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A comparative geological, tectonic and geomorphological assessment of the Charlotte, Regent and Madina landslides, Western area, Sierra Leone
Geoenvironmental Disasters Pub Date : 2021-07-19 , DOI: 10.1186/s40677-021-00187-x
Yusuf Alhaji Lahai 1 , Kelvin F. E. Anderson 1, 2 , Yaguba Jalloh 1 , Mohamed Kamara 2 , Ibrahim Rogers 3
Affiliation  

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.

中文翻译:

塞拉利昂西部地区 Charlotte、Regent 和 Madina 滑坡的地质、构造和地貌比较评估

这项工作的重点是三个滑坡事件,这些滑坡事件由于它们在 1945 年、2017 年和 2019 年记录的相关灾害而引起了公众的极大关注,即分别是夏洛特、丽晶和麦地那山体滑坡。研究了它们的地质、构造(结构不连续性)和地貌,即它们的 GTG 特征,以在它们与滑坡事件之间建立联系。进行了实地调查,特别是在夏洛特滑坡上,由于滑坡区相对平坦的部分上的植被和沉积物堆积,在一定程度上阻碍了地质结构的识别。遥感和 GIS 技术(地球图像和无人机图像)增强了滑坡几何和地貌参数的测绘和确定。岩石和土壤样本的实验室分析提供了滑坡的岩石学特征,并用于确定易滑土壤中的粒度分布。研究表明辉长岩的成分、可变的地貌特征以及不连续性的性质/模式和密度发生了变化。这些因素在很大程度上决定了降雨引发的滑坡的性质和规模。夏洛特的岩性与其他两个滑坡略有不同,与 Regent 和 Madina 滑坡的岩石相比,X 射线荧光 (XRF) 记录的二氧化硅 (Si) 和铝 (Al) 含量更高,铁 (Fe) 含量更低。该研究还揭示了岩石成分和风化深度之间只有微弱的相关性。滑坡突出陡坡(枯竭带)处的坡角陡峭(> 45 度),夏洛特、摄政和麦地那的海拔分别约为 270 m、200 m 和 470 m。与 Charlotte 滑坡不同的是,Regent 和 Madina 滑坡都处于活动状态,但在几何上,它们的面积、长度和跳动距离具有相对较大的方差,方差系数等于 1。从这项工作中获得的信息可以帮助理解滑坡特征并绘制敏感性图。
更新日期:2021-07-19
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