نوع مقاله : مقاله پژوهشی

نویسندگان

1 اقلیم شناسی دانشگاه حکیم سبزواری

2 ژئومورفولوژی دانشگاه حکیم سبزواری

3 ژئومورفولوژی، دانشگاه حکیم سبزواری

چکیده

در این تحقیق سعی شده با استفاده از روش‌های معمول ژئومورفولوژی، تحولات اقلیمی دوران چهارم در حوضه آبریز گرگانرود (تا گنبد کاووس) بررسی شود. بدین منظور، ابتدا با تعمق بر فرم‌های ژئومورفیکی در منطقه مانند تپه‌های لسی، سیرک‌های یخچالی و پدیده‌های کارستی تغییرات محیطی بررسی شد. سپس، با اتکا به تصاویر ماهواره‌ای و نقشه‌های توپوگرافی، سیرک‌های یخچالی منطقه مشخص و با روش رایت خط برفمرز دائمی در آخرین دوره یخبندان به‌دست آمد. با بررسی گرادیان دمایی (دما- ارتفاع) منطقه، نقشه هم‌دمای زمان حاضر و با استفاده از رابطه مزبور و ارتفاع برف‌مرز دائمی منطقه در کواترنر، نقشه هم‌دمای دوران چهارم ترسیم شد. نتایج به دست آمده و مقایسه دو نقشه حاکی از اختلاف دمای 4/9 درجه سانتی‌گرادی زمان حاضر با دوره کواترنر است. بررسی اشکال ژئومورفیکی کنونی نیز حاکی از استیلای آب‌وهوای سرد و مرطوب در دوران چهارم است که نتایج این تحقیق را تأیید می‌کند.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Geomorphologic assessment of climatic changes of Gorganroud basin in the Quaternary

نویسندگان [English]

  • Alireza Entezari 1
  • Abol ghasem Amir Ahmadi 2
  • Aman Mohammad Gharnjik 3
  • Ali Jahan far 2
  • Ali Akbar Shayan Yeganeh 2

1 Hakim Sabzevari University Climatology

2 Hakim Sabzevari University Geomorphology

3 Geomorphology, Hakim Sabzevari University

چکیده [English]

The Earth's current surface forms and phenomena are the result of climatic processes of last periods. These processes, because of climatic variations of regions, had different effect on the earth surface. The origins of the modern forms of earth related to transformations of two million years ago that scientists have called it the Quaternary period. Study of glacial erosion system is noteworthy for two view: first, there is still frozen areas in our time; Second, because during the Quaternary glacial, glacier surface was extended to today, therefore were involved in the formation of large areas that have already been released from the glacier. The case study is Gorganrood basin.
Materials and Methods
The geomorphic forms in such a loess hills, circus glacial and karst phenomena were studied environmental changes. The determined based on satellite images and topographic maps, circus glacial of area and determined snowline by the method of Wright in the last glacial period, then, based on the region gradient (high temperature) was drawn the map of isotherms presented by using of relationship and height of permanent snowline of area in the quaternary. One of the ways it can be determined is the permanent snow line in the cold Quaternary periods, Wright's method.
Discussion
According to calculations done of the standard error rate is less of linear than exponential relationship between rainfall- height, the regional climate is such that the results of the estimation of precipitation for the basin heights follow greater than exponential functions. The results of studies on the Quaternary climate of area and present time indicated that the mean annual temperature at the present time varies between 17.7° C in the plains to 6.8° C in the highlands. After the reconstruction was obtained an average temperature in the Quaternary period of about 3.7° C in low- height areas and about 7.3° C in the highlands. Using relationship annual temperature and altitude, zero isotherms or the permanent snow line curve, is obtained equal to 4175.8. Considering the past temperature conditions, evaporation rate was much lower than today, although precipitation may no significant difference with present. Going back the Caspian Sea, while its level changes isn’t subject to the terms on the open seas; indicates wet and dry climatic conditions  in the region during the Quaternary.
Conclusion
By comparing the present thermal conditions and Pleistocene period, we concludes that the temperature difference in the region is 10.4°C. Weighted average temperature of area in the past and the present is respectively of 4.4 and 13.9°C. As a result, the temperature difference between the present and the Quaternary Period in the basin is about 9.4°C. According to the evidence and morphological features of the region and climatic conditions for their formation, came to the conclusion that moisture conditions has been noticeable in the past. So, today existence evidence as lapie, alternate layers of loess and river sediments in fluvial terraces (Aq Ghomayshi), deposits that originated from the bottom of lake, river and glacier interactive Morin lower part of the local and regional Los confirmed the weather conditions.

کلیدواژه‌ها [English]

  • climatic changhes
  • geomorphological forms
  • glacial cirquses
  • Gorganroud
  • Quaternary