▲ Suweolbong was not only the first geological site in Jeju to earn a Geopark designation, but it is also highly regarded by scientists for its unique geological features. Photo courtesy Jeju Special Self-Governing Province
Suweolbong Tuff Ring not only claims Jeju Island’s westernmost tip, it also claims first place amongst Korea’s nine Geoparks. It was the first Geopark site designated by UNESCO’s Global Geopark Network and is highly regarded by volcanologists and geologists alike for its uniqueness.
Suweolbong is a 77-meter-high mount, or peak, of pyroclastic deposits, which is a lifted, almost-flat bed of layered rock. Pyroclastic rocks are made mostly (or solely) of volcanic rock. They are typically formed from airborne ash, lapilli (teardrop, dumbbell or button-shaped droplets of molten lava), and bombs (blocks of rock) spewed from the volcano, which then mix with rocks native to the area of eruption. They are commonly a result of volcanic activity.
There are three modes of transporting pyroclastic rocks: pyroclastic flow, pyroclastic surge, and pyroclastic fall. Suweolbong was formed by a pyroclastic surge, which is a fluidized mass of turbulent gas and rock spewed during a volcanic eruption. Having a higher gas to rock ratio, surges have a lower density than flows, causing it to be more turbulent, allowing it to go over high ground or hills, whereas a flow must travel downhill. Surges are therefore faster than flows, reaching speeds of hundreds of kilometers per hour. Current studies show that its originating volcanic vent lies several hundred meters in from the shoreline.
Most interestingly, however, is how Suweolbong’s individual tuff layers are closely correlated layer by layer, from its base to its outermost tip. This nearly perfect layering is unique and is the only one of its kind: no other examples have been located outside Jeju. Based on sediment studies of pyroclastic surge deposits, Suweolbong is the first depositional model found. It is discussed in several geological textbooks and literature, and it has become very famous among volcanologists and is often studied during field trips.
Suweolbong was formed 18,000 years ago. Its age was discovered by optically stimulated luminescence (as opposed to carbon dating, this is a method of dating minerals, in this case grains of quartz found in the tuff.) The measurement suggests that the eruption happened during the last glacial maximum (the time when the ice sheets were most widespread and when sea level was much lower than today).
As with nearly all of Jeju’s natural phenomena, a legend surrounds Suweolbong. About 370 years ago, a brother named Nokgo and a sister named Suwolee, traveled to Suweolbong in search of an herbal medicine called ogalp'i. This medicine was for their sick mother. Suwolee found it on the side of the cliff, but as she reached for it, she slipped off the edge, falling to her death. Nokgo cried for 17 days. His tears are the natural springs we see today, sputtering from the cliff's sides. The peak has also been given the name, Nokgomul oreum: mul means water, and oreum means climbing in Jeju.
As for visiting Suweolbong, because of its western location, it promises a magnificent sunset. Locals also say that on a clear day you can see China.
It is located halfway between Jeju City and Seogwipo City, on Seohoeseon Ilju Road. There is no entry fee.
For a complete list of the nine Geopark sites featured in this series, please visit our Web site. —Ed
ⓒ Jeju Weekly 2009 (http://www.jejuweekly.com)
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