Above the Pacific Ring of Fire…
[Click here for a more detailed tectonic map of Japan]
Located at the junction of four colliding continental and oceanic plates, the land of Japan is crisscrossed by tall mountain ranges and 7 volcanic zones. The chain of Japanese islands was mostly formed as underwater mountains and volcanoes thrust up by volcanic activity from the sea more than 1.6 million years ago. Collage tectonics or the accretion of bits of continental terranes is also considered to have contributed to the formation of Japan.
Almost three-fourths (or 72%) of Japan is covered in mountains interspersed by just a few plains. Most Japanese mountains, being very young (in mountains’ terms) are high and precipitous, with the exception of the older chain of mountains in western Japan. There are more than 500 mountains over 2000 m high. On the other hand, most valleys are deep and V-shaped, with short, swiftly-rushing rivers, often carving out steep-sided canyons and gorges. The Japanese rivers deposit so much sediment that they have the highest rate of fluvial sediment in the world.
Japan’s location above the Pacific Ring of Fire is the main cause for frequent earthquakes (1,500 tremors per year) and the presence of many volcanoes (in 7 volcanic regions) and hot springs across Japan. About 80 per cent of the world’s major earthquakes take place along the Pacific Ring of Fire, a narrow zone of volcanic activity that encircles nearly all of the Pacific Ocean.
The Japan ranks second, behind Indonesia, in the number of historically active volcanoes. 86 of Japan’s volcanoes are still active, or one-tenth of the 840 active volcanoes in the world. Consequently, they are monitored closely for signs of likely future eruptions. There are also more underwater volcanoes in the waters surrounding Japan than anywhere else in the world. When seaquakes occur below or close to the ocean, they may trigger tsunamis (harbor waves).
Did YOU know …
One of the world’s deepest and longest of ocean troughs lies immediately off the east coast of Hokkaido Island ?
Called the Japan Trench (also the Tuscarora Deep), the deep-sea trench forms the largest continuous area with a depth greater than 7.3m, one the 19 deepest spots in the world. In 1953, the Russian ship Vityaz made a depth sounding of 10.5 km, one of the deepest spots found in the Pacific Ocean.
Platetectonics.com explains the phenomenon like this:
Deep Ocean Trenches and The Ring of Fire
As the giant Pacific Plate moves steadily westward, its leading edge subducts below the Eurasian Plate and is recycled into the Earth’s mantle. This extended area of subduction results in intense earthquake and volcanic activity. Japan lies on the cusp of the Pacific-Philippine-Eurasian triple plate junction, where the complex interactions of three tectonic plates is unpredictable and loaded with potential activity.
When the Pacific Plate encounters the Philippine Plate, because it is older and more dense than the younger Philippine, it subducts below and results in the formation of a deep ocean trench. The Marianas Trench is 36,000 feet below sea level – the deepest known region of the world’s oceans. Take note of the ocean floor near the infamous “Ring of Fire.