How much do you know about the formation and geology of Jeju Island? First, take this quiz. You’ll find the answers at the end of the article.

 

Question 1

When did Jeju Island begin forming?

A) 350,000 years ago

B) 2 million years ago

C) 1 million years ago

D) None of the above

 

Question 2

Jeju Island can be defined as a:

A) Dome volcano

B) Volcanic tuff cone

C) Shelfal shield volcano

D) None of the above

 

Question 3

Jeju is 73 km long and 31 km wide, for a total area of:

A) 1,847km2

B) 3,251km2

C) 1,240km2

D) None of the above


Jeju’s nine Geopark sites are closely related to the island’s formation and geology. The province applied for membership in the Global Network of National Geoparks (GGN) in 2009. In the summer of 2010 a group of experts came to the island to inspect the proposed nine geosites. On Oct. 4 of that year, Jeju became the twentieth member of GGN. As such, the province was charged with the promotion of education and tourism in areas of scientific merit. These include areas of geological, archaeological, biological and cultural interest.

The concept of a geopark forces locals and governments alike to take a fundamentally new approach to the delicate balance of tourism, development and conservation. For the GGN, educating the public about an area’s geosites is of prime importance.

In other words, people need to be able to get more out their visit to a geosite than just getting a tourist photo, or to tick off another item on their bucket list. Instead, they must have access to visitor information offices or guided tours by trained volunteers. In this way they can gain an appreciation for the importance and fragility of the site’s geology, ecology, historic value, among other elements.

It should be noted that although the media often directly attributes Jeju’s geopark membership to UNESCO, the GGN is actually a separate entity. It is recognized by UNESCO’s Division of Earth Sciences, however, and receives logistical assistance from them.

 

The nine Jeju Geopark sites:

Mt. Halla and its geosite cluster

Manjang Cave

Cheonjiyeon Waterfall

The Daepo Columnar-Joints

The Seogwipo Formation

Seongsan Ilchulbong Tuff Cone

Sanbangsan Lava Dome

Yongmeori Tuff Ring

Suweolbong Tuff Ring

 

Mt. Halla, Manjang Cave and Seongsan Ilchulbong were made World Natural Heritage sites in 2007. And back in 2002, Mt. Halla and Cheonjiyeon Waterfall were designated by the UNESCO Natural Science Center as a “Man and the Biosphere Reserve.” They have all been by recognized by the Korean government as National Monuments.

 

Mt. Halla and its geosite cluster

This is certainly the most prominent and well-known feature of Jeju Island. Mt. Halla is the majestic mountain which we all can see and admire every day. It is also South Korea’s tallest peak at 1,950 meters.

According to the book “Jeju Island Geopark – A Volcanic Wonder of Korea,” Halla is a sloping shield volcano which is a classic example of volcanism on the Korean Peninsula in the last 2.5 million years

View to the south of Hallasan National Park from Eoseungsaengak.

View to the south of Hallasan National Park from Eoseungsaengak.

Geologists think it began forming about 780,000 years ago. Essentially there were many hydrovolcanic eruptions, which is volcanism under the surface of the ocean. This laid the base for later lava effusions that occurred above sea level and which over the course of hundreds of thousands of years and waves of volcanic activity, ultimately formed Mt. Halla.

An example of these layered volcanic events, of course, is the dating of rocks from the top of Halla at Baeknokdam crater, and those closer to the base. Baeknokdam rocks date back just a few tens of thousands of years. So the summit is relatively young.

And in terms of biodiversity, Mt. Halla is invaluable. It was designated as Natural Monument No. 182 back in 1966 and made a national park in 1970. Since then, the mountain has been mostly protected from human activity.

Other special features include Halla’s cultural heritage. Its grazing fields Jeju ponies at the the mid-mountain area — about 200 to 600 meters above sea level. There are historical records of these ponies being sent to the king as far back as the Goryeo in 1073.

There is also evidence of the Japanese Occupation on Halla, and in fact all around the island. Jeju was a very strategic spot for the Japanese military, with its proximity to China for its airstrips, and its potential to protect Japanese territory as U.S. military forces moved through the region in 1945.

There are two Japanese Army bunkers and three cave dug-out positions on the southwest part of Eoseungsaengak, on the north of the mountain. They were used to protect about 120 soldiers of an anti-aircraft division. It’s now a Registered Cultural Heritage, No. 307.

 

Manjang Cave

Manjang Cave is about 7,400 meters long, and in places can reach up to 30 meters in height and 23 meters in width. It is part of the Geomunoreum Lava Tube System and was formed by multiple lava flows sometime in the last 100,000 years or so.

It has a whole range of interesting features, including an upper and lower level, columns, cave coral, bridges, and ropy lava formations.

 

Cheonjiyeon Waterfall

Cheonjiyeon Waterfall is very important in terms of its biological diversity. The valley contains a warm temperate forest, with 447 species of plants, of which 17 grow only on Jeju. Evergreen trees, vines and ferny plants thrive there. They provide homes for many kinds of animals and birds.

