[Creative Cultivation Program] Japan's volcanoes are becoming active. Is this related to the Tonga volcano eruption?

Author: Xiao Long

Since the beginning of 2022, volcanoes in many parts of the world have become active, especially our neighboring country, Japan's Sakurajima volcano, which has erupted many times, and Fuji volcano also shows signs of erupting soon. Why does Japan have so many active volcanoes? Is it related to the volcanic eruption in Tonga in early 2022?

To know the answers to these questions, we have to start with global plate tectonics, because most of today's volcanoes are located on plate boundaries. After more than half a century of research, earth scientists have discovered that the earth is composed of six major plates, namely the Pacific Plate, the Indian Plate, the Eurasian Plate, the African Plate, the American Plate, and the Antarctic Plate. There is relative compression or stretching between these plates. Through compression, one plate will also subduct under another plate to form a subduction zone, such as the Mariana Trench. And the tension between plates will form a rupture zone, such as the mid-ocean ridge. These places are also the most active places for earthquakes and volcanoes on the earth, and more than 90% of volcanoes and earthquakes are distributed here.

Mechanism of volcano formation above the Japan Trench and subduction zone

The volcanic activity in Japan that we are discussing today is affected by the activity of the Pacific Plate. As the Pacific Plate has been moving westward for hundreds of millions of years, squeezing the Eurasian Plate to the west, the denser Pacific crustal material has been subducted under the Eurasian Plate, forming the deepest Mariana Trench on Earth, and generating a large number of volcanoes and earthquakes. From the global geological structure map, we can see that Japan is located on the western edge of the Pacific Plate, on the famous Pacific volcanic belt on Earth, which is often called the "Pacific Ring of Fire."

It is precisely because of this compression and subduction between plates that more than 200 volcanoes have been formed in Japan, of which about 100 are active volcanoes. Therefore, Japan is known as the "Land of Volcanoes". Among the volcanoes in Japan, the most familiar one is Mount Fuji, and the most active one recently is Sakurajima Volcano, which has also attracted everyone's attention.

Sakurajima is an active volcanic island located in Kagoshima Bay in southern Kyushu, Japan. It covers an area of ​​77 square kilometers and consists of three volcanic bodies. Sakurajima is only 4 kilometers away from the city of Kagoshima. Smoke can often be seen from the crater, and the white clouds floating over Sakurajima are often volcanic clouds.

Sakurajima itself is a volcanic island that grew out of the seabed, formed about 26,000 years ago. It was originally an undersea volcano. As the volcanic eruptions became more and more, the undersea volcano grew out of the sea and formed an island, just like Hawaii Island and many islands in the South Pacific region, which are all volcanic islands. Sakurajima's volcanic activity is extremely active, and the major eruption in 1914 caused great loss of life and property to local residents. This eruption formed a large amount of volcanic magma that filled the strait between Sakurajima and the Osumi Peninsula at the time, connecting Sakurajima to the Osumi Peninsula on the Kyushu mainland, and Sakurajima has since become a peninsula.

The continued eruption of Sakurajima in early and mid-2022 will also remind everyone of the volcanic eruption in Tonga in early 2022. What is the connection between these volcanic activities?

Although Japan and Tonga are far apart, one is in the northwest of the Pacific Ocean and the other is in the western part of the South Pacific Ocean. However, from the perspective of plate tectonics, they have a common feature, that is, they are both located on the west side of the Pacific Plate, and are located on the subduction zone formed by the westward compression and subduction of the Pacific Plate. They are important components of the Pacific Ring of Fire mentioned above.

Specifically, Japan's Sakurajima volcano is located to the west of the Japan Trench. Below the trench is the Pacific Plate that subducts westward. When the Pacific Plate subducts under the Eurasian Plate, as the subduction depth and pressure increase, the water in the oceanic crust sediments will be released. The water has a low density and will migrate upward to the lithosphere above the subducting plate. It is the addition of this water that lowers the melting point of the lithosphere, causing the rocks there to melt and form magma. After erupting to the surface, it is the volcanic rock we see. Because there is a large amount of gas in the magma, their density is smaller and they migrate upward faster. They often erupt first at the beginning of a volcanic eruption. This is a common phenomenon in volcanic activity.

The Tonga volcano was formed by the same mechanism, except that it was formed when the Pacific Plate subducted under the Australian microplate in the Indian Ocean, and the dehydration of the oceanic crust caused the melting of the overlying landform rocks. Multiple volcanoes are distributed along the subduction zone, forming the Tonga volcanic island chain. Among them, the major eruption that occurred in early 2022 was located in this volcanic island chain.

Therefore, to understand the distribution of volcanoes and the causes of volcanic eruptions, we must look for evidence from the structure and movement laws of the earth.

This article is produced by the Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting