Vertical geomorphologic zonation on the Northwest Sichuan Plateau and the effects of mountain hazards on the West Route of the South-to-North Water Diversion Project

Abstract

Vertical geomorphologic zoning on the Northwest Sichuan Plateau is obvious and elevations for different geomorphologic zones are: fluvial zone3800m;glacial margin zone 3800-4200m;and glacial zone4200m.Their correspondent principal geomorphologic processes are water erosion,thawing erosion and glacial erosion.The plateau terrain was formed as a result of the thawing erosion under the conditions of vast expanse tectonic uplift.Crystalline rocks of granite and limestone have higher strength against thawing erosion than Triassic epimetasediment rocks of sandstone and slate.Therefore,crystalline rocks are able to form high glacial mountains while Triassic epimetasediment rocks are not.However,Triassic epimetasediment rocks are prone to form hilly plateau terrain.The 1~(st) stage subproject of the West Route of the South-to-North Water Diversion Project is basically located along the boundary between the fluvial zone and the peri glacial zone,landslides,rock-falls and thawing solifluctions are major slope failure hazards and most of those hazards are of small-medium scales.There are a number of debris flow gullies where small-medium scale debris flows occur frequently in the project area,however,large scale debris flows may occur in the gullies of the fluvial zone.Thawing solifluctions are the main river sediment sources in the area and attentions should be paid to the effects of their sediment production on silting of the planned reservoirs.Geomorphologic processes are very sensitive to climate changes in the boundary area between the fluvial zone and the periglacial zone.