 

The Daepo Columnar-Joints

The Daepo Columnar-Jointed Lava Geosite (which is along Olle Course 8) is the best place to see columnar-jointed lava on Jeju — about 3 kilometers worth along the coast at Daepo-dong. Most of the joints are six-sided, but other variations, from four to seven-sides, are visible.

These remarkable structures are quite unforgettable, even for non-geologists.

This area in fact had great cultural importance as a coastal spring, which in Korean is called nonjitmul. The island’s basalt rock is quite porous and much of the rainwater just percolates through it  — that is, at least until it reaches the Seogwipo Formation. So instead of surface streams or rivers, the majority of Jeju’s fresh water collects at the coast. The reason is that sea water, which is denser than freshwater, allows for the fresh water to rise close to the surface, which is where villagers could get the water using shallow wells. Access to fresh water was something generations of islanders had to worry about constantly.

 

The Seogwipo Formation

The Seogwipo Formation is a rather technical geological entity. Geologically, it is a 100-meter-thick layer of volcaniclastic deposits which underlie almost all of Jeju Island. It’s significant for being more or less impermeable, so it greatly affects how Jeju’s groundwater collects and flows.

What is generally referred to as the Seogwipo Formation is the part that is an exposed outcrop next to the Seogwipo City Center. But in fact it’s under the whole island.

Now in the last decade or so, scientists have subdivided this outcrop into 10 fossil-bearing and four fossil-free units. From these layered structures, they mapped how sediments, lava flows, sand and mud from storms, as well as fossils, all came together and were deposited… especially by oceans currents and tidal processes.

 

Seongsan Ilchulbong Tuff Cone

Seongsan Ilchulbong or Seongsan Sunrise Peak as it’s commonly known, is a tuff cone along Olle Course 1. The tuff cone is a beautiful structure, and geologically, culturally and historically significant. And though an hour’s drive from Jeju City and the airport, in 2013 it became the first island site to attract over 3 million visitors in a single year.

Seongsan Ilchulbong is 179 meters high and has a diameter of about 600 meters. It rises from the ocean like a huge stone castle. It formed about 5,000 years ago during an eruption from the shallow seabed. Because of its sea cliff exposures, it holds a wealth of information about the formation of hydromagmatic volcanos found all around the world — in that regard it is considered by many geologists to be completely unique.

 

Sanbangsan Lava Dome

Sanbangsan Lava Dome is along Olle Course 10. It’s a 395-meter-tall lava dome that is around 800,000 years old, one of the island’s oldest rock formations. On the drive down to Seogwipo City along the 1135 Road, it suddenly rises magnificently in front of drivers in the southwest.

According to the book “Jeju Island Geopark – A Volcanic Wonder of Korea” (2013), its dome shape is due to a very viscous — and therefore slow — lava flow, which essentially oozed out instead of violently exploding.

Culturally, this site is important for Sanbanggulsa, or Sanbang Cave Temple, which is where Buddhist priests meditated in a cave that is 10-meters-deep, 5-meters-tall and 5-meters-wide.

In the area there are absolutely spectacular views from the temple, of Yongmeori Cliff, Mara Island, Gapa Island and the Hyeonjaeseom Islets.

It’s also known for the Hamel Monument, which marks the presumed spot on which Dutchman Hendrick Hamel and his trading vessel and crew ran aground in 1653. He was detained for 13 years in Korea, before escaping to Nagasaki in 1666.

 

Yongmeori Tuff Ring

Right next to Sanbangsan is Yongmeori Tuff Ring. This, as a hydromagmatic volcano, was more explosive and violent in its formation than Sanbangsan, particularly since the hot lava came into contact with cold seawater.

 

Suweolbong Tuff Ring

Suweolbong, which is along Olle Course 12. This is a remnant of a tuff ring on the west of the island. Its pyroclastic deposits are clearly visible and in excellent condition. It has a wealth of geological information — both volcanic and sedimentary. According to “Jeju Island Geopark,” its pristine condition and geological importance is unique in the world.

The area at Gosan-ri also has archeological importance, with earthenware fragments dating back 12,000 years. It is thought that Gosan-ri was the first place on the island settled by humans.

 

The Future

There are 21 new sites under consideration for inclusion over the next 10 to 15 years. These include Oedolgae, Biyang Island, and Sangumburi Crater, to name just a few.

For more information, the Jeju government Geopark Web site is geopark.jeju.go.kr.

 

 

This a reworked article, written by the author, which first appeared on KCTV English News. — Ed.

 

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Answers

 

Q1: B. Volcanic activity began 2 million years ago and continued to erupt into recorded human history.

Q2: C. Jeju is a shelfal shield volcano as it formed on the continental shelf of the relatively shallow southeastern Yellow Sea. Incidentally, for answer B, the tuff cone, this formation is quite common on Jeju. It’s a hydromagmatic volcano, meaning it erupted underwater and the lava’s reaction to coming into contact with the seawater determined its overall form. Seongsan Sunrise Peak is the most famous of these here. In Hawaii, it’s Diamond Head.

Q3: A. By comparison, the Hawaiian Island of Oahu is 1,545km2. Jeju’s a relatively small island, but like Hawaii it’s recognized the world over as being quite rich in geological marvels.