جستجوی مقالات مرتبط با کلیدواژه "eastern alborz" در نشریات گروه "جغرافیا"

The identification and analysis of the active tectonic or denudation processes through the analysis of the deformation and landform changes consist one of the fundamental objectives of the tectonic geomorphological studies. Rivers are among the groups of geomorphologic elements that flow on a wide range of different landforms and can reveal the critical relationships among uplift, lithology, and denudation of heights. With regard to the evolution of landforms, this group of information and the relations between them are preserved by the bedrock properties. River Incision is the primary mechanism by which landscapes adapt to climate change and tectonic forces. Among the many factors that affect the Incision rate, the distribution of slope and steepness of water channels can be systematically effective. The main purpose of this study is to investigate the sequence of mountainous and foothills landforms in Damghan region using slope changes and erosion-incision reaction of rivers on the surface of these landforms as one of the key factors in landscape evolution.

There are many models for calculating the river incision rate, but the most widely used is the SPIM model, which is presented in the form of the following equation:I=K*A^m*S^nThe SPIM model is based on simple geometric parameters, such as the slope and area of the drainage basin extracted from the DEM elevation map. Some parameters are related to energy considerations, such as the rate of energy consumption in the channel bed and ridges, in which case; m: 0.5 and n: 1 are used as experimental constants in the formula.In order to calculate the values of this index and prepare a river incision map, first the whole study area was divided into 64 sub-basins so that the resulting section values are suitable for surface interpolation. In the next step, the values of effective indicators in the SPIM formula including river slope, drainage surface area and erosion efficiency were calculated for each of the sub-basins. To calculate the erosion efficiency index, first the steepness values of the rivers of each basin were calculated from the formula of stream power incision, based on power regression, in the form of the following equation.S=K_s A^(-θ)In the above formula Ɵ is the amount of concavity and KSN is the amount of steepness.After obtaining the steepness values of rivers in each of the 64 catchments, the erosion efficiency relationship was used as follows:U=〖ksn〗^n*KU is actually the rate of elevation or change in altitude of the area relative to the base level, which was calculated using the radar interfrometry method to determine the amount of vertical displacements in the area.In order to prepare and analyze the slope and incision rate of rivers in Damghan region, and to convert point values into raster levels containing value, the inverse distance weighted interpolation method or IDW was used.

Comparison of longitudinal profiles taken from the slope map and incision rate of Damghan region shows the close relationship between these two parameters; Both of these parameters together play an important role in analyzing the tectonic status of the areas. In such a way that in examining the condition of the longitudinal profiles of the region from north to south, there are prominent features such as mountain belts or foreberg shapes; The slope rate and incision rate of the river increase and in front of where there are depression constructions such aspull apart basins or the end parts of longitudinal profiles that are based on alluvial plains, the slope rate and the following incision rate of the river decreases.Therefore, the analysis of longitudinal profiles taken from the slope map and incision rate of rivers in Damghan region can be effective in identifying and analyzing the effect of active fault mechanisms on the sequence of landforms in the region. the areas that have mainly high slope and incision rate of the river and are shown prominently in the longitudinal profile, represent the performance of faults in the form of transpressional, which leads to the formation of elevated landforms. In contrast, the concave areas in the longitudinal profile of the slope and incision of the rivers in the region are mainly representative of the areas where the gentle slope has led to a reduction in the slope of river systems and thus reduced river incision capacity.these areas are either mainly based on flat lands which are in the southern part of mountain structure in form of alluvial sediments or they are collapsed structures due to transtentional motion of faults such as Astaneh pull-apart basin.

The activity of faults with different mechanisms causes the uplift or subsidence of landforms to form a series of successive landforms in an active tectonic environment. The rise and fall of these structures have led to an increase or decrease in their slope which will effect on the waterway systems that flow on these landforms. Wherever the fault mechanism leads to an increase in the height and elevation of the landforms, the slope of the river increases and as a result the incision power of the river increases. From the analysis of longitudinal profiles taken from the slope map and the incision of the river, it can be concluded that this method is very useful in identifying the sequence of landforms affected by tectonic processes. In a way, by examining the process of changing these longitudinal profiles, we can understand how active faults function in shaping landforms in compressive or tensile form. Wherever the slope of the waterway is high and the incision rate of the river is high, it indicates the existence of a elevated axis. This landform can be a mountain ridge or even elevated forms among alluvial sediments.wherever the slope and incision rate of channel show low values, it can indicate the existence of a concave tectonic basin.

Landforms and their response to environmental changes is one of the most interested topics among geomorphologists. One of the landforms that is most affected by tectonic and erosion processes is the rivers. Rivers respond to tectonic processes that increase the height of landscapes and erosion processes that try to reduce the height of landforms. This reaction can be well studied by analyzing the longitudinal profile of the rivers. One of the effective parameters in the study of tectonic and erosional status of regions is steepness and concavity. These parameters can be examined in the form of Stream Power Law (SPL). This function is related to incision power of streams.This relationship in the form of the linkage between slope and drainage area of the river in a logarithmic plot based on power regression, extracts the values of two parameters, the steepness and the concavity of the channel. In fact experimental studies by other researchers have shown that there is a direct relationship between rivers steepness and concavity with tectonic – erosive processes in the regions. It generally accepted that steep landscape are associated with areas of high uplift rate and active tectonic. Rivers system are well adopted to tectonic processes to provide useful information about the rate of uplift in landforms. The steepness of rivers which depends on the declivity of channels is fraction of uplift rate. So we expect that if the amount of the steepness in the longitudinal profile of the river is low, the uplift rate is slight too and if the steepness is high, the uplift rate is intense too. Concavity index usually depends on bed material. But erosion efficiency has direct connection with incision power law and its steepness. But weakness of bed material especially alluvial can increase rate of erosion efficiency in channels. Erosion efficiency is the volume of sediment that is completely removed from the environment after erosion. Erosion efficiency is a function of sedimentary flux. This parameter can be directly related to the tectonic processes and characteristics of the bedrock. If tectonic processes lead to an increase in the height of the landforms, it can increase orographic precipitation in mountainous areas, and it can lead to increasing sedimentary flux, then erosion efficiency also increases. The main purpose of this study is to analysis the effect of active tectonic and erosion on equilibrium profile of the main rivers of the Damghan Mountain based on the Stream Power Law. These steepness and concavity parameters are influenced by set of lithological, geological, topographic and erosion factors. All of these factors are effective in location of knick points of rivers and are able to provide useful information about the geological and erosion status of the area

