Category: Jeju Island.

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Jeju Island (formerly transliterated as Cheju Island) is a volcanic island situated off the southern coast of the Korean Peninsula in the eastern margin of the Asian continent (Fig. 1). The island was produced by volcanic activity which occurred from about two million years ago until historic time. The island is 73㎞ long in the east-west direction and 31㎞ long in the north-south direction, having an area of 1,847 ㎢. Constructed upon the about 100 m deep continental shelf in the Yellow Sea, the actual size of the volcano is presumed to be larger than this when including the submerged part. The island has the typical morphology of a shield volcano, characterized by an overall gentle topography and an elliptical shape in plan elongated in the ENE direction (Fig. 2).

Basaltic to trachytic lavas occur extensively on the island together with diverse volcanic landforms, including Mt. Hallasan that rises 1,950 m above sea level at the center of the island and about 360 volcanic cones that are scattered throughout the island (Park et al., 1998; Park et al., 2000a; Park et al., 2000b; Park et al., 2000c). On the other hand, numerous hydromagmatic volcanoes (tuff rings and tuff cones) produced by explosive hydrovolcanic activity occur extensively in the subsurface together with intervening volcaniclastic sedimentary deposits (Sohn & Park, 2004; Sohn et al., 2008). This is because the volcanic activity of the island commenced in the continental shelf of the Yellow Sea where abundant water for hydrovolcanic explosions was available. Composed of an early-stage product of hydrovolcanism and a late-stage product of lava effusion, Jeju Island can be defined as a “shelfal shield volcano”, distinguished from ordinary shield volcanoes that were built entirely on land in the middle of a continent or oceanic volcanic islands built on the deep ocean floors. In this respect, Jeju Island has significant geological importance.

Mt. Hallasan is the symbol of Jeju Island and a representative product of the Quaternary volcanism in the Korean Peninsula and adjacent seas. Mt. Hallasan was designated as a natural monument (no. 182) in 1966 and a national park in 1970 because the mountain preserves the pristine morphology of a shield volcano unaffected by significant weathering or erosion. The mountain has been protected from human activity since then and is renowned for its unique ecology and biodiversity. The mountain could be thus designated as a UNESCO Biosphere Reserve in 2002. The Seongsan Ilchulbong is a beautiful tuff cone (Sohn & Chough, 1992), which stands for the early-stage hydrovolcanism of Jeju Island and represents the about 360 volcanic cones or “oreums” (Jeju dialect for volcanic cones) in Jeju Island. The tuff cone is renowned for its breathtaking beauty and scientific value. The Geomunoreum lava tube system is a representative product of the lava effusion, which occurred mostly during the late-stage of Jeju volcanism. The lava tube system is regarded as one of the extremely rare examples of lava tubes that have diverse carbonate speleothems in addition to volcanic speleothems.

The extreme beauty and unsurpassed scientific values of these three sites were acknowledged internationally when they were inscribed as a UNESCO World Natural Heritage in June 2007. Jeju Island boasts diverse volcanic landforms and volcanic features in addition to these three sites. The island also boasts outstanding scenery and unique culture and history, making it worth visiting at least once in one’s lifetime.

Geology and Evolution of Jeju Island

Jeju Island is a Quaternary shield volcano constructed on the c. 100-m-deep continental shelf off the southern coast of the Korean Peninsula in the Yellow Sea (Figs. 1 & 2). The island is composed of basaltic to trachytic lavas and numerous volcanic cones (Fig. 3, Park et al., 1998; Park et al., 2000a; Park et al., 2000b). These volcanic rocks were formerly assumed to have originated from plume-related hotspot magmatism (Lee, 1982; Park, 1994), but recent studies suggest that they more likely resulted from decompression melting of the shallow asthenosphere in response to dramatic changes in regional stress regime during the late Cenozoic (Choi et al., 2005; Choi et al., 2006).

Compilation of the borehole data from more than a thousand groundwater bores (Koh, 1997; Sohn & Park, 2004; Sohn et al., 2008) reveals that the basement of Jeju Island is composed of granite and silicic volcanic rocks of Jurassic to Cretaceous age (Fig. 4). The overlying U Formation is 70 to 250 m thick and composed of well-sorted, quartzose sand and mud (Koh, 1997). This formation is interpreted as continental shelf sediments that accumulated during the Pliocene before the onset of volcanism at Jeju (Sohn & Park, 2004). The U Formation is overlain by about 100 meters of basaltic volcaniclastic and fossiliferous deposits. These deposits are interpreted to be correlative with the Seogwipo Formation, which is exposed only in the south-central part of Jeju Island (Yoon & Chough, 2006). A number of paleontologic, paleomagnetic, stable isotopic, and geochronologic studies (Tamanyu, 1990; Lee et al., 1994; Yi et al., 1998; Li et al., 1999; Kim et al., 2000; Kim & Lee, 2000; Kim et al., 2001; Kang, 2003) reveal that deposition of the formation began at about 1.8 Ma and continued until c. 0.8-0.4 Ma.

Recent research (Sohn et al., 2008) reveals that the Seogwipo Formation in the subsurface consists of numerous superposed phreatomagmatic volcanoes intercalated with marine or nonmarine, volcaniclastic or non-volcaniclastic deposits with intervening erosion surfaces and palaeosol layers (Fig. 4). The widespread and continual hydrovolcanic activity together with volcaniclastic sedimentation, as represented by the Seogwipo Formation, is thus inferred to have persisted for more than a million years (from ca. 1.8 Ma to 0.8~0.4 Ma) under the influence of fluctuating Quaternary sea levels.

