Coastal Topography on Naepasudo Island, Taean

A sand spit, or gravel spit, is a sedimentary landform that develops on coasts dominated by wave action, commonly extending seaward from a coastal headland to block off a bay or estuary. Sand spits are mainly made up of sand and gravel, but the roundness of the gravel is generally not very high. The spit at Naepasudo Island, however, is composed of gravel with an unusually high degree of roundness rarely matched elsewhere, and its sorting is also very good, making it a highly distinctive and rare phenomenon. Naepasudo Island, whose gravel consists mostly of hard rocks such as quartzite and schist, is ringed by steep, linearly arranged coastal rock cliffs. This linear arrangement reflects the NE-SW and NW-SE trending structural lines common across Korea, which have not been greatly reshaped by wave action. Nevertheless, on these cliffs, strong frost action under the moist maritime conditions of the winter northwesterly winds detaches rock debris up to 15 cm across from the coastal cliffs. This debris is then rounded, transported and deposited by the sea to form a gravel beach. The gravel beach of the island has built up, at its southeastern edge, into a gravel spit or gravel bar 30 m wide and 300 m long, extending out to sea like a breakwater. This landform could develop because rock debris was continually supplied by frost action on the cliffs while ocean currents were able to transport and deposit it efficiently; indeed, the northeastern coast of Naepasudo Island experiences particularly strong currents in winter, and the straight, unindented coastline also helps this flow of seawater proceed smoothly. Such a coastal landform is rare, with few known examples in Korea or abroad, and it is considered to hold great academic significance for understanding sedimentation and its historical development along the west coast of the Korean peninsula. The name was changed from Coastal Topography of Naepasudo Island, Taean, to Coastal Gravel Bar of Naepasudo Island, Taean (announced 26 July 2021).

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Where it is

Region

Taean, Chungnam

Designation

Natural Monument · 천연기념물