عنوان مقاله [English]
Temperature and its changes are considered as an important factor in the physical weathering of rocks. The maximum influence of temperature is frost action and thermal expansion. The effect of temperature on the degradation of rocks, moreover temperature range, depends on the strength of rocks. During freezing, water in cracks and fissures of rocks is increased 8 to 11 percent in volume and this has a force of about 2000 pounds per square inch. The continued practice of freeze and thaw can cause small fissures, cracks and separation. The result of this process is formation of the Talus and debris cones (Blyth and Freitas 2005). Evidence of glacial geomorphology is one of the most visible legacies of the Quaternary period Climate change (Mahmoudi 1988). One of the most important legacies of Pleistocene climate in the highlands of the Iran, especially in the Alborz Mountains, West and North West of Iran is the dominance of the glaciers and related landforms (Yamani 2002). West region of Kurdistan province with collection wide variety of heights and glacial heritages in recent centuries has been studied by Iranian and foreign researchers including Van Zeist and Wright (1962), Wright (1980,1967,1962), Hutchinson and Cowgill (1963), Van Zeist (1966), Megard (1967), Pedrami (1982), El-Moslimany (1986), Brooks (1989), Bottma (1995), Snyder et al. (2001), Stevens et al. (2001), Wasylikowa (1966,2005), Ehlers and Gibbard (2004), and Wasylikowa et al. (2006). Given the rare geomorphologic studies in our country about weathering processes and zonation of morphoclimatic areas, this article aims to examine weathering and morphoclimatic processes in west and northwest of Kurdistan and classify weathered and morphoclimatic areas according to climate variables and glacial traces.
Materials and Methods
Based on the purpose of the research, this research has used some materials including topographic maps at scale of 1:50000, satellite images of Landsat-TM and ETM, Aster elevation model 1.5arc, Google Earth (126.96.36.19913) images, and 12-year period climatic data about average temperature and annual precipitation of eight synoptic stations. Toe-to-headwall altitude method used for calculating Holocene snowline and Peltier weathering regimes model is used for the weathering classification. For production and analysis of maps we have used software including Ilwis 3.3, ArcGIS 9.3, Globalmapper 12.1 and Excel 2007. Then, more analysis was conducted by ArcMAP software and various maps were produced. To calculate Holocene snowline in the study area based on theoretical and local knowledge using Landsat images, four mountainous series sites including Arbaba, Chelchama, Qalabard and Zarvah were selected to reconstruct Holocene snow-line. Based on the linear regression between temperature and precipitation and paleosnowline, wurm temperature and precipitation maps were prepared. Weathering map regimes, in considering the location of the stations in the Peltier weathering regimes model, was prepared using weighted method. Based on the results of weathering zones, wurm temperature and precipitation and the extent of glacial and periglacial landforms, wurm morphoclimatic map for the selected mountains series, was prepared.
Results and Discussion
The results showed that among seven weathering models in Peltier model, three conditions occur in the study area. In most mountainous areas mechanical weathering occurs in weak to moderate, this is because of high rainfall, more moderate chemical weathering occur in western Kurdistan and in other stations chemical weathering with frost action is dominated due to low temperature. Among morphoclimatic systems in the study area, glacial, periglacial and fluvial systems have occurred in wurm. Glacial erosion system at the altitude above 2000 meters and periglacial erosion system have occurred at the height of 1600 m to 2000 m in the mountains of West Kurdistan.
Remaining landforms in mountains, including cirques, glacial valleys, terminal and ground moraines, Talus and debris cones, nivation and others indicate the dominance of glacial agents in the wurm. Wurm most zones in the study area have been under the influence of moderate mechanical weathering. Poor chemical weathering has been dominant in the west strip area of Kurdistan. Remaining landforms in the Arbaba, Qalabard and Zarvah mountains including cones of debris flows, debris flow slopes and Talus, in Mountain crest to heights of about 1700 meters, are evidence of glacial erosion. Most of landslides are generated because of the prepared debris and materials from periglacial erosion. The results obtained from wurm rainfall in Zarvah and Qalabard mountains are largely matched with the results of Zeribar sedimentological and palaeobotanical study. Rainfall reduction and temperature drop during wurm period in the region has been accompanied with the steppe vegetation and lack of tree pollen.