جستجوی مقالات مرتبط با کلیدواژه « یخچال » در نشریات گروه « زمین شناسی »

Glaciers influenced by climatic factors and therefore as an important indicator in the study of climate change are studied. Although morphometric analyzes of glaciers based on the analysis of optical satellite data can provide an opportunity to measure ice outcrops, but the identification and determination of the buried glaciers underneath the Supraglacial moraines (accumulated debris on top of the glacial ice) and, consequently, the determination of the actual glacial body and their parameters, including the level and volume of the glaciers, are not possible based on optical satellite imagery. On the other hand, the existence of an ice cooling source underneath the glacial debris, which leads to a significant reduction in the surface temperature of the glacial debris, is a distinguishing feature for the separation of covered glaciers.
The over 2000 km long NW-SE trending Zagros Mountain belt extends from eastern Turkey to the Makran Mountains, forming a morphological boundary between the Iranian plateau and the Mesopotamian and Persian Gulf basins. The Zardkuh Mountain lies along the central Zagros Mountain Range (32°14'-32°38' N; 49°50'-50°15' E) in Chahar-Mahal and Bakhtiari province, Iran. The highest summit of this mountain chain is 4220 m a.s.l altitude. Small glaciers (mostly cirque glaciers) were first reported on the northern slopes of Zardkuh during August 1933. Other research has pointed to some glacial cirques on Zardkuh which have altitude about 3000m and located in small valleys on the N faces of the Zardkuh. Some new researches on the active glaciers of Zardkuh show the greatest glacier concentration around 1) Joft-zarde and Shahe Shahidan (Zarkuh) summits 2) around Sirdan summit and 3) Haft-tanan (Iluk) region. Based on the latest study, the current size of Zardkuh’s glaciers have estimated about 7.1 km2.
In this research, the expansion of natural glaciers of Zardkuh Mountain has been determined by the combined analysis of thermal (Thermal Infrared Sensor (TIRS) of Landsat 8), optical data (Operational Land Imager (OLI) of Landsat 8 and Quickbird image) and digital elevation data, based on Split Window Algorithm. For this purpose, the following steps are carried out: 1) Preparation of Landsat 8 TIRS and OLI images, Quickbird image and Digital Elevation Model with 10 m resolution 2) Radiometric correction and rectification of images to WGS-1984-UTM-Zone_39N 3) Detection of exposed ice of active glaciers using by short wavelength infrared and green spectral bands of Landsat and optical images 4) Creation of 3D model of active glacier by combination of DEM and Quickbird images / Landsat images 5) Estimation of Land Surface Temperature (LST) using by Normalized Difference Vegetation Index (NDVI) and Land Surface Emissivity (LSE) based on the Single Window Algorithm. The NDVI is calculated as a ratio between measured reflectivity in the red and near infrared portions of the electromagnetic spectrum. The land surface emissivity (LSE (𝜀)) is calculated based on the Proportion of vegetation (Pv) and NDVI. 6) Supervised classification of LST layer based on the sampling of ice and supraglacial deposits temperatures for each glacier (the presence of ice under sediments has already been confirmed in field visits) 7) Area calculation of ​​the glaciers based on the classified LST layer.
In this study, Land Surface Temperature (LST) layer were calculated for Zardkuh Mountain based on the single method algorithm. Furthermore, Land Surface Emissivity (LSE), Proportion of vegetation (Pv) and normalised difference vegetation index (NDVI) layers were calculated for the study area. The surface area of exposed ice of Zardkuh glaciers is detected by using the short wavelength infrared and green spectral bands by making RGB753 color composite which its spatial resolution has improved with Panchromatic band to 15 m and 3D model of glaciers. Based on the results of this study, the area of the exposed ice of glaciers were 123 hectares. The surface area of exposed ice and buried glaciers underneath the Supraglacial moraines of Zardkuh glaciers based on the described methodology, were measured about 201 hectares in August 2017. The area of ​​the Haftanan, Joftzarde, Kuhrang3 and Khersan glaciers has decreased and reached to 32, 31, 30 and 29 hectares, respectively.
