From Peninsula to Islands (400 thousand years ago - Now)
Separation from the mainland to the current form of the Oki Islands
When Oki first reappeared on the Earth's surface, it was covered with volcanic deposits and a very desolate place. As the land was eroded away by the rough waters of the Sea of Japan, “natural sculptures” such as dynamic, steep cliffs and fantastically-shaped rocks were formed. One of the distinguishing characteristics of Oki is that you can see many brightly colored cross sections of rocks formed through volcanic activity.
20,000 years ago during the glacial period, the Oki Islands had a land connection to the Shimane Peninsula. However, as global warming progressed and seas levels rose, Oki and the Shimane Peninsula were once again separated. Finally, about 10,000 years ago, the Oki Islands became the outlying islands they are today.
Large-scale volcanic activity, which ended nearly 400,000 years ago, formed the Oki Islands, but it was the rough waves, wind and rain of the Sea of Japan that eroded away parts of the islands to form what they are today.