| چکیده انگلیسی مقاله |
Extended abstract Introduction The attention of forefront foreign researchers has focused on glacier circus. Glacial cirque is the most important pattern of glacial erosion. Deep depressions with steep walls, flat floor or low slope, half-bowl shaped (crescent shaped) are created at high altitudes in the mountains margin by the erosion of mountain glacier (Ahmadi, Feiznia, 2012). The form of circus is a reflection of topography, geology, type and duration of glaciers (Derruau 1990). Distribution of circus and glaciers with different dimensions in particular mountain range depends not only on the topography of the mountain, but also on the slope direction (the sun) and the wind (Motamed (2003). The morphological effects of Quaternary glacial in Iran had been known, at least from the late 19th century (Jedari Eivazi, 2011). There is no comprehensive study about different shapes of the circus like land forms which have been created by lithology, direction and an amount of slope and territorial levels. The study area lies on the political sphere of three provinces of Kurdistan, Kermanshah and Hamadan between 34.752 to 35.223 latitudes (northern degrees) and 47.411 to 47.416 longitude (eastern degrees). In the study area, 52 circuses were identified, 20 of which belong to the north-northeast slopes, and the rest have been located in the south-southwest slopes. Initially, north-eastern and south-western slopes of Qorveh's mountainous region were divided based on the Wright method. An altitude, which 60% of circuses were higher than it, was considered as the permanent snow line altitude after identifying and counting the circus area according to the curved lines form and they were sorted in a descending order. The snow line altitude was estimated as 2,200 meters in the study area, and the snow line altitude difference in the northern and southern slopes was negligible. Circuses were divided into three categories due to the differences in the appearance (valley circus, domain circus, crater circus). The difference between valley circus and crater circus is that the valley circuses are extended along the foothills by the very small circus floor, long and narrow valley, while the crater circus is perfectly circular, wide and is surrounded by steep mountains. This kind of circus in southern slopes have extended in narrow and long valley along the foothills; on the other hand, in the northern slopes, they extended in wide valleys with no clear boundaries with ther neighboring lowlands. Domain circus was considered as an indicator to evaluate the characteristics of the study area's circuses. 2- Methodology Qorveh, Asadabad, Chenar Sofla, Kamshgran, Bolbolan Abad, Satre, Sonqor and Kangavar 1: 50,000 Topographic maps (Figure 2) and satellite images are among the investigated documents. Slopes of the snow line altitude was examined due to the impact of the slope direction on the permanent snow line altitude, because the effect of the slope direction on the solar altitude angle and precipitation is reflected in the land forms. According to the slope direction and the amount of it in the circus basins, the differences in circus features were explained. In this regard, the amount of avalanche of fertility or feeding in association with the amount of directon were used. 3- Results The results show that the effect of land slope direction has reflected in circus morphology rather than in the snow line altitude. This means in both northern and southern slopes, the crater-like land forms have caused concentration of glaciers in early drill, and the ice circus had little role in the development of their own. The slope of the land has completely destroyed the wall of early plains craters in the northern slopes, and the circuses are associated with lowlands by the wide open valley. In the southern slopes, circuses are connected with the surrounding area by long and narrow valley, and have maintained their crater-like forms more than the northern slopes. 4- Discussion and Conclusions The mountain peaks around the circus are almost all in the same height range, higher than 2800 meters, and connected with circular circus floor with the diameter of more than 4 km, and the valley width of less than 500 m. Such features in the form of main circus in the area refer to the existence of multiple crater forms in Quaternary in cold periods, and have provided fertile ground for the snow driven by the wind and avalanche. These features have influenced the scattering of circuses, in such a way that the dominant aspect of Qorveh mountain range had little impact on the Quaternary permanent snow line altitude. However, the direction affects the permanent snow line and the shape of the circus. The direction has effects not only on the snow line altitude, but also on the shapes of the circus in the study area. The difference between the snow line altitude in the northeastern slopes, which have better feeding situation, and the snow line altitude in the southwestern slopes is not noticeable due to the impact of the direction. Based on Chorly et al. (2007), Mo'ayyeri et al. (2011), Ramesht and Shoshtari (2004) and Talebi's (2002) findings, the northeast direction is the best direction to form a glacial cirque. The difference in the feeding or melting status of the glacier in the Qorveh mountainous area is not reflected in the permanent snow line, rather its reflection is evident in the shape of land forms resulting from the external processes. |