INTEGRATED METHODOLOGIES (FIELD, REMOTE SENSING, GIS) FOR THE ASSESSMENT OF LANDSLIDE DISTRIBUTION, HAZARDS, AND CONTROLLING FACTORS IN THE JAZAN AREA, SAUDI ARABIA

An integrated approach involving collections and analysis of field and remote sensing-based observations in a GIS environment was adopted to assess the distribution, nature, and the factors controlling mass movements in the Jazan area, Red Sea Hills. The Red Sea Hills in SW Saudi Arabia (Jazan area) are part of the Neoproterozoic (550-900 Ma) Arabian-Nubian Shield basement complex. The area is characterized by steep topography (average slope: 17°) and intense structural deformation (e.g., folds, faults, fractures); three major structural trends (N-S; NW-SE, E-W) were extracted from field (558 stations on the main roads) and satellite based observations, with the N-S trend being the dominant fabric. Jazan lies within the Afaf belt, a major (length: 400 km; width 50 km) N-S trending fold and thrust belt, that extends into Sudan as the Baraka belt. The following co-registered data sets and generated products were analyzed: individual (GeoEye, Google Earth) and temporal (ASTER, TM) VNIR images, digital elevation (SRTM, ASTER), and derived products (land use maps, stream networks, flow accumulation, slope angle and aspect, road azimuth, NDVI), and field observations along the roads (dip amount and direction for fracture planes). The extensive distribution of structurally-controlled planes of weakness, steep slopes, high precipitation (300-500 mm/yr), and man-made structures (e.g., road network) contributed to the development of landslides through: (1) destabilization of slopes and planes of weakness, and (2) flash-flood related mass movement. Individual maps were generated to rank (high: 3; medium: 2; low: 3) the hazards associated with: (1) high flow accumulation within ephemeral streams, (2) overland flow on steep slopes, (3) fracture planes dipping towards roads, (4) slope perpendicular to road, and (5) sub-parallel slope and fracture plane directions. An integrated hazard map was constructed from the sum of the individual hazard maps and the weights assigned to each of the maps were adjusted to reflect the known locations of landslides.