عنوان مقاله [English]
Introduction: The start of the Quaternary period, along with all geologists and geomorphologists and other geoscientists, has been accompanied by climatic changes, in other words, the spread of glaciers in high latitudes and high ground elevations. The glaciers and glaciers of the Quaternary Mountains have eroded the lake of these areas and created numerous geophysics at different altitude levels. In the first half of the nineteenth century, Swiss geologist Luigi Agassis studied the role of natural glaciers in the evolution of the landscape. After that, glaciers were considered as one of the processes in the formation of geophysics in geomorphology. Continuous assessment of glaciers is important in terms of global warming as well as water supply downstream. The evolution and variety of geomorphic forms of the Earth's surface is affected by various morphogenesis processes that have been active over time and have created distinct landscapes.
Methodology: In this study, in order to reconstruct and estimate the snowboard of the last Quaternary glacier period in the northern slope of Sabalan Mountain, Wright and Porter Methods (altitude of circus floor and altitude proportions) were used and past morphoclimatic condition based on geomorphologic evidence and temperature and rainfall of the Glacier Vorm period (using climatic evidence and climatic condition) was estimated. To better identify and reconstruct the glacier forms in the last Quaternary glacier period at the studied area, a combination of topography maps, field observations, satellite imagery, Digital Elevational Model (DEM), images received from Google Earth and climatic data was used. By identifying 25 circuses at different altitudes and based on the mentioned methods, the permanent snow line of the studied area was determined in the last the Quaternary glacier period. The basis of the Wright method is to determine the altitude that 60% of the circuses are above it. In order to estimate the temperature conditions and to prepare the companion map of the studied area, the regression equation between temperature and elevation was calculated in Excel software. Using this relationship and the raster computation function, a homogeneity map was prepared. The regression equation between precipitation and elevation was calculated in Excel software and then, using the raster computational function, a map of the plot was prepared.
Results and Discussion: The permanent flood line of the last Quaternary glacier (Vorm) in Northern slopes of Sabalan was 3242 meters in Wright method, the altitude ratio method was 3500 meters and the circus floor height was 3473 meters. According to Wright’s method, height of the permanent snow line in the last glacial period was 3869 meters and according to Porter’s methods (altitude of circus floor and altitude proportions) 3749.32 and 4017.5 meters, respectively. After calculating the height of the Quaternary permanent snow line in Sabalan Mountain by Wright’s method (3769 m) using Digital Elevational Model, the study area was divided into two parts: areas covered by permanent snow and adjacent areas of glacier or preglacial. After calculating the height of the Quaternary permanent snow line in Sabalan Mountain by Porter’s methods (altitude of circus floor 3749.32 m and altitude proportions 4017.5 m) using DEM, the study area was divided into two parts: areas under permanent snow control and areas outside permanent snow control. To prepare the coherent map, regression equation was calculated between temperature and altitude. The height of 4066 m was estimated as the snow line of the current permanent boundary of Mountain. Reconstruction of the temperature conditions of the study area in the last Quaternary glacier period, the average temperature was estimated to be 3.68 ° C cooler than the present. Also, the regression equation was calculated between precipitation and height in order to study the rainfall and moisture conditions of the study area. With regard to the current snow depth of the studied area, rainfall is reduced by 26 mm compared to Vorm.
Conclusion: The Wright and Porter methods estimate the snowfall of the Northern slopes of Sabalan in the Quaternary, 3242, 3473, and 3500 meters, respectively. Comparison of the results obtained for the height of the current snowboard line shows that the current snowboard at study area is 197, 48.5 and 317 m higher than the last Quaternary glacier period calculated by Wright and Porter methods (altitude of circus floor and altitude proportions), respectively. The necessary condition for the formation of glaciers is 0° C and an increase in precipitation compared to the current. According to the estimated snowfall height of the current in study area (4066 m), the current precipitation decreases by 26 mm compared to Vorm and also, the past temperature was estimated to be 3.68° C colder than the current. Therefore, increasing rainfall in the studt area (26 mm) in the past along with decreasing its temperature (3.68° C) compared to the present can prove the existence of Sabalan Mountain glaciers in the quaternary era.