This work focused on three landslide events that have attracted significant public concern due to the associated calamities they recorded in 1945, 2017 and 2019, i.e. the Charlotte, Regent and Madina landslides, respectively. Their geology, tectonics (structural discontinuities) and geomorphology, i.e. their GTG characteristics were studied to establish links between them and the landslide events.Field surveys were conducted, particularly on the Charlotte landslide, where the identification of geological structures was impeded to an extent by its obliteration by vegetation and sediment accumulations on relatively planar sections of the landslide area. Remote sensing and GIS techniques (earth imagery and drone images) enhanced the mapping and determination of landslides’ geometric and geomorphic parameters. Laboratory analyses of rock and soil samples provided the landslides’ petrological characterisation and were used to determine the particle-size distribution in the slide-prone soil.The study indicated a change in the gabbroic rock composition, variable geomorphological characteristics, and nature/pattern and density of the discontinuities. These factors, to a large extent, determined the nature and magnitude of the rainfall-triggered landslides. Charlotte lithology slightly differed from the other two landslides and recorded higher Silica (Si) and Aluminum (Al) and lower iron (Fe) from X-Ray Fluorescence (XRF) than rocks of Regent and Madina landslides. The study also revealed only a tenuous correlation between rock composition and weathering depth. The slope angles at the landslides’ prominent scarps (depletion zone) are steep (> 45 degrees) with altitudes of approximately 270 m, 200 m and 470 m above sea level for Charlotte, Regent and Madina, respectively. Unlike the Charlotte landslide, both Regent and Madina landslides are active, but geometrically, their area, length and run-out distances have relatively high variance with a coefficient of variance equals to 1. Information derived from this work can help understand the spatial variation in landslide characteristics and develop a susceptibility map.
In the event of natural disasters, Sierra Leone like any other country loses lives as well as properties and natural resources. Despite notable occurrences of small disasters in the country, only on August 14 th sugarloaf landslide and the resulting flash flood (twin disasters) which affected Regent and other communities in 2017 have captured both national and international attention due to their alarming impacts. To obtain a better knowledge on the nature of the disasters, this research considered the geological context of the landslide and focused on statistical analysis of the impacts of the twin disasters using Statistical Package for Social Sciences (SPSS). Geological field-based approach and self-administered questionnaires of both closed and open-ended questions, personal interviews and observations were adopted as research techniques. Descriptive statistics and qualitative analysis were used to analyze the data of the research. Relevant literature from books, journals, and newspapers was also consulted, including Radio, Television discussions and the internet. Slope destabilization that caused the Landslide was linked to the geology of sub-surface formation (highly weathered olivine gabbro), lineaments and the rate of weathering. Study showed remarkable economic, social and political impacts as a consequence of the twin disasters. Study also revealed that families assisted the most in both financial and non-financial ways to the victims, and renowned misappropriation of donated disaster funds. All variables tested using student t-distribution and chi-square test of independence accepted the hypothesis. Information obtained from this work could be fundamental for policy makers and development practitioners (Osuteye & Leck, 2017).
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.
Freetown has documented one of the most devastating landslides in the world in 2017. Many debates in the media, few scientific papers and technical documents, have argued with eloquence ascertaining human factors, particularly deforestation and urbanization, as the dominant causative factor. This notion seems to be widely accepted for all other slides by the communities, government agencies and departments. Therefore, this work attempts to expand on existing public knowledge by demonstrating the less influential or insignificant human factors which can have impacts on certain landslide occurrences in the Freetown Layered-Complex. The representative landslide considered for this study occurred beyond the vicinity of urbanized zone. Therefore, to establish a clear understanding of the actual causative factors, fieldwork and laboratory investigations were undertaken. During the field survey, we assessed the rock type, discontinuities, geomorphology and hydrological influence of the landslide. The specific rock series underlying the landslide was confirmed through thin section analysis at the National Minerals Agency (NMA). DCP tests and laboratory analyses enhanced the derivation of geotechnical properties of the residual soil/regolith.This work systematically presented how natural conditions, such as: geology (rock types and tectonic signatures), geomorphology, hydrology and the geotechnical properties of the slope soil, have interplayed in the occurrence of the landslide event. In addition, the slip surface of the landslide occurred at a depth below the reach of plant activities (2.6 m). This information may help modify public messages by institutions and can be a source of useful information for the country’s Landslide Disaster Management Department (LDMD).
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