GK:1.2.5 Volcanic Landforms and Karst Topography

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 Geography of Korea: I. Natural Environment > 2. Topography > 5) Volcanic Landforms and Karst Topography

5) Volcanic Landforms and Karst Topography

(1) Volcanic Landforms

During the Quaternary Pleistocene period the Korean Peninsula experienced sporadic volcanic activity. During this period there was volcanic activity in such places as Mt. Baekdu, Cheorwon-Pyeonggang, Ulleung-do Island, and Jeju Island. There were however some very small-scale eruptions during the Goryeo (918–1392) and Joseon (1392–1910) periods. Extant historical records indicate that Jeju Island experiences eruptions in 1002 and 1007 and that Mt. Baekdu experienced them in 1597, 1668, and 1702.

Mt. Baekdu (2744 meters), the highest mountain on the Korean Peninsula and known as the sacred mountain of the Korean race, was formed through volcanic activity during the Quaternary Cenozoic period. Mt. Baekdu towers over a wide lava plateau that sits at about 1600 meters in altitude. This lava plateau was formed by large amounts of basalt ejected over time from lengthy fissures in the earth’s crust. Mt. Baekdu is a stratovolcano; after forming the lava plateau, continuous eruptions from a single crater over time resulted in a building up of layers of hardened lava and pyroclastic materials.

Mt. Baekdu’s summit is thickly covered in a whitish pumice stone, and also snowcapped for about seven months of the year, thus the origins of its name, Baekdu, or “white head.” Volcanic pumice, a stone that is light enough to float in water, was ejected from the volcano as pyroclastic material during eruptions. At Mt. Baekdu’s summit is the Lake of Heaven (Cheonji), a caldera lake with a major axis of 5.3 kilometers and a minor axis of 3.5 kilometers (Figure 1-5).
Figure 1-5. Lake of Heaven (Cheonji) on the summit of Mt. Baekdu

Basalt was expelled throughout the Mt. Baekdu volcanic zone, which stretches down along the Macheollyeongsanmaek Range from Mt. Baekdu. The Mt. Baekdu volcanic zone stretches as far as Mt. Duryu and includes several volcanic peaks towering above 2000 meters, such as Ganbaek (2162m), Sobaek (2174m), Bukpotae (2289m), and Duryu (2309m), all of them surrounded by lava plateaus. Mt. Duryu, situated at the intersection of the Macheollyeongsanmaek and Hamgyeongsanmaek Ranges, is a tholoide volcano with trachyte tuff rocks that after forming at the end of the Tertiary period quickly became dormant.

The Cheorwon-Pyeonggang lava plateau was formed by lava spewing from fissures in the Chugaryeong tectonic valley. This lava, after filling the valley of the Hantan River, a tributary of the Imjin River, then flowed southward, and after passing present-day Cheorwon and Jeongok reached the area of Yulgok-ri, Paju city along the main branch of the Imjin River. The distance from Chugaryeong to Yulgok-ri is about 120 kilometers, and the Cheorwon-Pyeonggang lava plateau was formed along this stretch of wide river valley. Basalt can also be found in Anbyeon to the north of Chugaryeong in the Namdaecheon river valley as well as in Goseong. Further, another extensive lava plateau, contemporaneous in its formation with the Cheorwon-Pyeonggang plateau, can be found in Sangye-Goksan in Hwanghae-do province.

Ulleung-do is a volcanic island formed by an eruption from an undersea volcano some 2000 meters below sea level. The exposed portion of the island is only about 984 meters in altitude, but the height of the entire volcano reaches about 3000 meters, with a base area of some 1300 square kilometers. Ulleung-do, with an area of about 73 square kilometers, is a severely eroded tholoide volcano composed of basalt and trachyte agglomerate and tuff. On the island’s northern side is a caldera approximately 3.5 kilometers in diameter, in the center of which towers Albong, its central cone. The base of the caldera is comprised of the Nari basin at approximately 250 meters in height and the Albong basin at about 500 meters, together forming a two-tiered crater floor. These two basins are the only large plains on Ulleung-do.

Jeju is a volcanic island formed atop the continental shelf. Recent dating of rock forms reveals that the volcanic activity on Jeju began in Cenozoic Quaternary period. With the exception of Mt. Halla’s summit, a tholoide volcano formed of trachyte lava, the island of Jeju is largely a gently sloping shield volcano. This sort of terrain was formed through repeated large-scale basaltic lava flows moving out in all directions. The crater at the summit of Mt. Halla contains a crater lake called Baengnokdam. Compared to typical caldera lakes, this one is smaller. Further, Jeju is scattered with approximately 360 parasitic volcanoes of varying dimensions, as well as lava caves or tubes concentrated along its coasts, including the Manjanggul-Gimnyeonggul lava tubes (together designated Natural Monument No. 98) and the Hyeopjaegul-Ssangyonggul lava tubes (Natural Monument No. 236).

River formation on Jeju Island is weak. Although the island receives large amounts of rain, much of that precipitation seeps underground through fissures in the island’s basalt layer, resulting in marginal surface water. Almost all the island’s rivers and streams are so-called ephemeral rivers, flowing only during times of heavy rainfall. The water that seeps and flows underground later gushes up from springs along the coast. Thus, on Jeju water before it seeps underground is extremely precious.

(2) Karst Topography

Karst topography can refer to a variety of limestone formations carved by water. On the Korean Peninsula karst formations can particularly be found in Pyeongannam-do province, Hwanghae-do province, southern Gangwon-do province, and northeastern Chungcheongbuk-do province—places where the limestone layer of the Joseon Supergroup is widely distributed. Limestone caves and dolines are particularly prevalent in these areas.

Typically found clustered in groups on flat terrain, doline are sinkholes that have been formed through the slow corrosion of the ground by rainwater. But because the Korean peninsula’s limestone is found primarily in mountainous regions, its dolimes are mainly distributed on the flat river terraces found along the banks of rivers.

Korea’s limestone grottoes are well known among the public. Every year many tourists flock to such caves as Gosu and Nodong Caves in Danyang (Natural Monuments No. 256 and No. 262), Gossi Cave in Yeongwol (Natural Monument No. 219), Baengnyong Cave in Pyeongchang (Natural Monument No. 260), Hwanseon-Daegeum Cave in Samcheok (Natural Monument No. 178), and Seongnyu Cave in Uljin (Natural Monument No. 155).

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