A comparative Geological, Tectonic and Geomorphological assessment of the Charlotte, Regent and Madina Landslides, Western Areas, Sierra Leone

This work focused on three landslide events that have attracted significant public concern due to the associated calamities. The slides have been analyzed for their geology, tectonics and geomorphological (GTG) characteristics. In addition, an understanding of the link between GTG characteristics and the landslide events was established.To achieve this, field surveys were conducted, particularly for the Charlotte landslide, where identification of geological structures was perturbed by the obliteration of vegetation and sediment accumulations on relatively planar sections of the landslide area. GIS and remote sensing techniques enhanced mapping and determination of landslide characteristics, and laboratory analyses on rock samples provided the petrological characterization of the landslides.Results indicated change in rock composition (gabbro), variable geomorphological characteristics and the nature/pattern and density of discontinuities; these factors, to a large extent, determined the nature and magnitude of the rainfall-triggered landslides. Charlotte lithology slightly differs from and recorded higher Silica (Si) and Aluminum (Al) and lower iron (Fe) than rocks of Regent and Madina landslides. Study also revealed only tenuous correlation between rock composition and weathering depth. The slope angles for the landslides’ main scarps (depletion zone) are steep (>45 degree) with altitudes ≈270m, 470m and 200m above sea level for Charlotte, Regent and Madina respectively. Additionally, the area and length of the landslides have relatively high variance (CV=1) and the variance of their run-outs as well is high (CV>1). Finally, information derived from this work can be useful to understand the spatial variation in landslide characteristics and the development of a susceptibility map.