Morphotectonic Analysis of Sabalan Caldera and its Impact on Related River Basins and Alluvial Fans in the Northern Slopes

One of the most interesting landforms in the Sabalan massif landscape is the 12 Kilometers caldera-shaped circular fault. The fault has affected landforms, including catchments and associated alluvial fans. The purpose of this study was to analyze the role of Sabalan Caldera in the evolution of river basins and associated alluvial fans in the northern slopes. Morphotectonic indices including Stream Gradient Index (SL), Mountain-Front Sinuosity (SMF), Valley-Floor Width to Height Ratio (VF) and Transverse Topographic Symmetry Factor (T) were used in the present study. Besides, Topographic maps 1:25000, Geological maps 1:100000, Digital Elevation Model (Dem) with resolution of 20 meters, Landsat satellite image with resolution of 30 meters, Geographic Information System (GIS), Excel, Arch Hydro10 and Envi 4.8 as research tools, have been used to provide the quantitative and qualitative analyses of morphotectonic indices. Moreover, field observations and geomorphologic evidence have been used to verify greater confidence in the results. The findings from the calculation of morphotectonic indices and field observations, also geomorphologic evidence showed that the caldera range are still tectonically active. Moreover, the drainage network map obtained from the digital elevation model, revealed that the caldera collapse has changed the pattern of the drainage networks from the radial to the central state and then to the dendritic state. Likewise, this process has increased not only the area of the catchments but also the power flow of the rivers. As a result, the rivers using a loose formation of Lahar have incised fan systems and left behind the abandoned terraces and old fans.