Volcanoes are common in Japan and are found along and to the west of a line running approximately down the middle of the main island of Honshu, the southern island of Kyushu, and the northern island of Hokkaido. They result from the friction of tectonic plates as the Pacific Plate bends and passes under the Eurasian Plate. Magma forms at a depth of 60-120 miles and is forced to the surface. Many but not all of the 200-odd volcanoes in Japan are conical in shape, rising like Mt. Fuji in an increasing curve to great height: 12,385 ft in the case of Fuji and 8,338 ft. for Mt. Asama.
A significant number of volcanoes are considered active at present. Fuji last erupted in 1707 and Mt. Asama staged a large eruption in 1783, but others have been recently active. Sakurajima which looms over Kagoshima in southern Kyushu erupted in 1914, Mt. Bandai in 1888, and Komagatake in 1929. In the 1990s, Mt. Unzen near Nagasaki and Shimabara erupted with considerable loss of life since it was a tourist attraction at the time.
Volcanoes, being spectacular, beautiful, and close to human habitation, have been a preoccupation of the Japanese for centuries. Several major and minor gods in the Shinto pantheon are based on volcanoes. The imperial court in its early days appointed officials whose responsibility it was to propitiate any volcanoes which might threaten. In recent times, volcanoes have caused considerable loss of life and destruction of property. An example was Mt. Pinatubo in the Philippines in the 1990s. In Japan, Mt. Fuji could easily deposit ash in the heart of Tokyo if it were to erupt with the winds blowing toward the city. The eruptions in the Philippines and the increase in volcanic activity in Japan worry many that a period of hyper-activity has arrived.
While volcanoes conjure up visions of cataclysmic destruction in a magnificent pyrotechnic show, it is earthquakes that are a more common occurrence and threat. The destructiveness of an earthquake is likely to be far greater since they occur virtually everywhere in Japan, are violent, and give virtually no warning. The Tokyo (or Great Kanto) Earthquake of 1923 which killed over 100,000 people left not only vivid memories but photographs, motion pictures, and many other physical records of the destruction possible. Since 1923, several earthquakes have killed people, but there has been no large one of the same scale and, as in California, the time is ripe for another big one. Historical records suggest that a major earthquake should occur about every 70 years on average in the Kanto area. The 1995 earthquake in Kobe, which killed more than 5,000 people, occurred in an area less renowned for earthquakes, and therefore less well prepared, than Tokyo, but it certainly raises great concern about what will happen in the Kanto area when its turn comes.
Earthquakes result from the earth’s movement along tectonic plate boundaries and along fault lines where two layers of the surface are moving past each other. If pressure causes the two layers to stick and not move for a period of time despite increasing pressure, there may be sudden and massive slippage which causes a major earthquake. In the case of the 1923 ‘quake, the movement of the upper layer in some places was as much as six feet to the east and three feet to the south relative to the lower layer, plus there was some upward movement of the surface.
Considerable research is being done see if it is possible to predict a major earthquake. Artificial earthquakes are caused by explosives; magnetism and earth currents are monitored to see if there are major changes before large tremors; and animal behavior is recorded, but there is little progress in predicting when one might occur. Much more work is proceeding in reducing or controlling the damage which a major earthquake might cause.
Since minor earthquakes are nearly monthly experiences and moderate tremors common, the fear of a large quake is ever present. Whenever the cups in the cupboard start to rattle or the light fixtures sway, life comes to a halt while everyone waits and wonders whether this will be the big one. Everyone should stand in a door frame or hurry outside, but most wait to see if this one will justify the effort. Unfortunately, then, it will be too late.