변산반도 국립공원 내 산성화산암에 발달하는 주상절리의 특징

Abstract

The columnar joints which had formulated during the Mesozoic era are mainly related to Rhyolite or Andesitic. Particularly, it is expected to proceed several times during the later cretaceous period that the volcanic activity which was composed of tuffs created the columnar joints. This study aims to provide the basic knowledge of the research for the columnar joints in this area by analyzing the feature of the columnar joints which was results of the volcanic activity throughout the Jeokbyeokgang and Jiksopokpo(Falls) in Byeonsanbando National Park. This study has measured and analyzed the morphological characteristics of the section of the columnar joints. This study also has implemented a chemical and an optical analysis after collecting the samples of rock from the thirteen different sites. Then, it has researched the condition of the calculation of rocks in order to seize the relation with the surrounding rocks. Columnar joints of Jeokbyeokgang is distributed throughout six hundred meters long along the seashore. Mainly, almost of columnar joints is seen as vertical direction which is called colonnade structure and the maximum height would be ten meters. And Gyeokpori Fomation is founded underneath of the columnar joints in this area which is comprised Gomso Rhyolite. 125 cases of the length of a polygon side and 139 cases of the angle between the adjacent edges were measured in the Jeokbyeokgang. As a result of this investigation, it is discovered that the number of a polygon(N) is pentagon possesses almost half of it. The length of a polygon side(L) is 24.8% for 10cm excess less than 15cm. In addition, the angle between the adjacent edges() is 19.42% for 120° less than 130°. In comparison with the general formula of columnar joints, the unique feature was revealed that the lower part of lava flow has small colonnade and the upper part of it has big colonnade. Furthermore, in the case of BS-25, the entablature serves to the lower cooling surface. The upper cooling surface interaction the joint can be developed as similar to the onionskin shape. Study area of Jiksopokpo(Falls) has calculated the various polygon of columnar joints, 136 cases of the length of a polygon side, and 97 cases of the angle between the adjacent edges from the downstream of Jiksopokpo(Falls). As a result of this research, it is discovered that the number of a polygon(N) is 45.45 % for hexagon. The length of polygon side(L) is 26.47% for 20cm excess less than 35cm. In addition, the angle between the adjacent edges() is 24.74% for 100° less than 110°. It could be inferred to these following reasons that only the outcrop of columnar joints were shown to in the area from the Misunnamu bridge in Jiksocheon(Stream). First, due to the greater cooling rate the lower, Byeonsan Tuff could not solidify and the upper and Byeonsan Tuff above Jiksopokpo(Falls) also was affected by the greater cooling rate to solidify enough. Second, the columnar joints that had already formed could be disappeared by the corrosion of flowing water. This study aimed to differentiate from the existing research which mainly focused on the cooling process of the Balsaltic lava rather than exploring the columnar joints which were formed by Rhyolitic lava and volcanic clasts during the cooling process. In addition, both the results of this study and suggestion throughout the research will be useful for understanding the formulation of columnar joints which were formed by acidic rock or Rhyolitic lava. It also will contribute to inform the various geographical structure that exists in the area of Byeonsanbando National Park.