بازسازي شرايط اقليمي كواترنر و بررسي محدوده يخچالي و آثار يخساري در شيركوه يزد

Regeneration of Quaternary Climatic Conditions and Study of Glacial Range and Glacial Effects in Shirkouh of Yazd

تغييرات اقليمي از بارز‌ترين ويژگي‌هاي دوره كواترنر به شمار مي‌رود. لندفرم‌هاي سطح زمين در اين دوره دستخوش تحولات و تغييرات فراواني شده است، با توجه به شرايط اقليمي گرم و خشك در ايران مركزي و وجود آثار و لندفرم‌هاي يخچالي كه نشان دهنده شرايط اقليمي سرد و مرطوبتر گذشته است ما را برآن داشت تا با هدف بررسي شرايط اقليمي گذشته با شرايط اقليمي حال حاضر در اين منطقه بپردازيم. روش اين پژوهش روش مشاهده‌اي و تحليل مبتني بر عمليات ميداني و سنجش از دور است، بنابراين داده‌هايي از جمله نقشه‌هاي توپوگرافي، مدل رقومي ارتفاع 30، 10 متر، تصاوير گوگل‌ارث، داده هاي GPS عمليات ميداني و داده‌هاي آماري اقليم منطقه استفاده شده است.روابط رياضي، مدل‌هاي تجربي و نرم افزارهاي آماري و نقشه كشي از عمده ترين ابزارهاي مفهومي اين پژوهش را تشكيل مي‌دهند. نتايج حاكي از آنست كه خط برف مرز گذشته كه به روش رايت محاسبه شده در ارتفاع 2491 متر قرار داشته و حداكثر پيشروي مورن‌ها در دامنه‌هاي غربي_شمال غربي تا ارتفاع 1980 متري و در دامنه جنوبي تا ارتفاع 2218 متري ثبت گرديده است..در شرايط اقليمي حال حاضرخط هم‌دماي صفر درجه در ارتفاع 5440 متر و خط هم‌دماي 5 درجه يعني (خط تعادل آب و يخ) در ارتفاع 4780 متري است و هردو بالاتر از قله قرار ميگيرد، ارتفاع خط برفمرز دوره گذشته نيز براساس معادله دمايي در حد دماي 22 درجه امروز قرار دارد كه نشان مي‌دهد شرايط ايجاد فرآيندهاي يخچالي و به تبع آن ايجاد لندفرم هاي يخچالي در منطقه شيركوه يزد وجود ندارد.

Introduction due to the phenomenon of global warming that we are facing today, studies of glacier areas, and sub glacier and its effects are of particular importance, because by examining the past climate, future theclimate change processes are better analyzed. One of the most important climatic heritage of the 4th era in Iran's highlands is glacier geomorphology and its glacier phenomenon. Climate change is one of the most characteristic features of the Quaternary period. Landforms have changed a lot during this period. Due to the warm and dry climatic conditions in central Iran and the presence of glacial landforms which shows the cold and wet climate in the past, we decided to study the current climatic conditions in the region with the aim of studying the past climate conditions. Location of study area Shirkouh Highlands are located in 40 kilometers south-southwest of Yazd. Shirkouh is the most important infiltration mass of Central Iran. The mid-Jurassic Batulite of Shirkuh consists of three major units: granodiorite, monzogranite and leukogranite. Shirkouh mountainous has created two different worlds of climate at a short distance in its environs. The location of Shirkouh elevations in the direction of northwest-southeast is like a long wall against the air masses and it is a temperature moderator in the region. Methodology In the present study, first, by identifying the glacial landforms (circuses, moraines), the boundaries and extent of the last glacial period in the Shirkouh Mountains were determined and then by discovering their local-spatial relationship with climatic (temperature and precipitation) and morphological (elevation and direction and gradient) parameters, the temperature drop in the time of glaciers existence and the amount of ELA have been determined. In the first step, by using Digital Elevation Models (SRTM 30 meters from the American Geological Survey) and 10 meters DEM of the organization of mapping of Iran and the Google Earth image, the position of the circuses has been determined and then, their accuracy has been verified by field surveys. In the next step, the correlations between the quantitative characteristics of the glacial landforms with morphological (elevation, slope, slope direction) and climatic parameters (temperature and precipitation of14 weather stations of the region from 1985 to 2008) have been determined. Then, the amount of drop in temperature required to form a glacier in the last glacial period in the mountainous area has been calculated by comparing the current and the past ELA. Discussion and results Detection of glacial phenomenon of the Shirkouh area: Based on the circus reflected in topographic maps and satellite imagery (Google Earth) and field surveys in the Shirkouh mountains, 62 circuses were identified. Due to the Wright method by passing 60% of the glacier circus location in the Shirkouh region, the Quaternary snow line is located at an altitude of 2491 m. This line represents the height of the zero-degree companion in the glacial period, by which we can reconstruct the past temperature conditions. Field observations in the Shirkouh region confirm the existence of glacial conditions such as circuses, glacier valleys and moraines. Based on the meteorological data and current climatic conditions, the current zero-degree temperature line is at 5438 m height, above the peak. According to the temperature equation, the past snow line is situated in the range of 22 centigrade degree of today’s temperature. Regarding the paleo climate of the region: the distribution of circuses is different in Shirkouh altitudes. the highest number of circuses have northeast, north, west and east direction and the smallest of them have southeast and southern slope direction, respectively. The lowest circuses are situated in the range of 1800 to 1900 meters and the highest of them are located in the altitude range of 3800 to 3900 meters. Conclusion With the studies of the prior researches, including the Hagedorn, the glacier processes at this region were identified at the height of 1925 to 2240 meters in the Quaternary and Moraines have also been seen at a height of 1600 meters. According to the fact that during the past decades we are facing with the global warming, due to the amount of annual snowfall and the lack of glaciers feeding, in contrary to the Quaternary period, today, we are no facing with the glacial processes in the Central parts of Iran. due to the phenomenon of global warming that we are facing today, studies of glacier areas, and sub glacier and its effects are of particular importance, because by examining the past climate, future theclimate change processes are better analyzed. One of the most important climatic heritage of the 4th era in Iran's highlands is glacier geomorphology and its glacier phenomenon.