GK:1.2.4 The Coastal Regions and Seas of Korea
Geography of Korea: I. Natural Environment > 2. Topography > 4) The Coastal Regions and Seas of Korea
4) The Coastal Regions and Seas of Korea
(1) Coastal Regions
Korea is surrounded by sea on three sides and so has a long coastline. Prior to the coastline diminishment due to large-scale land reclamation projects from the early twentieth century, Korea’s coastline measured some 8693 kilometers, and 17,269 kilometers if one included the coastlines of all of its islands. Of particular note is the coast of Korea’s southwestern Jeollanam-do province, often cited as a world-class example of a deeply contorted ria coastline.
Korea’s western and southern coastlines are highly uneven, with many large and small bays and inlets as well as a wealth of peninsulas. Notably large bays of the west coast include Seohan Bay and Gyeonggi Bay, while smaller bays of that coast include Gwangnyang Bay, Daedong Bay, Haeju Bay, Namyang Bay, Asan Bay, Girorim Bay, Cheonsu Bay, Julpo Bay, and Hampyeong Bay. Among the notable peninsulas of the west seacoast are the Cheolsan, Jangyeon, Ongjin, Taean, Byeonsan, Haeje, and Muan Peninsulas. As for the southern coastline, notable bays are Boseong Bay, Suncheon Bay, Yeosu Bay, Gwangyang Bay, Sacheon Bay and Jinhae Bay, while its peninsulas include the Haenam, Goheung, Yesu, and Goseong. Some of these bays and peninsulas have lost their original shape due to land reclamation projects.
Korea’s eastern coast has less inlets and peninsulas and is relatively more monotonous than the country’s western and southern coastlines. Besides Donghan Bay, comparable in size to the west coast’s Seohan Bay, notable bays of the east coast include Ungi Bay, Najin Bay, Cheongjin Bay, Hamheung Bay, and Yeongil Bay, while the Hodo stands out as an east coast peninsula. It is known that Yeongil and Ulsan Bays owe their formation to faulting.
Examining the topography of the coastal terrain, there are clear differences between the east and west coasts, whereas the south coast has an intermediary character. The western coastline is characterized by its extreme irregularity and great tidal ranges, a reality that has resulted in the minimal development of sandy beaches but large tidal flats. One can, however, find some moderate sandy beach development on the west coast, but only in coastal areas or portions of islands that benefit from larger breakers formed by offshore landmasses, such as the Taean Peninsula, Anmyeon-do Island, and the Byeonsan Peninsula.
Tidal flats are a ubiquitous part of the topography of Korea’s western coast. Tidal flats are composed by the accumulation of mud, sand, and silt carried in by the tides. Covered during periods of high tide, these flats are exposed to the air during low tides. On the western coast the largest tidal flats are found around Gyeonggi Bay, the effluence point of major rivers like the Han, Imjin, and Yeseong. Large tidal flats have also developed at the estuaries of the Geum, Mangyeong, and Dongjin Rivers as well as on the southwestern coast, the effluence point of the Yeongsan River.
Because of its relatively even coastline, deep coastal waters, and active breakers, the eastern coast exhibits superior sand beach development. The larger of the sand beaches along the eastern coast are generally along major rivers. During periods of heavy rain the rivers running down the eastern coast carry seaward great quantities of soil, most of which is deposited on beaches. Windborne sand from these sand beaches has formed into coastal dunes beyond the beaches. These beaches and their topographical linked coastal sand dunes are also a major tourism attraction.
Along with sand beaches, the topography of the east coast is dotted with lagoons, sand bars, and land-tied islands. Along coastal Hamgyeongnam-do and Gangwon-do provinces in particular, many coastal lagoons can be found formed in small coastal inlets, representative examples being Gwangpo in Jeongpyeong, Sangpo and Hapo in Yeongheung, Chinapo and Gangdongpo in Tongcheon, Samilpo and Hwajinpo in Goheung, Yeongnangho and Cheongchoho in Sokcho, Hyangho in Jumunjin, and Gyeongpo in Gangneung. The east coast also abounds in coastal islands and sandbanks, so-called land-tied islands (yukgye-do), with two prime examples being the Galma and Hodo Peninsulas in Yeongheung Bay (Hamgyeongnam-do province, North Korea).
(2) Seas
The Korean Peninsula is surrounded by the Yellow (or West) Sea, Southern Sea, and East Sea. The Yellow and Southern Seas sit entirely on the continental shelf and so are relatively shallow; the Yellow Sea reaches average depths of less than 50 meters while the Southern Sea reaches on average around 100 meters. During the last ice age sea levels were about 100 meters lower than the present day, so what is now the Yellow Sea was entirely exposed land and what is today Jeju Island was also connected by land to the current mainland.
A marginal sea of the Pacific Ocean, the East Sea connects Korea, the Japanese archipelago, and the island of Sakhalin, all told covering an area of about a million square kilometers. Its average depth is about 1700 meters, though reaching to over 4000 meters in its deepest area. It has a very narrow continental shelf, where depths reach less than 200 meters.
The tidal range of the Yellow Sea is one of the greatest in the world. The reason for its tremendous tidal range has to do with the fact that it has a very shallow depth to begin with but also has a wide opening on the East China Sea, an extension of the Pacific Ocean. The mean spring tidal range for Asan Bay reaches 8.5 meters, with this number falling off as one moves north or south. In Incheon it is 8.1 meters, 6.2 meters in Nampo, 4.9 meters in Yongampo, 6.2 meters in Gunsan, and 3.1 meters in Mokpo. The tidal range for the Southern Sea decreases as one moves west to east: 2.5 meters in Yeosu and 1.2 meters in Busan. Such extreme tidal variations are disadvantageous for seaports along these coasts.
The tidal range of the East Sea is limited, with the mean spring tidal range reaching only between 0.2–0.5 meters. This minimal tidal range can be attributed to the fact that the East Sea is largely cut off from the Pacific Ocean by the presence of the Japanese archipelago and Sakhalin Island. The East Sea is an oceanic basin, a depression formed by tremendous fault activity during the early Cenozoic Quaternary.
The Korean Peninsula’s littoral waters are heavily influenced by the warm Kuroshio Current, which flows from the Pacific Ocean east of the Philippines northward along the eastern shelf of the Asian continent. The Kuroshio Current is one of the world’s most powerful. It divides to the southeast of Jeju Island into the Tsushima Current and the Yellow Sea Current.
The Tsushima Current in turn splits as it enters the East Sea, with one branch flowing north along the Japanese archipelago and the other branch becoming the Donghan (East Korea) Current and flowing northward along the peninsula’s eastern coast. The effects of the warm Donghan Current are felt as far north as the littoral waters of Hamgyeongbuk-do province, which has intense summers. The Bukhan (North Korea) Current, a branch of the Liman Current that flows southward out of the Sea of Okhotsk, flows along the coasts of Hamgyeongbuk-do and Hamgyeongnam-do provinces. The cold Bukhan Current contributes to the extreme winters felt as far south as Gangwon-do province.
The Hwanghae (Yellow Sea) Current that flows to the west of Jeju Island and northward towards the Yellow Sea is relatively weak. In summer the Hwanghae Current flows north towards the Bay of Bohai, but in winter its power becomes relatively weakened due to the northwest monsoons.
