Beomseom and Its Sister Islands Were Born Together 800,000 Years Ago

The three islands lined up off Seogwipo — Beomseom, Munseom, and Seopseom — likely formed around the same time about 800,000 years ago, new research suggests. Jeju's World Heritage Headquarters confirmed the dates through precision dating during an island-wide geological mapping project, and because the three islands sit almost in a straight line, researchers are now examining whether volcanoes erupted along a single line in the sea south of Jeju.

The key facts

• The new dates: Beomseom 804,000 (±4,000) years · Munseom 824,000 (±8,000) years · Seopseom 796,000 (±3,000) years — via precision argon-argon dating
• What changed: earlier potassium-argon dating had put Munseom and Seopseom at about 730,000 years; the new method re-measured all three
• Reliability: two samples from different spots on Beomseom returned the same age — the analysis reproduces
• Why it matters: the three islands line up across roughly 8km of sea off Seogwipo → possible linear volcanic activity under review
• Next steps: chemical analysis to test whether all three share the same magma source, and comparison with similar-age volcanoes like Sanbangsan

What this means for divers and travelers

For an instructor guiding Beomseom dives every day, this research lands close to home: the vertical walls divers glide along are literally cross-sections of an 800,000-year-old volcano.

Beomseom's signature dive features — the sheer vertical walls and the "Nostril" sea arch — are volcanic rock carved by the sea. And today, Korea's largest soft coral colonies (Natural Monument No. 442) grow on those ancient walls. A Beomseom dive is 800,000 years of geology and a living coral ecosystem in a single descent — and now our dive briefings can add: "this wall was born the same day as its sister islands."

From land, the Saeyeon Bridge promenade in Seogwipo gives you the three-islands-in-a-row view. To see it from inside the water, start with a boat discover dive.