Environmental resources and recent impacts in the Awassa collapsed caldera, Main Ethiopian Rift

The Awassa closed basin is formed by collapsed caldera of acidic volcano and is located within the Main Ethiopian Rift whose center is occupied by freshwater lake called Lake Awassa and big swampy area of Shalo. The basin is endowed with various natural resources such as water, vegetation, birds, etc. It is rich in fresh groundwater resource, which contains a lot of fluoride. Consequently, it is not suitable for drinking. There is thermal manifestation (Wondo Genet and Gara Quhe) in different parts of the caldera, which is characteristic feature of caldera collapse of shallow rooted acidic volcanoes. To characterize the basin water resources major ion chemistry, total coliform, dissolved oxygen, biological oxygen demand and chemical oxygen demand analyses were performed for selected surface and ground water samples. The physical and chemical data collected for this study showed that the natural resources are affected by human incursion since the establishment of the Awassa town. The surface and subsurface drainage is towards the lake and therefore, the lake is the main destination for any type of contaminants generated from urban activity and the caldera rim. (C) 2007 Elsevier Ltd and INQUA. All rights reserved.