تاثیر ارتفاع بر خصوصیات فیزیوگرافی زیرحوضه‌های آهکی (مطالعه موردی ارتفاعات زاگرس ایران)

کارستی فیکاسیون عمل انحلال سنگ‌های کربناتی، تحت تاثیر عوامل مختلف و حاصل دخالت مشترک مورفودینامیک درونی (ساختار زمین‌شناسی و لیتولوژی) و بیرونی (اقلیم، ارتفاع، پوشش گیاهی و زمان) است. ارتفاع به‌عنوان یک عامل بیرونی، بر مقدار بخارآب و گردوخاک موجود در هوا اثر می‌گذارد، شرایط دمایی و بارشی را تغییر می‌دهد و فرم نهایی زمین از این تغییرات تاثیر می‌پذیرد. هدف این مقاله، بررسی تفاوت‌های فیزیوگرافی زیرحوضه‌های آهکی زاگرس با توجه به تغییر ارتفاع و تفسیر تفاوت‌ها در زمینه ی عناصر دمایی و بارشی است. با توجه به وسعت 381140 کیلومترمربعی زاگرس و پراکندگی لیتولوژی آهک در مناطق ارتفاعی مختلف، با استناد به منابع اسنادی (نقشه‌های زمین‌شناسی 1:100000، لایه ی مدل رقومی ارتفاع با قدرت تفکیک 12.5 متر و نقشه‌های توپوگرافی 1:50000) ابتدا زیرحوضه‌های واقع در این نوع لیتولوژی تفکیک شد. سپس پارامترهای فیزیوگرافی (طول حوضه، مساحت، فاکتور فرم، فاکتور شکل، نسبت کشیدگی و ضریب ناهمواری) زیرحوضه‌ها نیز برآورد شد. بررسی خصوصیات فیزیوگرافی حوضه‌ها در زمینه ی ارتفاع نشان می‌دهد که کشیدگی و طول زیرحوضه‌ها با افزایش ارتفاع در کل زاگرس با ضریب تبیین 0.5 بیشتر می‌شود. نتایج حاصل شده نشان می دهد که افزایش ضریب کشیدگی و طول حوضه در مناطق آهکی، دال بر انحلال بیشتر است و فاکتور شکل و فاکتور فرم با ضریب تبیین 0.53 برای کل زاگرس، نزدیک شدن شکل هندسی حوضه به مربع و مستطیل را نشان می دهد و تقریباً نتایجی همانند ضریب کشیدگی حوضه را منعکس می سازد. فرسایش در سطح یک حوضه ممکن است توزیع همگن یا ناهمگن داشته باشد؛ در صورتی‌ که ضریب ناهمواری در یک حوضه زیاد باشد، نشان‌دهنده ی تغییر توزیع فرسایش از همگن به ناهمگن است. در مناطق آهکی هر چه ارتفاع بیشتر می‌شود، ضریب ناهمواری به دلیل فرسایش ناهمگن سطحی به‌ طور متوسط 0.6 درصد افزایش می‌باید.

Effect of height on the physiographic properties of limestone sub-basins (A case study of Zagros Heights of Iran)

