Introducing Mount Hallasan Volcano

[BrickFielder]

Introduction
My intention is to produce a series of articles (depending on interest) which introduces ideas about volcanic and earthquake activity. I want to go slightly off the beaten track to explore oddities, volcano hazards, analysis methods, Wonders and Mankind’s impacts. Keep in mind I am not expert (corrections gratefully received), but hopefully these will at least give a flavour of some different places in the world and provide a few minutes escape from people’s troubles.

Introducing Volcano Mount Hallasan (halla volcano)

The Setting

Mount Hallasan forms the backbone of Jeju Island in the Korea Strait to the south of mainland South Korea. Jeju is the largest island in the nation and is a very popular tourist destination amongst both Koreans and foreigners alike. Besides its incredible scenery and natural riches, the island’s enduring popularity is in part down to the fact that South Koreans weren’t permitted to travel abroad until the late 1980s. The island is home to 660,000 people but hosts 15,000,000 visitors per year.Jeju means ‘huge village across the sea,’ and has its own distinct culture, which is quite different from that of the mainland.

Attractions include hello kitty Island, maze land and loveland (A bit naughty).  Manjanggul Cave on the island is one of the largest and longest lava tube caves in the world measuring up to 30 meters high and 23 meters wide and stretches for a staggering nine kilometers.

Cheonjeyeon Waterfall also known as the Pond of God originates from the ceiling of a cave and it comprises three sections. Around the subtropical falls you can find the rare and unique Solipnan reeds and Skeleton fork ferns.

There are beaches around the entire island though the two most famous among tourist are Hyeopjae Beach and Jungmun Beach.

Animals include the leopard cat, damselfish, the Jeju horse, green sea turtle, black-faced spoonbill and steller sea lion. It embraces four major ecosystems which are alpine coniferous forest, temperate broadleaf forest, warm temperate evergreen lucidophyll forest, and temperate grass land. There are occasional typhoons in summer and fall as well.
Jeju is said to be home to 18,000 gods and goddesses. They are loved, feared, worshipped and placated at home and at village shrines, in the island’s shamanistic rituals and Buddhist temples, on mountain peaks and other sites sacred to Taoist belief.

The Tectonic Environment

Mt. Halla, or Hallasan, is considered to be a rare example of a shield volcano built on a continental tectonic plate. The island is located behind the Ryukyu Trench, the collisional boundary between the Eurasian plate and the Philippine plate. Gravity inversion indicates the island is developed above and along a ridge. The structure shows positive correlation with a high magnetic anomaly distribution that could indicate existence of volcanic rocks. One suggestion is that the high gravity anomaly belt is formed by folding/buckling process under compressional environment and which causes decrease of pressure beneath the lithosphere along the belt accelerating melting of basaltic magma. An alternative hypothesis is that the basaltic magma beneath the island could be caused by episodic lithospheric folding. 

The Volcano
Hallasan is a shield volcano on Jeju Island in South Korea; it is the highest mountain in South Korea. Han represents the universe, and la means "pull". Both words mean that the mountain is high enough to pull the universe. Inside the crater is a lake called Baengnokdam meaning "white deer lake". It is formed by the collapse of the top of the ridge by the movement of magma underground. Depending on the season, the circumference of the lake is up to 2 kilometers with a depth up to about 100 meters.
 Eruptions of basalt and trachyte lava built the island above sea level, and it now reaches a height of 1,950 metres (6,398 ft). A large volcanic crater over 400 m (1,300 ft) in diameter tops the volcano. About 360 parasitic cones, or oreum in the Jeju dialect, are found on the volcano's flanks. Most of them are cinder cones and scoria cones, but there are also some lava domes and about 20 tuff rings near the coast and offshore, which were formed by underwater phreatic eruptions. 

Volcano Past Activity

A report from the Korea Institute of Geoscience and Mineral Resources (KIGAM) surprised volcanologists by dating Jeju’s most recent volcanic eruption to 5,000 years ago. The research team, led by Jin-yeong Lee, radiocarbon dated carbonised wood (charcoal) below the basalt layer at Sangchang-ri, Seogwipo City, to 5,000 years old.  The resulted in a designation of active which is disputed.

While scientific evidence of volcanism on Jeju Island is proving difficult to confirm, one piece of historic evidence suggests that the island was active much more recently than 5,000 years ago. The “Dongguk Yeoji Seungram,” a Joseon Dynasty geography textbook includes this seemingly eye-witness account.

“In June 1002 CE, a mountain arose in the middle of the sea. There were four giant holes at the top of the mountain, out of which red liquid flowed and soared, and thick smoke plumed for five days. All the red liquid hardened and became stone like roof tiles.”

The account has long puzzled geologists, particularly as few clues were given as to the location of the eruption. The most fancied site had been Biyangdo, an island off of Jeju’s west coast, followed by the peaks of Songaksan and Dansan, both in the southwest of the province.

Discussion

This is not a volcano that would be on a top list of volcanoes to create major issues, yet it remains a sleeping enigma and should probably warrant more investigation. I bet most of the 15 million visitors to Jeju do not even know they are visiting a potentially active volcano. Just do not google Jeju loveland .