Songjiho is a lagoon located in Oho-ri, Jugwang-myeon, Goseong-gun, Gangwon Province. It has a radius of 5.56km, a basin area of 5.4㎢, a depth of 2.0-3.8m (5m at the deepest point) and a water surface area of 495,000㎡.
The sea level rise from the Holocene Epoch (since 6,000 years ago) to the last glacial period (15,000 years ago) shaped the shorelines almost like today’s and sand bar developed as longshore sand deposits grew parallel to the shore.
The current landscape was formed as the sand bar had filled in the indentation of the shoreline.
Offshore from the Songjiho beach, there is a granitic island named Jukdo, which caused sand spit to develop by blocking the waves.
(Sand spit: a deposition bar of sand or gravels in a shape of long and narrow hook near the mouth of a bay)
The Jukdo stands 500 m offshore at high tide while it gets attached to the land by the sand spit at low tide. As the sand spit, tapered toward the Jukdo, grew to connect the tied island to sand beach, it formed a tombolo.
(Tombolo: a landform in which sand spit grows and gets attached to the islands offshore)
The shorelines of the Songjiho illustrate a variety of weathered micro-topography such as tor, gnamma, groove and tafoni; these were formed by the sea level changes which occurred when felsic magma that intruded into granitic faults cooled.
Granite formed deep in the earth under high pressure and temperature ascends to the earth’s surface by crustal uplift and erodes away after it went through physical and chemical weathering; the subsequent development of rugged surface on it is called weathered micro-topography. Felsic dike intrusion dates back to 83 million years ago during the late Cretaceous and is distributed horizontally 70-10cm wide and 20m long.
Landscapes on the shorelines of the Songjiho have been affected by several compound factors, e.g., differential weathering along the faults and joints of granite, sea level rise after the last glacial period, and resistance of granite and felsite to weathering.
Seonangbawi (rock) is an iconic landscape showcasing the effect of differential weathering on felsite dike; its top and bottom are of granite while its middle is of felsite connected to the top and bottom.
