Ulreung volcano, also known as Ullung, forms a small 10-km-wide island about 100 km east of the coast of the central Korean Peninsula. The high point on Ulreung-do (Ulreung Island) is 984-m-high Seonginbong Peak. The trachyandesitic Ulreung stratovolcano is truncated by a caldera. Ulreung was the site of a major explosive eruption at the beginning of the Holocene that produced pyroclastic flows and deposited ash across the Sea of Japan (East Sea) in central Honshu.