Brittle Fracture and Lake Level Change at Beseka:Main Ethiopian Rift, Metehara Area
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Date
2007-07
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Abstract
In early 1960’s, the surface area of Lake Beseka was only 3 km2. In 1976, the
lake area was estimated at 27.5 km2 and now it covers around 41km2 (Tamiru
et al., 2006). The lake gauge height is about 0.71m in 1976 and 5.6 m in 2006
which almost increased by about 5 m in the last 30 years.
The rocks are affected by NNE-SSW faults and fissures. The faults within the
area of investigation have very atypical morphologies. Profiles across fissures
constructed by Trimble GPS and field observation indicate that the fractures do
not show the morphology of typical faults. The footwall remains flat and the
concave hanging wall curves up to ward the fault plane.
Generally 487 data of edge matching opening direction are taken and weighted
according their horizontal displacement to gave the total opening direction
113.4o, which is in agreement with the overall E-W direction.
The elevation of water level Lake Beseka is lower than the elevation of water
table of wells in the Abadir farm as well as the elevation of Awash River. Hence,
the flow of groundwater is towards Lake Beseka.
The Abadir Farm- a suger cane plantation south of Beseka-is mainly placed
within the lake’s catchment area, which is affected by ground cracks in rainy
seasons. The recharge to the groundwater coming from this plantation affects
the lake level to rise. In addition to the flow of ground water, the tectonic hot
springs as well as cold springs, which are also the main factors to the
expansion of the lake, come through these structures in the direction of SSWNNE. The curve of the lake level fluctuation shows an increment with time while
climatic data do not show any anomalies. Therefore, climate has not any
impact/influence on the lake level rise.
The extension of Lake Beseka results with flooding and salinity of Abadir farm
land and endangering of the routes (road and railway) from Addis Ababa to
Djibouti. The expansion of Lake Beseka has necessitated the raising of the level
of the road and railway line repeatedly.
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Beseka:Main