The largest landslide dam in Turkey: Tortum landslide

摘要

The gigantic Tortum landslide blocked the Tortum River and formed the largest landslide-dammed lake in Turkey measuring 8500 m length, 2500 m width and a surfacial area of 6.77 km~2. Large and deep-seated landslides are prevalent along the steep slopes in the Tortum Valley. The Tortum landslide, located 90 km to the north of Erzurum, is one of the typical cases in the region. In this study, the characteristics, age, possible causal factors, grain size distribution and environmental impacts of the Tortum landslide, as well as the landslide dam and related lake volume, were investigated. The landslide occurred as a rapid-rock slide in the Cretaceous interbedded limestones with clastics. The surface of the rupture formed along the bedding plane. Pre-failure topography was reconstructed to estimate volumes of the Tortum landslide, dam and related dammed-lake area. Grid by number analysis is used to determine grain size distribution of the landslide dam. On the basis of the topographic reconstructions, the volumes of the displaced mass and the landslide dam were estimated as 223 million m~3 and 180 million m~3, respectively. The dam reached a maximum height of 270 m and impounded 1820 km~2 of mountainous drainage area, forming a lake with 538 million m~3 of water on the Tortum River. Geomorphometric parameters of the dam and dammed lake were compared with examined worldwide case studies. Based on the radiocarbon ages, the Tortum landslide occurred in the middle of the 17th century. The landslide-dammed lake resulted in positive environmental impacts in its vicinity, causing a change in the micro-climate of the region, providing opportunity for hydropower generation, and the development of a fishery and tourism.