نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه جغرافیا، دانشگاه زنجان

2 آب و هواشناسی، کارشناس واحد حقیقات اداره کل هواشناسی گیلان

3 هواشناسی کشاورزی، کارشناس سازمان هواشناسی کشور

4 ژئومورفولوژی، دبیر ناحیه یک استان قزوین

چکیده

توپوگرافی یخچالی در کوهستان‌ها، یکی از شواهد تحولات آب‌وهوایی کواترنر در ایران است. توده‌ کوهستانی شاه البرز، مرتفع‌ترین کوه در نیمه جنوبی البرز غربی است که نقش مهمی در ساختار و مورفولوژی منطقه دارد. شواهد ژئومورفولوژیک، نشان از حضور یخچال‌های کوهستانی در این توده‌ کوهستانی دارد. برای بررسی شواهد ژئومورفولوژی یخچالی در کوه شاه البرز از روش‌های تجربی مانند روش پورتر و تحلیل فرایند-فرم، استفاده شده است. در دامنه شمالی که به شدت توسط فرسایش آبی دستکاری شده، چهار سیرک یخچالی شناسایی شده است. برخلاف دامنه جنوبی، در محل پیوستن دره‌‌های دینه‌رود و رود الموت، شواهدی از یخ‌رفت‌ها، دیده می‌شود. ارتفاع خط تعادل برف و یخ در دوره‌ پلیستوسن با استفاده از میانگین ارتفاع کف سیرک‌های یخچالی، 3560 متر اما در شرایط حاضر، 4900 متر است. با توجه به حداکثر پیش‌روی زبانه‌ یخچالی تا ارتفاع 1800 متر در دره‌ اصلی شاهرود،  قلمرو یخچالی در پلیستوسن، احتمالاً تا ارتفاع 2000 متر بود.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Geomorphology of late Pleistocene mountain glaciers in Shah Alborz Mountain- Western Alborz

نویسندگان [English]

  • Reza Khosh raftar 1
  • Nima Farid Mojtahedi 2
  • Ebrahim Asaadi Oskouei 3
  • Kambiz Nowrouzpour Shahr Bijari 4

1 Department of Geography, Zanjan University

2 Hydrology and meteorology, expert of the facts unit of the General Directorate of Meteorology, Gilan

3 Agricultural meteorology, expert of the National Meteorological Organization

4 Geomorphology, the secretary of Qazvin province

چکیده [English]

-Intrudaction
One of the evidences of the Quaternary climate changes in Iran , are glacial topography in mountainous areas. Understanding glacier forms such as cirques, as the accumulation of snow and ice sites and mountain glaciers supply, is very important in glacial geomorphology. Shah Alborz Mountain situated in Alborz chain system and is the only famous peak in southern part of Western Alborz. The mountain masses, including parts of Taleghan and Alamut catchment areas. Glaciers cirques topography is gentile and the main dividing lines as cliffs generally. Some of the cirques has large holes, so the native peoples called the Alborz chall (pit) mountain. The northern flank of the Shah Alborz, especially in areas where the Tertiary formations formed, influenced by water erosion processes and floods heavily. According to different formations in divide line, middle and down slopes have different landscapes.
The main objective of this paper is reconstruction of paleo-glacier equilibrium lines during the Pleistocene in the Shah Alborz Mountain (western part of the Alborz Mountain Range, Iran).
 
2-Material and methods
The main objective of this study is to identify evidence of Pleistocene geomorphological mountain glaciers on the northern flank of the Shah Alborz Mountain using experimental methods(such as Porter and  Wright methods) and field studies. Two main access routes to Shah Alborz peak include:
1-The North slope route (Alamut), respectively: Qazvin Plain – Rajae dasht- Moalem kolaye-Garmarud-hiking to Shah Alborz summit and cirque of C from Evank village.
2-The South slope route (Taleghan), respectively: Qazvin - Taleghan- Hassan Jvn village-hiking to the summit.
 After reviewing the available literature, field studies take place by using of GPS and collection data was transferred in maps of 1 : 25,000. For analyze temperature and precipitation, used synoptic stations of Taleghan (southern slope) and Moallem Kalayeh(northern slope)data . Exception of the initial field visit for general identifying, the main field works in three stages, was conducted in the summer of 2013. After identifying the glacial landforms, coordinates and other characteristics of each landforms were recorded. To display data from ArcGIS version 9.3 and analysis of location and altitude of the digital terrain model(DEM) with resolution of 90 m(SRTM) and 30(SRTM)was used .In the end, after geomorphological mapping and profiles drawing, analysis was performed on the relationship between glacial landforms and prevailing processes in the Pleistocene.
In this study, morph metric parameters of the cirque-like features with use of digital elevation model(DEM) and topographic profiles have been considered and analyzed.
 
 
3-Results and discussion
Pleistocene glacial reliefs were studied in Shah Alborz mountain based on field works and satellite image analyses. According to field studies and analyzing, glacial landforms were divided into two main groups, namely:
 
-Erosional landforms
One of the most striking landforms in Shah Alborz mountain are  glacial cirques that key to the reconstruction of Pleistocene Equilibrium Line Altitude (ELA).Cirques are an amphitheater-like shape, formed at the head of  glacier valley.
Evidence indicates the dominance of glacial erosion ice and permanent snow. According to studies, on the northern flank of Shah Alborz in the Pleistocene, there were four glacial cirques from West to East A, B, C and D, respectively. Cirque of C to 205 hectares area is the largest glacier circus in Sah Alborz Mountain. But there was no circus in southern slopes.
 
 
-Depositional Landforms
Depositional Evidence comprised of a variety of moraines, which represents preiglaciers territory. There is a huge amount of moraines in Shah Alborz cirques. Adequate supply of c and d cirques leads to the formation of a large glacier toungue.Therfore, in C and D cirques and its downstream valleys, the highest moraines can be viewed. Using Porter and Wright methods, Equilibrium Line Altitude (ELA) in the Pleistocene, was estimated to be 3472 and 3660 meters respectively.
 
 
4-Conclusion
The main objective of this research is reconstruction of the altitude of paleo-glacier equilibrium lines during the Pleistocene in the northern flank of Shah Alborz Mountain (western alborz of Iran). More glacial landforms identified in this study are, Erosional type, glacial cirques mainly. Probably in the Quaternary, in Shah Albrz, four cirques  in the northern flank and two in southern flank had actived. Snow and ice equilibrium line in Shah Alborz was located at a higher altitude than other regions like the Shahrestanak, Jajrood Valleys and Alam Kohe Mountain. At present, the areas above the height of 2000 meters are in periglacial territory or cryo-nival. In terms of Morphdynamic process, ice and melting in outcrops, gelifluction and Solifluction in fine-grained material of slopes are prevails.

کلیدواژه‌ها [English]

  • cirques
  • climate change
  • geomorphologic heritage
  • Shah Alborz mountain