عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The vast central part of Iran located in territory of desert with dry climate. Relatively flat topography, the low height, dry environments and the vast fetch was the dominant process in these areas is wind erosion. The dominant landforms of this process are concentrating of ergs across the deserts in central of Iran. In this study, the morphology of wind erosion on Dasht-e- Lut has been studied. Because the climate condition and local thermal cyclone systems play a vital role in guiding the prevailing winds and Aeolian in the Lut Depression. Therefore it seems that the current morphology of dunes is effect of power thermal convectional cyclone in Lut Depression as the hottest surface in the world. This system, guidance the wind directions in the Lut desert and this subject established of original hypothesis of research. The aim of this study are examined the wind erosion, sand transport directions and eventually the effect factors on the situation of settled the Lut erg.
The study area
Lut desert is a asymmetry depression and located in the east of Iran which is about 54,000 square kilometers. This tectonic depression has direction north to south and divided into smaller zones in divided. With regards Lut desert in Iran is low and warmest the local area, Thus, two major wind erosion landforms are very vast and it has established a unique level. The Lut erg located in east of Lut Desert and covered zones with 52 kilometers width and 152.5 square kilometers is a biggest erg mass in Iran. Yardangs also about 120 km long and about 80 kilometers width in the western half lowland of Lut desert and covered hills parallel combination of the clay, sand and salt are formed by wind erosion.
Materials and Methods
In general, this study is based on a comparative analysis. Previous studies through the research of the Library methods are collected. Much information through observation, measurement, recording and interpretation have been using of aerial photo, satellite images and analysis of them by software. Position of aeolian landforms by using the various software recorded on digital maps and profiles identified being drawn. Measurements on images of Landsat ETM and IRS have done in ENVI software. To draw the final maps and graphics figures the Freehand and Photoshop software are used. For analysis of settled of sand erg in Lut desert, the first evidence for dominant winds and dunes form the morphology of yardangs and gravel on the surface is determined. The samples barkhans indicate the prevailing winds direction for each point of the Lut desert. Then, based on the type of dune forms a range of wind directions over the Lut erg has been fitted and drawn. Finally patterns of local pressure adapted on Lut and wind directions and sand movement in the area has been rebuilt.
Results and Discussion
Lut desert in summer is the hottest location in Iran. Under these conditions, the temperature gradient in convective wind in this desert and winds blowing to high speed and sand transport very fine. To determine the direction of the prevailing wind in the Lut desert area, the asymmetric profiles of sand dunes and direction of yardangs determine the dominant wind direction. In the Lut erg there are different types of sand dunes. Distribution and morphology of these dunes can determine the dominant wind direction. In the eastern part of the Lut yardangs the barkhans with convexity of them show the northwest winds prevailing. In the shoth of yardangs the convexity of bakhans shows the west direction of dominant wind. Then, in the southeastern part of the Lut erg there are group of barkhans that show the South wind and finally in the main erg the blowing from the southeast to the northwest directions can be seen as well. These directions of blowing wind up the erg and the height of the erg in the center of the Lut between the erg and yardangs are closed. Clearly, the wind directions can be reconstructing a pattern of a low pressure system over the Lut desert.
Lut desert has a higher temperature than its surroundings. In this condition form the adiabatic climb and pressure gradient between Lut and the high mountains surrounding can be form a local convectional cyclone. The northeast winds in the surface, carried the sands on the Lut surface and carried them to the south. Eventually these particles move to northeast and deposit on main erg of lut.
If the concentric circles drawn on the territory wind erosion of Lut, three domains can be defined concentric pattern on the scope of a special resolution and restored. This convergent wind convective systems and synchronize the rotation period of extreme volatility in the central part of the Lut. During this process converges towards the center of rotation gradually climbs and sand pyramid shape in the central part of the Lut. All this is evidence of a system dominated the summer convective instability as a major factor in the development of Lut desert proves Landform available.
Key words: Lut, Thermal Cyclone, Local Convectional Cyclone, Erg, Wind Erosion.