A volcanic massif drifted from the south and collided with the Japanese mainland

A volcanic massif drifted from the south and collided with the Japanese mainland


Izu is a peninsula located near Tokyo, and juts out into the Pacific Ocean. Today the area is a famous hot spring destinations, attracting tourists throughout the year. However, even as this peninsula seems an integral part of Honshu Island,  geological research has clarified that the origins of this area go millions of years back in geological time, and to much southerly location compared to now.

Izu was born  as a submarine volcanic massif, possibly over 20 million years ago, in an area near the present-day Iwo jima Island (located in the Pacific Ocean). We call this area the South Sea, due to the fact that along with the land, seas also change due to tectonic motion and this South Sea was a water body of the distant past. This landmass was located on the Philippine Sea plate, which is steadily moving northwestward with respect to the main Japanese islands. As a result, the volcanic massif drifted northward and eventually ‘collided’ with the main island of Honshu, gradually forming the present day peninsula.

Izu was created through epeated volcanism and crustal upliftment and later shaped through erosion. The landscape here resembles sceneries of comparatively southerly locations, and this resemblance prompted the Nobel Prize winning author Yasunari Kawabata to observe the following way:  peninsula that came from the southern seas. He described this land in the following way:

People say Izu is a land of poets. 

Historians say Izu is a miniature of Japan.

I add: Izu is a land resembling the south.

Izu is an art gallery that has every possible landscape of mountains and sea in its possession.

The whole Izu Peninsula is one large park…

Yasunari Kawabata Opening lines from”Introduction to Izu”

This observation also aptly describes our Geopark. Whereas Kawabata based his description on the appearance of the landscapes, our tale is rooted in scientific exploration about crustal formation, volcanism and landscape changes, all of which are also parts of the larger story of the creation of earth’s crust and the movement of continents and landmasses.

 


Nashimoto limestone Kawazu-cho. Memento of the southern seas: fossils of the forms of life that once inhabited the South Pacific.

A schematic depiction of the events that accompanied the northward movement of Izu Peninsula and its collision with the Honshu. We can still see the sediment that accumulated in the channel between Honshu and the island just before the collision at Oyama cho near Mt. Fuji and some locations in the Izu peninsula. 

 

The northward movement of the Philippine Sea Plate has been verified with paleomagnetic analysis of the rocks of Izu Peninsula and the area of the sea around it.

A close examination of the marks left by the geomagnetic field on the rocks of various periods proves that the latitude of Izu Peninsula became higher with time– this is an evidence that the volcanic massif actually journeyed from a smore southerly location due to tectonic motion.