naser mashhadi

The study of dunes morphology provides a valuable tool for investigating wind systems and the identification of sand sources (removal region). The wind direction is the primary factor controlling the dune shape and elongation. In deserts jubject to wind from different directions and with comparable magnitude, dunes are formed having different morphologies. The sand dunes are either perpendicular or parallel to the wind direction. The purpose of this study was to analyze the morphology of sand dunes under bimodal winds using conventional models. Observations showed that the linear (seif) dunes formation are due to the elongation of a barchan horn. These dunes are created by a bimodal wind regime with a strong peak from the result of northwest and west winds and a weaker peak from the east winds with a divergence angle of 135°. Sinuous crest lines of seif dune grow directly by west and east winds. The study showed that the evolution trend of the sand dunes of the region, under the strong northwest wind, first shield dune transforms into a dihedral barchans. At this stage, wind erosion on the back of the sand pile (shield dune) leads to the formation of a crest perpendicular to the wind direction and then to the formation of a slip face downwind. According to the effect of the magnitude and change of direction in the Westerly and Easterly winds, the western wing of barchan begins to extend and turns into a dentate seif dune.

The aim of the paper is to assess the morphological characteristics, mobility, and distribution of sediment particle size as maturity indicators of young dunes. The results indicated that according to the Equivalent Sand Thickness (EST) parameter and the wind direction variability parameter, the morphology of the sand dunes was determined as linear. The climatic index of sand dune mobility using meteorological data of Qom, Kashan, and Ardestan synoptic stations in a 27-year period showed that the sand mobility index (M) for sand dunes is 210, which is in the range of fully active dunes. The Grain Size Distribution and the scatterplots diagrams of sorting, skewness, and kurtosis versus the mean size of particles in differentiating the types of sand dunes showed that the relationship of sorting and skewness versus the mean size is effective in showing the dune's mobility. Sediment grain size parameters can be used as an indicator for transport environment and spatial changes. The studies of this research showed that based on grain size characteristics and climatic index, the sand dunes are the simple linear type with full activity. The transport environment in the dune sediments of the upwind sector is more energetic than the dune sediments of the downwind sector

The desert environment is aeolian, being dominated by the wind. The dynamics of wind erosion are driven by both natural processes, including climate and its fluctuations, and human activity. Separating the climatic and anthropogenic causes of wind erosion can improve the understanding of its driving mechanisms. The aim of current research is to evaluate the spatio-temporal dynamics of the aeolian process based on the sand dunes morphology and the analysis of the spatial correlation between wind erosion dynamics and climate fluctuations. Based on meteorological, remote sensing and field observations data, the impacts of climate fluctuations on the temporal and spatial changes of the aeolian process were evaluated according to the indicator of the creation and expansion of sand dunes .MODIS remote sensing data was used to study the sand dunes morphology. The temperature, precipitation, wind speed and other meteorological data used in this study were all derived from two synoptic stations of Qom and Kashan. The analysis of the elongation and form of the sand dunes as the wind direction indicator showed that the studied area is affected by the winds region of the Qom (northwest and west). The results of climate studies showed that over the last 27 years, the region has a rising temperature trend, while the average precipitation in the region has decreased in the same period. The relationship between drought conditions and aeolian process showed that the region experienced severe drought conditions more than normal or abnormally dry conditions during 1369 to 1395.

Lowlands, playas, and downstream portions  of rivers in desert areas contain vast reserves of fine-grained sediments, such as silt and clay, as well as soluble materials including a variety of salts. Surfaces created by the combination of these materials can become periodically susceptible to wind erosion. Thus,they are considered to be major dust sources on a global scale.Depending on the spatio-temperial distribution and composition of salts and fine materials, some proportions of these areas areusually either covered by an evaporite salt crust or disperedsoil.Crust is a relatively thin consolidated soil surface layer or seal that is more compact and cohesive than the material immediately below it. When crusts are formed, particles are bound together and become less susceptible to abrasion by blowing soils compared tothe less stable material below the crust. Both crusted surfaces and dispersed soils are morphologically and geochemically dynamic and can respond rapidly to changes in the local environmental conditions.These changes can be natural, such as the frequencies of surfacedrying and flooding by rainwater or the changing groundwater levels, or can be the result ofanthroponic activitiesproviding salt resources for economic use.Over time, the continued operations of both mechanical and chemical processes on lowland surfaces ultimately lead to the decay of salt crust integrity.Crusts usually provide a protectionagainstan underlying ‘fluffy’ layer of sedimentsrepresentingas salty sediments of dust-size fractions with notably low bulk densities.Wind erosion activity occurs particularly when the crust is disturbed or broken by different activities, such as  salt extraction or vehicular traffic flow.In all desert areas of Iransodium sulphate (Na2SO4) salts are deposited based on humidityand temperatureconditions, as well as groundwater levels and degrees of salt solubility (concentration). These areas usually occur between downstream of covered pediments and upstream of playas.Traditionally, these areas arevalued forsodium sulphate salt extraction,whichcontributes to the economy of the local population in several ways.The study area  was the lowland area of Ivanki, which was one of the areas undergoing wide sodium sulfate extraction. According to the residents, this area providedsand sources forwind erosion and air pollution.It was often a source of emission made by the existingmaterials not only because of wind erosion, but also due tosodium sulfate extraction.This paper investigated the effect of sodium sulfate extraction on creating or exacerbating wind erosion through a collection of sediment samples taken at the sodium sulfate extraction site and their grain-size testing.

