Weathering processes, structural degradation and slope-structure stability of rock-hewn churches of Lalibela (Ethiopia)
Published:January 01, 2010
G. Delmonaco, C. Margottini, D. Spizzichino, 2010. "Weathering processes, structural degradation and slope-structure stability of rock-hewn churches of Lalibela (Ethiopia)", Weathering as a Predisposing Factor to Slope Movements, D. Calcaterra, M. Parise
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Lalibela is located in the northern–central part of Ethiopia, c. 600 km north of Addis Ababa in Northern Wollo (Ahmara Region). The town, which has about 12 000 inhabitants, is situated at an altitude of 2500 m. In its centre a unique complex of 11 rock-hewn Christian Orthodox churches is located, cut out of the rock some 800 years ago. Their construction is attributed to King Lalibela (1167–1207). All the churches exhibit widespread evidence of structural damage and weathering processes, which are posing a serious problem for the preservation of the monuments. Preliminary geological field surveys, in situ geotechnical analyses and laboratory tests have been carried out in the area to understand the cause of weathering and the likely consequences on the structural stability of the churches. Laboratory tests on volcanic materials detected a deep alteration of rocks as a result of the widespread presence of montmorillonite. This is the primary cause of the progressive deterioration of the physical and mechanical characteristics of the slope-forming rocks in Lalibela. Major consequences are the alveolar weathering of churches' façade, the degradation of the roofs and a reduction of rock strength, which are causing a progressive structural instability in some rock-hewn monuments. Also, sliding of façades along bedding joints was detected. Understanding the weathering processes affecting the Lalibela churches allows the detection of problems and the timely implementation of medium- to long-term protection strategies for conservation of the monuments.
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Weathering as a Predisposing Factor to Slope Movements
This volume is intended to provide an up-to-date overview of the approaches, methodologies and techniques devoted to better understanding of the weathering conditions of rock masses on slopes. According to the local conditions, a variety of slope movements may take place and involve weathered rock masses. Shallow and rapid soil slips evolving to debris flows are probably the most common type of slope movement. At the same time, deep-seated, intermittent landslides can also affect large volumes of weathered rocks and soils. Despite the high frequency of landslides in weathered materials, and the damage and casualties they repeatedly cause, little is known about the relationship between weathering and slope movements. This book presents worldwide case studies, where a variety of geological and geomorphological settings are discussed. The content is divided into three sections: the first is devoted to broad aspects of the weathering/landslide processes; the second and third sections include papers dealing with igneous/metamorphic and sedimentary weathered rocks, respectively.