▲ Formed 700,000 to 800,000 years ago, Mt. Sanbang is one of Jeju’s oldest rock formations, and is a must-see for tourists, geologists and mythology enthusiasts alike. Photo courtesy Jeju Special Self-Governing Province
Although Jeju is a comparatively small island, it is home to the highest number of parasitic volcanoes in the world.
A parasitic volcano is a secondary volcano created by the eruption of a main or larger volcano. Mt. Halla underwent over 100 eruptions, forming a bubbling of volcanic domes around it. On Jeju there are 368 of these domes, or as Jejuites like to call them, “oreum.” “Oreum” is a noun sprung from the verb “mount,” implying a small hill or peak that is easily climbed.
As for which oreum is the most popular, we often like to point to Mt. Sanbang. Its looming height of 345 meters is impressive in its own rite, but there’s more to it when we think about its geological status, as well as its embedded historical and legendary treasures.
Unlike other oreum, Mt. Sanbang sits like an enormous bell, plopped upon the southwestern planes of Jeju.
It was formed 700,000 to 800,000 years ago, making it one of Jeju’s oldest rock formations.
Because of its bell or dome-like shape, it is called a lava dome. Lava domes result from the slow effusion of sticky, or viscous felsic lava from a volcanic vent. The viscosity of the lava — which is the measurement of a fluid’s resistance to flow — prevents it from flowing too far from the vent, allowing it to cool quickly, creating a solid dome over the vent — like dried ketchup at the base of the tube.
Furthermore, because of this swift solidification of lava, Mt. Sanbang also has columnar joints. Columnar joints are naturally formed heptagonal, hexagonal or square vertical pillars formed by rapidly cooling Aa lava — which is thick and viscous, and flows slowly like honey, says Dr. Jeon Yong Mun of the World Natural Heritage Management Bureau.
Columnar joints are formed when the lava flow’s surface cools from the top down, as well as the bottom up, meeting in the centre, like the touching of fingertips, says Dr. Jeon. This is what formed the Daepodong Columnar Joints in Seogwipo, Jeju, because the lava flowed like a river outward and cooled upward and downward at relatively the same rate, but this is not the case for Mt. Sanbang.
Mt. Sanbang did not cool perfectly vertically, rather it cooled like a blossoming flower, where the columns spread or fell open like petals as they cooled. This is because the lava began cooling from the inside out, lowering to about 30 degrees Celsius, while the outside, top layer remained hot at 1,000 degrees Celsius, says Dr. Jeon. This allowed the outer tips of the columns to relax and splay outward, with gravity. This spreading or curving of the columns exhibits lobate geometry, says Dr. Jeon.
“We say it’s like a turtle,” he said, because the finished product resembles a turtle shell.
The vertical columnar joints, at about two metres in width and more than 100 metres in height, are well exposed on the southern wall. Also, beneath the jointed lava is a thick layer of volcanic breccia, which is a cementation of loose fragments of various or the same rocks. In this case, it is composed of fragments of trachyte: pieces of the vent’s lava that cooled, possibly causing a collapse of the dome, then was picked back up by the lava flow, piling, building and cementing. This suggests that the dome underwent explosive eruptions before it settled, and formed the columnar-jointed dome we see today.
It is this layer of breccia that overlies the oldest rock formation on Jeju: The Yongmeori Tuff Ring.
Another famously-unique feature is Mt. Sanbang’s natural cave. In fact, “sanbang” literally means “a cave inside a mountain.” The cave is located on the southwest side of Mt. Sanbang. It is only 10 meters in length, five meters high and five meters wide. Though its measurements are small, a Buddhist temple was built within it: Sanbanggulsa or Sanbang Cave Temple.
In the Goryeo period, Monk Hye-II placed a shrine of Buddha inside the cave. With the Buddha facing east, overlooking the forest and witnessing the sunrise each morning, the cave officially became a temple, becoming one of the only cave temples in South Korea. Along with its secluded location, its small waterfall of spring water, and the ancient pine trees that line its entrance, it comes as no surprise that this is a place of spiritual solitude.
The Sanbangsan Temple and the Bomunsa Temple, which hold relics of Buddha, are also located at the foot of the mountain.
Also, because Mt. Sanbang sits along the coast and is 395 meters above sea level, it is often ringed with clouds, giving it a very mysterious presence. The upper half of the mountain has its own climatic conditions and is protected for botanical research. Mt. Sanbang is the only location on Jeju where boxwoods grow naturally, granting it the title of UNESCO Natural World Monument No. 376
There is a climbing trail on the northern face of Mt. Sanbang. Finding the trail, however, is another matter, but the view from the top is worth the search. But be careful, don’t get too close to the southern edges, which are marked with sharp cliffs, weathering pits and scree slopes, some as high as 200 meters.
As for legends, Mt. Sanbang is teeming with them. It is said, that because of its dome shape, it appears as though it could fit inside Baengnokdam Lake, Mt. Halla’s crater. Legend says that a clumsy hunter accidentally shot a god in the behind. So the god, in a fit of rage, scooped out Mt. Halla’s peak and chucked it to the west at the hunter, forming Mt. Sanbang.
As for Mt. Sanbang’s cave, a legend explains that a male mortal and the female spirit of Mt. Sanbang were in love. One day, however, a male spirit fell in love her as well. To compete for her love, he sent the mortal to the front lines of war where he quickly died. But, the female spirit remained faithful to her mortal lover, weeping continuously over his death. Her tears are said to be the sprinkling waterfall inside Mt. Sanbang’s cave.
Mt. Sangban is open all year round. Each season presents its own kind of beauty. In winter you may visit anytime between 8:30 a.m. to 6 p.m. In summer, it is open one hour later.
ⓒ Jeju Weekly 2009 (http://www.jejuweekly.com)
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