Abstract
Many, large-scale landslides are observed in the areas along the Min Jiang and the Zagunao He, tributaries of the Chang Jiang (Yangtze River), located in the tectonic zone of the Huaxia System, Longmensan Mountains, Sichuan Province, China. The landslides are regarded as the reactivated and colluvial-deposits-slide type. Geologically, the study areas comprise the sediment ranging from Cambrian to Triassic Periods overlying granite of Proterozoic Era, which was then subjected to severe tectonic movements with the formation of nappe structure and to weak or moderate metamorphism. Among the strata, Silurian and Devonian phyllite is in the condition of very low shearing strength due to fracturing and argillization. More than 80% of the landslides are occurring in the strata ofSilurian to Devonian phyllite.
A triggering factor of the landslides is considered to be downcutting by river erosion. The landslides show a composite form from mountainside to the present river bed, and seem to have occurred periodically with descending movement of the river bed since geological age. Recently, deforestation and excavation of the foot of the slope for road construction have accelerated the occurrence of landslide. The landslide often causes the stoppage of a river in addition to the breaking of houses and agricultural land and the blockade of a road. It will bring about severe ecological and socio-economic damage to people on the site as well as in the upstream and downstream regions.
