Jeju Island In Korea South is the important volcanic island. Jejudo is a volcanic island, 130 km from the southern coast of Korea. The largest island and smallest province in Korea, the island has a surface area of 1,846 km2.A central feature of Jeju is Hallasan, the tallest mountain in South Korea and a dormant volcano, which rises 1,950 m above sea level. 360 satellite volcanoes are around the main volcano.