Elevations in the southern part of the Korean Peninsula are generally lower than those in the north. Only about 30% of the ROK consists of lowlands and plains. The principal lowlands, all bordering the Yellow Sea along the west coast, include the Han River Plain, near Seoul; the Pyongtaek and Honam plains, south of the capital; and the Yongsan Plain in the southwest. Mt. Halla (1,950 m/6,398 ft), on volcanic Cheju Island, is the nation's highest point, while Mt. Chiri, or Chii (1,915 m/6,283 ft), is the highest point on the mainland.
Principal rivers of the ROK include the Han (514 km/319 mi), with Seoul near its mouth; the Kum (401 km/249 mi) and Yongsan (116 km/72 mi), which water the fertile plains areas of the southwest; and the Somjin (212 km/132 mi), in the south. The longest river in the ROK is the Naktong (521 km/324 mi), which waters the southeast. Yellow Sea tides on the west coast rise to over 9 m (30 ft) in some places, while Japan Sea / East Sea tides on the east coast rise only about 1 m (3 ft).