Slope Stability Studies Of Wabane Caldera, Western Cameroon: Impact Of Hydrology, Hydrogeology And Human Factors On Landslide Initiation

Slope analysis within the Wabane caldera was carried out to establish their stability after the 20th July 2003 landslides. A site with semi-circular fractures was selected for the installation of a vibrating wire displacement meter and avibrating piezometer. Displacement, rainfall and pore water fluctuation were recorded from May to December 2005 in an attempt to assess the behavior of these slopes with varying rainfall intensities throughout the period. The resultsindicated an increase in displacement with rainfall and pore pressure from May to September and a subsequent decrease from October to December. This demonstrates the interdependence between rainfall, pore pressure and displacement. The mean monthly rate of displacement recorded was 132.3 mm/month. The highest rate of displacement from regressive plots was approximately 0.01 mm/min for the months of August/September. These are low threshold values, and one can therefore infer that they represent the beginning of a possibly new cycle to landslides projected to occur again in the future. Prolonged rainfall and increased pore water pressure had been determined as the immediate factors responsible for the initiation of the 2003 landslides

Physico-chemical, mineralogical and chemical considerations in understanding the 2001 Mabeta New Layout landslide, Cameroon

Landslides are part of natural catastrophic disasters destroying both biological and physical entities including loss of human lives. An evaluation of soil properties involved in landslides is significant in itsmanagement. To this effect, soil samples from the 2001 landslide occurrences in the Mabeta New Layout, Limbe, Cameroon were analysed using standard techniques to determine texture, pH, electrical conductivity (EC), bulk density (Db), water absorption percent (WA), linear shrinkage, plasticity index (PI), loss-on-ignition (LOI),mineral content and major cations. Results obtained were: bulk density (0.89 – 1.08 g/cm3), LOI (19.4 - 25.7%), water absorption (23.4 – 29.1%), linear shrinkage (5.4 – 8.3%), volume shrinkage (4.8 – 8.5%), PI (13.5 –20.75%), major cations ((Fe2O3 : 9.91 – 23.24%), (Al2O3 : 9.88 – 28.48%), (CaO : 0.73 – 1.3%), (MgO : 0.55 –2.80%), (K2O : 1.06 – 1.59%), (Na2O : 0.77 – 0.89%)), pH (5.17 – 6.90) and EC (16.53 – 149.20ìS/cm). Values from physico-chemical analyses, secondary minerals abundance index (SMAI) and chemical index of alteration (CIA) of the soils were reflective of particles with high potential for sliding. With major contributions from favourable slope, seismic and hydrologic forces, the event occurred

Geotechnical and physico chemical properties of clays associated with landslides in volcanic and metamorphic terrains in Cameroon, Central Africa

Comparative studies of geotechnical properties of soils from landslide scars within volcanic rocks in Alou Sub-Division located in the Bambouto caldera and from a major landslide scar within Precambrian metamorphic rocks (gneisses and granites) located at Kekem indicated a range of bulk densities of 0.93 to 1.12 g/ml and water content from 27 to 44% from the volcanic terrains while bulk densities and water content in the metamorphic rocks ranged from 1.14 to 1.52 g/ml and 7 to 35% respectively. Granulometric analyses based on the determination of Atterberg's limits indicated the predominance of silts of high plasticity in both areasalthough the proportion of the fine fraction (clay, silt and fine sand) was generally higher in the volcanic rocks. Mineralogical properties obtained from X-ray diffraction (XRD) patterns indicated the predominance of feldspars, chiefly microcline and gibbsite, with appreciable proportions of clays (montmorillonite, kaolinite, goethite, chlorite and halloysite) within the volcanic rocks while the gneisses were dominated by quartz and muscovite with some proportions of montmorillonite, kaolinite and feldspars with the clay fractions being more variable in the volcanic rocks (13 to 44%) than in the metamorphic rocks (23 to 29%). The presence ofmontmorillonite, a type of clay which has the ability to absorb water and swell, is an indication of a major contributor to the susceptibility of both terrains to sliding when subjected to high rainfall. This was revealed by data on intense precipitation during the specific months of the landslide events which led to elevated groundwater levels with raised pore water pressure in the highly weathered and loose materials resulting in increased shear stress and reduced shear strength with the eventual failures of the slopes causing the landslide disasters witnessed in both geological terrains.Keywords: Landslide scars, geotechnical properties, montmorillonite, Cameroon Volcanic Line, metamorphic rocks, high rainfall

