of large-scale landslides was made according to the different relationship of time and space. An explanation was made based on the knowledge of geological structure and climatic change. This paper put forward an opinion of the Kun-Huang Motion. In addition, three types of genetic schemes were summarized. Furthermore, four typical landslides were selected as the objects of study in order to analyse the genetic scheme and evolutionary phase. At last, combined with the technology of Geographic Information System, hazard regionalism was output as the result of analysis. The results of this research were stated as follows:(1) 116 large-scale landslides were found in the study area. And the total volume of earthwork is about ten billion m3. The petrofabric of landslide-prone includes clay stone, mud stone, half-diagenesis glutenite during the down pleistocene series, red mudstone, semi-rigid glutenite gravel semi-hard rock group during Tertiary system and Cretaceous system; metamorphic rock groups during lower proterozoic erathem,etc. The distribution of tertiary mudstone landslide is the strongest in the region both of quantity and intensity. Due to the differences of geological background environment around the study area, the distribution of landslides in each basin, on both sides of the main stream or Tributary stream have uneven spatial distribution of developmental characteristics.(2) Six ideas have been summarized for indirect sampling from the landslide of the research.①the bottom of the landslide was covered by loess,②the top of terrace which was covered by landslides③landslide schistose structure formed by internal high temperature,④the bottom of barrier lake⑤the bottom of water phase material in the scattered-type landslide⑥organic carbon at the top of the landslide underlying material. There are six periods of cluster induces of 80 thousand years,50 thousand years,30 thousand years,10-8 thousand,5 thousand years and nowadays. And each of them had the different induces of the main cause: seismic trigger of 8 m80 thousand years, seismic and precipitation trigger of 50 and 30 thousand years, seismic trigger of 10-8 thousand years, precipitation trigger of 5 thousand years and precipitation and human engineering trigger nowadays.(3) Kun-Huang motion is the transformative and formative periods of landscape structure and amorphous phase in the north of Kunlun mountains, during the motion, there were two stress changes. Due to reduced river erosion base level caused by overall uplift of the plateau, the Jishixia was cut off and the variation of river erosion base level led strong headward erosion of the Yellow River. Then the cut of Lijiaxia, Songbaxia, etc, was mainly formed by the strong tectonic movement during the second and third phase of Kun-Huang motion, which leading to the NNW watershed tectonic uplift strongly and reducing the regional erosion base level. NNW mountains which have been studied accelerated uplift during the second and third phase of Kun-Huang motion. Since the late Pleistocene, there have been two strong tectonic sub-periods of 80000 years and 30000 years, but none of them have the overall characteristics.80000 years tectonic movement concentrated in the Guide Basin, and 30000 years' tectonic movement mainly showed in the regional deep fracture Zama mountain, which was obviously uplift. They were the prelude and epilogue of the second phase of the Gonghe movement.(4) Three kinds of common genetic model have been summarized in study area, the dissolution-creep-rip-cut type; rip-dump-cut type; and creep-rip-cut type.(5) Combined with GIS, assessed the hazard of the study region. The result of assessment showed as follows: the area of high risk region is 789.46km2, accounting for 8.0547% of the whole region, the area of middle risk region is 1626.86 km2, accounting for 16.5986% of the whole region, the area of low risk region is 3407.78km2, accounting for 34.7691% of the whole region and the stable region is 3977.08km2, accounting for 40.5776% of the whole region.