The formation of Japan’s archipelago and northern Apls of Japan

The edge of the Eurasian continent split off due to the elevation of magma what started
forming Japan’s archipelago 21 million years ago.
Afterwards the split between the continent and the strip widened out gradually 16 million
years ago when submarine volcanos erupted one after another.
The expansion of the split (the Sea of Japan) stopped and Japan’s archipelago was formed
15 million years ago. But it was split into east and west by Fosa Magna, big channel
due to the different directions of the Japan trench and the Southern Trough trench.
Then magma in the underground of the Fosa Magna rose up, formed land and bridged
the east and the west 12 million years ago.
And the seabed of the Japan sea moved toward east and pushed the archipelago causing
upheaval and forming northern Apls of Japan due to the earthshaking and the elevation of
the mantle of the continent 2 million years ago.
Then earthshaking intensified all over the archipelago 300 to 400 thousand years ago and
then volcanic activities formed mountain ranges between the coast of the Sea of Japan and
Matsumoto area. It made the river Chikuma east bound from north bound , and Matsumoto,
Nagano and Iiyama basins were formed by the sedimentation of mud and rock.

 

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