Ulleungdo is a South Korean island, the main part of Ulleung County, North Gyeongsang Province, South Korea, in East Sea. This island is at 37°30'N 130°52'E. The part of this island is the peak of the mountain. This mountain is a large stratovolcano which rises from seafloor. The formation time of this volcanic mountain is between the Cainozoic Third Era and the Cenozoic Fourth Era. The highest peak of Ulleungdo is Seonginbong peak, 984 meters. There are Nari Basin and Albong Basin which are made by collapsing Caldera crater in the northern slope. Ulleungdo is a pentagon shape. The length of east and west is 10 km and the length of south, and north is 9.5 km, and the total length of seashore is about 56.5 km.