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بازسازی برف مرزهای پلیوستوسن در حوضهی جاجرود | ||
| پژوهش های جغرافیای طبیعی | ||
| مقاله 3، دوره 43، شماره 76 - شماره پیاپی 571693، مهر 1390، صفحه 35-50 اصل مقاله (1.77 M) | ||
| نویسندگان | ||
| مجتبی یمانی1؛ علی شمسی پور2؛ مریم جعفری اقدم3 | ||
| 1دانشیار دانشکده جغرافیا، دانشگاه تهران | ||
| 2استادیار دانشکده جغرافیا، دانشگاه تهران | ||
| 3دانشجوی کارشناسی ارشد ژئومورفولوژی، دانشگاه تهران | ||
| چکیده | ||
| پژوهش حاضر با ماهیّت بنیادی، تلاش دارد تا رابطهی میان جهت ناهمواری‌ها و گسترش سیرک‌های یخچالی را بررسی و سرانجام برف‌مرزهای آخرین دورهی یخچالی کواترنری را در حوضهی آبریز جاجرود تعیین کند. سیرک‌ها، جریان‌های یخرفتی و سنگ‌های سرگردان مهمترین لندفرم‌های یخچالی و شواهد تغییرات اقلیمی موجود در حوضهی مورد مطالعه بهشمار می‌روند. نقشه‌های توپوگرافی، زمینشناسی، تصاویر ماهوارهای ETM+ و داده‌های اقلیمی دما و بارش ماهانه، ابزارها و داده‌های مورد استفاده در این پژوهش هستند. همچنین از نرم‌افزار Arc GIS 9.3 و سایر نرم‌افزارها برای تجزیهوتحلیل داده‌ها استفاده شده است. در این راستا، با استفاده از تصاویر ماهوارهای و بازدیدهای میدانی، موقعیّت سیرک‌های منطقه شناساییشده و برای بازسازی خطّ تعادل برف و یخ گذشته (ELA)، از میان روش‌های پنج‌گانه پورتر، روش مطالعهی ارتفاع کف سیرک و از روش رایت نیز برای برآورد حدّ برف‌مرز آخرین دورهی یخچالی استفاده شده است. برای بررسی وجود رابطه میان گسترش و پراکندگی سیرک‌های منطقه با جهت ناهمواری‌ها، از آزمون توان دوم کی پیرسون (مجذور X) استفاده شده است. نتایج نشان می‌دهد که 8/38 درصد از سیرک‌های منطقه رو به قطب و 7/24 درصد سیرک‌ها در دامنه‌های رو به استوا شکل گرفته‌اند؛ همچنین خطّ برف‌مرز وورم با استفاده از روش پورتر، ارتفاع 3072 متر و با استفاده از روش رایت، ارتفاع 3095 متری را نشان می‌دهد. برف‌مرز کنونی با استفاده از داده‌های دما و بارش، ارتفاع 3720 متری را نشان می‌دهد، درحالیکه بیشتر پژوهشگران قبلی این مرز را بالای 4000 متر تعیین کردند. | ||
| کلیدواژه‌ها | ||
| برف‌مرز؛ تغییرات اقلیمی؛ حوضهی جاجرود؛ کواترنری؛ یخچال کوهستانی | ||
| عنوان مقاله [English] | ||
| Renovation of Pleistocene Snow Line on Jajroud Basin | ||
| نویسندگان [English] | ||
| mojtaba yamani1؛ Ali Shamsipour2؛ M Jafari Aghdam3 | ||
| چکیده [English] | ||
| Introduction Since determining climate zones in the mountainous areas are considered as height levels, so researchers have more attention to get height numbers that identifies a special border of different agents erosion control. That is why, for studying development of mountainous areas, reason for studying evolution mountainous areas, researchers are trying to determine the snow line in glacier and preglacier. Jens Esmark and Jean de Charpentier (1824) for the first time have studied in basis of early discoverage and spread out the subject, which glaciers were covered a vast area of land surfaces in the past. In Iran often researchers for evaluate and simulate of quaternary climate, attentions to glaciers evidences and snowlines, biologic evidences and playa and lakes traces. The present survey with the symbolic identity is a struggle for analysis the connection between the directions of unevenness and the development of glacier cirques and at last the determination of quaternary snow line which at the present exist in the area of Jajroud basin. Methodology To this end, descriptive statistics in order to evaluate theoretical theory background of research field visits to prepare images and to control data map base and finally analytical technique has been used. According to the research goal and to achieve the desired results, areas cirque form maps, temperature and precipitation datas as the main variables of the area in determining Snow lines have been analyzed and evaluated. In this regard, the statistics of 52 stations have been used. Considering the correlation between elements of temperature, precipitation and high temperature and precipitation maps of past and present of the area was drawn. By using topographic maps, aerial and satellite photographs, field visits, the use of GPS to determine position of the cirques and about expanding morain, glacier shapes of area (with emphasis on the glacier cirques) was identified. Among the styles of quintuple Porter in order for of optimum Equilibrium-line Altitudes (ELA) and the study Cirque – Floor Method has been used, because according to Porter, the glacier that only fills the cirques its steady-state ELA typically lies not far above the average altitude of the cirque floor (CF). So using this suitable method (the study Cirque – Floor Method) is to determine the height of equilibrium line altitude in the past(Porter, 2001, 1068). From the wright method for assessing the limitation of snow line of the last period of glacier has been used. In this method by determining the site of small cirques and passing 60 percent line of them permanent snow linw is determined. In order to survey the coordination between the spread and development of the area cirques with the direction of uneven nesses, from the Chi – Square Test ( square of X) has been used. Results and Discussion Results indicate that the existences of a connection between the unevenness directions and the spread of cirques in the area have been used. In from that 38.8 present of the area cirques towards the pole and 24.7 present of the cirques in the direction towards equator have been placed. Studies show that the average height of the glacier circus floor in Jajroud basin, 3061 meters and the amount of fashion or view is 3072 meters. posing Average for Circus of poles equal to 3355 m and for the circus of the equator equal to 3567 meters. Also the determinations of the snow line with the use of Porter method at the height of 3072 meters and the use by the method of Wright at the height of 3095 meters have been shown. comparing obtained results with previous researchers comments shows that Schweizer the border of permanent snow now is now southern of Alborz approximately 4400 meters in the northern slopes of Alborz be calculated at about 4200 meters, in findings of Dreschand bobek the permanent snow line already in the Alborz from 4000 to 4200 m and in cold periods is of 3400 to 3600 meters. Zamani the snow line in the Alborz in the last glacier period using the Porter Model in 2748 meters height and using Wrights models is in the height of 2720 meters. also Eyvazi calculated The snow line in the southern Alborz range, in 4400 meters height. Conclusion Comparing obtained results with previous researchers comments shows that Schweizer the border of permanent snow now is now southern of Alborz approximately 4400 meters in the northern slopes of Alborz be calculated at about 4200 meters, in findings of Dresch and bobek the permanent snow line already in the Alborz from 4000 to 4200 m and in cold periods is of 3400 to 3600 meters. Zamani the snow line in the Alborz in the last glacier period using the Porter Model in 2748 meters height and using Wrights models is in the height of 2720 meters. Also Eyvazi calculated the snow line in the southern Alborz range, in 4400 meters height. | ||
| کلیدواژه‌ها [English] | ||
| climate change, Jajroud basin, Mountain glacier, Quaternary, snowline | ||
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