Bongrae Waterfall is 2 km away from Jeodong port and located on the way to Seonginbong Peak. The 30-m high waterfall is the largest in Ulleung-do. Nari basin, located at the northwest of the waterfall, allows rain and snow to permeate underground. Melted snow and rain water joins Bongrae Waterfall. Because the discharge quantity of the fall reaches 3,000 tons a day, it is an important source of fresh water for the southern part of Ulleung-do including Dodong and Jeodong. The waterfall is composed of 3 layers of visible rocks. Trachyte and tuff make up the first upper layer and agglomerates form layer 2 and layer 3. Trachyte in the upper layer of the fall has higher structural resistance against erosion compared to the other two types of rocks. The waterfall is formed in different layers of rocks as the rocks vary in hardness. This phenomenon is known as differential erosion. It is expected that trachyte in the upper part of the fall will collapse if tuff and agglomerates continue to erode in the future, causing Bongrae waterfall to retreat further upstream. On the way to Bongrae Waterfall, there is a talus slope resulted from the accumulation of varying sized rocks at the base of the slope or valley. During the summer, the air between the rocks are cooled due to limited sunlight exposure and low temperature and high moisture content of the rock surface. The dense cold air moves downward between the rocks. ‘Punghyeol’, or ‘wind caves’ are created when the cold air mass collides with a warm air mass and the air mass absorbs surrounding heat and evaporates thus becoming even cooler.