The Evaluation of the Factors Effective on the Appearance and Evolution of Alluvial Fans at the Southern Slopes of Joghatai Mountains by Emphasis on Tectonic Role (in West Sabzevar Limit)

The aim of this study is to examine the factors effective on formation and evolution of alluvial fans at the southern slopes of Joghatay mountains at the West Sabzevar in Khorasan Razavi province. To achieve the above objective, firstly the limit of 25 of the basins and alluvial fans by using the maps, aerial photography and with help of software GIS were identified. And using some geomorphic indicators the effective processes were analyzed . the used indices in this study are as the following: The ratio of valley floor width to Valley's depth (Vf), Gradient along the river (SL), Basin shape ratio (BS), Topography symmetry Factor transverse (T), Catchment asymmetry index (Af), Mountain front sinuosity (Smf), Mountain Front Alignment of indicator shrinkage (Fd), Integral index over the facade (Hi), and Iat index which provides an average of the results of the above indices. The results of the study indicate that 71.5 percent of the indexs introduce the region from tectonic point of view as active up to semi-active region. This issue is showed also in Iat index that is obtained from other indicators.On the basis of this index, 4% of the areas (West Sarough) have a very high active tectonic condition 56% of basins have high tectonic condition And 40% of areas have a medium tectonic condition.So all indicators confirm the role of tectonic factors on the development of alluvial fans. In addition, the emergence of relatively large alluvial at the end of some small basins confirm this issue. After this, the effect of common factors including litho logy and tectonic with respect to the nature of active faults in the region can be mentioned, Including the active thrust faults that thrusting soft sediments and marl Pliocene and Eocene flysch units on the hard and Pliocene conglomerate. And has had a great impact have on the provision of sediment and development of alluvial fans in this area. In addition, in some cases through creating blocking hills, divert the main channel of the river from its previous path And has created multi-sectoral , asymmetric and sliced fans. Thus it can be said in the development of alluvial fans of the area, tectonic factor is the most important one and then is the litho logical factor And the study findings show that there is a high correlation between the feedign basin area with the alluvial fan areas.