Jeju Province

Jeju Province wraps the volcanic island of Jeju-do off South Korea's southern coast, the country's largest island and a UNESCO World Heritage volcanic landscape with the 1,947-metre Hallasan shield volcano at the centre, the lava-tube cave systems of Manjanggul, and the parasitic-cone (oreum) landscape across the lower slopes. The tide here is a moderate mixed semidiurnal signal modulated by the Korean Strait and the Yellow Sea geometry. Mean range at the Jeju harbour gauge on the northern coast is about 1.6 metres, climbing past 2.5 metres on the largest spring tides and dropping near 0.7 on neaps. Two highs and two lows of unequal size each day, with the asymmetry varying through the lunar month. The northern coast at Jeju City reads a different signal from the southern coast at Seogwipo, where the open Pacific exposure runs a smaller swing. The defining cultural feature is the haenyeo women divers tradition. The haenyeo (sea women) of Jeju have been freediving for abalone, conch, sea urchins, and seaweed in the cold coastal waters around the island for centuries — UNESCO inscribed the haenyeo culture on the Representative List of Intangible Cultural Heritage in 2016. The diving collective is the foundational institution of the matriarchal-leaning Jeju society, with mothers passing the trade to daughters and the village association (jamsu-hwe) governing the diving grounds. The diving calendar runs year-round but the cold-water months from December through March push working dives to brief sessions; summer months allow longer working time. The volcanic island has no surface rivers — the lava-tube hydrology drains rainwater underground and feeds it back to the coast through submarine springs that the haenyeo work around. The Hallasan volcanic runoff that does reach the coast drops sediment at the river mouths that the divers know to avoid. Working dive boats out of Jeju City and Seogwipo, the inter-island ferry from Jeju to Mokpo and Wando on the mainland, the Jeju Olle hiking-trail coast, and the Seongsan Ilchulbong sunrise peak on the eastern tip all read the table for different windows. The Korea Hydrographic and Oceanographic Agency (KHOA) publishes the authoritative tide tables.