Abstract:
در طی کواترنری، نیروهای تکتونیکی با دخالت تغییرات اقلیمی منجربه ایجاد لندفرمها و یا تغییرشکل در فرمهای قدیمی درههراز شدهاند. پادگانهها، لندفرمهای بهجامانده از دوره کواترنری هستند که مطالعه آنها تغییرات محیط را طی این دوران مشخص میکند. در پژوهشحاضر، فرآیندهای دخیل در تشکیل پادگانههای درههراز و نقش رسوبات آذرآواری دماوند در تغییر رفتارآبی رودخانههراز و تشکیل دریاچه سدی در محل آباسک مورد بررسی قرارگرفته است. برای دستیابی به این هدف روش تحلیلی و بازسازی زمانی تغییرات بهکار گرفته شدهاست. تکنیک کار، مقایسه مورفومتری پادگانههای دریاچهای و سدهای یخچالی- پیروکلاستی به چهار روش بازهبندی منطقه مورد مطالعه، مقایسه ارتفاع و ضخامت رسوباتآبرفتی، تعیین حدود گسترش رسوبات دریاچهای و بازیابی حدارتفاعی موانع محصورکننده درههراز استوار است. نتایج بهدست آمده نشانداد که سطوح ارتفاعی پادگانهها هم دارای اختلاف ارتفاع بوده و هم توالی نامنظم دارند. بالاترین سطح پادگانه در کوهنل 630 متر از بستر درههراز ارتفاع داردکه نشان میدهد علاوه بر تغییر سطحاساس، فرآیندهای یخچالی از عوامل مرتفع شدن سطوح پادگانه درمنطقه بودهاست. بررسیها نشانداد طی دو دوره براثر بسته شدن دره توسط فعالیت یخچال و آتشفشان همگام باهم، در محل آباسک دریاچهای ایجاد شدهاست. این سد گدازهای بهتدریج طی هولوسن شکسته شده و در حالحاضر پادگانههای نهشتهگذاری دریاچه قدیمی در دوسوی درههراز قابل مشاهده هستند. با توجه بهشواهد بهجا مانده از این رسوبات در درههراز درنهایت مدل رقومی جریان یخچالی- لاهاری بازسازی شد.
Introduction During the Quaternary, tectonic forces have been implicated in climate change as a result of landforms or deformations in the ancient forms of the Haraz Valley. The terraces are solid landforms from the Quaternary period whose study of environmental changes during this period. But in the studied basin, in addition to climate change and intrusive fault-tectonics, volcanic activity has had the greatest impact on the processes governing the region. Haraz basin Although it has an area of more than 3779 square kilometers and is located on the border between East and Central Alborz, its basin is different from other neighboring basins. So that their forms and processes are genetically incompatible with processes in the region and exhibit specific structural complexity. One of the available forms is the diversity of alluvial surfaces that can be observed along the Haraz valley. Given that the totality of these alluvial surfaces, due to the youngness of the Haraz Valley, does not coincide with the present river process, the most important issue that may arise here is that these erosional surfaces have their effects on the slope. The Haraz Mountains are visible, were they merely influenced by the flow dynamics of the Haraz River? Otherwise what factor or factors contributed to the formation of these levels. There are three hypotheses for achieving the morphogenesis of Haraz terraces in the study area:A: Damavand lava intrudes through the valleys into the main valley of Haraz and forms a barrier lake in its upstream, forming morphogenesis of alluvial terraces of Haraz; B: Morphogenesis of haraz terraces is caused by glacier activity in the area;C: Damavand volcano deposited its pyroclastic material along the main arterial path of the Haraz and formed this vast surface of alluvial terraces in the area;Materials and methodsTo this end, analytical and temporal reconstruction methods of change have been employed. The technique is based on comparing the morphometry of lake terraces and glacier-pyroclastic dams with four methods of rehabilitating the study area, comparing the height and thickness of alluvial sediments, determining the extent of lake sediment distribution, and recovering the extent of barrier confinement.Result and discussionInvestigating the findings of the research and their comparisons and analyzes, it can be concluded that the terraces of the Haraz valley in this area are significantly different in terms of the thickness and height of the sediment and in the processes affecting their formation and alteration. The height of the alluvial surfaces at the outlet of the Gazane valley is 630 m. However, the height of alluvial surfaces in the Abe Ask reaches 200 meters above the river bed. The highest elevation of the terrace is at the outlet of Fire Valley to Haraz 2065 m. Therefore, this difference in altitude of the alluvial surfaces is not only related to the change in the basement level, but also to the interplay of glacial and volcanic activity of Damavand. The sequence of alluvial terraces is not evident in all the studied periods. While in the water of the ski in the travertine (interval 1) four levels, in the six intervals, four levels and in the Nova range three levels are visible. Other areas have an alluvial terrace surface. The genesis of the sediments of the terraces under study indicates a significant difference. Although the glacier has the most significant activity in producing and consequently the formation of alluvial terraces in this region and is dominant in genus, volcanic pyroclastic sediments have been active in sync with the glacier and evidence of temperature volcanic activity is observed among all glacial sediments. So that they are sometimes deposited on ice in the form of a Lahar layer and occasionally as a layer of ash or other pyroclastic material.Various researchers have already commented on the creation of lava barrier lakes in the Haraz Valley and the valleys around Damavand Peak (Alaei Taleghani, 2012; Yamani et al., 1977). Many are full of ice, not yet. Damavand's new volcano, which coincides with glacial and interglacial periods, has been able to throw pyroclastic and lava materials out of successive eruptions.ConclusionThe results showed that the elevation levels of the terraces had both an elevation difference and an irregular sequence. The highest level of alluvial terrace in the Nell Mountains is 630 m above the Haraz valley bed, indicating that in addition to changing the basin level, glacial processes have been a factor in elevating alluvial levels in the area. Surveys showed that the lake was formed during two periods due to the closure of the valley by the activity of glacier and volcano together. This lava barrier was gradually broken during the Holocene and nowadays the depositions of the old lake are visible across the Haraz valley.KeywordsHaraz River, Dam Lakes, Alluvial Terrace, Damavand Volcano
Machine summary:
براي دستيابي به اين ه دف بر اساس تفاوت ه اي لندفرمي که در منط قه وجود داشت ، شش بازه مط العاتي براي کل منط قه در نظ ر گرفته شد: شواهد فعاليت هاي پيروکلاستي دماوند در دره هراز بر مبناي نقشه زمين شناسي و با توجه به مشاه دات ميداني، آتشفشان دماوند بيشترين حجم مواد پيروکلاستي خود را در دامنه شمال شرقي تا جنوب شرقي تزريق نموده و انبوه اين مواد موجب تنوع در لايه ه اي رسوبي پادگانه ه ا و در بالادست دره گزانه موجب تشکيل درياچه و تعيين اولويت مورفوژنز پادگانه ه اي ه راز در اين بخش از دره ه راز گرديده است .
بيشترين ضخامت رسوب مربوط به رسوبات رس و سيلت به ضخامت ٢/٩٦ متر مي باشد (به تصویر صفحه مراجعه شود) شکل ٧: رسوبات پادگانه ها با ژنز درياچه ايي در مسير آب اسک به رينه بازه ٣: شواهد تغيير سطح اساس در بررسي شکل شماره ٨ وجود سط وح ه موار و نسبتا گسترده که از ط ريق يک پرتگاه فرسايشي و با چينه بندي پادگانه اي مسلط به بستر کنوني رود ه راز ه ستند نشان مي ده د انشعاب ه اي فرعي زه کشي ، گالي ه اي عميقي در اين سط وح حفر نموده اند.