24253

GEOG2 1124

كارشناسي ارشد

ژئومورفولوژي - ژئومورفولوژي و آمايش محيط

علوم جغرافيايي و برنامه ريزي

مهرماه 1403

138 ص.

عبدالله سيف

حوضه يخچالي لار , متد هوفر و لويس , سيرك يخچالي , ارتفاع خط تعادل

رودخانه لار سرشاخه¬ي اصلي و پر آب رودخانه¬ي هراز مي‌باشد. طول رودخانه¬ي لار 70 كيلومتر بوده و مساحت حوزه آبگير آن بالغ بر 1250 كيلومترمربع برآورده گرديده است. رودخانه¬ي لار داراي آب دائمي ‌بوده و يكي از شاخه¬هاي مهم و پرآب هراز بشمار مي‌آيد. ارتفاعات موجود در حوضه لار از قلل مهم يخچالي كواترنري ايران محسوب مي¬شود. قلل و حوضه¬هاي يخچالي متعددي در اقصي نقاط حوضه لار در طي دوره كواترنري يخچال¬زايي داشته¬اند. در اين پژوهش در حوضه لار زير حوضه¬هاي يخچالي تفكيك گرديد، كه از دو زيرحوضه دلي¬چاي و دره لار جهت محاسبات ارتفاع مرز برف¬هاي كواترنري انتخاب گرديد. در مرحله اول طي مطالعات كتابخانه-اي و بازديد ميداني و با بكارگيري تكنيك¬هاي ژئوماتيك اشكال مهم ژئومورفولوژي يخچالي شناسايي گرديد. با شناسايي و ترسيم 148عدد سيرك يخچالي در حوضه¬هاي منتخب، انواع لايه¬هاي مورد نياز تهيه و با بكارگيري روش¬هاي ارتفاع كف سيرك، لويس و هوفر ارتفاع مرز برف هاي ديرينه برآورد گرديد. حوضه دلي¬چاي با تعداد 68 سيرك كوچك و بزرگ يخچالي بيشترين سيرك و حوضه گل زرد والرم هر كدام با تعداد 3 سيرك كمترين تعداد سيرك را به خود اختصاص داده¬اند. نتايج محاسبات كف سيرك بدين شرح مي¬باشد: ميانگين ارتفاع كف سيرك كل حوضه لار (148 سيرك يخچالي) 3409 متر برآورد گرديد. رقوم ارتفاعي پيشروي يخچال¬هاي وورم در انتهاي دره¬هاي دل¬¬چاي 2739 متر و دره لار 2597 متر رديابي گرديد. سپس طي بازديد ميداني و بررسي شواهد ژئومورفيك يخچالي، محاسبات ارتفاع مرزبرف-هاي گذشته با متد هوفر و لويس انجام شد. ارتفاع خط برف با متد هوفر در انتهاي دره دلي¬چاي و لار به ترتيب3382 متر و 3247 متر محاسبه گرديد و ارتفاع خط برف با متد لويس در انتهاي دو دره دلي-چاي و لار به ترتيب 3376 متر و 3412 متر محاسبه گرديد. با تركيب و هم پوشاني لايه¬ها و ژئوفرم¬هاي يخچالي، نقشه¬هاي ژئومورفولوژي يخچالي زيرحوضه¬هاي لار تهيه گرديد. نتايج اين پژوهش نشان داد كه در استيلاي دوره¬هاي سرد كواترنري نيمه شمالي و غربي حوضه لار از شدت يخچال¬زايي بيشتري برخوردار بوده است و غني از شواهد ژئومورفيك يخچالي از جمله يخرفت¬ها و سيرك¬هاي يخچالي مي¬باشد. به همين علت يخچال¬هاي كواترنري ضمن حركت خود در امتداد دره-هاي اصلي باعث حمل و جابجايي رسوبات شده است.

Lar glacier basin , Hofer and Louis method , cirque floor elevation , equilibrium-line altitude

Quaternary Glaciation In The Warengeh River Basin Lar, Alborz

جغرافياي طبيعي

Lar River is the main and full tributary of Haraz River. The length of the Lar river is 70 kilometers and the area of its catchment area is 1250 square kilometers. Lar River has permanent water and is considered one of the most important and abundant branches of Haraz. The elevations in the Lar basin are considered as important glacial peaks of the Quaternary period of Iran. Several glacial peaks and basins in the extreme parts of the Lar Basin have been glaciated during the Quaternary period. In this research, sub-glacial basins were separated in the Lar Basin, which were selected from the two sub-basins of Deli Chai and Dara Lar Valley for calculating the height of the quaternary snow boundary. In the first stage, important forms of glacial geomorphology were identified through library studies and field visits and by using geomatic techniques. By identifying and mapping 148 glacial cirques in the selected basins, all types of required layers were prepared and by using cirque floor height, Louis and Hofer methods, the height of the paleo-snow border was estimated. Deli-chai basin with 68 small and big glacier circuses has the most circuses and Gol Zard Waleram basin has the least number of circuses with 3 circuses each. The results of the circus floor calculations are as follows: - Se Sang basin with 33 cirques and an average of 3784 meters - Divasiyab Basin with 27 glacial cirques and an average of 3614 meters - Vararo Basin with 25 glacial cirques and an average of 3233 meters - Larba valley basin, 25 glacial cirques and an average of 3775 meters - Dry river basin with 25 glacial cirques and an average of 2333 meters - Sefidab basin with 7 glacial cirques and an average of 3233 meters - Lar branch basin with 7 cirques and an average of 3567 meters - Siah Chal basin with 7 cirques and an average of 3145 meters - Siya-plus basin with 6 cirques and an average of 2871 meters - Al-Ram basin with the number of 3 circuses and an average of 3451 - Golzard basin with 3 cirques and an average of 3310 meters The average cirque floor elevation of the entire Lar basin, including 148 glacial cirques, was estimated to be 3409 meters. The height of the advance of Wurm glaciers in the valleys of Delchai valleys was 2739 meters and Lar valley was 2597 meters. Then, during the field work and checking the glacial geomorphic evidence, the height of the past snow borders was calculated using the Hofer and Louis method. The height of the equilibrium-line altitude at the end of Delichai and Lar valleys was calculated as 3382 meters and 3247 meters, respectively, with the Hoffer method, and the height of the equilibrium-line altitude was calculated as 3376 meters and 3412 meters at the ends of the two Delichai and Lar valleys with the Louis method. By combining and overlaying layers and glacial geoforms, glacial geomorphology maps under the Lar basins were prepared. The results of this research showed that during the cold periods of the Quaternary, the northern and western half of the Lar basin had more intense glaciation and is rich in glacial geomorphic evidence, including glaciers and glacial cirques. For this reason, the Quaternary glaciers have moved sediments while moving along the main valleys.

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