VALLEY SLOPE DEFORMATION BY INTERACTION OF MASS ROCK CREEP,TALUS CREEP AND RAPID LANDSLIDES ALONG THE KALI GANDAKI RIVER IN THE HIMALAYAS OF WESTERN NEPAL

In its upper and middle course, the Kali Gandaki river in Western Nepal flows across the Himalayan ranges more or less following tectonic lineaments (NNE—SSW). In this paper we focus our attention on certain slope deformations along the valley flanks of the middle course, especially on very narrow sections of this large transverse valley. Although the valley experienced several Pleistocene periods of strong glaciations and the powerful river flowing through it currently ranks as the second largest in Nepal we find a number of those amazing valley constrictions in the studied area which should not be ascribed to differences in rock resistance against erosion or to active tectonic control. It can best be explained by deep\|seated rock creep (Chigira,1992), a process which is frequently connected with landslides or rockfalls and must have developed during late Pleistocene and Holocene, i.e. since the valley was deglaciated. In order to prove this thesis we shall describe the situation by means of three case studies between the villages of Rukse (upstream) and Beni (downstream). Another fourth example of gravitational slope deformation described in this paper is located downstream of the reach of previous valley glaciations. Here, too, deep\|seated rock creep is considered to be responsible for the observed mass movements and thus for slope deformation.