Estimate of Snow-line in the past Glacial in Dalakhani Basin


Shahdi Beheshti University


1-Introduction The expansion of permanent snow-line in glacial period left behind its evidence as cirque, valley wide, polished rocks and Moraines in low land. As considering climate zones as elevation level, the height express geomorphic system and dominant erosion processes. The goal of this research is to determine snow-line in last glacial period at Dalakhani Basin, Northeastern of Kermanshah. Area of the basin is 819 square kilometers and Songhor city is located in the basin. Minimum of its elevation is 1500 meters and the maximum is 3300 meters. 2- Methodology The materials we used include Topographical map (1:25000) and (1:5000), geological map (1:100000), elevation data of Aster, field research. At first, the cirques were detected based on field research and Topographical map. Then snow-line in the last glaciation was determined by using Wright method. Isotherm map of the last glacial period was provided by using regression of temperature and elevation and the height with 60 percent of the cirques. Sediment samples from the area (six sites) were used to calculate granulometry, deposition parameters and microscopy analyses. Statistics parameters were calculated by Folk method and microscopic studies on thin sections of sediments 1 mm to .063 micron was applied for tracking the source. 3– Discussion The result was shown that the glacial domain was located upper than 2820 meters in the last glacial period. The mean temperature of the domain is up to 5.38C at present, so the mean temperature was -5.38C at the last glacial and in winter it has probably been more reduced that caused the glaciers to create a variety of erosional land forms. The high percentage of the samples with angled deposition which despite their transport by water the angles have not been rounded because of low distance and it expresses the glacial origin. Cumulative curves obtained from the granulometry of the samples were drawn for coarse particle and the Sorting indicators of the granulometry were more than 1 so they indicated the combination of large and small particles in the sediment. Microscopy of thin sections shows about 70-40 percent angular particles. The roundness of most particles was poor. Due to the accumulation of sediments in the position and location of samples, the angled sediments do not show aeolian origin. Accordingly, the assumption that physical weathering due to lack of contact with the destruction processes such as daily temperature difference is not acceptable. The areas below the snow-line has expressed that they has received more rain in the glacial period and flood flows moved the sediment and deposited them in lower elevations on which some cities such as Songhor are located. Thus, according to the results of the granulometry that represented sorting poorly and also Microscopic result that it was calculated to have a high angular percentage of deposits, it was possibly with Glacial origin. The sediments were moved to lowland by the floods preglacier. Transport in short distances did not have enough time to eliminate the angles by the current flood. Thus climate change and the subsequent evolution of the system were acted in the region. 4– Conclusion Dalakhani Catchment with an area of 819 km and elevation ranges between 1,500 to 3,300 meters has recorded evidences of glacial periods as small or large cirques and U shape valleys. The results showed that the maximum evidences were located above 2820 meters. The elevation is the permanent snow-line in last glacial period, which the average temperature is 5.38 degrees Celsius at the present. In other words, the average temperature at the last cold period in Dalakhani basin has decreased by 5.38 degrees Celsius. Other researches have showed lower elevation on snow-line and temperatures in the same conditions probably due to the orientation of slopes in front of wet air mass and the sun.