Role of karrens in deterioration of Taq-e Bostan reliefs (northeast of Kermanshah city)

Taq-e Bostan historical region is located in the northeast of Kermanshah city and is considered as a part of Prow - Bistoon karst region. Bisetun limestone formation with northwest - southeast dominant trend is the main lithology in the region. Tectonic activities during Cenozoic have created several faults, joints and fractures in these rocks. The chemical composition of the carbonate rocks, the rock mass structures and regional climatic factors provide a favorable condition for the occurrence of karstic features such as karren. Karrens of the region were formed as the result of interaction between the intrinsic (including lithology, thickness of the layers and presence of joints and fractures in the rock mass) and environmental (including weather, rainfall and altitude) factors. Based on the field studies, turbulent flows due to rainfall have caused to the rillenkarren developing on inclined surfaces. Also, turbulent flows due to snow melting on nearly vertical walls of the rocks have created wandkarren. On the other hand, several types of trittkarren have been formed by turbulent flows due to both rainfall and snow melting in the region. Water seepage along the joints and fractures of the rock mass has widened them and created karren cavities in the region. Therefore, forming of karrens on the surface of the rocks reduce its the mechanical resistance against the morphogenetic factors and thereby provide a suitable condition for erosion and deterioration. The authors are of the opinion that formation of karrens close to the monuments is a warning about deterioration of monuments due to the dissolution. On the basis of the obtained results, it is premature to recommend the application of ditches above the area as a protective treatment for diversion of water flow and avoid surface water contact with the monuments.