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Table 3 Comparative GTG Characteristics of the Charlotte, Regent and Madina landslides

From: A comparative geological, tectonic and geomorphological assessment of the Charlotte, Regent and Madina landslides, Western area, Sierra Leone

Landslide ID Geological Condition Geomorphological (terrain) Condition Tectonic Fabric Triggering Factor Causative Factor Soil Type Failure Type
Charlotte Landslide (S1-CH) Rock type is Norite with an altitude of 320 /40 SW. Elevation: 270 m; Slope angle: 450& Slope aspect: NE. The 4 + m regolith section on the right forms immediate post slide gully Longitudinal open cracks (NE-SW) on both flanks of the landslide and trellised open joints (<  2.5 cm) with running water attached to them. Rainfall, Orugu stream erosion & urbanisation Rock joint orientation and Clay rich layer towards the bedrock. This zone is overlain by porous and permeable regolith. Clayey gravel
(Low plasticity clay)
Composite type (Rock fall & Rotational)
Regent Landslide (S2-RT) Olivine gabbro (OG with Dolerite dykes. It is slightly weathered to fresh. ≈ 10 m upper part of the rock is weathered. Rock altitude: 320/ 40 SW Elevation: 470 m; Slope angle: 600& Slope aspect: N Jointed rock with two different joint orientations or more (NNW-SSE & NNE-SSW) caused two phases of failures. Rainfall & urbanisation Geology (Slide prone zones linked to weathering along WNW-ESE joints) and steep slope (> 590) Silty gravel
(Highq12 plasticity silt)
Translational &Wedge-typesliding(Broadly deepseatedtranslationalslide
MadinaLandslide(S3-MD) Olivine gabbro intrudedby Dolerite dykes.Shallow colluvial soil of ≈ 1.3 m at headscarp,which thickens at flanks.Rock altitude is290/60NNE Elevation: 200 m; Slopeangle: 540& Slopeaspect: SW. Debrisbulge at slide toe andsedimentary pile 1 m tothe NW-SE valley(fault zone) No visible lineaments (fractures/cracks and joints) on the main body. Rainfall, stone mining & Slope excavations Combination of shallow colluvial soil and presence of tension cracks behind the edge of the slope. Silty-Clayey gravel
(High plasticity)
Shallow Translational slide