Integrated Geological and Geophysical Studies to Investigate the Landslide Zones and Study its Impact: a Case along the Road Section within Kurar Kebele, Dejen Woreda, Central Ethiopia
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Date
2017-06
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Addis Ababa Universty
Abstract
The current integrated geological and geophysical investigations were conducted in Kurar Kebele of Dejen Wereda, Central Ethiopia, to map the subsurface geological features, delineate and characterize the landslide affected sections and generate inputs assisting to recommend possible mitigation measures. To deal with this problem electrical resistivity sounding, seismic refraction methods were applied along with geological mapping and assessment of landslide prone areas. The study results revealed three layers with distinct physical characteristics, particularly electrical resistivity and density. The uppermost colluvial deposit is characterized by relatively enhanced resistivity values with slightly wide ranges (17-95 Ω-m) reflecting its heterogeneous nature in terms of grain size, moisture content and degree of compaction. This resistive layer is underlain by a very conductive and relatively impermeable bed (layer) composed of silt, clay and marl. From its resistivity responses this layer is inferred to contain considerable amount of moisture content /fluid. Compared to the second, the third layer is resistive and is attributed to weathered and fractured limestone.
Geological mapping and remote sensing data analyses (raster calculation) indicated that in this area about 83% of the landslides occurrences are associated with the upper unconsolidated talus materials (colluvial deposits) and only 17% with the limestone. Such phenomena are encountered over landforms characterized by slope angles (gradient) ranging from 100 to 450 and wherever occurred they caused huge damages on infrastructures and natural environment, including farm lands and immensely affected the socio economic conditions. Rainfall intensity and distribution that recharges the ground as well as human activity (poor land use practices, deforestation, and excavation) are found to be the major triggering factors that slope instabilities with subsequent mass movements. Rotational slides and debris slide are the common manifestations triggered by rain fall.
Key words: landslide, natural environment, rotational slide, debris slide
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Keywords
Landslide, Natural environment, Rotational slide, Debris slide