The largest island, Jeju-do, lies off the southwest corner of the peninsula and has a land area of 1,825 square kilometers. Other important islands include Ulleung and Liancourt Rocks in the Sea of Japan and Ganghwa Island at the mouth of the Han River. Although the eastern coastline of South Korea is generally unindented, the southern and western coasts are jagged and irregular. The difference is caused by the fact that the eastern coast is gradually rising, while the southern and western coasts are subsiding.