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About Jeju Island :: Seongsan Ilchulbong Tuff Cone

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Summary
Site name : Seongsan Ilchulbong Tuff Cone
Site area : 1.688㎢ (core zone: 0.518 ㎢, buffer zone: 1.17㎢)
Inscription date : 6. 27, 2007
Designated as Natural Monument No. 420 in 2000

Introduction
Seongsan Ilchulbong, also called ‘Sunrise Peak’, is an archetypal tuff cone formed by hydrovolcanic eruptions upon a shallow seabed about 5 thousand years ago. The 182 m-high tuff cone, dominating the eastern seaboard of Jeju Island like a gigantic ancient castle, not only preserves its bowl-like crater but also provides excellent sea-cliff exposures of diverse internal structures. These features have great geologic values in that they provide a basis for interpreting eruptive and depositional processes of hydromagmatic volcanoes worldwide in addition to the past volcanic activity of the tuff cone.

Geological Characteristics
The Seongsan Ilchulbong Tuff Cone is a small volcano formed by Surtseyan-type hydrovolcanic activity upon a shallow seabed about 5 thousand years ago when the sea level was identical to that of the present (Sohn & Chough, 1992; Sohn et al., 2002). Volcanic cones or “oreums” (Jeju dialect for volcanic cones) in Jeju Island are mostly scoria cones formed by Hawaiian or Strombolian eruptions. They are composed of dark-colored and vesicular volcanic rock fragments, called scoria (“Song-i” in Jeju dialect). On the other hand, Seongsan Ilchulbong and several other oreums in Jeju Island are hydromagmatic volcanoes that were formed by explosive interaction of hot ascending magma and seawater or ground water (Sohn, 1996). Hydromagmatic volcanoes are classified into tuff rings and tuff cones based on crater size, height, and the slope angle (Wohletz & Sheridan, 1983; Vespermann & Schmincke, 2000). Seongsan Ilchulbong Tuff Cone has the typical morphology of a tuff cone with a height of 182 m, crater diameter of about 600 m, and dip of strata up to 45 degrees. The crater floor is 90 m above sea level.

Abundant water could permeate into the volcanic vent of the Seongsan Ilchulbong Tuff Cone during its eruption (Sohn, 1996). The erupted volcanic materials were therefore very wet and sticky, resulting in numerous depositional features that are indicative of the wet eruptive condition of the tuff cone (Sohn & Chough, 1992). The wet hydrovolcanic activity continued until the end of the eruption. The tuff cone could therefore have a bowl-like crater unfilled by scoria and lavas.

The Seongsan Ilchulbong Tuff Cone is surrounded by precipitous cliffs except for the northwestern flank because of erosion by marine waves. The tuff cone therefore provides superb geological cross-sections of the volcano from the intracrater deposits to the marginal strata. Diverse geological structures exposed on the sea cliffs have great geological importance because they provide a basis for interpreting eruptive and depositional processes of hydromagmatic volcanoes worldwide in addition to the past volcanic activity of the Seongsan Ilchulbong Tuff Cone.

There are numerous hydromagmatic volcanoes in the world similar to the Seongsan Ilchulbong Tuff Cone. However, it is probably the only example of a hydromagmatic volcano that has the typical morphology of a tuff cone and shows diverse internal structures along the sea cliff exposures. Because of the scientific values in addition to outstanding beauty, the Seongsan Ilchulbong Tuff Cone could be inscribed as a UNESCO World Natural Heritage site and is worth preserving permanently as a natural heritage of humankind.

Landscape
On the Jeju Island coastline, the eastern tip is suddenly met by a steep, colossal, cliffed elevation like a castle that surrounds a crater. This is the spectacular Seongsan Ilchulbong Tuff Cone. It is a magnificent sight, whether viewed from the sea, land or from above. On the slopes of the cliff, the stratifications in the tuff preserve both the birth and history of the volcano; they present nature’s unsurpassed beauty.

At daybreak, in particular, as the sun rises above the horizon, a curiously solemn mystique surrounds the tuff cone. On the southeastern tip of the crater, a wall has collapsed; erosion has caused the height of the wall to swoop down to an elevation similar to that of the crater basin. However, it is through this opening that one can indulge in the fantasia created by the scenery below; the sea cliff, the wide open sea and the sapphire blue waves that break up into a frothing mist.

Natural Ecosystem
The Seongsan Ilchulbong Tuff Cone can be divided into four areas: inside of the crater, north-west facing slope outside of the crater, rock cliffs of the outer crater wall, and sand dunes at the coast. Each area is covered with different vegetation. A grassland of Miscanthus sinensis-Artemisia princeps community and the arrow bamboo (Pseudosasa japonica) community cover the inner part of the crater. North-west facing slope outside of the crater is covered with the black pine (Pinus thunbergii) community, an evergreen shrub community composed of Orixa japonica and Hedera rhombea, and Zoysia japonica grassland community. Rock cliffs of the outer crater wall is covered with a evergreen vine community composed of Hedera rhombea and Trachelospermum asiaticum. Sand dunes at the seashore are covered with Vitex rotundifolia-Calystegia soldanella community and Peucedanum japonucum-Imperata cylindrica var. koenigii community.

The terrestrial vascular plant flora is composed of 222 taxa (190 species, 29 varieties, and 3 forms belonging to 186 genera and 77 families). Among them, 18 taxa are ferns, 3 taxa are gymnosperms, and the rest 201 taxa are angiosperms.

There are 6 rare plant species: a fern Crypsinus hastatus, an orchid Neofinetia falcata, two parasitic plants of Aeginetia indica and Orobanche coerulescens, and two other herbaceous plants of Arisaema heterophyllum and Glehnia littoralis. Among them, Aeginetia indica is an important plant in terms of plant distribution. This species, which belongs to the family Orobanchaceae and is parasitic to the roots of a grass Miscanthus sinensis, occurs in Japan, Taiwan and other southeast Asian countries, but in Korea it can be found only in Jeju Island and is growing in the crater of Seongsan Ilchulbong. Another parasitic plant, Orobanche coerulescens within the family Orobanchaceae, occurs rarely on the sand dunes of the coast of the Seongsan Ilchulbong Tuff Cone.

In addition, about 300 species of marine algae are growing in the shallow waters off the coast. Many new species were found in this area, among which a red alga Dasysiphonia chejuensis is the type specimen of the new genus Dasysiphonia.

Value of Seongsan Ilchulbong
The Seongsan Ilchulbong is a hydroclastic volcanic feature on the coastal flank of the Jeju volcano. Composed of a mix of breccia, lapilli tuff, stratified tuff and bedded tuff, it was formed by a Surtseyan-type (Icelandic) eruption from a shallow sea bed in the Late Pleistocene Epoch (120,000-40,000 years ago). It is a 179 m high castle-like feature with a bowl-shaped summit crater 570 m in diameter. Wave erosion has exposed the internal sedimentary structures and stratification.Tuff cones are a type of volcano formed by violent explosive eruption where magma interacts with water. Jeju Island has many such (phreatomagmatic) volcanoes and has become internationally important for the study of them. Seongsan Ilchulbong is distinctive because almost all of its outer structures have been eroded by wave action leaving cliffed sections that expose its internal structures and stratification. This enables the eruptive process be understood in ways not possible elsewhere. The fortress-like Seongsan Ilchulbong tuff cone, with its walls rising out of the ocean, is a dramatic landscape feature, and has exceptional exposures of its internal structures and stratification though almost all of its outer structures have been eroded by wave action, making it a world-class location for understanding Surtseyan-type volcanic eruptions.

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