Extended abstract1 IntroductionVarious factors influence the karstification process in the dissolution of carbonate rocks. Karst is common influence result of internal morphodynamics (geological structure and lithology) and external morphodynamics (climate, altitude, vegetation, and time). They affect the karstification of the demise of carbonate rocks. Karst is the result of numerous methods that occur in calcareous zones and climatic, geological, and hydrological conditions, and its effects can be seen in multiple forms, such as pits and caves above and below ground. One of the climate indices that determines the environmental conditions is the amount of moisture and its changes. The presence of water is a significant climate factor in karst development. They reflected in the formation of the environment in several Forming systems: in the high elevations and latitudes as glacier systems, in the piedmont as ice sheet systems, in the marginal zone as ice tab and mudflat systems, in the lower zones as runoff and in the smaller pit as waterfall system (Seif et al., 2015). The solubility of carbonate rocks is sensitive to temperature changes (Ghobadi, 2009: 142); Limestone dissolution is more rapid at low temperatures and in colder climates, and the amount of karst erosion in cold and humid regions is much higher than in hot and humid regions (Zanganeh Asadi et al., 2002). With the impact of elevation on temperature and precipitation, erosion processes and consequently the face of the Earth and geomorphological phenomenon change (Alipour et al., 2017). The purpose of this paper is to investigate the physiographic differences of calcareous Zagros subbasins concerning altitude variation and the interpretation of disagreements concerning temperature and precipitation elements.2 MethodologyIn this paper, considering the karst features and the effect of dissolution on the basin in terms of physiographic properties (shape parameters), slope, roughness (topographic parameters) in the Arc Map, the basins of the rivers that were located in the calcareous zones were determined. The settings of such as environment, basin area, and rivers length, minimum and maximum height were calculated. The shape and topographic parameters of the basins were estimated, by using the existing relationships, and then the final rank of the basin's main waterway was obtained based on the Australian method. The collected data were entered into Excel software. Finally, linear regression equations between altitude as the independent variable and other parameters as the dependent variables were estimated to investigate their variation concerning the altitude factor. They were also studied in elevation classes, different climatic zones, and distance to the fault.3 Results Investigation of the estimated linear regression relation between height as an independent variable and other parameters as a dependent variable at different ranks indicates that with increasing elevation, area, roughness coefficient, length, elongation ratio, and basin shape factor become less and form element lower. Increasing the area of subbasins at ranks similar to elevation implies that surface erosion overcomes linear erosion. When corrosion is direct, the intermediates are usually less extensive, and the basins are consequently getting smaller. However, the subbasin area increases due to elevation in single lithology, and as in similar waterways. Due to the karstfission effect on basin dimensions and their influence on climatic elements, the subbasin area has grown and increased the area of the subbasin has made the erosion from the line (water) to surface (dissolution) more inclined. In 297 subbasins with rank 2 and 3 northwest Zagros, there was no significant relationship between altitudes with other parameters except ruggedness. That is, their coefficient of explanation was less than 0.4, and it could not be analyzed solely by the height factor. Examination of these parameters indicates that their changes, sometimes with increasing altitude, are minor and occasionally unanticipated and sometimes have no specific direction. As the river rises, the area of the subbasins also increases. We identified in the southeastern part of the folded Zagros, 48 basins. In each rank basin, there is a direct correlation between height and other parameters. It means that all of them are affected by altitude. They increase with the coefficient of all of them, except the form factor, it has grown. In low Zagros, 68 catchments in calcareous zones, with ranks two to four, it was considered that the regression relationships between altitude and parameters except the form factor had a direct correlation with the difference that this unit had higher correlation coefficient than the other Zagros units.4 Discussion ConclusionsThe physiographic coefficients of the basins in the calcareous zones, the change in temperature and precipitation due to elevation changed. The transformations of karstification can analyze the change in temperature and precipitation mdash; these changes reflected in different parts of Zagros (except for the folded northwest Zagros). The increasing of the coefficient of explanation in low altitude Zagro indicates that due to the physiographic characteristics of the basins, the role of climate change (temperature and precipitation) in this part of Zagros can be better traced. The examining factor such as basin physiography due to the increase of altitude shows that the elongation and length of the subbasins increase with increasing. And it is reflected almost like the basin drag coefficient. Erosion at the basin surface may have a homogeneous or heterogeneous distribution. If the coefficient of roughness is high, it indicates that the distribution of decay has become seamless. In calcareous regions, as the altitude increases, the ratio of hardness increases too because the distribution of erosion becomes heterogeneous. Investigation of the physiographic characteristics of the watersheds concerning altitude shows that the elongation and length of the basins increase with increasing Zagros with an explanation coefficient of 0.5. The results show that increasing the coefficient of elongation and length of the basin in calcareous zones lead to more dissolution, and the form factor, with a ratio of explanation of 0.53 for the whole Zagros indicate the geometric shape of the basin to square and rectangle. It almost reflects results similar to the basin drag coefficient. In calcareous areas, as the altitude increases, the coefficient of roughness increases by an average of 0.6% due to heterogeneous surface erosion.Morphometric study of Zagros calcareous subbasins about climatic factors indicates that several factors affect these properties, only some of which are related to dissolution conditions; Crashes, landslides, topography, faults, seams and crevices, and any other factors can affect these properties that may be addressed in separate studies.