How did Japan break away from the Korean Peninsula?

The East Sea we see today was not a sea that existed from the beginning. About 20 million years ago, the landmass that were once connected split apart, creating the East Sea as we know it today. Then, how did the Japanese archipelago move at that time?

In this video, starting from the imagination of clearing away all the water from the East Sea, we explore the actual appearance of the seabed—which we usually cannot see—and trace the path of the Japanese archipelago's separation.

In particular, we examine the "swinging door" model, which suggests that the Japanese archipelago did not simply drift eastward like a ship, but rather opened by rotating in opposite directions like two doors, along with the paleomagnetic records found in the rocks that serve as the evidence.

We also trace, one by one, the warm-sea fossils remaining in the Pohang Basin, the similarities between rocks found in Busan and Kyushu, the center of rotation near the Korea Strait, and the massive underwater topography remaining on the bottom of the East Sea. If you remove 200m, 1,000m, 2,000m, and over 3,000m of water, massive landforms beyond our imagination are revealed on the seabed of the East Sea. They extend from the Korean plateau, the Usan Trough, and the Ulleung Basin to the Japan Basin, reaching a maximum depth of 3,762m.

And Dokdo, which we know as a small island, also presents a completely different appearance. The part exposed above the water is merely a portion of the summit of a massive underwater mountain, with the height from the seabed to the summit reaching approximately 2,300m.

Even more surprising is the fact that the East Sea is not a sea that is continuously expanding. The movement of the Japanese archipelago stopped between about 15 million and 10 million years ago, and research is now also investigating traces showing that the East Sea actually began to narrow again after that period.

The horizon of the East Sea that we gaze at every day. Beneath it lie valleys thousands of meters deep, massive underwater mountains, and traces of the landmass that split apart about 20 million years ago.

If you watch this video to the end, you will gain a new perspective on “why the straight coastline of the East Sea became the way it is today” and the process of how the Japanese archipelago separated from the Korean Peninsula.

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