The volcanic island of Jeju, located 130 kilometers from the southern coast of the Korean Peninsula, has an extensive system of lava tubes. These natural conduits through which magma once flowed are now empty caves that are some of the largest in the world. These caves, apart from providing opportunities for scientific research, are popular tourist destinations.

The most impressive is the Geomunoreum Lava Tube System formed by the flow of basaltic lava when the Geomunoreum volcano erupted some 300 - 200 thousand years ago. The volcano has an elevation of 456 meters and lava flowed down to the coastline 13 km away, and while doing so, created numerous lava tubes. The Manjanggul Lava Tube represents the largest cave in this system. It stretches for 8,928 meters and its passages are up to 30 meters high and 23 meters wide.

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The insides of the tube is adorned with multi-coloured carbonate decorations and innumerable cave formations commonly found in lava tubes. They include lava stalactites and lava stalagmites, lava columns, lava flowstone, lava helictites and lava blister, cave corals, benches, lava raft, lava bridges, lava shelves and striations. At the end of the one of the passageways open for tourists, is a massive lava column formed when a large amount of lava spilled from the upper level down to the lower level. This intimidating column stands 7.6 meters high and is the largest known in the world.

Some 30,000 common bent-wing bats (Miniopterus schreibersii) have taken permanent residence inside the tube, forming the largest colony of bats so far known to be living in Korea. About 38 types of cave creatures have been identified inside the Geomunoreum Lava Tube System, the most common of which is the Jeju cave spider (Nesticella quelpartensis).

Entrance to the cave. Photo credit

The world's largest lava column in Manjanggul cave. Photo credit

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Sources: Wikipedia / Wondermondo / geopark.jeju.go.kr / jikimi.cha.go.kr