Tsushima splits Asia’s busiest short sea between Korea and Japan
The Korea Strait runs about 200 kilometres wide between the Korean Peninsula and southwestern Japan, averaging near 100 metres deep as it ties the East China Sea, Yellow Sea, and Sea of Japan. Tsushima Island cleaves it into a deeper western channel and the Tsushima Strait.
A Kuroshio branch—the Tsushima Current—pushes warm water north into the Sea of Japan before splitting along Asian and Japanese coasts. Ferry nets link Busan and Geoje to Fukuoka, Tsushima, Shimonoseki, and Hiroshima, while commercial lanes feed southern South Korean ports. Other boats shuttle between Tsushima and Fukuoka, and between Jeju Island and the Korean mainland. Both South Korea and Japan hold their territorial waters in the strait to just three nautical miles from shore so that international traffic can pass freely.
Pleistocene low stands may have linked Japan to Eurasia across a narrowed strait. In the coldest phases the Sea of Japan may even have become a frozen inland lake, cut off from warm inflow. In the sixth century Baekje carried Mahāyāna Buddhism to Emperor Kinmei’s Japan across these waters; Mongol–Korean fleets tried Japan in 1274 and 1281, ravaging Tsushima yet failing. Joseon’s 1419 fleet later struck Wokou bases there. Korea afterwards granted Japanese traders limited privileges. May 1905’s Battle of Tsushima and the 25–26 June 1950 Battle of Korea Strait wrote modern naval chapters into the same choke point.
Talk of a Japan–Korea undersea tunnel has simmered for decades without matching the Channel Tunnel’s reality. Its natural stepping stones are short: roughly 50 kilometres of water lie between Busan and Tsushima, and about the same between Tsushima and Iki. West of Tsushima the channel plunges to around 227 metres, far deeper than the strait as a whole.
Source: Korea Strait
