Jukam Shingle Beach was formed by high waves of Ulleung-do. The beach is surrounded by sea cliffs made of trachyte agglomerate and phonolite. Jukam Shingle Beach is 500 m long and 20 m wide and covers an area of 9,500㎢. When the shingle beach was eroded by waves, resistant rocks remained to form a cape or a sea stack whereas the weaker deposits weathered and eroded away to form into a shape of a bay. A sea cliff is developed where a protrusion of a rocky surface is directly influenced by the waves. On the other hand, coastlines develop due to sedimentation that occurs in bays where waves are weaker. Waves wear down fragments of rocks that make up the coastline, forming round gravels or shingles. Shingles are composed of diverse rocks including trachyte, phonolite, and basalt. The cliffs near the shingle beach are composed of agglomerates (coarse accumulations of volcanic material), tuff, trachyte flows (alkaline magma that has cooled close to the surface), and phonolite (iron-rich extrusive igneous rock that has cooled close to the surface). Spheroidal weathering, also called onion skin weathering, is commonly observed in rocks of trachytic composition. In addition, sea stacks caused by differential erosion (removal of weaker rocks near sea level) are also found.