Hydrochemistry of shallow groundwater and surface water in the Ndop plain, North West Cameroon

This study was conducted on the hydrochemistry of shallow groundwater and surface water in the Ndop plain, North West Cameroon. The objectives were to determine the physico-chemical characteristics of water, controls on water chemistry and suitability for drinking and irrigation. Forty-six shallow groundwater and 26 surface water samples were investigated. Field measurements of physical parameters were preceded by chemical analyses of the samples for major ions and F-. About 69% of the water sources had pH values below 6.5, classifying the water as barely acidic. Electrical conductivity (<282 μS/cm) and total dissolved solids (<183 mg/l) were low suggesting low-mineralised and freshwater. The relative abundance of major ions (meq/l) was Na2+>Ca2+>Mg2+>K+ for cations and HCO3->>NO3 -≥ Cl->SO42- for anions. Major ion concentrations were low, and within the WHO guidelines for drinking water, but F- concentrations were much lower (<0.39 mg/l) and below guideline value. Main water types and proportions were Na-HCO3 (53 %), Ca-HCO3 (35 %) and a mixed Na-Ca-HCO3 (11%). Predominant processes influencing water chemistry were incongruent dissolution of silicate minerals and cation-exchange of Na+ in rocks for Ca2+ in water. The low major ion concentrations indicated low water-rock interactions and short residence time. The analysed water was suitable for irrigation.Key words: Water chemistry, hydrochemical controls, drinking-irrigation quality, Ndop plain, Cameroon

The geological control and triggering mechanisms of landslides of 20th July of 2003 within the Bamboutos Caldera, Cameroon

No Abstract.Journal of the Cameroon Academy of Sciences Vol. 7 (3) 2008: pp. 191-20

Hydrochemical characteristics of groundwater in sedimentary, metamorphic and volcanic aquifers in Ndian Division, South West Region, Cameroon.

Wells and springs are the dominant potable water sources in the area of study used by the population. Studies of the characteristics of aquifer types and the hydrochemistry of groundwater in sedimentary, metamorphic, and volcanic aquifers in the southern part of Ndian Division indicated the presence of the following three types of aquifers-sedimentary (alluvial), metamorphic (weathered/fractured gneisses) and volcanic (jointed basalts and pyroclastic materials). Fieldwork involved collecting details on rock characteristics such as the mineralogy, grain-size and texture. Physical parameters (pH, EC and temperature) were measured in-situ. Cations were determined by AAS and anions by ion chromatography. The pH values for sedimentary aquifers (5.50-8.00), metamorphic (6.10-7.40) and volcanic (5.80-7.60), reflected slightly acidic, neutral and basic water sources. The mean concentration of total dissolved solids (TDS) in the groundwater increased from metamorphic (8.84 mg/l), to volcanic (17.08 mg/l), and to sedimentary (40.48 mg/l) aquifers, representing the degree of mineralisation in these rock types. Alkalinity increased from metamorphic (14.53 mg/l), volcanic (19.18 mg/l), to sedimentary (57.64 mg/l). Based on the electrical conductivity, all the water sources were suitable  for drinking and for irrigation. Relating the major groundwater chemical facies to their geologic occurrence showed that the water in sedimentary rocks was characterised by Na-HCO3 (90%) and Ca-(HCO3)2 (10%), in the metamorphics by Na-HCO3 (100%) and in the volcanic aquifers by Ca/Mg-(HCO3)2 (70%) and Na-HCO3 (30%) water types. Based on WHO (2004) norms for potable water, 37 water sources were suitable for drinking and one water source (open well at Bekora) unsuitable due to excess nitrate and bromide concentrations of 77.28 mg/l and 0.08 mg/l respectively. Relatively based on EC and TDS, the most mineralised water was found in the sediments, the volcanics intermediate and the least mineralised water was in the metamorphic formations. The results constitute useful baseline information for future provision and management plans of water resources in the area.Keywords: Ndian Division, rock types, hydrochemistry, physical properties, groundwater, unconfinedaquifers

Investigating the Management of Geological Hazards and Risks in the Mt Cameroon Area Using Focus Group Discussions

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