Hallasan
Hallasan is a shield volcano comprising much of 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, named 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 was designated as a South Korean Natural Monument number 182 on October 12, 1966.
Names
Alternate English names for the mountain include Hanla Mountain and Mount Halla, and older English sources refer to the peak as Mount Auckland. Hallasan is written in Hangul as if it were Hanrasan, but is still pronounced 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 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, and drainage is also better than any other place in South Korea, but its soil is relatively infertile. The volcanic island was constructed, starting in the Pliocene epoch, on the continental shelf, which is about 100 m below sea level in the 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. According to Goryeosa, its last eruption was in 1007 CE, while geological evidence suggests its last eruption was around at least 2,000 years ago. This 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 thick at its top. In the lower part, there is a high-concentration stream sediment layer of the Tamna 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 Tamna 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, 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 vectors from the AWS are analyzed. When the south winds flow into the sea, sea winds form around Hallasan, and a 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.Tendency of maximum temperature by Hallasan
In order to understand the tendency of maximum temperature in Jeju Island, the area where the highest temperature occurred when the wind was weak was surveyed and analyzed. In the morning, when the reverse layer is formed and the wind is weak, the warm air of the lower layer is raised when the air movement between the upper and lower layers is blocked, and it is placed on the upper floor by the sea breeze, which affects the temperature rise in the mid-mountainous area.The occurrence of the highest temperature coincides with the formation position of the eddy, and when the wind is weak, the eddy forms in the middle mountain region. When the wind is weak, the warmth is accumulated in the middle layer, so the maximum temperature in the mid-mountainous area is higher than the maximum temperature of the low-altitude coastal area by about, and or higher on the downwind side.
When the wind is blowing at, a weak sea breeze coming from the sea is formed on the coastal area and peak temperatures are mainly observed during the daytime.
Tendency of minimum temperature by Hallasan
The change of the minimum temperature varies depending on the degree of cooling of Hallasan and the intensity of the wind speed. When the wind blows due to the predominant sea breeze, the air cooled in Hallasan descends to the coastal area and induces a decrease in temperature. When the synoptic wind blows strongly, the cold air of Hallasan moves to the downwind side and the lowest temperature appears. The lowest temperature in the downwind area is lower than in other areas, and the lowest temperature often occurs at night.When the weak northwestern synoptic winds blow, low temperatures occur in the eastern part of Jeju Island. The chill of the top of Hallasan descends downhill along the mountain range and is collected in the eastern part of Jeju Island so the morning temperature drops considerably.