مناطق مورفوكليماتيك و مورفوديناميك كنوني و آخرين دوره يخچالي دركوهستان بيدخوان

Recent and Relict Glacial Morphodynamic Regions in Bidkhan Mountain

شواهد ژيومورفولوژي يخچالي در مناطق كوهستاني نقش بسزايي در شناخت وضعيت اقليمي گذشته و بازسازي شرايط مورفوكليماتيك و مورفوديناميك حاكم در كواترنري پسين دارد. هدف اين پژوهش، تعيين و بازسازي مرزهاي مورفوكليماتيك و مورفوديناميك در آخرين دوره يخچالي وورم و شناسايي مرزهاي اين قلمروها در كوهستان بيدخوان مي‌باشد. به اين منظور، از روش‌هاي توصيفي و مطالعه‌ي كتابخانه‌اي، بازديدهاي ميداني براي شناسايي اشكال و درنهايت روش تحليلي استفاده‌شده است. نقشه‌هاي توپوگرافي1:25000 ، عكس‌هاي هوايي منطقه به مقياس 1:55000 سال 1334 و 1:20000 سال 1344 و داده‌هاي اقليمي دما و بارش ماهانه و نرم‌افزار Arc GIS 9.3ابزارها و داده‌هاي مورداستفاده در پژوهش هستند. در اين راستا، با استفاده از عكس‌هاي هوايي و بازديدهاي ميداني، تعداد 32 سيرك در منطقه شناسايي شد. سپس از ميان روش‌هاي پنج‌گانه پورتر براي بازسازي خطّ تعادل برف و يخ گذشته، روش ارتفاع كف سيرك براي برآورد حد برف مرز آخرين دوره يخچالي استفاده‌شده است. نتايج نشان مي‌دهد در حال حاضر مرز پايين قلمرو قاره‌اي خشك به‌طور متوسط در ارتفاع 3150 متري، قلمرو نيمه‌خشك ارتفاعات 2500 تا 3150 متري را شامل مي‌شود. بر اساس مرز برف تعيين‌شده در آخرين دوره يخچالي كواترنر حد پاييني قلمرو مجاور يخچالي 3166 متر مي‌باشد كه منطبق با برف مرز پيشين مي‌باشد و ارتفاعات كمتر از 3166 متر تحت قلمرو قاره‌اي خشك بوده‌اند.

In order to study the development of mountainous areas, researchers try to determine the snow-lines in glacial and inter-glacial periods. Bidkhan mountain is located in the southeastern part of the central Iranian volcanic belt (i.e. Sahand-Bazman zone) in 29? 35 to 29? 40 northen latitude and 56 ? 25 to 56? 30 eastern longitude. Glacial and periglacial processes were effective in changing Bidkhan mountain morphology. Here we seek the relationship between these morphological features and current morphclimatic regions and climate change . This study attempts to identify geomorphological evidence in the face of climate change and the relationship between these shapes in Bidkhan Mountain and current morphodynamic areas also climate change in the region. The preglacial forms say that most of the hereditary forms in areas outside the range of Quaternary glaciers, are the result of the cold climate. In this paper, information is associated with inherited forms of Bidkhan mountain can be used as indicators to demonstrate the preglacial conditions Material and Method Research methodology is descriptive and analytical. Data have been collected in two ways: from library to study the theoretical basis and research background, and in field to control basic maps information, and to identify landforms. To obtain necessary data for this research topographic maps of 1:25000, Landsat image Tm30m, Aerial photos:1:55000 and monthly precipitation and temperature data of synoptic station in Baft and Sirjan stations were employed. Also Arc GIS9.3 and ENVI4.8 softwares were used for image processing and analysis of spatial data.With regard to the relationship between temperature and precipitation with the present altitude morphoclimatic regions were recognized in the region , these regions were determined using Peltier(1995) Method.Cirques were distinguished using topographic maps, aerial photos and field survey. To carry out the investigation, descriptive method, field survey, and analytical methods were employed to study geomorphologic evidence of climate change. Results and Discussion In this paper we focus on glacial and periglacial processes that are major geomorphologic agents in Bidkhan Mountain. According to tempreture gradiant and Peltier morphoclimatic classification method, present morphoclimatic in Bidkhan is semi-arid and arid. Based on Topographic maps, aerial photos, satellite images and field survey , 32 cirques were recognized (Table1) in the study area. According to the results of this method, snowline was located at 3095 meter. By using precipitation and tempreture current snowline is determined at 5500 meter. Congenital features in Bidkhan Mount hillsides were identified which are the results of cold and humid climate during past times and are used as paleoclimatic/morphological indicators. Reconstruction of paleoclimate of this region was determined through literature review of the data published for this region and other similar regions in the northern hemisphere in addition to using geomorphologic phenomena. Study of geomorphological evolution of the landscape of the region showed that the geomorphological features in mountain Bidkhan has been influenced by Quaternary climatic changes at least. Average snow line by right method is 3100 meter , however current snow line is 5500 meter according to tempreture gradiant. Based on the results of snowline determination and topographic features, average snow line on the northern and southern slopes, are respectively 3220 and 3129.13 meters, which show about 91 meters difference. Moreover, about 71% of ciques are located on the northern slopes that indicates the effect of topography on the formation of glacial cirque . According to the snow line in the last ice age glaciations, glacier and periglacier processes affected the study area. This is in contrast to current climatic data which shows the study area is affected by arid and semi arid morphoclimate. Additionally, one of the important reasons for the formation of glaciers in this mountain is the volcanic features and thick debris blanket on the surface of glaciers. Consequently, the formation of glaciers at these heights has been affected by the lithological conditions, as it has been affected by the temperature and precipitation changes.