In this paper, potential of remote sensing to study the actual extent of Zardkuh glaciers in Zagrous Mountains in Iran by estimating LST distribution with the help of Landsat 8 OLI and TIRS sensor bands provided. Remote Sensing technology data such as Landsat 8 TIRS proved as an efficient one to estimate LST. Single window algorithm methods are applied to calculate the LST from TIRS data. Based on the results of this study, the area of the glaciers (surface and buried ice) in comparison with previous studies, shows a significant decrease in the past decade.

The study of the past glaciers and its effects are the most important subjects of the quaternary period. The most important climatic evidence of the quaternary is also in the mountains of Iran, especially in the Alborz, west and northwest of the country is glaciers and related landforms. Geomorphologic studies focusing on glacial and periglacial landforms allow us to get a better insight into the spatial diversity of present and past climates. The Chehelcheshmeh and Saral Mountains are among the coldest mountainous regions in the country.These regions during the quaternary period was mainly influenced by glacial processes. The aim of this study was to reconstruct the quaternary snowline and morphodynamic zones based on glacial evidence.
2- Chehelcheshmeh and Saral Mountains are located 46 degrees, 28 minutes to 46 degrees and 58 minutes east longitude, and 35 degrees and 34 minutes to 36 degrees north latitude. The method of this research is analytical-descriptive and data collection method is library and field. The data used in this study includes aerial images, DEM, topographic maps and geological maps, and analysis tools including Arc Map version 10 and Gradistat version 4 software. In this research to recreate the glacier zone we used Wright and Porter methods. The permanent snowline in the Wright method is equivalent to an elevation of 60% of the cirques in the area above that height. For calculation of ELA in the method of cirque-floor altitudes, a mode has been used for classified data. For laboratory studies in this research, we used two granulometry and microscopic methods for three sediment samples. For granulometric Process, we used Seave analyzes for particle with a diameter of more than 2 mm and Laser analysis for sediment grains with a diameter of less than 2 mm. Then, based on laboratory studies and field observations (to better control and identify the landforms) and with the help of aerial imagery, the study of elevational digital model and the study of geomorphologic landforms was identified evidence of each of glacial and periglacial morphodynamic zones.
3- In the survey of the study area, 25 glacier cirques were identified, some of which are well seen by the surrounding landforms. Distribution of glacier cirques showed that the glacier extent was down to 1280 meters high. In accordance with the Porter's cirque floor altitude, the final limit of the quaternary snowline was 2483 meters above sea level, which considering the active glacier valleys, glacial evidence was also seen below this elevation. In the field observations, it was found that glacial deposits are located in the Ghezel Ozan river and at a height of 1900 meters. To determine the sedimentation environment, the results of Laser and Sieve analysis on the samples showed that the studied area is affected by the processes of freezing and melting in a cold environment by preserving plant remains and heterogeneous distribution and particles bad sorting. Maintaining feldspar minerals is another result of laboratory work, which indicates severe mechanical erosion and very low chemical erosion in the study area. The lack of clay and colloidal sediments confirms this.The glacial and periglacial morphodynamic zones in this research were studied using their evidence that was identified many of the relevant landforms including Cirques, Glacial valleys, Tills, Erratic rocks, Solifluction lobes, Rock cracking , Moraines, Avalanches and Rock steps.
