Hazards from Mass Movements in Mountain Regions

Abstract

Hazards arising from mass movements are a common problem in mountain regions, particularly in a temperate humid climate, where the annual rate of precipitation in the form of rain or snow is fairly high. Such conditions occur for instance in the entire Alpine-Himalayan belt, in the Rocky mountains, in the Andes, and in New Zealand. Mass movements are primarily the consequence of gravitational force, although their triggering may be of a different origin (e.g. earthquakes). The types of mass movements existing in nature can be classified according to whether the masses are moving by themselves (intrinsic mass movements such as creep or slides), or whether they are carried by an external transporting agent (e.g., water, air or ice). In the case of intrinsic mass movement, the affected regions may be shallow (surficial movements), or they may reach very deep into the rock substratum. Furthermore, the movements may be slow as in creep or fast as in slides. Evidently internal creep, catastrophic slides and external flow phenomena present entirely different kinds of mechanical problems. Furthermore, it will be shown that the ultimate “cause” of all mass movements lies in the general pattern of landscape development. A landscape must be considered as an open system that is in a dynamic state which may or may not be equilibriated. In particular, it has been found that there is a tectonic predesign in many phenomena involving mass movements which, at first sight, one might consider as caused entirely by ’external’ (water, ice) agents. A series of case studies of various types of mass movements made by our institution in Austria describe results from measurements over mountain fractures, and valley closures, leading to the establishment of tear scars and slides. In addition, some cases of the effect of external agents (mud and debris flows!) will be described.