Mountains cover 70 percent of Korea, especially in the eastern and northern parts. Well-developed arable plains, mostly in southern and western parts of the peninsula, are generally small and separated by successive mountain ranges. The highest mountains are in the northeast.
Mount Paektu, a dormant
volcano on the border with China, is the highest mountain in Korea at . The southern extension of Mount Paektu, a highland called
Kaema Plateau, was mainly raised during the
Cenozoic orogeny and partly covered by volcanic matter. It is bounded by the
Rangnim Mountains to the west and the
Hamgyong Mountains to the east. The principal
drainage divide (named
Baekdu-daegan) runs north to south, beginning with the Rangnim Mountains bisecting the north and continuing down the eastern side of the peninsula as the
Taebaek Mountains. Several lower, secondary mountain ranges, including the
Kangnam Mountains and
Sobaek Mountains run southwest from the main dividing range. They developed along the tectonic line of
Mesozoic orogeny. Some significant mountains include
Mount Sobaek (),
Mount Kumgang (),
Mount Seorak (),
Mount Taebaek (), and
Mount Jiri (). Unlike most ancient mountains on the mainland, many important islands in Korea were formed by volcanic activity in the Cenozoic orogeny. Jeju Island, situated off the southern coast, is a large volcanic island whose main mountain,
Mount Halla (), is the highest in South Korea. Ulleung Island is a volcanic island in the Sea of Japan whose composition is more
felsic than Jeju. The volcanic islands tend to be younger, the more westward. Because the mountainous region is mostly on the eastern part of the peninsula, the main
rivers tend to flow westwards. Two exceptions are the southward-flowing
Nakdong River and
Seomjin River. Important rivers running westward include the Amnok River, the
Chongchon River, the
Taedong River, the
Han River, the
Geum River, and the
Yeongsan River. These rivers have extensive
alluvial plains and provide an ideal environment for
wet-rice cultivation. The peninsula has of coastline. The southern and southwestern coastlines of Korea are particularly irregular, forming a well-developed
ria coastline, and most of Korea's small islands are found here. This convoluted coastline results in mild seas and a calm environment allowing for safe navigation, fishing, and
seaweed farming. The Yellow Sea on the western coast has an extremely high
tidal range – at
Incheon, around the middle of the western coast, it can get as high as . This has led to broad
mudflats along the south and west coasts. In contrast, the east coast facing the
Sea of Japan (East Sea) is steep and mostly straight, with sandy beaches. ==Geology==