Udo Island (Soiseom), located about 2km from Jongdal-ri, Gujwa-eup, Jeju-si and 3.8km from Seongsan Port, Seogwipo-si, is an inhabited island and is shaped like a cow lying down with its head raised. The part corresponding to the head is called Someori Oreum, and the people of Udo call it ‘Seommeori’. It works. A ferry runs from Seongsan Port to Dongcheonjin Port on Udo Island and takes about 15 minutes.
The southeastern slope of the Oreum plunges straight into the sea, forming a 100m high coastal cliff, and the northern slope, which was destroyed by a lava outflow, connects to Udo Village on a gentle lava plateau, making the Oreum an island itself. Soemeori Oreum is an underwater crater of a tuff ring. On the inner slope of the crater, you can see a crater ring surrounded by a reservoir and a folding screen, and in the center of the crater, 'Mangdongsan', a crater called Al Oreum, rises. Parasitic volcanoes of two different types can often be found around the coastline of Jeju Volcano Island, where two different types of parasitic volcanoes exist simultaneously in one crater, and this is called a single-type, double-type volcano. In other words, the tuff ring is a product of underwater eruption activity created in the shallow sea of ​​the marine environment, and Mangdongsan, a crater, is composed of scoria, a product of terrestrial eruption activity. The formation process of this volcano can be briefly summarized as follows.

In an environment where the first crater is exposed to the shallow sea or the intertidal zone around the coastline, contact with water is smooth, forming a tuff ring crater made of volcaniclastic sediments. Vapor explosive activity caused by water-magma contact leaves behind various sedimentary structures such as turbidity flows (surtgeyan flows) in the sedimentary layers of the tuff ring. The volcanic body that has grown itself due to this sedimentation activity is transformed into a terrestrial environment where contact with water is difficult, and it transitions to a terrestrial eruption, the so-called Strombolian eruption. The lava flow from the crater due to land eruption activity flowed while destroying the northern slope, creating the surface geology of Udo, and the lingering effects of the subsequent volcanic activity created craters like Al Oreum, which can be interpreted as the creation of Udo and Someori Oreum. . The current form of Someori Oreum is the result of physical coastal erosion caused by waves that continued after the eruption activity. The coastal vertical cliffs of Oreum, which is a coastal erosion landform, have developed sea erosion caves and sea cliffs created by sea erosion. The vegetation of Oreum overall shows the characteristics of grassy Oreum, and there are some pine trees and pine trees at the top of the mountain. There is a forest planted with cedar trees.