Determination of Tectonic Activity Based on the Morphology of Alluvial Fan Systems (Case Study: the Northern Slopes of Sabalan Volcanic Mount)

Alluvial fans are one of the most prominent phenomena in fluvial geomorphology, which are found mostly on the mountain front. These landforms are affected by climate change and tectonic activity and record their effects. Therefore, we can use them to understand climate change and tectonic activities. The aim of this study was to determine the tectonic activity in the northern front of the Sabalan mountain through the morphology of the fan systems. by doing such research to a certain extent of damage to life and property due to natural disasters can be prevented. In this paper, the geomorphic indices of related to cachments such as RLP (Real Long Profile), TLP (Theoreitical Long Profile), ILP (Incision Long Profile), Stream Concavity Index (Sci), Asymmetric Factor (Af), Hypsometric Curve (Hc), Hypsometric integral (Hi), Drainage Basin Shape (Bs), Relief Ratio (Rr) and Alluvial fan indices, including, Bull method (2008), and field study have been used. GIS and Arc Hydrow software have been used to draw maps and analyze data. In general, and taking into account the interpretation of all the indicators used in this study, also library and field studies, we concluded that the subsidence of the central part of the Sabalan mass during the quaternary period was accompanied by the formation of a circular fault (caldera) and other sub-faults in the apex of the fan systems. These faults, in addition the uplift of the fans apex and lowering the base level of them, by creating longitudinal valleys and channelizing the surface currents, cut the lahar flows at the head of the fan systems. Consequently, the morphology of the fan systems in the study area related to active tectonics. In addition, the rule of glacial periods during the eruption of the Sabalan volcano, with generation of Lahar flow, played a decisive role.