Comparing the development potential of karst sinkholes in parts of high and folded Zagros Case study: Parao-Biston and Kabirkoh

Introduction

Several factors are involved in the speed of formation and development of these dissolution forms. In this research, two massifs of folded Zagros and high Zagros have been compared in terms of effective factors in the development of karst sinkholes. For this purpose, the Paraw-Biseton karst massif from the high Zagros and the Kabirkoh karst massif from the folded Zagros were selected and the effective factors in the development of karst sinkholes in these areas were investigated.

Methodology

In terms of political divisions, the Paraw-Biseton mountain range is located between the cities of Kermanshah, Sanhe and Harsin. This mass is a part of the high Zagros zone with a northwest-southeast trend, and a part of it is located in the Sanandaj-Sirjan metamorphosed zone. Its area is 930.5 square kilometers and its circumference is 449 kilometers. Paraw Mountain is the highest point with 3385 meters above sea level and the minimum height of the studied area is 1284 meters. The Kabirkoh karst mass is located in the folded Zagros region. This mass extends in a northwest-southeast trend from near Ilam city to the border of Khuzestan province for a length of 162 km. Its area is about 2530 square kilometers. The highest height of this mass is 2790 meters. The geomorphology of Paraw-Biseton mass is a combination of rock walls, hogbacks and rock scurps that are severely broken and faulted. The geomorphology of Kabirkoh shows an eroded anticline with a northwest-southeast axis.

The modified AHP method was used to prepare the development potential map of karst sinkholes in each of the studied areas. For this purpose, firstly each class of the studied layers was scored based on the number of sinkholes identified in that class, and then by forming a data matrix, the scores of the classes of each criterion were compared in pairs. In such a way that the score of other classes is minus the score of the standard class and as a result the diameter of the matrix is equal to zero. In the next step, the formula P = 0.08*A + 1 is applied to the positive numbers of each house from the previous matrix, and we reverse the negative numbers according to the similar house in the table. At this stage, the diameter of the table becomes equal to one. In the next step, by dividing each house of the previous matrix by the total of each column, a new matrix is obtained, which shows the score of each house of the matrix. At the end, by averaging each row of the matrix, the score of the class specific to it is obtained. All the steps mentioned above are done for each layer and we apply the scores obtained in the Arc GIS software to the classes of each layer and it is valued according to the new scores. Then, by averaging the used layers, the karst sinkhole development potential map is obtained.

Results and Discussion

To investigate the role of effective factors in the development potential of karst sinkholes, the factors of temperature, precipitation, altitude, slope, distance from the fault, lithology, aspect and vegetation were studied. After implementing the modified AHP model, the final map of the development potential of karst sinkholes of Paraw-Biseton and Kabirkoh massifs was obtained. This map was classified into 5 classes: very low, low, medium, high and very high by the method of natural fractures in the Arc map software, and the area and percentage of each class of sinkhole development potential was obtained. According to the results, 12.75%, 18.89%, 22.20%, 28.20% and 17.95% of Paraw-Biseton karst mass and 20.67%, 26%, 22.32%, 20.9% and 10.11% of Kabirkoh mass have very low, low, medium, high and very high sinkhole development potential, respectively.

Conclusion

The results of investigating the development potential of karst sinkholes show that 68.35% of the Paraw-Biseton massif and 53.33% of the area of Kabirkoh massif have medium to high potential in terms of the development of sinkholes. The comparison of the situation of the two massifs shows that the Paraw-Biseton massif and Kabirkoh massif are almost similar in terms of precipitation factors, altitude, slope, lithology and slope direction, but the examination of the classes that have the largest number of sinkholes and the highest score of the AHP model shows that in the Paraw-Biseton massif, for the precipitation layer, the class with 550-650 mm, for the altitude class with above 3000 meters, 0 to 10 degrees for the slope layer, the north for the aspect layer have the highest scores. in Kabirkoh massif, the highest scores for the precipitation layer is 750 to 810 class, for the altitude layer is 1800 to 2200 class, for the slope layer is 10 to 18 calss and for the aspect layer is the north floor. Also, the highest score for the lithological layer is the layer containing thick limestone (Biston Limestone for Paraw-Biseton and Kozhdam Formation for Kabirkoh). Examining the condition of temperature layers, fault density and vegetation shows a clear difference in the conditions of these layers. Paraw-Biseton massif has a more suitable condition for the development of karst sinkholes in terms of temperature, but with these features, the 11-13 degree layer has the highest score for both massifs. The Paraw-Biseton massif has a much higher density in terms of the number of faults, and for this reason, the class between 0 and 200 meters distance from the fault has the highest score in this massif, but it can be said that in the Kabirkoh massif, faults have a very weak role in the development of karst sinkholes, and the highest number of sinkholes are located in the class at a distance of 2500 meters from the fault. In terms of vegetation, Kabirkoh massif is in a better condition and the highest number of sinkholes is located in the forest layer with medium density. In general, it can be said that the Paraw-Biseton massif as a part of the high Zagros has a higher potential.