The sodium sulfate extraction sites were identified based on local information and interpretation of satellite images. The areawas located in the southwest of Eyvankey City between covered pediments and internetworks of playa.It occupied an area of approximately 5000 ha. The sampling points were identified based on geological and geomorphological studies.SThe sampling wascarried out at the summer season.  4Four sites were considered for sampling;two sites asthe control sites and two sites forsodium sulfate extraction. In the control sites, only one sample was taken from the topsoil (natural land) without manipulation and extraction, whilethe samples in the other two sites were taken from 3horizons: a) soil samples fromthe degraded surfaces; b) samplesoriginated fromthe extraction horizon; and c) samples from the lower layers (without manipulation and extraction).Thus, 8 samples were totally collected.The obtained samples were granulated by the common dry-sieving method.Granulometric statistical analysis wasdone for each sample by using GRADISTAT software. 

According to the ambrothermic diagram, drought conditions prevailed in the region for about 7 months of the year. This drought couldthe aggravating wind erosionparameters, such as soil moisture and vegetation cover. The warm period corresponded to the warm seasons (spring and summer).Anemometer measurements showed that the study area was affected by erosive and strong winds blowing from the north, northwest, and east.Land cover studies revealedthat more than 60% of the soil surface in the control samples was preserved by the crust with particles larger than 2000 microns. However, after crust destruction for sodium sulfateextraction, the effect of crust cover was less than 45%. In other words, the soil surface lost 25% resistance to wind erosion.In the process of sodium sulfate extraction, the soil under the crust, which contained soil particles, along with a significant amount of powdered sodium sulfate particles, was exposed to wind erosion.Our studyshowed that the frequency percentage of vulnerable particles changedfrom about 10% in the surface layer in the control samples to about 50% in the middle and lower layers of the extracted areas. This meant that the region was about 5 times more sensitive to wind erosion.Studies on the statistical parameters of the samples demonstratedthat the average particle diameters significantly and regularly changed from very coarse sands (surface layers of the control samples or natural lands) to coarse sands (degraded surface layers),fine sands (middle layers), and finally very fine sands (bottom layers), which indicatedincreasedsensitivity to the wind erosion process from the surface layer (crust) to the bottom layer. 

In this research, field observations, mechanical analysis of soil particle granulation, and investigation of wind characteristics showed that a very high potential ofdust emission from degraded crusts triggered by open extraction. Spatial changes and displacement of removal areas caused bysodium sulfate reduction duringthe extraction periodled tofurther environmental destruction and wind erosion intensification. The results revealeda significant complexity in the relationships ofthe flux of dust emitted from thecrust degraded by sodium sulfate extraction and natural surface crust withthe threshold wind speed required for wind erosion, which suggests furtherresearch to be conducted in this regard in the future. Keywords:sodium sulphate, wind erosion, evaporative crust, granulometry, soil conservation .

Due to the intense and unprincipled changes in land use, it is necessary to detect land cover/use change over time using satellite imageries for sustainable land management. This study aims to monitor land use and land cover changes, model and predict their status in the next 15 years in Jagin plain, Jask coastal desert. In this study, Landsat satellite images of 1987, 2003 and 2018 were used to detect changes. After applying geometric and atmospheric corrections on the images, land use maps  of each year at 11 land use /land cover classes including farmlands, aquaculture, erg, halophyte, mangrove, habitable zones, nebka, vegetation affected by water flow vegetation (rangeland), bare lands, were prepared using hybrid classification method. The Markov chain forecasting model was used to validate the model in the first stage, and was used in the second stage to predict land cover/land change in 2033. Comparison of the simulated map of 2018 and the real map with the Kappa coefficient of 83% confirmed the capability of the Cellular Automata Markov Chain in predicting of land cover/land changes. According to the results, in 2032, agriculture lands in the region will have an upward trend and grow by 74% compared to 2018. Habitable zones, marine access network and aquaculture lands will also increase during the study period. In the study area, vegetation and riverbed vegetation areas show a downward trend and will mainly converted to agricultural lands. Sand dunes, which are among the main threats to people and mangrove forests, will be extended by 2032, threatening the southern part of Sorglam village and the eastern part of the mangrove forest.

