Analyzing the effect of climatic parameters on weathering of rocks using the Lewis Peltier model -Case study: Southwest of West Azerbaijan Province

From ancient times, stone has always been a symbol of stability and strength, and ancient human beings took refuge and chose to settle in mountains and mountainsides (Santos et al, 2018: 2). However, rocks on the ground or near its surface decay and decompose gradually due to factors such as weathering (Memarian, 2000: 2). Climatic geomorphology is a scientific field in which shape and distribution of landforms are analyzed according to climate type. Specific weathering processes affected by the climate are in place in different morphological zones (Jafaria Aqdam et al., 2012: 1). The present study seeks to investigate the lithology of southwestern mountainsides of West Azerbaijan province using Lewis Peltier model.

Peltier weathering and morphogenetic models were used in the present study. Topographic, geologic, isothermal and isohyetal maps were produced using Inverse Distance Weighted (IDW) method in GIS environment. Temperature and precipitation ​​were analyzed using different graphs and tables to determine drought and humidity conditions. 

Results indicated that the northern mountainside is wider and thus, its ​​precipitation 407-477 mm and temperature of 15-17 ° C have the greatest impact on the region. Data collected from four synoptic stations in the province with a common 30-year reference period (1986 to 2018) were used to investigate weathering and morphological condition of rocks in the study area. Table (1) shows the location of these stations. Climatic data such as average annual temperature and precipitation were reviewed and corrected in ArcGis environment. Then, ArcGis was used to create a basic database to store data and prepare relevant maps. Weathering regimes are determined based on the Peltier chart (1950). In this diagram model, two variables -average temperature and annual rainfall- are used and weathering regimes are divided into seven classes each of which represents a type of weathering condition. The model of morphogenetic regimes is more similar to a climatic or vegetation classification than a weathering model. In this model, two variables of average temperature and annual precipitation are used and morphogenetic regions are divided into nine different classes. Areas having a low temperature are mainly classified as glacial areas and areas having a high temperatures and low rainfall are classified as arid and semi-arid areas. Areas having a high precipitation and temperature classified as temperate and cold areas. To apply Peltier model to the study area, the specifications of synoptic stations were first presented separately in a table. Then, zoning was performed based on the square value of temperature and precipitation using IDW method and then, the percentage of area covered by each ​​temperature and precipitation class was determined. Precipitation class of 407-477 mm covers 32.67 percent of the area. Moreover, temperature changes in the region indicated that 15-17 ° C temperature range has covered the largest part of the study area with a percentage of 39.41. The values of temperature and precipitation along with the results of Peltier model indicated that a very low level of weathering is present in the study area. Farahmand et al. (2015; 10) have shown that temperature and precipitation parameters in this region depend on elevation. To determine the morphological condition of the region, it was divided based on its climatic conditions. To determine the accuracy of weathering results, a map of geographical directions in the region was produced. Vegetation and soil in western and northwestern parts of West Azerbaijan province have a pretty good condition. These were divided into three different classes and weighed based on the weighing parameter. Result was presented as a map and a table in which mechanical weathering with a lower-intensity had a weight of 1 and chemical weathering with a higher-intensity had a weight of 3. The classification results are consistent with Hanafi et al. (2002; 72) who introduced mechanical weathering as a factor leading to rock disintegration in northwestern Iran due to climatic conditions. They are also consistent with Maghsoudi et al. who used climatic parameters of temperature, precipitation, and weathering intensity to determine weights for the Peltier model. In mountainous areas of the country such as Zagros, Alborz and northwestern Iran, low temperature and frost may lead to a low level of mechanical weathering (Maghsoudi et al., 2010; 36).