1 استادیار گروه جغرافیای طبیعی، دانشکده جغرافیا، دانشگاه تهران
2 کارشناس ارشد اقلیم شناسی، دانشگاه تهران
3 دانشجوی کارشناسی ارشد اقلیم شناسی، دانشکده جغرافیا، دانشگاه تهران
عنوان مقاله [English]
Weathering occurs when rocks of the land surface are affected by physical, chemical or biological processes and break down to small pieces. This operate occurs by wind, water and climate (Rich, 1950). Lewis Peltier models in climatic geomorphology are as the best sources for recognition of weathering processes, those geologists and other related sciences use them to identify and interpret the forms of surface (Fowler and Petersen, 2003, 5). The average annual temperature and mean annual precipitation are two variables that have major roles in weathering. Peltier using these two variables, described the seven models can identify different types of weathering phenomena (Peltier, 1971, 214-236). Fowler and Petersen (2003) applied Peltier models using GIS software in America and classified this country to different weathered regions. Iran's Geographical location, exposed many villages and cities in the high-risk zone. (Afrakhteh, 1997, 120). Considering of rare geomorphologic studies in our country about weathering processes, this article aims to paid and analysis weathering and morphogenic processes in North western of Iran and classify weathered and morphogenesis areas according to climate variables, and ultimately offer a comprehensive plan from the mentioned process.
Materials and Methods
In this study for investigation the weathering and morphogenetic regions at the North Western of Iran, data of average annual temperature and precipitation were collected from website of Meteorology organization. After reconstruction of shortcomings statistics, from all stations of region, 28 synoptic stations which have appropriate data period were selected and then a database established in ArcGIS software and data were recorded in this software. Then more analysis done in ArcMAP software and various maps were produced. In order to identify weathering conditions at the study area, Peltier models were used. Among seven peltiers models, two graphs for analysis of weathering condition in study area were selected. These two models are as follows:
A. Weathering processes: According to this model the most humid and the hottest areas have maximum chemical weathering, and the driest and the coldest areas have minimum chemical weathering.
B. morphogenetic Regions: In this model morphogenetic regions are divided into nine different categories. Areas with low temperatures, mainly are glacial regions and high temperatures areas with low rainfall are part of arid and semi arid ones; and areas with high precipitation and temperatures are parts of moderate and Savanna regions.
Results and Discussion
Precipitation of study area showed that there is two maximum rainfalls in this region that one of them is located at the South western shores of the Caspian Sea and other is located at western slopes of the Zagros Mountains in Kordestan province. While the minimum rainfall appearing in North stations such as Jolfa station. Temperature condition is very different, so that there is a minimum temperature in two stations in Sarab and Khalkhal cities, while the maximum temperature is in Gilan province due to vicinity to the Caspian Sea. In terms of morphogenetic, from nine morphogenetic classes in the Peltier model, five statuses in climatic classes have happened in study area. According to the geomorphogenetic map, more parts of the area are in dry regions, the stations that located at the South western shores of the Caspian Sea and western slopes of Zagros in Kordestan province are moderate and Savanna. Major characteristics of these areas are maximum activity of fluvial system and effect of ice and wind are low to moderate level. Only Bandar Anzali station was in oceanic climate. Among the seven models of weathering classes in Peltier models, five statuses happening in North Western of Iran. In the most parts of mountainous regions, there are weak to moderate mechanical weathering. While in stations of the south western coast of the Caspian Sea in Gilan, as well as Western slopes of Zagros in Kordestan, and south parts of Western Azerbaijan province, due to heavy precipitations, chemical weathering is more moderate type, rather than severe one. And in many other stations, due to abundant of rainfall and low temperatures, chemical weathering with frosting occurs.
The results showed that among seven weathering models in Peltier model, five models happened in North Western of Iran. Most parts of the study area are located in semi-arid regions and the most important Geomorphodinamic characteristic of these areas, are the effects of wind and moderate to severe water flow activity. Weathering processes in the South western shores of the Caspian Sea and western slopes of the Zagros in Kurdistan province are moderate and near to Savanna. Main characteristic of these areas is maximum water activity and the effect of ice and wind is between low and moderate level. Also there are a weak to moderate weathering in most parts of mountainous regions. While in stations of the south western coast of the Caspian Sea in Gilan and also Western slopes of Zagros, in Kurdistan and south of the Western Azerbaijan province, due to heavy precipitations Chemical weathering is more moderate to severe type. And in many other stations due to abundant of rainfall and low temperatures, chemical weathering associated with frosting occurs