Geomorphic Response of Alluvial Fans to Tectonic Activity and Climate Change in South Plain of Birjand

Alluvial fans as one of the major geomorphological forms of water reservoir are very important, such that most of urban and rural centers of Iran, especially in central and eastern sections are located on alluvial fans. They are usually controlled by geomorphological forms of tectonic activity along with climate change. Alluvial fans are located in the southern half of the drainage basin of Birjand. Due to their proximity to the city and the residential areas, they are very important. BagheranMountains in the south part of Birjand are part of Sistan area. The most important rock units in the upper Cretaceous include ophiolitic mixture, flysh, congelomerate and the oldest unit is related to that era. In this study the geomorphology evidence of the area has been used to investigate the morphotectonic activity. In order to do this purpose, we used sime indices. Review of the samples of sediment aggradation and drainage network on alluvial fans show how climate and tectonic have influenced them. Field observations and sediments granolometry have been used for this purpose. The results of the analysis also show young tectonics and dynamic processes of external activities intensity performance in the region. Also granolometery analysis of the area as evidence of tectonic activity result in alluvial fans landforms transitional to the bajada plains indicated that climate change and wind erosion have higher intensity on landforms.