Studying the Stability of the Proximity and Interaction Effect between Geomorphic Systems of Alluvial and Aeolian Landforms in Petergan Playa

The natural contrast between alluvial and aeolian geomorphic systems on the western margin of the Petergan Playa creates a balanced and stable environmental condition, while human intervention in the one of these systems leads to environmental instability and natural hazard expansion. In this paper, having determined the territory of the alluvial and aeolian landforms, morphology and origin of aeolian shapes have been carried out by stepwise method and the geomorphology of alluvial shapes has been studied and classified using satellite images, aerial photographs and field surveys. The morphotectonic response of alluvial systems in contrast to the aeolian systems has been calculated using neotectonic indices. Finally, using the indices of motion, velocity, contact angle, and variations of the alluvial and aeolian landforms extracted at two different time points from the satellite images, the types of contrast and possible contact between them are determined and analyzed. According to the results, in 10 years about 11.3% of the territory of alluvial landforms has been converted to aeolian ones. Thus, aeolian systems overwhelm the region's alluvial systems. The predominance of aeolian systems has been made by diverting and blocking the flow of water and flowing over the channel shores caused by the movement of sand dunes and in many cases ponds and other channels have been created along the main channel of the river. The permanent alluvial systems in the area show stable and cyclical behavior so that the dominance of alluvial systems decreases to a certain extent during the activity seasons of the aeolian systems. The research findings show that during the 10-year period, only 1.8% of the territory of the aeolian landforms in the region has been converted to alluvial landforms. This type of contrast can be observed along the permanent river of Tajnood which passes through the sand dunes on the eastern slope of Mount Khaje.
Extended Abstract
1-Introduction
 More than 30 percent of the earth surface is covered by deserts. Although there are not many habitants in these places, these lands are mostly privileged spaces for distinctive economic and cultural activities. Development and expansion of dune hills and dune fields are the most obvious form of desertification. Dune fields are not just covered by aeolian landforms, so in present dry regions, interactions between alluvial and aoelian systems are completely obvious. The Petergan Playa drainage basin is approximately 4300 km2 in the vicinity of Afghanistan country which has a cool semi-arid climate. In this area sand dunes and fields are the most widespread. Natural interaction between these two systems in western margin of the Petergan Playa has created a balanced and stable environmental condition, while human intervention in one of these systems leads to environmental instability and expansion of hazardous conditions.
2-Materials and Methods
In this study, two groups of geomorphic forms with completely different morphogens are investigated which consist of alluvial and aeolian. The territory of the main alluvial and aeolian landforms in the region are determined, then the study of morphology and origin of aeolian forms have been carried out by stepwise method and the geomorphology of alluvial forms has been studied and classified using satellite images, aerial photographs and field surveys. In this section, based on the computation of geometrical indices of rivers, including: width, depth and ratio of width to depth, the pattern of rivers channel is studied. Morphometric calculations of sand shapes on the riverbed and shoreline and alluvial forms of alluvial fans in the area have also been carried out using aerial photographs, satellite imagery, and field surveys. In this step, considering the role of active morphotectonics in the deformation and displacement of alluvial landforms and finally sand dunes, active morphotectonic indices including: mountainous frontal sinusitis, channel pathway abnormalities and dimensionless hypsometric index have been investigated. Finally, the types of interactions between these two groups of landforms are classified according to the predominance of the activity of the alluvial and aeolian systems at the contact site. Accordingly, only six distinct class types can distinguish how these two types of landforms interact.
3-Results and Discussion
According to the results obtained in the period of 10 years, about 11.3 percent of the territory of alluvial landforms has been converted to aeolian ones. Thus, aeolian systems have the most influence on the region's alluvial systems. The predominance of aeolian systems has been made by diverting and blocking the flow of water and flowing over the channel banks caused by the movement of sand dunes; and in many cases ponds and other channels have been created along the main channel of the river. The permanent and temporal alluvial systems in the region have different behavior, interacting to Aeolian systems. These systems could dominate the aeolian systems especially in regions like Ahangaran Mountains because of neotectonical activities. According to the results obtained in a period of 10 years, only 1.8 percent of the aeolian landforms in the region are converted to alluvial landforms. The interactions of permanent rivers in the region show stable and cyclical behavior so that the dominance of alluvial systems decreases to a certain extent during the activity seasons of the aeolian systems. These interactions are observed alongside of the permanent river, Tajnood, which passes through the sand dunes on the eastern slope of Mount Khaje. An overview of the overall balance of transformations found in the activity of sand dunes and alluvial landforms over a period of 10 years indicates that this trend is positive in favor of sand dunes of more than 9.5 km2. Given the purpose of this study in examining the natural trend of desertification processes in the face of desertification, it is observed that the trend of activities of natural desertification factors in the study area is expanding. In the meantime, the trend of natural desertification factors emerging in the form of alluvial landforms relying on tectonic forces is not significant against desertification processes.
4-Conclusion
Chronological study of the depositional interaction between alluvial and aeolian systems which are created in certain landforms in the surface of the ground, presents the condition and the trend of regional landscape considering the geomorphological and ecological characteristics. Interactions between alluvial and aeolian systems and the process of sediment transition between these two systems in the studied region result in changes of one system or both systems. Climate changes in relation to the interaction of these systems can create conditions to dominate alluvial systems which can also change the condition to favor Aeolian systems. Meanwhile, tectonic changes play a role in increasing the alluvial systems' capabilities over aeolian systems. In some limited cases, the dominance of alluvial systems in the region over aeolian ones is the result of alluvial system empowerment based on tectonic changes in the region.