The Landslide Hazard Mapping theme (1989-1992) was undertaken as the GARS Latin America Project and was initiated to address the global concern of natural hazards of geologic origian through landslide hazard mapping.

Ground instability caused by landslides is one of the most widespread geological hazards and is one of the main processes by which landscapes evolve. Landslides are characterised by movements of solid rock, debris or soil that are driven by gravitational forces. These can range from chaotic movement of large quantities of material down steep unstable slopes to more progressive movement. Landslides can form a wide variety of deformation and displacement features that can be observed at the ground surface. As a result of this deformation, the landscape is forever changing and must be mapped and understood in detail in order to assess its future behaviour with respect to landslide activity.

Objective of the Landslide Hazard Mapping theme

The main objective of the GARS Latin America Project was to develop a new methodology in landslide hazard mapping using remote sensing data from optical and radar systems and Geographic Information System (GIS) technology in order to generate a map of landslide susceptibility from which to oreint prevention against potential risk and for land management.

Aim of the theme

The aim of the theme was to perform a quantitative geomorphological study to map slope discontinuities and landslides fromsatellite data.

Study Location

The research was performed in the Chicamocha Valley, Colombia (Andes Region)

Methodology

Landslide hazard mapping was performed using a combination of field survey, optical remote sensing data, from Landsat TM and SPOT, and radar data, from the ERS and JERS satellites.

The initial step in landslide hazard mapping was to generate a Digital Elevation Model (DEM) of the test site. One possible technique was to use stereo image pairs obtained by the SPOT system to generate a DEM using specific DEM extraction software. However, due to the persistence of cloud cover in this geographic location, cloud free stereo SPOT data were hard to obtain. Alternative sources to the optical SPOT data were then assessed for the cost-effective generation of a DEM and monitoring of landslide activity.

The first alternative technique was to use an optical stereo image pair comprising of a vertical-view image from TM and an oblique-view image from SPOT. The second alternative technique was to use radar data from the ERS and JERS satellites, these systems allowing ground observation thourgh cloud and also at night.

The optical stereoscopic data were used to visually interpret the lithology, identify discontinuities and perform land-use classification of the ground. The landforms and relief perception of the stereo data were also used to digitise the boundaries of the landslides and the head scarps of debris flows.

The extracted DEM was used to conduct quantitative geomorphological mapping of the surface slope, exposures and drainage networks

Information extracted on the geology, slope, land use, discontinuities and drainage networks were key parameters for determining the critical conditions for relative landslide susceptibility and were combined with the DEM in a GIS to produce a map of potential landslide susceptibility.

Results

The main outputs from the GARS-Latin America Project were:

• Landslide susceptibility map at the scale of 1:50,000 for the upper Chicamocha Valley, Colombia
• Detailed methodology for landslide hazard and susceptibility mapping

Publications

Progress reports were published in the IUGS 'EPISODES' magazine (1992 & 1993).

For further publications, please contact ITC, Université de Paris-VI or BRGM

International Collaboration

Instituto de Investigaciones en Geociencias, Mineria y Quimica (INGEOMINAS), Colombia
Bureau de Recherches Géologiques et Minières (BRGM), France
Centre National d'Etudes Spatiales (CNES), France
Groupement pour le Developpement de la Télédétection Aerospatiale (GDTA), France
International Institute for Aerospace Survey and Earth Sciences (ITC), Netherlands
Université de Paris-VI, France