Why is Japan an archipelago


Volcanism in Japan

The volcanoes of Japan belong to the northwestern Pacific fire belt and are distributed in several zones over the 4 main islands, as well as the island chains belonging to Japan, which lead to Taiwan and the Mariana Islands. The Japanese archipelago consists of 3922 islands. There are 265 volcanoes classified as potentially active on them. Most of them are on the island of Honshu. The volcanoes in southern Japan have been most active in recent years.

Tectonics of Japan

The volcanism of Japan is characterized by the subduction of the Pacific plate, whereby the situation is rather complex, as 4 plates are involved: in the north the Pacific plate pushes under the Okhotsk and in the east under the Philippine and Asian plates. In the south, the Philippine plate is subducted under the Asian continent. This situation now leads to two crossing points (triple-junctions) of the plates, as well as to plate boundaries that not only run parallel to the coastlines in north-south direction, but also to those that strike in east-west direction. The plates are in constant motion along their borders. If the plates jam, then enormous tensions build up, which are discharged in the numerous earthquakes in Japan.
A mountain range that is still in the unfolding stage extends through the entire archipelago. It occupies 73 percent of the total land area of ​​Japan.
Due to the subduction and the melting of the oceanic crust in the earth's mantle, magma rises behind the subduction zones, which is very tough and contains a lot of water. Most eruptions are correspondingly explosive. In addition, lava domes are often formed.

Images from Japan

The far north of Japan

In northern Japan, the Kuril island chain ends at the northern end of Hokkaido. One of the most famous volcanoes on this island is the 733 m high Usu. Lava domes are typically formed when it erupts. Its last outbreak was in 2001.
The Tokachi-dake forms the center of Daisetsuzan National Park and was last active in 2004. Tokachi consists of several stratovolcanoes and lava domes. The Daisetsu volcano is also a group of several volcanoes and domes that formed in a 2 km diameter caldera. The volcanic island of Oshima-Oshima in the Sea of ​​Japan is also known. Two stratovolcanoes of basaltic to andesitic composition overlap on the small island.

Well-known volcanoes in central Japan

Japan's most powerful volcano is the 3776 m high Fuji. It is not only close to the capital Tokyo, but also at a kink between the borders of the Filipino and Asian plates. There are practically no active volcanoes in a zone of 400 km southwest of this kink. Northwest of Mount Fuji is the 2568 m high complex volcano Asama. He has been active a lot in the recent past.
Ontake-san (revered mountain) is the second highest fire mountain in Japan and last erupted in September 2014. Numerous mountain hikers were surprised by this outbreak and 47 were killed. This disaster sparked a discussion about whether not all volcanoes in Japan should be closed.

In the south of Japan

Aso is one of the most famous volcanoes on Kyushu. In the caldera there is not only the active Naka-dake but also a well-developed tourist center. The last Aso eruption so far was in October 2016.
Kirishima is a volcanic complex with more than 2 individual volcanoes. In 2011, the Shimone-dake hit the headlines here when a series of powerful eruptions caused volcanic bombs to fly all the way to the motorway.
Sakurajima is located a little south of Kirishima and was permanently active until recently. This volcano has become famous for its many volcanic flashes. In 2016 the volcano was only active sporadically.
Unzen is similar to Kirishima in that it is also an entire volcanic complex. It is not far from the city of Nagasaki, which was destroyed by an atomic bomb during World War II. In 1991 47 people died in a pyroclastic flow. Among them the volcanologist couple Krafft.
Suwanosejima is located on an island in the very south of the Japanese archipelago. The 799 m high volcano has a caldera in which there are 4 craters. The volcano is always sporadically active and mostly produces strombolian eruptions.

As of 2016

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