بررسی آثار یخچالی کواترنر و تأثیر آن بر عدم شکل‌گیری مدنیت و سکونتگاه مهم شهری در دشت آسپاس

نویسندگان

چکیده

  ماهیت بیشتر شکل‌ها و فرایندهای بیرونی زمین اصولاً تابع شرایط اقلیمی حاکم بر یک منطقـه در طـول زمان است. بنابراین، آثـار و شـواهـد تغییرات اقلیمی دوران چهارم که مهم ترین آنها وجود آثار یخچالی باقی مانده از آن دوره است، توانسته پدیده‌های گوناگون ژئومورفولوژی را در سطح خارجی پوسته زمین بر جای بگذارد و با توجه به این آثار و شواهد می‌توان شرایط اقلیمی گذشته را بازسازی نمود.دراین تحقیق جهت شناسایی آثار یخساری در منطقه مهمترین ابزار وشواهد موجود شامل، شاخص‌های مرفیک، آثار و شواهد اقلیمی، آثار و شواهد میدانی، آثار و شواهد انسانی و آثار و شواهد آزمایشگاهی مورد بررسی قرار گرفتند.تعیین خط برف دائمی در دوره یخچالی که به روش رایت صورت گرفت، نشان داد که دمای متوسط سالانه صفر درجه سانتی گراد در ارتفاع 2600متری منطقه قرار می ­ گرفته و وجود بالغ بر 255 سیرک بزرگ و کوچک نشـان می‌دهـد که در دوران سرد یخچالـی سیرک‌ها به عنوان یکی از منـابـع تغـذیـه کننـده بسیـار غنـی بـرای تشکیل یک پوشش یخـی در منطقه به شمار می‌رفته اند. شواهد ژئو مورفولوژی موجود وجود بیش از یک خط تالوگ در دشت که به جای جریان‌های آبی، سطوح یخی عمل کرده است را تایید می‌کند.همچنین برای تأیید تسلط یخچال‌ها بر منطقه به عملیات گرانولومتری و مورفوسکوپی و نتایج حاصل از آن پرداخته شد که اکثر نمونه‌ها از نوع رسوبات یخچالی هستند.. توزیع فضایی روستاهای دشت که دقیقاَ از حرکت و شکل‌زائی زبانه‌های یخچالی پیروی می‌کند (به صورت خطی در مرکز دشت) و وجود تپه‌های باستانی عملکرد یخچال‌ها را تایید می‌کند. همچنین می‌توان عدم توسعه مدنیت و سکونتگاه ‌ های مهم شهری در این منطقه را به برودت هوا وحرکت غیر متمرکز یخ در گذشته نسبت داد که موجب عدم شکل گیری منابع آب زیر زمینی قابل توجه شده است.

کلیدواژه‌ها


عنوان مقاله [English]

Evaluating the effects of Quaternary glaciers on the lack of civilization and main urban habitation in Aspas plain

نویسندگان [English]

  • A. Amirahmadi
  • A. Maghsodi
  • T. Ahmadi
چکیده [English]