4- Investigation of glacial and periglacial evidence showed that quaternary snowlines in the mountains of Chehelcheshmeh and Saral compared to the investigations carried out on the Alborz, Zagros and central iran mountains at lower altitudes. Different climate of Kurdistan mountains compared with other parts of Iran is one of the main reasons for the low elevation of snowline in the region, so that the minimum temperatures in the synoptic stations of Zarrineh Obato and Heazrkanian that located in two catchment basins in the cold seasons it is mostly critical and one of the coldest parts of the country. Sedimentological evidence and laboratory analysis also indicate a cold environment in the study area mainly influenced by snow melting processes and mechanical processes, in many instances, irregular arrangement and bad sorting are observed and coarse particles constitute the highest weight percent. In the study of field evidence, many landforms and processes were identified that, considering the distribution of glacial evidence in the present, lower boundary of the periglacial morphodynamic active zone was introduced the 2750 contour.

Quaternary glacial and interglacial conditions were alternately and they left geomorphological evidence overwhelming that it can be used to determine the extent of glacier and snow-borders and the study of climate change last period. It is possible due to the fact that external processes such as weathering, water erosion current and range motion could not eliminate the debris of Quaternary glacial erosion completely. Form cirque is a reflection of the topography and geology, the type and duration of glaciers. Structure stone, cracks and gaps is an important factor in a cirque cliffs and deep of cirque basins. When in the mountain, peaks height exceeds a little limit permanent snow, glaciers often in cirques. The study area lies on the political sphere three provinces of Kurdistan, Kermanshah and Hamadan between 34.752 to 35.223 latitude and between latitudes 47.411 to 47.416.
Initially north-eastern and south-western slopes of the Qorveh mountainous region was divided to Wright method. Altitude, which was 60% of cirque higher than, was considered as the permanent snowline altitude after identifying and counting cirque area of the curved lines form and sort them in descending. The position, height and geomorphological features around the cirque were identified. Snow line was estimated height of 2,200 meters on the total area of this method, and it was not much different on the northern and southern slopes. The altitude of more than 60% of cirque were the height of 2200 meters in both slope. 1.The method is based on the present conditions Hydro-geomorphology state of minimum temperature during the Quaternary through the legacies of morphological climate changes in the Quaternary in the mountainous region Qorveh. Although the place is cold and semi-arid regions of the country due to the current temperature and precipitation conditions, but experienced cold and frost likely transition phase to warm phase cold during the Quaternary. Accordingly, is used primarily method documents the library has and field.
Permanent snowline altitude was estimated of 2200 meters due to the dispersion cirque and Wright method. Analysis of the current isotherm map shows the annual average temperature this height of 8.8 ° C. This is the height of a lower temperature than the average temperature of current regional during the Quaternary. Average Quaternary temperature has been -0.12° C. But in this area there is an obvious difference in quaternary permanent snowline in the North East and South West and this is in contrast to research results that suggest the snowline altitude difference in such domains. 1. Conclusion, Keywords
The land surface of the slope aspect influence is undeniable on the durability snow and feeding more glaciers in mountainous regions temperate areas of the Earths, but this effect certainly cannot be justified only with snow border. Mountain sinuosity altitude difference, the slope of the lower areas of the mountain sinuosity, extent and dimensions of the cirque and who to cirque associated with low levels of around two domains are factors that should be considered in this impact. Morphology and dominant lithology Qorveh cirque on topographic and geological maps show both sides of the Qorveh Mountain their primary form of crater-like and holes with the same height, conducive to the accumulation of snow, this has affected the ice and snow on the same quaternary snow line in two domains. In fact, early topographic conditions that follow the form tectonics, the formation of more than 60% of the cirque at a height that is known today as the permanent snowline altitude (2200 m).

Of all glaciers used as indicators of climate change, cirque glaciers are probably the optimal ones to use. Due to their small size and volume, their response time to positive or negative changes in mass balance is rapidly manifested, often within a couple of years. Singh (2011: 144) suggested that this implies that a sustained negative mass balance, lasting no less than a decade, will rapidly lead to a reduction in size and vice versa. In the quaternary period, glacial and interglacial conditions have occurred in turn in the earth`s history and laid out by geomorphological evidences are undeniable that can be used to determine for snowline borders and equilibrium line altitudes and so on; for studying climate change in that period. It is possible that the reason for external processes of changing the Earth could not have completely cleared away the glacial landforms that remained from of quaternary glaciation.
