Hallasan National Park (9.6 km), Seokgulam Trail (1.5 km), Gwaneumsa Trail (8.7 km), Donnaeko Trail (7 km), and Eoseungsaengak Trail (1.3 km). The longest trail is Seongpanak Trail which takes about 4.5 hours. Hallasan comprises 153.112 km of the Jeju Island. It rises 1.950 m above the sea level which means the highest mountain in South Korea. This mountain was formed in the fourth Cenozoic era by outburst of volcano. It is mostly composed of basalts. It is extending east and west, and it has high and gradual descent. On the other hand, the south part of the mountain is steep. In the
Kell (volcano) valleys. Within the Prizrak caldera complex are at least three partially nested calderas, each about 3 to 5 km in diameter. Kell is the largest of several small stratovolcanoes, composed mainly of lava, in the innermost portion of the caldera. The caldera also contains lava domes. The innermost caldera is thought to date from the Late Pleistocene. The activity of the volcano appears to have ceased in post-glacial time; there is no evidence of recent volcanism or hydrothermal activity. Kell (volcano) Kell () is a small extinct Holocene stratovolcano. It is located just north of the Zheltovsky volcano, within the