Natural hazards along the Bamenda escarpment and its environs: The case of landslide, rock fall and flood risks (Cameroon volcanic line, North-West Region)

Abstract

Bamenda town is situated on the North Northwest slope of the Bamenda Volcano (2621m) which is a stratovolcano situated along the Cameroon Volcanic Line precisely between Mount Bambouto (2740m) and Mount Oku (3011m). The general morphology shows the presence of an escarpment of about 150m high, which separates Bamenda town into Up Station and Down Town areas. Rapid population increase in the town of Bamenda (500,000 inhabitants) has pushed the inhabitants to settle along the slopes of the Bamenda Mountain and close to river channels thereby exposing themselves to landslide, rock fall and flood hazards, with negative environmental and socioeconomic impacts. These hazards usually occur during the rainy season and are provoked by natural and anthropogenic factors. The area consists of volcanic (ignimbrites, trachytes and dolerites) and plutonic (granites and gneisses) rocks. Geotechnical analysis of the soils shows that the soils have low bulk density (1.32-1.59), low specific density (2.20-2.58); high porosity (47.92-64.28 %); water content exceeds 35.2%, and predominance of fine grain particles. Atterberg limits indicate that the soils are plastic in nature. Cohesion is low (2.60-7.20 kPa) the angle of internal friction values vary from 25.5 ᵒ to 28 ᵒ . These parameters indicate that the soils are predisposed to landslides. The model employed in realizing the risk maps uses parameters such as; slope, type of material, nature of river, the presence of rocks and/or escarpment and influence of geotechnical parameters. The obtained risk maps indicate settlement areas at risk. This approach can assist in town planning, risk mitigation, environmental and civil protection.