변산반도 국립공원에 분포하는 주상절리

Abstract

Columnar joints are shown in various forms throughout the country. In particular, areas where columnar joints are distributed have excellent land scape, academic value and educational value. Among them, the relatively well-preserved landscape is located in the national parks(Mudeungsan National Park, Juwangsan National Park, and Byunsanbando National Park). Among the columnar joints distributed in Korea, most of the well known ones are developed in the Cenozoic basaltic rocks. However, columnar joints are developed in the acidic volcanic rocks of southern Korea, and there are unknown columnar joints that need investigation. This study focused on the formation of such columnar joints, which have not yet been studied extensively. The purpose of this study is to investigate the morphology and formation process of columnar joints in acidic volcanic rocks. According to previous studies, columnar joints developed in acidic volcanic rocks are distributed in Jeokbeokgang of Buan, Jido, Jeungdo of Shinan, and some area of anjaedo, Goheung, Yeosu, Sacheon-Goseong, and the Juwangsan National Parks. Among them, the study is about the columnar joints distributed within Byeonsanbando National Park of Buan. The park is divided into two sides. The columnar joints in the Jeokbeokgang area sited in the coastal parts have been developed in three forms. First one has developed in the vertical side, which shows a form diminished in length of polygon side, from upside to downside. It also has observed peperrite. The second one has a entablature and has developed a lotus-shaped vertical side columnar joints. Third one is the columnar joints developed into different shapes of upper Gomso Rhyolite and the lower Gomso Rhyolite. The columnar joints distributed in some area of Jeokbeokgang take up high rate of square and pentagon. Length of polygon sideis is within 20cm, but the thing of less than 10cm is the most. The columnar joints distributed in some area of Jiksopokpo are mostly vertical side. Most columnar joints has distributed in the ground of mountain trails, on a small scale, but the thing of Jiksopokpo has been developed up to 7m. The rocks constituting columnar joints are rhyolite and rhyolitic tuff. The fragments of rocks in the Jeokbyeokgang area are several millimeters. The phenocryst minerals of about 1mm in size are mostly feldspar and show albite twin. The rocks in the Jiksopokpo area consist of feldspar phenocryst, quartz and glassy minerals of 2~3 cm in size, and the rate of SiO2 is 69.30wt%~76.69wt%. The columnar joints of the Jeokbyeokgang and jiksopokpo areas are rhyolite and rhyolitic tuff with similar chemical composition but different morphological characteristics. The reason for such results is considered to be due to the difference in cooling rate rather than the difference in chemical composition. The columnar joints of the Jeokbyeokgang area are characterized by various cooling surface morphologies and cooling rates due to lower unconsolidated layer, runoff of water, and other rhyolite intrusion. Columnar joints on byeonsan tuff in jiksopokpo area have characteristic columnar joints developed from acidic rocks because there are few factors that change the cooling rate.