Landslide Diversity in the Rwenzori Mountains (Uganda)

In the Rwenzori Mountains, at the border between Uganda and the D. R. Congo, landslides frequently occur and cause fatalities and substantial damage to agricultural land and infrastructure. Up until recently, no information on the landslide characteristics, occurrence or spatial distribution was available. The use of archive inventories and field surveys however allowed identifying the key mass wasting processes in this region and their triggering and controlling factors. Here, we present the results of these multi-temporal archive and field inventories. The Rwenzori mountains are diverse in lithology, topography and land use patterns. This diversity in landslide controlling factors is also reflected in the types of landslides that occur in this 3000 km(2) large region. The majority of the Rwenzori Mountains consists of steep slopes on gneiss, mica-schists and amphibolite lithologies. A dominance of shallow translational soil slides is observed in gneiss while the amphibolite is found not to be prone to such landslides. This is in sharp contrast to the lowlands, which are characterized by gentle slopes and a rift alluvium lithology. In contrast to what was expected, the largest landslide densities are found in these lowlands where large, deep-seated rotational soil slides with head scarps up to 30 m depth prevail. In both the lowlands and the uplands, slope gradients appears to be the main topographic predictor for the spatial occurrence of landslides. Finally, concerning landslide triggering events, in both the archive inventory and the field surveys, rainfall-triggered landslides are the most common but co-seismic slides were also observed.