Goseong Tertiary Basalt (Gangwon Peace Region National Geopark)

Goseong, Gangwon-do, is a representative distribution area of alkaline basalt from the Tertiary Period of the Cenozoic Era in Korea. The Tertiary basalt appears as rounded dome shapes with filled craters on the ridges above 5 to 7 parts of mountains such as Goseongsan, Oeumsan, Dwitbaejae, and Unbongsan. The basalt produced in this area contains various types of mantle xenoliths and materials from beneath the crust. Therefore, in the basalt distribution area of Goseong, materials from deep within the crust can be directly observed with the naked eye. In addition, columnar joints are characteristically well developed in the Tertiary basalt of Goseong, and talus (dolseoreong), which are rock debris formed by the breaking of these columnar joints and flowing down from the mountain tops to the lower parts in multiple branches, can also be observed. This is formed when hexagonal columnar joints develop in the basalt mass created by volcanic activity, and as these columnar joints break, they cover the slopes' valleys or ridges. These rock debris are very common landforms observed in mountainous areas, but rock debris composed of basalt are very rare.