دانشگاه فردوسی مشهد
عنوان مقاله [English]
The effects of climate change in the Quaternary period, especially in glacial periods of Iran, is less-known and under-studied. Although there have been some studies on some quaternary glaciers in Iran such as Alborz, but no study has to date investigated the East and North East regions of Iran in this regard. Binalud altitudes in the Northeast of Iran are amongst the regions which have the potential for the creation of glaciers and glacial conditions due to an altitude of more than 3000 meters and being located in the pathway of cold Siberian currents, especially in the cold periods of the year.
2. Materials and methods
The aim of this study is to identify glacial evidence and determine the permanent snow line of the last Quaternary period in Binalud heights. At first, the border area was determined using 1: 50000 topographic maps. In order to create the current isorain and isothermal maps of the region, the temperature and precipitation data of the stations of Mashhad, Nishaboor, Torogh, Akhlamad, Chenaran, Shandiz, Torqabeh, Kang, Golmakan, Arsalan, Ami Abad, Soltan abad and Chakaneh were used. With the help of this data and the digital elevation model of the area and according to the correlation between elements of temperature, rainfall and altitude, the current isorain and isothermal maps were drawn in the Arc GIS software.
Then, according to the form of curves on topographic maps of 1:50000, satellite images, and aerial photographs of the region, the areas under the ice sheet and glacier Cirques that mark the rule of glacial climates in the past were determined. Also, the previous permanent snowline of Binalud Mountain was estimated through Wright and Porter’s method. Then, the isothermal map of the area in the past was obtained using the height of the snow line and the adiabatic temperature drop. In order to prepare the past isorain map, after overlaying the current isothermal and isorain maps of the area in the Arc GIS software, their correlation spot was determined and using the relationship between precipitation, current temperature and the past temperature data, the past isorain map of area was prepared. Then, through field operations, the forms created by glaciers, including glacial valleys, Cirques and moraines were identified and finally, the data were analysed.
It is worth mentioning that in order to control and gather complementary information from field works and to study the literature and various methods of studying glaciers, the library method has been employed. In general, the current study is a fundamental research in which the analytical – historical, descriptive and experimental methods have been used.
3. Research findings
The first step for following the effects of Quaternary glaciers in the mountain ranges of Binalud is the evaluation of forms based on the morphic indicators on topographic maps of 1: 50,000 and the use of satellite images. Over 39 large and small Cirques were counted on the heights of Binalud that have been distributed between 2050 to 3380 meters of height. The density of Cirques in the elevation of 2350 to 2500 meters is more than the other heights, such that about 50% of them are concentrated in this elevation. Among the important factors based on which the existence of late Quaternary glaciers in the studied area may be proved is climatic evidence. To investigate the changes in climatic elements such as temperature and rainfall, the quantitative amounts of these parameters are needed. The current isothermal map of the area demonstrates that the minimum annual average temperature in the region at an altitude of 3300 meters is 3 ° C and the maximum annual average temperature at an altitude of 870 meters is 15.5 ° C. To estimate the past ambient temperature, after determining the permanent snow line border of the area in the past, the correlation between the temperature and altitude of the station was calculated using linear relationship and its linear equation was T = -0/005 H + 19/148 . Then, using this equation, the adiabatic temperature drop of 0.62 ° C was calculated for every 100 meters. Afterwards, using the altitude of the past permanent snow line border of Binalud and its adiabatic drop, the past isothermal map of the area was prepared. The minimum annual average temperature of Binalud at the time of the dominance of glaciers was -5.8 ° C in the altitude of 3308 m and the maximum annual average temperature was 9.5 ° C at the 870 meters altitude. Comparison of the current and past isothermal maps of the area indicates that in the Quaternary period, Binalud Mountain was about 8 ° C colder than the Present. Of course, the difference has not been the same for all parts of the region and it increased under the effect of altitude, such that the maximum temperature difference has occurred at the highest part and the minimum difference is related to the lowest point of the area. Also, the current isorain map of the region demonstrates that the minimum average annual rainfall is 196 mm, while the maximum average rainfall is 551 mmm in the highest point of the region. The isorain map of area in the Quaternary period indicates that the minimum precipitation in Quaternary was equal to 369 mm in the lowest points and the maximum amount of precipitation was 832 mm in the highest parts. Comparing the current and past isorain maps shows that in the period in which ambient temperature was 8.8 ° C less, the amount of ambient humidity was significantly different from the current rainfalls. Accordingly, during the glacial period, the precipitation was observed more than twice at lower altitudes and approximately 1.5 times more at high altitudes. This amount of change in the environmental temperature and humidity, along with the existing formation of (schists and shale) the region has created fundamental changes in the area’s morphogenesis system, in a way that there are currently no evidence of the Glacier morphogenesis system.
Wright’s method which is known as one of the most popular methods for determining the permanent snowline is based on counting small Cirques and calculating the height of their output entries (Ramesht quotes Parizi, 2013, 117). Based on the Cirques counted through Wright’s method, the 60% line of the region’s Cirques was determined. This altitudinal line determines that 60% of the Cirques are located above this line. By calculating this line, the permanent snow line in the studied area during the dominance of glaciers at an altitude of 2345 meters is estimated.
Discussion and conclusion
The results of this study suggest that the minimum average annual temperature of Binalud during the reign of glaciers at an altitude of 3308 meters has been 8.5 ° C and the maximum annual average temperature of the region has been equal to 5.9 ° C. Comparing the current and past Isothermal maps of the area, it is indicated that in the Quaternary period, Binalud mountain had been about 8.8 ° C colder than the current time. Of course, the difference has not been the same for all parts of the region and it increased under the effect of altitude, such that the maximum temperature difference has occurred at the highest parts, while the minimum difference has been related to the lowest point of the area. The minimum precipitation in the Quaternary period was equal to 369 mm in the lowest points and the maximum amount of precipitation was 832 mm in the highest parts. Comparison of the current and past isorain maps of the area indicates that in the period that ambient temperature was 8.8 ° C less, the amount of ambient humidity was significantly different from the current rainfalls. Accordingly, during the glacial period, precipitation was observed more than twice at lower altitudes and approximately 1.5 times more at high altitudes. According to our surveys, about 39 glacial cirques have been identified in the area, the minimum height of which is 2100 meters. According to the results, the permanent snow line in the region is located at the altitude of 2360 meters.