Tectonic predesign of mass movements, with examples from the Chinese Himalaya

The genesis of landslides has traditionally been ascribed essentially to exogenic, nontectonic causes. Thus, it has generally been assumed that progressive erosion oversteepens slopes until they become unstable and collapse by forming slides; the specific triggers in each case would be exogenic influences such as, for instance, an extreme weather period. This paper shows that in practically all cases of mass-movements, endogenic processes are also of fundamental importance. In the first place, a landscape responds as a complex open system existing in a quasi-stationary state at the edge of chaos in which an endogenic input and exogenic outflow of mass and energy occur; this quasi-stationary state can become unstable resulting in landslides. In the second place, a direct predesign is present because of endogenic causes, viz. by a former or the present geotectonic stress field. Thus, some common notable contentions regarding the origin of landslides are shown to be false. A better understanding of the mechanisms for landslide genesis is illuminated using examples from the Chinese mountain ranges at the east end of the Himalayas. In these particular cases, the orientations of mass movements are directly controlled ('predesigned') by the present-day local tectonic stress. (C) 1998 Elsevier Science B.V. All rights reserved.