مورفومتری لغزش بزرگ سیمره و بازسازی تأثیرات لندفرمی آن در کواترنری پسین (رشته کوه زاگرس در ایران) (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
زمین لغزش سیمره یکی از بزرگ ترین لغزش های شناخته شده جهان است که در جنوب غرب ایران قرارگرفته است. هدف این پژوهش بررسی ویژگی ها و تأثیرات ژئومورفولوژیکی این زمین لغزش است. برای دست یابی به این هدف، از تصاویر ماهواره ای، نقشه های توپوگرافی، نقشه های زمین شناسی، نقشه های رقومی استفاده شده است. روش پژوهش تجربی و بر پایه تحلیل داده های میدانی است. برای این کار، فرآیند رخداد زمین لغزش، علل وقوع و خصوصیات مورفومتریک زمین لغزش در سه بخش سطح لغزش، توده ی لغزشی و مؤلفه های جابه جایی لغزش به همراه رسوبات ته نشست شده در دریاچه های سدی سیمره و چینه شناسی آن ها مطالعه شده است. نتایج مورفومتری زمین لغزش شواهدی از نقش عوامل گوناگون در آن است. در میان آنها زیربری لایه های آهک آسماری توسط رود سیمره و کشکان مهم ترین عامل رخداد آن می باشد. این لغزش موجب تشکیل دریاچه سدی در پشت توده ی لغزشی شده و این دریاچه در اثر تکرار لغزش دارای پادگانه های متوالی است. نتایج مورفومتری دریاچه به ویژه برآورد حجم آب (642/45 میلیارد مترمکعب) و رسوب دریاچه (422/23 میلیارد مترمکعب) و مقایسه زمان پر شدن این حجم آبی (8/19 سال) با توجه به حجم آب ورودی به دریاچه (3/2 میلیارد مترمکعب در سال) با مدت زمان لازم برای ته نشست تمامی این رسوبات (5/1913 سال) نشان می دهد دریاچه چند مرحله و در نتیجه تکرار انسداد رود سیمره توسط تکرار زمین لغزش تجدید شده است. چینه شناسی رسوبات دریاچه ای تجدید محیط دریاچه ای را در چهار مرحله روشن می کند. توالی پادگانه های دریاچه ای و سایر شواهد، مقیاس های متفاوت تکرار زمین لغزش بزرگ سیمره را تأیید می کند.A Morphometry of the Large Saymarreh Landslide and Reconstruction of its Landform Effects in the Late Quaternary, the Folded Zagros, Iran
Introduction
Saymarreh landslide is one of the known largest landslides in the world that is located in the southwest of Iran. The purpose of this study was to compare the characteristics and geomorphological influences of this landslide with the largest landslides of the world. Saymarreh landslide is one of those large landslides that have undergone significant geomorphological, historical, and cultural changes during the Holocene era. The evolutionary trend of this landslide is highly complicated; in fact, it is one of the most important characteristics of large landslides. This landslide formed several dam lakes, and their formation were frequently repeated. However, it is not clear that whether the formation and evolution of the lakes were due to the river erosion sequences or the repetition of Saymarreh landslide.
Methodology
A large number of researchers believe that Saymarreh landslide is the largest landslide in the world, but some researchers do not believe so and introduce other landslides as the largest ones. Thus, by performing detailed investigations into the region, the geomorphic features of this landslide and its evolution was probed. To achieve this goal, ETM2002 satellite images, IRS of PAN and LISS III satellite images of 2004 and 2006, topographic maps, geological maps of SRTM DEM, and ArcGIS software were employed. The research method was empirical and it was based on the analysis of the field data. In this regard, the process of the landslide formation, its causes and morphometric characteristics in three classes of slide area, mass movement and displacement parameters along with deposited materials in Saymarreh Dam lakes were studied.
Result
The results relevant to the morphometry of the landslide indicated that various factors were involved in the occurrence of Saymarreh landslide. Among these factors, undercutting of the Asmari limestone layers made by Saymarreh and Kashkan Rivers, particularly in front of the landslide, was the most important cause of the landslide occurrence. The landslide had formed a large lake behind the slide mass and had formed sequential terraces due to repeated slides. The results of the morphometry of the lake, particularly through the estimation of its water (45.642 Gm3) and sediment volume (23.422 Gm3), and comparison of the time taken for filling of the water volume (19.8 years) with the time required for deposition of the whole sediment volume (1888 years) showed that the sediments have not been deposited only during one stabile period of the lake and the lake has been renewed at least at several stages. As a result, the reoccurrence of Saymarreh landslide at several times led to the obstruction of the Saymarreh River. Stratigraphy studies on the lake sediments and the age of its terraces clearly implied the renewal of the lake at least at 4 stages. The sequences of the lake terraces and other evidences confirmed the different scales of the reoccurrence of the large Saymarreh landslide.
Discussion and conclusion
This landslide obstructed the Saymarreh and Kashkan rivers and led to the formation a large lake in that region. The lake depleted after destructing the landslide mass, and there was a change in the direction of the Kashkan River.
The main triggering factor for this landslide was undercutting of Saymarreh and Kashkan rivers. Other factors included the direction and the angle of the slope, steep structural slopes, and gravity. The results obtained from the morphometry of Saymarreh Lake and stratigraphy of the lake sediments demonstrateed that Saymarreh landslide had been reactive several times and led to formation of the lake at several stages.