Thereafter, the proto-Jeju Island is inferred to have grown up above the fluctuating Quaternary sea levels and lava effusion became dominant, resulting in the plateau- and shield-forming lavas of Jeju Island together with numerous volcanic cones. The K-Ar ages of these lavas range generally between 0.8 and 0.03 Ma (Tamanyu, 1990; Lee et al., 1994), suggesting that the construction of Jeju Island was almost completed just before the Holocene. After the last glacial maximum 18,000 years ago and during the middle Holocene when the coastal regions of Jeju Island became suitable for hydroexplosions, explosive hydrovolcanic eruptions occurred at several places along the present shoreline. These Late Pleistocene to Holocene hydrovolcanic eruptions resulted in several tuff rings and tuff cones with fresh morphology, including the Suwolbong, Songaksan, Ilchulbong, and Udo tuff rings/cones (Sohn & Chough, 1989; Chough & Sohn, 1990; 1992; 1993). There are also historic records of minor eruptions afterwards about one thousand years ago, although it is uncertain where these eruptions occurred.

There are more than 300 volcanic cones in Jeju Island. Most of them are scoria cones except for about a dozen phreatomagmatic volcanoes. The latter can be divided into two groups depending on stratigraphy (Fig. 4): those that underlie the plateau-forming lavas and those that overlie the lavas (Sohn & Park, 2005). The younger ones include Suwolbong, Songaksan, Ilchulbong, and Udo tuff rings/cones. The older ones include the Dangsanbong, Dansan, and Yongmeori tuff ring/cone complexes. The latter protrude through the later plateau-forming lavas mostly in the southwestern part of Jeju Island where the altitude is low and the overlying lavas are relatively thin (50 to 60 m; Koh 1997).

Fig. 1: Jeju Island is a Quaternary shield volcano constructed on the sea. 100-m-deep continental shelf off the southern coast of the Korean Peninsula in the Yellow Sea.

Fig. 2

Fig. 3: Geological Map of Jeju

Fig. 4: The basement of Jeju Island is composed of granite and silicic volcanic rocks of Jurassic to Cretaceous age.

Inscription Procedure

“Jeju Volcanic Island and Lava Tubes” was inscribed as a World Natural Heritage by UNESCO at the 31st World Heritage Convention on June 27, 2007. This is the first World Natural Heritage inscribed in the Republic of Korea. The Republic of Korea and the Jeju Self-Governing Province have tried their best to achieve this inscription since 2001 and it took 6 years to accomplish this mission.
The Republic of Korea and the Jeju Self-Governing Province carried out scientific research for 5 years. After compiling all the necessary information for the nomination, the Republic of Korea and the Jeju Self-Governing Province submitted the proposal to UNESCO in January, 2006 for the inscription of three serial sites, Mt. Hallasan, Seongsan Ilchulbong Tuff Cone and Geomunoreum Lava Tube System (Geomunoreum, Bengdwigul Lava Tube, Manjanggul Lava Tube, Gimnyeonggul Lava Tube, Yongcheondonggul Lava Tube and Dangcheomuldonggul Lava Tube). The delegate of the International Union for Conservation of Nature (IUCN), which is the official organization for evaluation, visited Jeju Island in October, 2006 for an on-site evaluation, and the IUCN strongly suggested the inscription of the Jeju nominated sites.

Twenty one State Parties at the 31st World Heritage Convention, that was held at Christchurch, New Zealand, inscribed the nominated the “Jeju Volcanic Island and Lava Tubes” as a World Natural Heritage unanimously.

The inscribed sites cover 18,845 ha, and they include the core and buffer zones of 9,475 ha and 9,370 ha, respectively.
The IUCN noted that volcanic systems are relatively well represented on the World Heritage List and that there is an increasingly limited potential for further inscriptions of volcanic sites on the World Heritage List. The IUCN also recommended that States Parties considering further nominations of volcanic sites should consider the principles suggested in section 5.2 of the IUCN evaluation of Jeju Volcanic Island and Lava Tubes.

The IUCN adopted the following statement of Outstanding Universal Value.

Jeju Volcanic Island and Lava Tubes is a coherent serial property comprising three components. The unequalled quality of the Geomunoreum lava tube system and the exhibition of diverse and accessible volcanic features in the other two components demonstrate a distinctive and important contribution to the understanding of global volcanism.

Criterion (vii)
The Geomunoreum lava tube system, which is regarded as the finest such cave system in the world, has an outstanding visual impact even for those experienced with such phenomena. It displays the unique spectacle of multi-colored carbonate decorations adorning the roofs and floors, and dark-colored lava walls, partially covered by a mural of carbonate deposits. The fortress-like Seongsan Ilchulbong tuff cone, with its walls rising out of the ocean, is a dramatic landscape feature, and Mount Hallasan, with its array of textures and colors through the changing seasons, waterfalls, display of multi-shaped rock formations and columnar-jointed cliffs, and the towering summit with its lake-filled crater, further add to the scenic and aesthetic appeal.

Criterion (viii)
Jeju has a distinctive value as one of the few large shield volcanoes in the world built over a hot spot on a stationary continental crust plate. It is distinguished by the Geomunoreum lava tube system, which is the most impressive and significant series of protected lava tube caves in the world and includes a spectacular array of secondary carbonate speleothems (stalactites and other decorations), with an abundance and diversity unknown elsewhere within a lava cave. The Seongsan Ilchulbong tuff cone has exceptional exposures of its structural and sedimentological characteristics, making it a world-class location for understanding Surtseyan-type volcanic eruptions.

Category: Jeju Island