بررسي آثار يخچالي كواترنري زنجان رود

The analyse of Quaternary glacial effects of Zanjanrood

نواحي كوهستاني شمال غرب ايران كه ارتفاع بيش از 2500 و عرض جغرافيايي بالاتر از 36 درجه شمالي دارند، شرايط مساعدي براي گسترش يخچال هاي كواترنري داشته‏اند؛ بخصوص اينكه در شرايط كنوني هم در اغلب موارد جز سردترين مناطق كشور شناخته مي شوند. در ارتباط با يخچال كوهستان‏هاي با بيش از 3000 متر ارتفاع اين منطقه، مثل؛ سبلان و سهند، مطالب زيادي نگاشته شده، ولي در مورد يخچال هايي مثل؛ ارتفاعات زنجان، كه بلندترين قله-هايش كمتر از 3000 متر ارتفاع دارد، سخن كمتري به ميان آمده است. غلبه دشت هاي نسبتاً هموار و وسعت كم مناطق مرتفع بالاتر از ارتفاع برف مرز دايمي كواترنري اين‌گونه مناطق، به فرايند يخچالي، شرايط فرم سازي كمتري داده است. با اين وجود، پراكندگي مورن‏هاي سرگردان و دره‏هاي U شكل در شمال و جنوب زنجان رود، همراه با پايين بودن متوسط دماي سالانه كنوني اين مناطق (ايستگاه زنجان 4/11 درجه سانتي گراد) حاكي از تسلط فرايند يخچالي كواترنري است. به همين منظور ابتدا با شناسايي آثار سيركي منعكس‌شده در نقشه-هاي توپوگرافي 50000/1 منطقه، مبادرت به برآورد ارتفاع برف مرز دايمي كواترنري به روش رايت گرديد. سپس با جمع‌آوري و اصلاح داده هاي آماري ايستگاه هاي اقليمي منطقه، خطوط همدماي كنوني و گذشته ترسيم گرديد. بر اساس خط همدماي پنج درجه سانتي‌گراد گذشته، ارتفاع خط تعادل آب و يخ گذشته برآورد گرديد(603 متر). كمترين ارتفاع حوضه در نقطه خروجي در حدود 1103 متر است، كه بيان‌كننده خارج شدن يخچال هاي كواترنري از حوضه زنجان رود و وارد شدن به قزل‌اوزن است، در صورتي كه شواهد ژيومورفولوژيكي منعكس كننده چنين وضعيتي نيست. به همين منظور در يك مطالعه قدم به قدم ميداني به بررسي شواهد ژيومورفيك ناشي از يخچال هاي كواترنري منطقه مبادرت گرديد. نتايج حاكي از آن است كه خط تعادل آب و يخ در ارتفاعي بالاتر از ارتفاع خط همدماي پنج درجه و منطبق با خط همدماي 16/2 درجه سانتي گرادي گذشته در ارتفاع 1550 متري بوده است.

1-Introduction Glacial evidences are one of the most important evidences that could be forcast the past and future climatic changes (Abramowski et al) that was studied according to the researches of glacial aboutexpandingand the research of glacial evidences (Solomina et al). Nevertheles should be payed attention that as the researches had verification, shouldn’t have expected that there be all kinds of glacial features and evidences, but according to the regions glacials nature and different physiographic properties of regions, could trace, diverse range of of glacial evidences and affets that it is obvious that would be different with other places (Stroeven et al). quaternary climatic changes according to spacial topography of Iran, has heritated features and landforms, like glacial circs, morains, and specialy erratic blocks, that sometimes is found a lot arount high parts of Iran. Geomorphologists have specified the hight of permanent snowline by the effects of mountains circs and reconstructe the situation of quaternqry tempreture according to its hight tempreture difference with current tempreture. In this way, analyse the geomorphological processes of that time. Also could determine the most extreme ice tenons by morains, wanderer rocks, glacial valleys, and the analyses of ice sediments and consider its hight as the hight of ice and water equilibrium line. Available written experiment about glaciers return to the beginning of 19th centur experiment about glaciers return to the beginning of 19th century (Haririyan 1369, 133). About the study of north west mountain glacials of Iran, it was studied the eastern ranges of Sabalan by Esfandiyari DarAbad (1388), glcial valley landforms of Sahand by Rajabi and Bayati khatibi (1387), The hight of glacial equilibrium line in Sabalan mountain by Dalal Oghly (1382), mountain ranges of Talesh by Tahooni (1383) and Mahmoodi (1380). For confirmation and argued the main reson of research (means the glacier effects of Zanjan rood basin), it was analysed the tempreture, precipitation, and permanent snow line of current and its comparison with quaternary era. 2- Methodology The research method was on the base of theses steps: At first the needed layers like digital elevation model, slope, aspect and contour were made by 1:50000 maps and SRTM picturs in Arch GIS 10.1 and Global mapper 13 and base on that, the needed analyses in the next steps were done. Then meteorologic data of the regionstations were collected and reformed. The relation between tempreture and hight and also between precipitation and hight was analyesd by SPSS software and base on that relations and countours of the region, the isothermal and precipitation line were depicted by Surfer8. To this perpose it was used 15 precipitaion and 13 tempreture stations of inner and outer Zanjanrood with the duration of 11 years (1380-1390). Counting zero?C of the past era, tempreture changes of that time than current time was analysed for the hight of quaternary snowline. The evaluated change acount was diminished from current tempreture and evaluated the past tempreture and also the past isothermal line was depicted and analysed by the use of topographic layer on surfer software. 3– Discussion According to reflected circs effects in 1:50000 topographic maps of Zanjanrood, 265 effects of glacial circs were specified (table2 and figures3 and 4). The most circs effects were identified on the hights of 2200-2400 (totally 112 circs). After that the circs was orderd decendingly according to the hight specification and a hight that situated 60% of the circs upper than that hight, evaluated and were identified as the hight of permenent snow line. This line was the expretion of the past hight of zero? isothermal that could reformed the past tempreture situation. The evaluation of glacial effects on contours was shown that the permenent snowline in this part of Iran was on the hight of 2270 meters. The following stepswere performedfor this purpose: The analyses and reformation of the sitiuation of tempreture in current and the past; the analyses and reformation of the sitiuation of precipitation in current and the past; the analyse of climatic sitiuation; the evidences of ice and water equilibrium line of the region. 4– Conclusion There are evidence such as Cirque glacier, U-shaped valleys eart rokes in basins Zanjanrood whit over 36 degrees of latitude and at altitudes above 1600 m, that we tried to rebuildthe permanent snowline andequilibrium line water and icealtitude of quaternary with respect toits.Results indicatethat thepermanentsnowline of Quaternaryhas beena altitude2270meters, and waterand iceequilibrium line has beenaaltitude1550m, however,temperature of thequaternary in the lowestcatchment part had of2/3degreesattheheight of1103meters, andtheheight is abovetheelevation oftemperatureof fivedegrees(equilibrium line water and icealtitude), butdo nothaveglacier to this place,becauseofthe geomorphologicalconditions.