Jeju Island, or Jejudo, is an oval-shaped volcanic island measuring approximately 73 kilometers from east to west and 41 kilometers from north to south. In the heart of the island stands Hallasan Mountain, a 1,950-meter mountain. Created entirely from volcanic eruptions, Jeju Island boasts a diverse and unique volcanic landform, so much so that the island itself could be seen as a 'museum of volcanoes. ' On land, over 360 oreums (*Oreum refers to parasitic volcano in Jeju dialect) of varying sizes can be seen, while some 160 lava tubes are spread out across the island and are situated underground. It is extremely rare for so many oreums and lava tubes to be found all on a single island that is as small as Jeju Island.
As such, Jeju Island was designated as a Biosphere Reserve by UNESCO in 2002, a World Natural Heritage site in 2007, followed by a Global Geopark in 2010, proving its value by becoming the only place on Earth to receive all three UNESCO designations in natural sciences.
Jeju Island is now undisputedly a 'treasure island of environmental assets' for the whole world to appreciate and protect.
Before the formation of what is now known as the volcanic island of Jeju, the entire area was a shallow sea of unhardened clay and sand bed (Unconsolidated sediments: U Formation). Approximately 1.8 million years ago, magma erupted from underneath the sea floor breaking through weak strata and interacted explosively with water, resulting in hydromagmatic volcanic activity which left multiple tuff rings and tuff cones. For an extensive period of time thereafter, these volcanic bodies were repeatedly eroded by waves and mixed with marine sediments, ultimately forming what we know to be the Seogwipo Formation.
After the Seogwipo Formation was deposited, Jeju Island in its original state gradually arose above sea level. Some 550,000 years thereafter, lava began to erupt and create far-reaching lava plateaus and piled on layer after layer, forming a shield volcano in the shape of a warrior's shield centered around Hallasan Mountain.
It was after the last Glacial Age approximately 18,000 years ago when the sea level almost rose to the current level that hydromagmatic volcanic activities began to take place around Jeju's coastal areas, creating hydromagmatic volcanic bodies such as Seongsan Ilchulbong Tuff Cone and Songaksan Tuff Ring. No further volcanic activities have been reported since last being recorded some 1,000 years ago, finally forming Jeju Island as we know it today.
Jeju Island itself is a shield volcano that resembles a warrior's shield lying on the ground. Distributed across the Island are approximately 360 oreums (parasitic volcanoes) which include landforms such as cinder cones, tuff rings, tuff cones and lava domes.
A cinder cone refers to a cone-shaped volcano formed by large amounts of cinders, lava and volcanic ashes spewed due to the explosiveness of magma. Locals call this red stone 'song. '
Tuff rings and tuff cones are other forms of oreum commonly seen along the seashores. When hot magma meets underground water or surface water (sea, lake, stream, glacier, etc.) while rising toward the Earth's surface, magma rapidly cools down while water boils up. Such explosive reaction resulting in an extremely strong eruption is called hydromagmatic volcanic activity, which is how approximately twenty of Jeju's oreums were formed. Another form of oreum is a lava dome, formed by slow extrusion of viscous lava, as seen in Sanbangsan Mountain or the northwestern face of Baengnokdam Crater Lake.
A shield volcano is a type of volcano, usually formed by fluid lava flows. Shield volcanoes are named for their low profile and gentle slope, resembling a warrior's shield. Such landform is created as broad sheets of lava steadily accumulate, unlike explosive volcanic eruptions.