In order to investigate the power incision law, the DEM map in 30m resolution was used to extract the channels. For extracting the rivers, the D8 algorithm method was used to calculate the flow direction. In this method, the flow path of each pixel that fall on the lower pixel with a lower slope was calculated and the flow directions was determined. In this regard, we first need to create a DEM map with the least inconsistency. This method focuses on extracting central flows in valleys and reducing parallel flows. After extracting the channels, their slope-area logarithmic diagram were plotted. The regression line considered for the logarithmic plot is the power regression, which is the relation of the river incision power. In this regression, the slope of the regression line is concavity and the intercept of line is steepness. To obtain information about lithological features of the area that are effective in analyzing the concavity and steepness parameters, the geological map of Damghan and Shahrud was used. The study area is part of the mountain structure of Eastern Alborz and has several active faults. North Damghan Mountain is located on the southern side of eastern Alborz between 36。14'0.3" to 36。18' 82" and 55。00' 26" to 53。59' 56" in north of Iran plateau. There are different outcrops of lithostratigraphic formations from Precambrian to Quaternary in this area. Geologically speaking, the study area is composed of set of over thrust blocks and nappes. The thrust faults and nappes within piggy back style have pushed eastern Alborz stratigraphy sequences on each other. The folds in the region have a strong connection to thrust structures and nappes. These folds are of different types and sizes but most of them are inclined and recumbent because of widespread compressive component in eastern Alborz.

The three main rivers of the region, CheshmehAli, Astaneh and Tepal, were studied. All three rivers flow on the colluvium bed in the upstream and alluvial bed in the downstream. And all three affected by faults in some areas. Some such as CheshmehAli River in the southern part, has flowed into a fault valley. The activity of faults along the rivers, both in the resistance and alluvial parts has led to uplift of the rivers. These effects are seen in the high values of steepness index and low values of concavity index. The increase in the stream incision is seen in both the upper and lower section of the rivers due to the activity of faults in the region. But the steepness is higher in the upstream which is made of colluvium sediments. While in the downstream due to weakness of alluvial sediments the rate of erosion efficiency is higher. Therefore the change in the rate of steepness, concavity and erosion efficiency, in addition to active tectonic, is strongly affected by the bedrock of channels. Each rivers that is most faulted also has higher values of the steepness index. CheshmehAli River, part of which is located completely in the faulted valley, has the highest rate of steepness compared to other rivers. The Astaneh River has been affected by the Astaneh fault in several parts, and the fault has led to the uplift of the river by cutting off the Quaternary sediments. The high values of steepness parameter in this river confirm existence of active tectonic. The Tepal River in its upper part shows high values of steepness parameter, but in the downstream part where the river flows on agricultural lands, the rate of erosion efficiency has increased and in contrast the rate of steepness parameter has decreased. This is due to human activities that have caused the rate of erosion to exceed the rate of tectonic processes. Therefore, human activities are able to transform the relationships between internal and external processes that are effective in changing landforms.

The results show that reaching the equilibrium profile in each river depends on a set of factors include erosion, tectonic and lithology. Fault in the channel path leads to an increase in the height and slope of the river channel and erosion accurse in response to this change. Tectonic processes increase the incision capacity of rivers as a result of increasing the slope of the channel, which increase the volume of sediments produced in the river. Of course, like that Tepal River, we must consider the role of human activities in increasing the rate of erosion efficiency. Key Words: Eastern Alborz, Damghan, Active Tectonic, Morphotectonic, SPL Model.

The present study carried out to identify neo tectonic activity of the Gorgan River basin in Golestan province، in North of eastern Alborz range is investigated by four geomorphic indices including the stream– gradient index (SL)، drainage basin asymmetry (Af)، reveres symmetry of topography (T) and mountain front sinuosity (Smf). Result from the analysis is accumulated and expressed as an index of relative active tectonics (Iat)، which divided into four classes from relatively low to highest tectonic activity. The high class values low tectonic activity for Iat mainly occur in the south and southwest of the Gorgan River Drainage Basin، while the rest of the study area has classes of Iat suggesting moderate to low tectonic activity. The results of this study، show that high values of T-vectors are related to Gorgan River are resulted from Caspian، segments of North Alborz and Khosh yeilagh faults activity. In this area increase trend of tilting collimate with faults can be reason the existence of an active tectonics region in the west part of the eastern Alborz. Other results of this study show low Smf and high SL values. The rate of tectonic activity in this area will increase from north to south. This increase can be related to the position of peaks stream length-gradient index along the fault and segment fault. Also value of drainage basin asymmetry is calculated for all of the sub catchments greater or less than 50 that shows tilt for each stream toward West or East. Length of the T- vector in eastern Alborz proportionate with measure of tilting and class of active tectonics. On the other hand، other results of this research are high levels of tilt and drainage basin asymmetry. The results of the review to propose the relative active tectonics index in the region، represent areas with focus on low tectonic activity in the central part of Gorgan Drainage Basin، while other areas have moderate to high categories were tectonic activity which indicates the study area is neo tectonically active.