چكيده لاتين :
1. Introduction
In most parts of the world, like Iran, including many forms find the reason for their existence cannot be interpreted by current processes (Jedari-e- eivazi, 1381, 67). In geological terms, this principle is the present situation is the key to the past. This is the first time has called by "Charles layer" as Uniformitarism (Ramesht et al, 1386, 4). Today, relying on various forms of glacier, very sensible decrease in temperature and glacial processes repeated expansion in the quaternary has been proven repeatedly. Glaciers are in equilibrium and interaction strongly with their environmental elements; and because show a great sensitivity against them, Slight variations in environmental conditions, is reflected on it. So many valley glaciers are considered sensitive and appropriate indicators in identifying inconsiderable environmental changes. In other words, the natural equilibrium is defined by them (Ramesht et al, 1381, 55). Geomorphic and civil evidence in Karaj River Basin suggest past climate is different than currently and they are represents the superior environmental situation for the Civic Centers establishment, affiliated with environmental factors –herding systems - in past. Therefore, in this study we tried to pay to reconstruct environmental conditions of Karaj in quaternary in period of minimum . After determining the climatic conditions in period of minimum in the basin, were examined to roll of the situation in geomorphic evolution in the basin and its relationship with herding systems in Karaj plain. The basin is limited by Chalous basin in north, Lar and Jajrood basin in east, Kordan and Taleghan basin in west, and Kan basin in south. Karaj river was built Amirkabir Dam on, is originates from Palan-garden mountain in central Alborz. After crossing the river from the eastern Karaj city, after joining the Jajrood-in south of Varamin- Salt Lake leads.
Many scientists and theorists have study and theorized about quaternary environmental changes. Including studies of the past can be noted to Blanford (1873), Bobek (1959,1963), Write (1963, 1968), Huckriede (1968), Krinsley (1970), Pedrami (1982), Motamed (1367), Mahmoud (1367), Ramesht (1371,1381), Jedari-e-Eivazi (1381), Yamani (1386), Zamani (1388) and many masters and PhD thesis under the supervision of geomorphology professors in Tehran, Isfahan etc..
2. Materials and Methods
This study relies on the study of geomorphic forms and artifacts found in the region. In the research process, base of land Information is maps 1: 50,000 of Armed Forces Geographical Organization. Using Surfer, layers of Icefirefields, Snow Line and the Water-Ice equilibrium were determined by Wright method. In Wright method, Line 60 percent Icefirefields be higher than it used to be known as the permanent snowline. Secondly, climate information of synoptic stations, collect and by using of Wright method, was used to analyze the present and past climatic conditions. In the third stage, according to studies of climatic, topographic maps, geological maps, satellite images and field observations were examined to determine the Water-Land equilibrium. And finally adding archaeological studies, herding systems was explaining in region. The entire process required for mapping and data analysis software, Global Mapper, Surfer and Digital Elevation Model (DEM) is used.
3. Results and discussion
Heat and humidity reconstruction in period of minimum
Mapping the past isotherms map is possible by using the permanent snow line. In Wright method, Line 60 percent Icefirefields be higher than it used to be known as the permanent snowline. This line indicates the height of 2700 m in basin Karaj. Based on the survey basin above the snowline, about 604 km from basin Karaj was under the ice. Determine the isotherms lines according to 128193 height points were harvested. The results of the evaluation annual mean temperature map the in the period of minimum shows the average annual temperature in the basin was around zero degrees Celsius. To extract the vector map isorain lines at the current time, at first the relationship between altitude and mean annual precipitation was measured. Isorain map also shows the 1.5 times current rain was falling in the study area. Digital Evaluation via interpolation the past isorain maps states that the average annual precipitation in the basin was 783 mm fall down. Thus, despite the domination of moisture and intense reduce evaporation by cold of zero, all possible assumptions for the growth of a wet and cold climate of the region is determined.
Conclusion
U-shaped glacial transitions are known to valley trough. In the case of Karaj Basin mega floods caused by ice melting in Para glacial, passages of glacial was erosion in much of the water flowing violently. However, in some areas, we are seeing the effects of glacial excavation. For example, Zamani (1388) notes the moraines of the valley Shahrestanak length of 5800 m, a thickness of 200 m and an area of 3.5 km at the end of the waterway. Motamed (1382) also the suspended valley above of the Aderan has known evidence of glacial erosion in area. Karaj ice tongues after Feeding of Icefirefields in the basin extends the slope to the south and at altitude of 1300 meters, itʹs drilling evidence fades away gradually above the plain. In fact, this altitude is the Water-Ice equilibrium line that corresponded to the 10 ° C isotherm on quaternary period of minimum maps. Karaj glacier along its passage split alluvial fan deposits deeply in the easternmost Karaj city and so glacial phase should occurred the last evolutionary phase and after major alluvial fans formation. Karaj big glacial valley length, Varange rood to the lower basin, 92 km is obtained.
As mentioned above the height of 1300 meters, the evidence of glacial transitions cannot be observed. In fact, the this boundary to plain flow of water from the melting ice tongues Karaj plain to the local level (altitude 1200 m) have erosion. Geomorphic evidence at altitude of 1200 meters, shows the bifurcated channels that spread on Karaj plain and was fed to melting of ice water. Formic evidence indicates the lake of Karaj plain include: bifurcated channels, terrace, lake sediments, single point height, catoctin, brick and pottery kilns, ancient Hill and names that represent civilization dependent on lake. Lake overflow is obtained of the village Shesh in Mahdasht functions.
Key words: period of minimum, permanent snow line, Water and ice equilibrium line
