Geology, geomorphology, geodiversity and geoconservation of the Sof Omar Cave System, Southeastern Ethiopia

Abstract

The Sof Omar Cave System, a spectacular and extensive cave system in Southeastern Ethiopia represents a maze of dry cave passages, which subsequently were crossed by a subterranean watercourse formed by the Weib River, forming combined underground passages of a total length of 15.1km, the longest and most extensive in Ethiopia. The Sof Omar cave and subterranean river system developed on Jurassic limestone beds particularly on the Gebredarie Series (massive, crystalline limestone beds intercalated with thin marl and mudstone beds). The cave system and the subterranean River developed along a generally horizontal outline within a 20m thick layer. The Sof Omar gorge is a wide but shallow doline, whose central section is incised by the ancient surface route of the Weib River. Prominent half dolines opening toward the sink and resurgence areas, as well as consistently inward dipping limestone beds at these localities imply collapse phenomenon. Karstification triggered by rift-related uplifting and extension during the mid-Miocene East African rifting, accompanied by extensive collapse along bedding planes likely initiated the caving process. The rifted and collapsed chambers were later widened by slow but persistent dissolution. The dry cave passages were formed earlier than the subterranean river course, though the latter might have partly followed the pre-existing cave passages and enlarged them to form the current subterranean river course. The Sof Omar caves are still at the heart of the cultural and religious life of the local population, where the dry cave passages, domes, and chambers are considered as important religious and cultural locales. With its subterranean river, large chambers connected by narrow and long rift passages, a unique and prominent sinkhole above the caves, wooded gorge teeming with numerous and unique tropical plant and bird species, the Sof Omar Cave System and adjoining gorge has outstanding scenic values. Apart from these naturally outstanding values, what makes the Sof Omar Cave System unique and unsurpassed in the world is its cultural significance. The caves form part of the cultural and religious life of the local population leading to the unique harmony between nature and culture. The cave system and its adjoining forested gorge is a natural–cultural heritage site that requires an active geoconservation.