Role of hydrodynamic parameters in origination and revolution of Karstic phenomena " Ashkout Mountain, Mahmoudabad, Northwest of Iran"
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Abstract:
Introduction

Karstification is a complex process which is controlled by parameters, related to soluble rocks and water. It is affected strongly by surface and underground hydrology. in dense limestone areas, there are pitted formations superficially. Holes, fissures, fractures and conduits have been made a complex hydro geological circumstances for the underground currents. Relationship of fissures and fractures with groundwater make a Karstic morphology. There are lots of studies about Karsts, due to their importance in human life, for example Baomin (2009), Luhmann and Hung Chak (2012), Mostafa (2015) in addition to Iranian researches such as Rezaei Moghaddam and Ghadri (2005), Behnia Far (2009) and Maghami Moghim (2016). The study area has not been studied yet in spite of its various Karstic features. In this study it has been tried to study the role of hydrodynamic factors in Ashkout mountain karstic morphologies’ origination. This mountain located at the northeast of Mahmoudabad, in southeast of western Azerbaijan and the northwest of Iran. Its climate is cold and semi-arid, upon to Amberger climate scale. The average amounts of precipitation and temperature are about 338.3 mm and its average temperature is 9.4 C° respectively.
Methods and Material: In this research, after extensive library studies, more works have been done on field studies. Due to the climatic conditions and topography, field studies took the most time. Accordingly, after identifying the karst forms, measurements of their physical dimensions were performed. Subsequently, the position of each of them was taken using Gps and marked in the map of the region. Recording of the karst formations to adapt them to karst phenomena and to more accurately identify them. They took place. Also, the graphic design was provided for those karstic phenomena in the area, such as dissolved tubes that could not be taken on the ground. The study of the region's climate was carried out based on the data of the weather station. The maps of this study were mapped with Arc GIS software.

Results And Discussion

Some morphological features of Ashkout mountain resulted from surface water action, which Karen is the most important one. Grik Karen is one of the most substantial ones, which generated because of the structural phenomena, weathering and solution at the southwest and northeast of Ashkout mountain limes. Dissolution corridors are another features which generated due to structural fracturing over the study area’s limestone. They can be mostly observed at western slope. In this section, the inter bedded limestone, light limestone and lime conglomerate located in beneath, middle and upper beds respectively. Some layers have been overturned, which caused that the Karstic layer bedding can be obvious superficially and expose to dissolution factor. In western slope, which bedding has been disturbed by faulting, the lime conglomerate turned in to abyssal sides with sharp banks. Other limestone has been dissolved and formed fovea which called solution- bedding corridor. Karstic street is another feature that developed on some parts of southern slope, parallel to road plunge. It has 20, 5 and 200 meter, width, deep and long respectively.
Some other morphologies, originated due to surface water accumulating in fissures, fractures and holes. solution pipes are the most important ones. there are cylindrical holes on Ashkout surface. They are not dead-end form and vertical, but, they have a horizontal pipe at the end of vertical hole, with about 90 ° angle. Vertical wells are another forms of morphologies in Ashkout mountain area which located in light limes in western slope over a carbonate rock bonnet. This bonnet has vertical walls and has 1.5 meter and 7-meter diameter and deep respectively. Dissolution Dolin is also another feature, generated because of the same phenomenon in southeast of Ashkout on light lime, containing chert. It has about 10-meter diameter and more than 1 meter deep. Caves are the other features, generated by groundwater. 20 caves were determined in field survey in the study area. Underground conduits are another phenomenon which originated in rock walls of Ashkout mountain. These conduits got observable due to faulting and fracturing. Some of them are springs that have come out of the steep slopes.
They called Karstic conduits, because they have some special size, form and path. These conduits are divided into 3 branches, include abyssal, cascading and natural. Karstic bridge is also another phenomenon, generated due to same process. Water erosion has made a natural bridge shape rock body, called natural bridge. There is a limestone body at north of the mountain, which its upper part disturbed and its base remained. In this body there are two Karstic bridges in southeast and northeast directions.

Conclusion

Although, the structural properties have significant role in karstification, rock sensitivity to dissolution processes and hydrodynamic forces have more major quota. Some portion of waters, originated of precipitation, run off superficially along the slope or entered the fissures, fractures and joints. They made Karstic morphologies such as Grik, dissolution conduits, dissolution-bedding conduits and Karstic streets. Other portion made some features such as Pan, Dolin, Dissolution pipe and vertical well, through the deep penetration into the lower layers. Finally, the other portion of waters, flow beneath the layers like a river or canal current and made some other features such as caves, underground conduits, natural tunnels and Karstic bridges. Considering the currents diversity and Karstic water location, various dissolution morphologies have been originated. Underground conduits have been made by kinetic-dissolution force of groundwater through the joints, fissures and fractures. Limestone is the main host of these phenomena. Surface water, in some cases, penetrated towards the limes bedding and has made some dissolution structures such as pipe form tunnels. Natural tunnels and lime bridge were at the first of groundwater conduits which generated by northwest faulting in Ashkout mountain. External phenomena, separated some parts of mountain main body during the time, via surface erosion and slopes collapse, to make natural tunnels and Karstic bridges. The overall result of these study is that climate of this area is not enough contemporaneously, for the Karstic morphologies. Therefore, the past eras can be considered as the main forming factor.

Article Type:
Research/Original Article
Language:
Persian
Published:
Geography and Development Iranian Journal, Volume:16 Issue: 50, 2018
Pages:
75 - 94
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