نوع مقاله : مقاله پژوهشی
نویسندگان
گروه جغرافیای طبیعی، دانشکده علوم زمین، دانشگاه شهید بهشتی، تهران، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction: Investigating the geomorphology of glaciers and the changes in their past climatic conditions is one of the major topics of mountainous territories. This research has been done to investigate the evidence of glaciers in the past climate of Kona Goorg valley in the northwest of Piranshahr by using field observations and laboratory work and reconstruction of temperature and precipitation. Also, the identification of the sequence of new and old terraces in this area and their comparison and correspondence with the terraces of the Zevka river, the main branch of the Little Zab river, have also been investigated.
Materials and methods: The data used in this research included topographic maps, Landsat 8 images, climatic data, field observations and sampling. The studied area and elevation data were measured and extracted from 1:50000 topographic maps and during repeated visits with GPS. The stages study were include of field operations, sediment samples from the Kona Goorg valley and photographed, collection of rock samples, completion of field data and evidence of glacier activity in the Quaternary.
Results and discussion: The results obtained by Porter's method, the snow-boundary area of the region is 2563.6 meters, and with the method of the maximum height of lateral moraine, the height is 2571 meters. The temperature and precipitation anomalies are 6.45 degrees Celsius and 233.8 mm, respectively. XRD test showed that chlorite and illite minerals are the most abundant in the surface sample and kaolin mineral is more abundant in the deep sample. Glacial evidences include the side moraines are stretched up to a height of 2272 meters. The glaciers in the form of new terraces, which are probably related to the Wurm period, are located on both sides of the valley at a lower altitude, and the old terraces are located at a higher altitude (2606 meters) with a difference of 60 to 80 meters from the valley floor. The northern valley of the region extends to a height of 2720 meters and the southern valley to a height of 2686 meters and has preserved its U-shaped shape to some extent. One of the main property of Kona Goorg cirques is its elongated shape. Three alluvial terraces have been identified on the edge of the river.
Conclusion: In general, evidences and effects of glaciers related to paleoclimate in the study area show that the study area was affected by glacier activity in the late Pleistocene and even in the Holocene. The remains of terraces and glacial drifts at lower altitudes than the glacier cirques show three cross-sections of slope change, which in some slopes are cemented glacial deposites in the middle of piles of new moraine, it has an exterior. The granulation and XRD test of the glacial sediment samples together with the reconstruction of temperature and precipitation is indicative an increase in precipitation and a decrease in temperature in the past compared to the present.
کلیدواژهها [English]
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