The effect of tectonics on the formation of alluvial fans and their pedogeomorphic analysis (Case study: Hashtgerd-Kordan, Alborz Province)

Alluvial fans are common geomorphological depositional landforms that have especial importance considering soil and water supply. The objective of this study was to evaluate the influence of tectonic activities in the formation of alluvial fans in Alborz Province and their pedogeomorphic analysis. In view of this morphotectonic indicators including stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf) were calculated and the sum of tectonic activities were analyses using Iat index. The pedogenese time and the sediment ages were calculated using clay accumulation index in order to evaluate the evaluation of alluvial fan geomorphic levels. The results of morphotectonic indices showed that the study area is tectonically an active region. Dissected mountain front, the v shape valleys, non- symmetry of drainage basin as well as the young basins of alluvial fans demonstrated the tectonic activity of the study area. The tectonic activity could affect the shape, area and the thickness of alluvial fans sediments due to substitution of alluvial fans that cause evolution of them. The alluvial fans evaluation in the study area conducts whit tectonic properties that could cause to from alluvial fans with higher generations area as well increasing sediment thickness.