Sand and dust storms occur when unchecked, strong or turbulent winds combine with exposed loose soil dry surfaces. These conditions are usually exacerbated by human activity and land use change in semi-arid and arid regions. The Damghan region, due to its geoecological structure, has created a special features in the arid region on the closed basin of Haj Aligholi. At present the ecosystem balance of the region is affected by anthropogenic exploitation and wind activities. The aim of this study was to investigate the priority of sand resources in the aeolian process. In this study, we were compared the composition and variations of grain size in land natural units (landforms) and human activity - based units (Landscape). In each unit of sand source were taken soil or deposit samples. The results of granulometry show that Agricultural Land Unit contain more than 60% of particles larger than 2000 microns; As a result, this unit is more resistant to wind erosion than other units. Whereas, this value is about 15% for the most sensitive landforms (alluvial plain with water erosion). On the other hand, the granulometry results of particle below 2000 micron indicate that Agricultural Land Unit contains the most vulnerable particles to wind erosion. This means that agricultural land has a high potential to provide sand resources in the process of wind erosion.

Over exploitation of natural resources during recent years has led to the intensifying of desertification phenomenon and hence serious determination is required to deal with it. This study aims to identify the adverse factors in desertification intensifications in Shekarouye using IMDPA model in order to undertake preventive and managerial measures.  To this end, four criteria of soil, vegetation, climate and water were selected each having further sub indicators. Weighted average of each criterion’s sub-indicators and the four criteria, respectively led to the composite value of each criteria and total desertification intensity. Total desertification value was classified into four classes of negligible to low, moderate, severe and very severe and the related maps were prepared. Results showed that vegetation criterion with the value of 2.66 (very severe) and water criterion with 1.9 (moderate), respectively were the most effective and negligible criteria in intensifying desertification. Water electric conductivity with 3.11 (severe) and water sodium absorption ratio with 1.1 respectively had the highest and lowest impact on desertification. Total desertification measured 1.6 (moderate). Of the total desertification area 20310.45 ha (56.81%) and 15436.78 (43.18%) respectively fell into the moderate and negligible to low classes.

wind erosion process is the most significant geomorphic processes in many of the earth's arid region that influences the landforms and landscape features according to the action of either erosion or sedimentation. The Damghan erg in the north of Iran (covering an area 4375 ha) is found in the east of the Haj ali gholi closed basin. Fixing all of the sand dunes of the erg have been carried out since 1971.The removal region of the erg occupies a special position in the Damghan region, because the geocompnents permit various possible forms of agriculture exploitation. In recent decades, due to the advances in technology on groundwater harvesting, large areas of the removal region have been developed for land use changes. So that the changed area where increased to more than10784 hectares in 2009. It is evident that such extensive changes has considerable influence the natural balance of the aeolian processes. So that, temporal and spatial variation occurs on Sediment availability. These variations have resulted in a considerable increase in formation and height of the new sand dunes of between fixed older sand dunes. This paper is an attempt at explaining the influence of various land cover change affects in removal region (aeolian process) on the development and morphological characteristics new sand dunes.

Wind erosion is one of the most important natural processes in arid and semi-arid areas, occurring as a result of erosive winds. Wind speed, frequency and duration should be considered in studies related to wind erosion. Kashan Erg is one of the most important sand dunes complexes in Iran. To study the relationship between the wind characteristics (Uni- directional index, windness index, wind duration and frequency) with Erg morphology and also study the changes of sand flow rate in various regions, anemometers data were obtained from synoptic stations of Kashan, Ardestan, Jangalbani Badrod, Garmsar and Qom. Then, the interpolation map of sand transport and interpolation map of average and maximum wind in Kashan Erg were drawn using GIS software. Finally, the analysis results showed that the interpolation map of sand transport corroborated the results obtained from interpolation map of average wind, because sand transport rate and average wind speed were reduced from east to west of the Erg. Therefore, it is found that wind frequency and duration have more important role in the sand transport and morphology of the study area as compared with the wind speed. In addition, the comparison of Erg morphology and anemometer results in different stations showed that the spring and summer winds had the highest role in the Erg morphology.

