جستجوی مقالات مرتبط با کلیدواژه « glacier » در نشریات گروه « زمین شناسی »

The study of the past glaciers and its effects are the most important subjects of the quaternary period. The most important climatic evidence of the quaternary is also in the mountains of Iran, especially in the Alborz, west and northwest of the country is glaciers and related landforms. Geomorphologic studies focusing on glacial and periglacial landforms allow us to get a better insight into the spatial diversity of present and past climates. The Chehelcheshmeh and Saral Mountains are among the coldest mountainous regions in the country.These regions during the quaternary period was mainly influenced by glacial processes. The aim of this study was to reconstruct the quaternary snowline and morphodynamic zones based on glacial evidence.
2- Chehelcheshmeh and Saral Mountains are located 46 degrees, 28 minutes to 46 degrees and 58 minutes east longitude, and 35 degrees and 34 minutes to 36 degrees north latitude. The method of this research is analytical-descriptive and data collection method is library and field. The data used in this study includes aerial images, DEM, topographic maps and geological maps, and analysis tools including Arc Map version 10 and Gradistat version 4 software. In this research to recreate the glacier zone we used Wright and Porter methods. The permanent snowline in the Wright method is equivalent to an elevation of 60% of the cirques in the area above that height. For calculation of ELA in the method of cirque-floor altitudes, a mode has been used for classified data. For laboratory studies in this research, we used two granulometry and microscopic methods for three sediment samples. For granulometric Process, we used Seave analyzes for particle with a diameter of more than 2 mm and Laser analysis for sediment grains with a diameter of less than 2 mm. Then, based on laboratory studies and field observations (to better control and identify the landforms) and with the help of aerial imagery, the study of elevational digital model and the study of geomorphologic landforms was identified evidence of each of glacial and periglacial morphodynamic zones.
3- In the survey of the study area, 25 glacier cirques were identified, some of which are well seen by the surrounding landforms. Distribution of glacier cirques showed that the glacier extent was down to 1280 meters high. In accordance with the Porter's cirque floor altitude, the final limit of the quaternary snowline was 2483 meters above sea level, which considering the active glacier valleys, glacial evidence was also seen below this elevation. In the field observations, it was found that glacial deposits are located in the Ghezel Ozan river and at a height of 1900 meters. To determine the sedimentation environment, the results of Laser and Sieve analysis on the samples showed that the studied area is affected by the processes of freezing and melting in a cold environment by preserving plant remains and heterogeneous distribution and particles bad sorting. Maintaining feldspar minerals is another result of laboratory work, which indicates severe mechanical erosion and very low chemical erosion in the study area. The lack of clay and colloidal sediments confirms this.The glacial and periglacial morphodynamic zones in this research were studied using their evidence that was identified many of the relevant landforms including Cirques, Glacial valleys, Tills, Erratic rocks, Solifluction lobes, Rock cracking , Moraines, Avalanches and Rock steps.
4- Investigation of glacial and periglacial evidence showed that quaternary snowlines in the mountains of Chehelcheshmeh and Saral compared to the investigations carried out on the Alborz, Zagros and central iran mountains at lower altitudes. Different climate of Kurdistan mountains compared with other parts of Iran is one of the main reasons for the low elevation of snowline in the region, so that the minimum temperatures in the synoptic stations of Zarrineh Obato and Heazrkanian that located in two catchment basins in the cold seasons it is mostly critical and one of the coldest parts of the country. Sedimentological evidence and laboratory analysis also indicate a cold environment in the study area mainly influenced by snow melting processes and mechanical processes, in many instances, irregular arrangement and bad sorting are observed and coarse particles constitute the highest weight percent. In the study of field evidence, many landforms and processes were identified that, considering the distribution of glacial evidence in the present, lower boundary of the periglacial morphodynamic active zone was introduced the 2750 contour.

Of all glaciers used as indicators of climate change, cirque glaciers are probably the optimal ones to use. Due to their small size and volume, their response time to positive or negative changes in mass balance is rapidly manifested, often within a couple of years. Singh (2011: 144) suggested that this implies that a sustained negative mass balance, lasting no less than a decade, will rapidly lead to a reduction in size and vice versa. In the quaternary period, glacial and interglacial conditions have occurred in turn in the earth`s history and laid out by geomorphological evidences are undeniable that can be used to determine for snowline borders and equilibrium line altitudes and so on; for studying climate change in that period. It is possible that the reason for external processes of changing the Earth could not have completely cleared away the glacial landforms that remained from of quaternary glaciation.
Material and This research is a basic research; thus the main goal of it is the extension of the quaternary glaciation theory by data analyzing and finding relationship between mountain direction and elevation; and creation of glacier landforms. This research wants to find an answer for these questions: 1) is there correlation between glacial geomorphologic evidences in Haraz valley from altitude and distribution? 2) Is quaternary glacial border in Haraz valley in the last glacial maximum located in different altitude or not? If the answer is yes what are the causes of these differences? 3) What is the relation between volume and distribution of glacial cirques and topography and relieves direction? This research's hypotheses are: 1) Extent, volume and frequency of glacial cirques are more in the northern slopes than southern slopes this issue first of all depends on the precipitation volume. 2) The average of glacial cirques altitude and glacial terminus in northern slopes of Haraz valley is lower than southern slopes. Methods or models which are used to answer this issue can be classified in two groups: first, methods and models which are used in the main part of report, containing contour line methods, this is used to restoring the continental and hydrologic data. In the second part which is used for analyzing data, among the methods that Porter suggested, cirque- floor altitude method is selected for this research. When a glacier just fills a cirque, its steady-state equilibrium line altitudes (ELA) typically lies not far above the average altitude of the cirque floor and cirque floor altitude has sometimes been used as a convenient proxy for former ELAs. This research has been based on the comparison between cirques elevation and determination of the extension of glacial toes in the equator-faced slopes and the pole-faced ones. All data and analyses have been shown with use of ArcGIS and SPSS softwares that illustrated on the different thematic maps.
The analysis of foundation of glacial cirques in dissimilar altitudes has initiated with reconnoiter of those cirques that are located in 100-meter contour lines, and then they have analyzed with the statistical methods to obtain permanent snowline in last glacial maximum in octagonal aspects in the Haraz valley. To compare the mean altitude of glacial cirques and the altitude that there is the most frequency of the cirques, it has calculated arithmetic mean and “mode”. The results of this study showed that there is a significant difference between the observed frequencies and the expected frequency and distribution of these cirques was promoted by the mountain aspects; i.e. poleward slopes that receive relatively less energy than equatorward slopes are more appropriate location to formation of cirques and other glaciers features.
According to the calculated equations, temporary snowline is estimated 4938 m in the equator-faced slopes and 5605 m for the pole-faced ones. Based on the synthetic of statistical analysis and cirque floor altitude method, the former ELA has been 2799 m in the study area and modal value is 2706 m. The modal value in the pole-faced ones is 2874 m and in the equator-faced slopes is 2941 m.