GIS-Based Susceptibility Mapping of the Fentale–Metehara Blisters and Blister Caves in the Main Ethiopian Rift: Implications for Their Conservation

Abstract

The biggest and most spectacular blister caves in the world are found in the Fentale–Metehara area, in the Main Ethiopian Rift, where we inventoried 639 blisters and blister caves in an area of 80 sq. km straddling between the southern foot of Fentale volcano and the northern shore of Lake Beseka. The blisters were formed by a unique geological process involving up-doming of fluid-rich pyroclastic flows due to pressure of gases entrapped in the progressing flow, and subsequent breaching of some of the hollow domes. These unique geological heritages have been threatened, in some cases already destroyed, by various man-made and natural factors such as the unprecedented expansion of Lake Beseka, extensive infrastructure development (roads, railways, settlements and urbanization, and large-scale irrigation schemes), and younger fissural lava flows. In order to systematically determine the degree of threat quantitatively and qualitatively and evaluate the probability of destruction of any of the blisters and blister caves, we applied GIS-based frequency ratio model and non-hierarchical cluster analysis techniques and produced a susceptibility map of the area. The susceptibility map, validated using the degree of fitness technique, indicates that most of the blister field falls within very high to high susceptibility of destruction, implying that the destruction of most of these spectacular features is imminent particularly due to expansion of Lake Beseka and the Metehara town. This calls for concerted effort by the local authorities to devise mechanisms to protect the threatened blisters and blister caves along with mitigating the impacts of the expanding Lake Beseka. The susceptibility map will be helpful to guide and prioritize conservation efforts.