Geological and Geomechanical Properties of Abraha-Atsibha and Wukro rock-hewn churches and its surroundings, Tigray Region, Northern Ethiopia

Abstract

Globally well-known ancient rock-hewn churches are present in Ethiopia in general and particularly in the central and eastern parts of Tigray regional state. They are important sites of heritage and tourism. Most of them are facing destabilization problem in different degree due to natural and anthropogenic factors. Among the affected, two churches hewn into sandstone located near Abreha-Atsibaha and Wukro (Kirkos/Cherkos church) in Tigray region were chosen for detailed study in terms of geological and engineering geological condition of the rocks in to which they are hewn. Both of them are affected by weathering and seepage. Both are carved into Mesozoic Adigrat sandstone that occupy higher elevations in topography, red in color and with iron and silica-rich alternating bands. Petrographic data suggest that the rock is dominated by quartz followed by feldspars; opaque and heavy minerals; pore spaces and carbonate/iron/silica cement. The rock is characterized by low to medium unconfined compressive strength. The alternating bands with varying mineralogical composition differ in mechanical properties and are responding differently to weathering and erosion. This is resulting in the development of minor spalling, pitting etc in the pillars, walls and roofs of the churches. Keeping the geological condition in view remedial measures are to be planned to minimize deterioration with time.