Landslides: A Guide to Researching Landslide Phenomena and Processes

Introduction

The surface of the earth, both on land and beneath the oceans, continually undergoes modifications by mass movements that operate in response to gravitational forces. Landslides represent one type of these mass movements and describe ‘the movement of a mass or rock, debris or earth down a slope’ (Cruden, 1991). In this chapter, the term ‘landslide’ will include all types of gravity-caused mass movements, ranging from rock falls and topples and a variety of slumps and slides to flows of different materials. Varnes (1978) provided an idealized schematic presentation that displays the features of a landslide in soil material (Figure 1). The system of landslide classification devised by Varnes (1978), completed by concepts defined in IAEG Commission on Landslides (1990) and Cruden and Varnes (1996), has become the most widely used system in the English language. Hungr et al. (2014) proposed a new version of the Varnes classification to reflect recent advances in the understanding of landslide phenomena and the materials and mechanisms involved, including 32 landslide types in rock and soil materials supplemented by examples and references.

Figure 1.

Schematic representation of an idealized landslide according to Varnes (1978) that was slightly modified

Landslides are a component of the erosion process, which is described as a continual leveling of the surface features of the earth. Although precipitation, earthquakes, and volcanic eruptions are the principal natural drivers of landslides, in many cases, landslides result directly from disturbance of hillsides during road construction or other human activities. Landslides occur in all geographic regions of the world in response to a wide variety of natural conditions and triggering processes that include storms, earthquakes, and human activity. These phenomena belong to natural hazards (i.e., geohazards) because this environmental process is responsible for direct damages that can be expressed in thousands of deaths and injuries each year and monetary losses in the billions (Schuster, 1996; Petley, 2012). Indirect damages include long-term economic disruption and population removal. According to the definition adopted by United Nations Disaster Relief Organization (UNDRO) in 1979 for all potentially damaging natural phenomenon or natural hazards (UNDRO, 1980), a landslide hazard is ‘the probability of occurrence, within a specified period of time and within a given area’. Landslide risk is the term developed to describe the expected degree of loss due to a landslide according to the following definition: ‘risk meaning the expected number of live lost, people injured, damage to property and disruption of economic activity due to a particular natural phenomena, and consequently it is the product of a specific risk and elements at risk’.