  Evaluating the effects of Quaternary glaciers on the lack of civilization and main urban habitation in Aspas plain     A. Amirahmadi ( * )   Assistant Professor of Geomorphology, Tarbiat Moallem University, Sabzevar, Iran   e-mail: amirahmadi@sttu.ac.ir     A. Maghsodi   Coach Geomorphology, Islamic Azad University –Abade Branch, Abade, Iran.     T. Ahmadi   M.A Student of Geomorphology, Tarbiat Moallem University, Sabzevar, Iran    Received: 15 January 2011 / Accepted: 13 August 2011, 17-20 P     Extended abstract   1-introduction   Environmental change issue, as one of the environmental problems, has attracted scientist’ attention. Geomorphology is one of the sciences that trace the environmental changes based on geomorphological evidences. Evidences represent that, in earth history, climatic setting of every region has often changed and therefore geographical and geomorphological conditions have altered. Since the formation of civilization focuses especially cities depend on morphologic setting of regions, great flat plains with low and smooth surfaces are favorable places for habitation but plains in mountainous regions, as Aspas plain, don’t provide appropriate situation because of the lack of favorable geographical parameters.       2-Theretical Bases   Geographical thought in the nineteenth century was considered, and the base has evolved. According to this theory, the course of civilization begins its simplest form, and ultimately leads to urban civilization. In all transition periods, the geographical environment is considered. In the context of evolutionary theory, in addition to features of the fourth period (Quaternary) Plain Aspas climate constraints, geomorphic and topographic distribution and accumulation in human settlements have been effective.     3-Discussion   Aspas plain, in north of Fars province, lies 45 km of Eghlid county and is located between 30 ْ 17 ََ and 30 ْ 40 ََ N latitude and 52 ْ 15 ََ and 52 ْ 54 ََ W longitude. In spite of appropriate climatic and topographic situations, greatness, fertility and enough surface water, rural and urban regions are not developed so and even there is not any urban focus. There are only some villages linearly in the center of plain. Therefore the assumption of coldness of weather and glacier activity can account for the limitation of habitation in mentioned plain. This study, also, aims to find the reasons of habitation problem of Aspas Plain by evaluating and comparing the climatic and geomorphological characteristics in present and quaternary periods.   In this study, topographic maps at a scale of 1:50 000 and Geological maps at a scale of 1:100 000 were used for the identification of glaciers effect as well as permanent snow line. Rainfall statistics of Abadeh, Eghlid, Eyzadkhast, Sadeh, Samirom, Hana, Dorodzan and Kaftar stations were used for preparing Iso-precipitation lines. Granulometric technique and morphoscophy operation were done on sediments to determine the type and percentage of deposits, and therefore the type and percentage of sediments in terms of their glacial, eolian and fluvial origin. Consequently, geomorphologic, climatic, human and experimental evidences were utilized for identification of glacial remnants.     4-Coclusion   Sinusoidal form of topographic contours in topographicl maps reveals the previous glacial activivity of study area. These surfaces often have been formed by the movement of ice sheets along with mountainous glacier tongues. Determination of permanent snow line by Wright method revealed that mean annual temperature is zero centigrade in the altitude of 2600 meter above sea level. The evaluation of recorded cyclical temperatures shows that the previous and present temperature difference is 9.86 degrees C. in the middle and 9 degrees C in the heights of study area. The mean annual 5 degrees C line was not recognized in the old iso-term map. The highest iso-term was 3 degrees C. in the middle of plain. This means that the lowest point of plain had been located above the equilibrium line of water and ice. Therefore the surface of the plain had been appeared as an icy domain in most of the year. Field evidences represent that there is just one talweg in the plain that has acted in stead of fluvial flows in icy surfaces. The existence of 255 small and large cirques shows that cirques had operated as one of the important feeding resources of ice sheets of study area in cold glacial periods. Granulometric and morphoscophic tests were obtained for the confirmation for the valuation of glacial operation and effects of the study area. Performed operations on samples of sediment confirmed the activity of glaciers in study area so that the results of granulometry reveal that most of samples are glacial deposits. Also, morphoscophic operations show that most of samples comprise a high percentage (57%) of sediments that have formed by glacial activity. Spatial distribution of villages, which follow the form and movement of glacial tongues (linear in the center of Aspas plain), as well as the antique hills confirm the glacial activity.     5-suggestions   The movement of ice on surfaces, like the movement of water, has 2 different states. Concentrative movement of ice that is called glacier, transport morain deposits with special grading and usually results in the formation of till and morain sheets with the high capacity of reservation of groundwater resources. Unconcentrative movement of ice wich is product of sheet movement of glaciers, forms an undulate surface composed of a layer of sand, with a thickness of more than 10 centimeters that does not have important effect in the formation of groundwater resources. The second type of ice movement has formed in Aspas plain and therefore, except in small parts of alluvial fans in south of plain, there are not considerable groundwater resources. 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کلیدواژه‌ها [English]

  • glacial effects
  • quaternary
  • Aspas plain
  • civilization
  • urban habitation