Hallasan () is a shield volcano on Jeju Island in South Korea. Its summit, at , is the highest point in the country. The area around the mountain is a designated national park, the Hallasan National Park. Hallasan is commonly considered to be one of the three main mountains of South Korea, along with Jirisan and Seoraksan.
The Hallasan Natural Reserve is a natural monument to South Korea. The Hallasan Natural Reserve was designated as a natural monument on October 12, 1966.
Names
Hallasan is the highest mountain in South Korea and is worshipped by people as they believe that gods and spirits live on the mountain. Alternate English names for the mountain include Hanla Mountain or Mount Halla and older English sources refer to the peak as Mount Auckland. Hallasan is written in Hangul as if it were Hanrasan (); however, it is still pronounced as Hallasan. In the past, Hallasan has been known by numerous other names in Korean including Buak (/), Wonsan (/), Jinsan (/), Seonsan (/), Dumuak (/), Burasan (/), Yeongjusan (/), and Hyeolmangbong (/).
Geology and geography
Hallasan
Hallasan is a massive shield volcano which forms the bulk of Jeju Island and is often taken as representing the island itself. There is a Korean traditional local saying that "Jeju Island is Hallasan, and Hallasan is Jeju." The mountain can indeed be seen from all places on the island, but its peak is often covered in clouds. The mountain has been designated Korea's Natural Monument no. 182.
The soil of Hallasan is mostly made out of volcanic ash, volcanic sand, and lapilli. The organic contents of the soil are higher than any other soil in South Korea, but drainage is also better than any other place in South Korea. The soil is not the best for farming. The volcanic island was constructed, starting in the Pliocene epoch, on the continental shelf, which is about 100 m (300 ft) below sea level in that area. Eruptions of basalt and trachyte lava built the island above sea level, and it now reaches a height of . A large volcanic crater over in diameter tops the volcano. About 360 parasitic cones, or oreum () in the Jeju language, 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. The most recent eruptions are estimated to be about 5,000 years ago, which puts the volcano into the active classification, meaning it has erupted in the last 10,000 years. The designation as active is not agreed to by all, as more monitoring and study are needed to better understand the volcano.
Baengnokdam
There is a crater lake on Hallasan called Baengnokdam (/), meaning "white deer lake". It is formed by the collapse of the top of the ridge by the movement of magma underground. There is a legend attributing the name of the lake to otherworldly men who descend from heaven to play with white deer. Depending on the season, the circumference of the lake is up to with a depth up to about .
The configurative rocks of the eastern and western walls of Baengnokdam are different. The eastern wall is covered with basalt lava 2–5 m thick at its top. In the lower part, there is a high-concentration stream sediment layer of the Tamra layer. The western wall is made of the trachyte lava dome. The volcanic wall formed by the eruption of the lava should be composed of lava, analysis. However, the eastern wall is composed of the clastic sedimentary sediments, so it is not a crater by lava eruption but a pit crater. Namely, the trachyte magma, which formed the Baengnokdam trachyte, was elevated on the dome, and the trachyte magma formed lava dome at its top. The inclination and direction of the Tamra Formation of Baengnokdam cannot be measured directly at Baengnokdam, but it is N10W of slope and 30NE of slope measured near the valley below North Baengnokdam, 1,580 m above sea level.
Impact of topography
Tendency of wind change by Hallasan
In order to understand the tendency of temperature change in Jeju Island, the short-term forecasting model of Halla, the weather data of the Korean peninsula, and the wind vector of AWS is analyzed. When the south winds flow into the sea, sea winds form around Hallasan, and the sea breeze is formed on the downwind side of the sea. On the coast, winds and the sea breezes gather around the coasts to form a persistent eddy, and the highest temperature occurs in the region where the eddy occurs.