Why Jeju Is a Volcanic Island: Oreum and Basalt제주는 왜 화산섬인가: 오름과 현무암

Everything distinctive about Jeju — the black stone walls between fields, the grandfather statues (dol hareubang), the strange cone-shaped hills — comes from one fact: the island is a volcano. Jeju was built by eruptions over roughly the last two million years, centered on Hallasan, a shield volcano rising about 1,950 meters, the highest peak in South Korea. Scattered across its flanks are 368 smaller volcanic cones called oreum in the Jeju dialect — the largest number of parasitic cones on any single volcano in the world. Underground, rivers of lava once drained toward the sea, leaving behind hollow tunnels; Manjanggul is one of the largest lava-tube caves on Earth, and the Geomunoreum lava tube system is so exceptional that UNESCO inscribed "Jeju Volcanic Island and Lava Tubes" as Korea's first World Natural Heritage site in 2007. The island's dark basalt shaped its culture too: porous volcanic soil holds little surface water, so villages grew around springs, and generations of islanders stacked lava stones into the low walls and tomb enclosures you see everywhere. Today you can hike the crater rim of Seongsan Ilchulbong at sunrise, walk a kilometer inside a lava tube, and climb a grassy oreum in the afternoon — a full volcanic biography in one day.