نوع مقاله : مقاله پژوهشی
عنوان مقاله [English]
Longitudinal profile morphometry of the mountain valleys, provide a numerical and quantitative indicators for researchers of geomorphology to draw form-processes conclusions from the morphological evolutionary state of mountainous units. Morphological Behavior of the valley’s longitudinal profile, could be a sign of predominant processes and their interactions with topography.13 valley’s basins in mountainous area of Sahand (Western Azarbayejan,Iran) were delimited with a homogenouse lithology.To homogenize criteria in different valleys, each basin outlet was bounded at the absolute height of 1800m. In each valley, main drainage paths, were drawn using Arc Hydro Model (V.2). Coordinates of the location of each point on these paths (Longitudinal profile) were extracted from digital elevation model and python programming languge was used to make it automate. In this research five Low-level (Geometric, Topologic), twenty Mid-level (Statistic, Topographic), and four High-level (2L-3L.R, P.C.I, C.C.I, E.R.R) morphometrical indices were used and run.The Percent of profile concavity (P.C.I), shows that longitudinal sections which are located in the northeast hillside of Sahand mountain has a higher level so that is a sign of more concavity ratio and thus more profile evolution.The profile concavity index (C.C.I) has also similar trends. Elevation Relief Ratio (E.R.R) and 2D to 3D length ratio (2L-3L.R) shows a higher levels in the southwest hillside. Eventually, under consideration of these four morphometric models, it’s possible to observe clear differences in the evolution of longitudinal profiles which are located in the north to northeast hillsides of Sahand mountain in comparison with south to southwest part of this mountainous unit, which is corresponded perfectly with sunny hillside and slopes located in the shade.
Geomorphometry is a scientific branch on the basis of measurements, computational geometry, topography and morphology of the earth's surface and their temporal deformation. Geomorphometry is a quantitative analysis of the earth's surface. Geomorphometry is a quantitative analysis of the earth's surface (Pike,1995,2000a: Rasemman et al., 2004). Digital Elevation Model (DEM) is used as an input for many geomorphometric models. Many researchers of geomorphology had studied in the field of morphometrical modeling of geomorphological features. Some of them had studied longitudinal and profile sections of mountainous valleys, until estimates glacial and fluvial valleys and the dominant conditions of their evolutionary phases. Several different morphometrical models have been employed in various field of geomorphology included deserts, mountains, plains and costal environments. Some of them had a tectonic or geologic approaches others have a morphogenic views. But in general, almost all of them are using mathematical, geometrical and physical equations and relations for investigating land surface phenomena.
In recent study, Digital Surface Models(DSMs), published by the Japanese Space Agency in May and October 2015, in 30m spatial resolution were used. This data is extracted from ALOS satellite images. This data is based on global 3D topographic DSM data (5m grid version) which is the most accurate elevation data in the global scale (T. Tadono et.al,2014). For extracting rivers, valleys, rural and urban centers, topographic maps published by Iran National Cartographic Center (NCC) were used. Drainage basin of each valley were delimited from Digital Elevation Model (DEM), Topographic maps and Hillshade model with using Arc Hydrology model in the Arc GIS package. Then, the longest drainage path from the outlet to the highest tip of each valley’s basin was drawn in the form of vector-based geometry. Each of vector layer divided into the vertices with a high density. Each vertex has an xyz coordinate which is stored in the form of txt and ASCII file formats. Data stored in the txt and ASCII files imported into python environment and was prepared to programming with. Morphometrical modeling, measurements and progressive algorithms were automated using python, in order to morphometry of longitudinal profiles purposes. Morphometrical results are classified into three main classes: including low-level (or basic), mid-level (or prerequisite) and high-level (or advanced) morphometrical indices.
Results and discussion
Morphometrical indices shows that longitudinal profile concavity ratio is clearly different at north to northeast and south to southwest aspects in this mountainous unit. Numerical value of this index is maximum in northeast aspects and the rate is minimum at southwest part. Profile concavity and convexity index (C.C.I) has a similar trend and shows a clear difference between northeast and southwest slopes. Elevation Relief Ratio (E.R.R) has a completely different trend and reaches to the maximum and minimum values at southwest and northeast slopes respectively. The ratio between 2D and 3D longitudinal length shows a higher value in the northeast slopes or generally northern slopes.
In this paper, longitudinal profile of Sahand’s valleys were modeled using 4 morphometrical indices (Including: 2D to 3D length ratio, profile concavity, Concavity and Convexity Index, and Elevation Relief Ratio). Results gotten from Profile Concavity Ratio show higher values of longidudinal profiles located on the noertheast valleys of sahand mountain, which suggest more morphological profile evolution. Concavity Index shows similar trends. Both Elevation Relieaf Ratio and 2L-3L.R have a higher value in the southwest slopes. with taking into account these 4 advanced morphometrical models, recognizable differences in evolution of logtidunial profiles of north to northeast slopes in Sahand mountain were detected. With regard to the fact that quaternary glaciation played a major role in the main mountainous unit of Iran, glacial and subglacial process had played a recognizable change on mountainous area especially the height above 3000m and higher latitude bands. Because of high latitude (near 37 Degree) and elevation (more than 3600m), Sahand mountain was affected by glacial and subglacial erosion. In the higher latitude bands, because of more winter inclination angle, southern slopes recive sunlights in a wider angle and so there is a difference between northen and southern slopes from the view point of radiation energy absorbtion. Eastern slopes have a lower radiation energy campared with western one and thus leaded to the less energy balance. Furthermorem, north and northeast slopes of the Sahand mountain are in the vicinity of Caspien sea water body, so it had received more precipitation during glacial phase in relation to Siberian cold wind. Despite of being young and having igneous lithology, Sahand mountain shows morphological evidence of glacial and subglacial evolution of longitudinal profiles due to the favorable climatic condition such as enough winter snow. These morphometric indicators are perfectly adjusted to the slope aspects and morphological changes are synchronized with glacial and subglacial process. Finally all these morphometric indices programed and designed in python Tkinter GUI programming enviornment and a GIS toolkit named Longi-Profile Analyzer V.1 prepared fundamentally for longitudinal profile analizing.