Jeju Island is Korea’s largest volcanic island created by persistent volcanic activity from 1.8M years ago to the historical period. The island has a geological structure characterized by repeated layers of 3- to 5-meter-thick volcanic ejecta. Multiple streams of lava of different properties erupted and formed layers, creating various volcanic landforms such as columnar jointing, cascades, lava caves and tumuli. There are also hydro volcanoes including Seongsan Ilchulbong, Suwolbong, and the Dragon Head Coast, which are formed when scorching hot lava met water and erupted.