The presence of Damghan Erg in West of Damghan Playa indicates high wind activity in this desert region. Due to technological advances and population growth in recent decades, large parts of past land uses have changed. These changes can exacerbate wind erosion and affect lands sedimentation. In this study, first, the land use maps of years 1974 and 2003 were prepared. The comparison of these maps shows that a significant area of rangelands have been converted to agricultural lands. Also, part of the agricultural lands has been converted to residential and industrial lands and a small area of ​​agricultural lands has been dilapidated. The soil or surface sediment were sampled in three treatment as old agricultural lands (that they have preserved their use), new agricultural lands (that they were formerly rangelands) and ranelands (with five replications). Soil particles grading have been studied by sieves of 2000,1180,600,250,150,75 and less than 75 micron based on the weight and frequency percent of each particle size class and indicators of particle (diameter mean, skewness, sorting and elongation) were specified using software GRADISTATE. At last, land sedimentation assessment was identified based on the abundance of particles with a diameter less than 2000 micron (susceptible to erosion). The results have been prepared as 7 maps that they express region sedimentation in each particle size class. Particles dispersion map with diameter larger than 2000 micron indicates stable particle dispersion against wind erosion and other maps show unstable particles dispersion. Comparing the land use map with particles dispersion maps show that the most unstable particles dispersion is in rangelands, the least dispersion of them is in agricultural land and rangelands have more sedimentation than the other treatments.

Nowadays, desertification is one of the ecological crises of the world. To control Desertification, having a clear understanding of its factors and processes is necessary. KALMAND Protected Area region of Yazd with area of 71269.37 Hectares’ was considered to evaluate current Condition of desertification using ICD. Iranian Classification of Desertification (ICD) was presented by M. Ekhtesasi and S. Mohajeri in 1995. First of all, available data were collected and basic studies were done. The data were entered in GIS and basic maps were produced through interpretation of aerial photos and satellite images using Arc view software. Ten desert homogenous units were separated according to the studies and by overlaying Geomorphology, land use and vegetation cover maps. In next stage, effective factors in Desertification including three environmental factors, three anthropogenic factors, soil erosion Index, resilience potential and reconstruction of ecosystem were scored in a range of 0-10. Afterward, according to the sum of scores and comparing with table of desertification severity Index, final desertification map was produced. The result showed that based on ICD models, the areas is classified into low and moderated desertification. The environmental factors were determined as the main factor in desertification. Most main criterion in desertification of this region was Soil Degradation

Grain size is one of the most obvious characteristics in many studies of Aeolian erosion, Ergs, moving of sand dune, etc. Comparison of Grain size and morphoscopy between new and old sand dunes in an Erg, help us to identify the sources sand and control reactivity sand dunes. This study, as first step, by aerial photography and satellite imagery attempting to identify areas were sedimented. Then Sediment samples took place from the new and old sand dunes and Sediment grain size parameters were evaluated and compared. By the statistical analysis determined that, there were no significant differences in the mean of diameter and median in new and old sand dunes. But the mean of skewness and kurtosis was shown to have difference. The mean of diameter in new sand dune is 176 µ and old one is 160.4 µ. In the old sand dunes Skewness were positive and in new one is negative. The mean of moving distance in new sand dune is less than old one. Because old sand dunes have Haloxylon plants we observe Particles less than 64 microns and greater than 500 microns. Morphoscopy compared showed that the new sand dunes have a halo form with a little roundness that indicating sediment transport by wind and old one have bright form and angular that indicating sediment transport by water.

Kashan Erg is one of the most important sand dunes complexes in Iran. It is included the most important various type of sand dunes in Iran. This study was performed to compare the granulometry of aeolian sediments in different sand dunes and also from plinth to crest of transverse dunes that located in Kashan Erg’s north. In order to determining different statistical variables، aeolian sediment sampling was conducted in different sand dunes. Then، the sample’s granulometry test was done based on dry sieve analysis. Finally، statistical parameters such as mean diameter، Sorting، Skewness، Kurtosis، d10، and d90 were determined. The results showed that the mean diameter، Sorting، d10 and d90 parameters have significant differences at the 95% significance level between the stabilized sand dunes and active ones. Moreover، it was found that in transverse sand dunes، there are a significant difference at the 95% significance level between mean diameter and d90 parameters in bottom of the stoss side and lee side.