Gumunso
Gumunso is a swamp in Dongjeom-dong, Taebaek, Gangwon Province, South Korea. Unique in Korea, it features a river piercing through a mountain. It is known for its geological value, as its stratigraphic continuity is well-preserved. Gumunso names the surrounding village and neighborhood.
With an area of 685,109 m2, the "Ordovician Deposits and Topography of Stream Erosion of Gumunso" is a part of Gangwon Paleozoic National Geopark and is the 417th Natural Monument of South Korea. In Gumunso, the Jigunsan and Makgol Formation from the Lower Paleozoic Ordovician period can be found. The two streams Cheoramcheon and Hwangjicheon meet in Gumunso, and could be considered the start of the Nakdong River.
Name
The name Gumunso is a Hanja version of the name Gumuso, where "구무" is a Middle Korean term for "hole". A purely native-Korean name is Tturunae. Historical documents such as the geological survey included in the Veritable Records of Sejong and Daedongyeojido records the name as Cheoncheon. The hole itself is called Jagaemun.Formation and history
Formation
During the Ordovician era, the Taebaek region was underseas, with organisms like coral depositing limestone that would form today's Gumunso. When sea became isolated from rest of the ocean, it dried up, becoming extremely salty in the process. Rectangular imprints left by salt crystals can be found today in Gumunso.Additionally, around Gumunso, sedimentary rocks can be found which were deposited during the Paleozoic Era, approximately 520 to 460 million years ago. Features like trilobite fossils and stromatolites can be seen. Further upstream is the Jigunsan Formation, which contains abundant fossils. In 2000, calathid fossils were discovered in the Gumunso-adjacent Makgol Formation, the first to be found in the Korean peninsula.
The hole was formed as a result of erosion. Around 70,000–30,000 years ago, the stream formed an Ω-shaped meander, sharply turning right at Gumunso instead of passing through it. Eventually, the erosion carved a small channel through the limestone, reducing the flow to the meander. Ten thousand years later, the hole was fully formed, and the weakened meander dried up. Today, the land where the meander used to be consists of farmlands and is called sagundari.
Modern
Sinjŭng Tongguk yŏji sŭngnam, a 1530 geography book, notes: "The Hwangjicheon is located 110 ri west of Samcheok-bu. Its waters flow south for about 30 ri, piercing through a small mountain and continuing southward—called Cheoncheon".During the Japanese colonial period, the Japanese dug a tunnel next to Gumunso in 1937 to build a road to transport coal and workers.
On 2000 April 28, the "Ordovician Deposits and Topography of Stream Erosion of Gumunso" was designated as the 417th Natural Monument of South Korea.
In September 1998, the Taebaek city reduced the number of neighborhoods from 16 to 8, and merged Dongjeom-dong and a part of Jangseong-dong together. The resulting dong was named Gumunso-dong.