Material and This research is a basic research; thus the main goal of it is the extension of the quaternary glaciation theory by data analyzing and finding relationship between mountain direction and elevation; and creation of glacier landforms. This research wants to find an answer for these questions: 1) is there correlation between glacial geomorphologic evidences in Haraz valley from altitude and distribution? 2) Is quaternary glacial border in Haraz valley in the last glacial maximum located in different altitude or not? If the answer is yes what are the causes of these differences? 3) What is the relation between volume and distribution of glacial cirques and topography and relieves direction? This research's hypotheses are: 1) Extent, volume and frequency of glacial cirques are more in the northern slopes than southern slopes this issue first of all depends on the precipitation volume. 2) The average of glacial cirques altitude and glacial terminus in northern slopes of Haraz valley is lower than southern slopes. Methods or models which are used to answer this issue can be classified in two groups: first, methods and models which are used in the main part of report, containing contour line methods, this is used to restoring the continental and hydrologic data. In the second part which is used for analyzing data, among the methods that Porter suggested, cirque- floor altitude method is selected for this research. When a glacier just fills a cirque, its steady-state equilibrium line altitudes (ELA) typically lies not far above the average altitude of the cirque floor and cirque floor altitude has sometimes been used as a convenient proxy for former ELAs. This research has been based on the comparison between cirques elevation and determination of the extension of glacial toes in the equator-faced slopes and the pole-faced ones. All data and analyses have been shown with use of ArcGIS and SPSS softwares that illustrated on the different thematic maps.
The analysis of foundation of glacial cirques in dissimilar altitudes has initiated with reconnoiter of those cirques that are located in 100-meter contour lines, and then they have analyzed with the statistical methods to obtain permanent snowline in last glacial maximum in octagonal aspects in the Haraz valley. To compare the mean altitude of glacial cirques and the altitude that there is the most frequency of the cirques, it has calculated arithmetic mean and “mode”. The results of this study showed that there is a significant difference between the observed frequencies and the expected frequency and distribution of these cirques was promoted by the mountain aspects; i.e. poleward slopes that receive relatively less energy than equatorward slopes are more appropriate location to formation of cirques and other glaciers features.
According to the calculated equations, temporary snowline is estimated 4938 m in the equator-faced slopes and 5605 m for the pole-faced ones. Based on the synthetic of statistical analysis and cirque floor altitude method, the former ELA has been 2799 m in the study area and modal value is 2706 m. The modal value in the pole-faced ones is 2874 m and in the equator-faced slopes is 2941 m.

The equilibrium-line altitude (ELA) is generally dependent on the accumulation of snow which is influenced by the regional distribution of snow precipitation and local redistribution of snow by wind. Due to the effect of wind-blown snow on ELAs, the terms temperature-precipitation equilibrium-line altitude (TP-ELA) and temperature-precipitation wind equilibrium-line altitude (TPW-ELA) is introduced to distinguish between glacier ELAs reflecting the general winter precipitation and ablation season temperature in a region and glacier ELAs that are influenced by either snow deflation or accumulation (such as on cirque glaciers). In this study the TP-ELA in presently glaciated (Zardkuh and Oshtorankuh) and non-glaciated (Dena, Garein and Shahoo) areas is calculated. The altitude of small glaciers is also used to estimate the TPW-ELA. Based on this approach, regional climatic TP-ELA in Zardkuh, Oshtorankuh, Garein, Shahoo and Dena mountains is between 4400 to 4500 m a.s.l.(above main summits of the Zagros Mountains) TPW-ELA is around 3850 m a.s.l. in Zardkuh and Oshtorankuh Mountains which is 650 m lower than the regional TP-ELA. The present small glaciers in Zardkuh and Oshtorankuh are the result of leeward accumulation of wind-blown snow on small glacial cirques.