Morphological characteristics and distribution of bouldery slope landforms in Unbongsan, Goseong, South Korea

Unbongsan Mountain is a volcanic edifice with a unique landscape, which is located alone between granite mountains in Goseong-gun, Gangwon-do. The slopes of the mountain are partially covered with talus and block streams consisting of large basalt bouders. The geological features of this mountain have been investigated in detail. However, their overall distribution patterns and development processes are not well known. This study aims to classify these bouldery landforms through mapping the location of basalt blocks, the analysis of the morphological characteristics of the slope, and field surveys on the large boulders. The exposed boulders are concentrated in the western valleys of the mountains and are rarely found in the eastern slopes. Field data show that all the boulders are composed of basalt rocks with columnar joints, and that there is a long-axis isotropy related to the elevation and gradient of slope. In addition, the result of TPI and slope analysis for DEM indicate that block stream was mainly distributed along the valley, and the talus appeared in the steep ridge and the lower part of the cliffs. The slope classification indicates that flat mountain tops, basalt cliffs, talus, and block streams develop in sequence, as the distance from the center of the mountain increases. The bouldery landforms of Unbongsan Mountain illustrate the process of slope change that appears as a slope retreat in a volcanic edifice.