Assessment of the impacts of ground fissuring in the Main Ethiopian Rift: the case of the rift margin areas of Siltie Zone, southern Ethiopia, East Africa

This paper presents the impact assessment of ground fissuring in rift margin districts of Siltie Zone in southern Ethiopia, which is located at the western margin of the central portion of the Main Ethiopian Rift. Field investigations, literature reviews and interviews were employed in the study. Faults are the major structural units in the area shaping the landscapes as well as determining the size and positions of recent alluvial deposits. The geology of the area is made of rhyolitic ignimbrites at the bottom followed by basalts, and scoria cones are also common. Overlying this stratigraphy are thick unconsolidated alluvial deposits, at places reaching up to 70m and filling grabens created by the regional faulting. Almost all the settlements and agricultural practices are concentrated on this fertile recent sediment. The area is frequently affected by ground fissuring that mainly occur as vertical cracks and ranges from discontinuous hairline fractures to open ground cracks up to 1200m long, as much as 0.5m to 6m wide, and up to 5.2m deep. The fissures are aligned in NNE-SSW directions, the average strike being N16 o E. Manmade structures such as homes, water pipelines and storage tankers are destroyed by the fissuring. Agricultural lands and trees are also severely damaged. This heavily affected the food security in the districts since most of the residents are farmers. Some extensions of the fissures however are not exposed to the surface rather formed underground caves and sinkholes and will be future dangers in the area and need proper buffering.