Evacuation Plan Prepared for Mt. Fuji Eruption

The prefectural governments of Shizuoka, Yamanashi and Kanagawa adopted the first comprehensive evacuation plan on Thursday to prepare for a possible eruption of Mount Fuji, Japan's highest peak. The evacuation plan calls for 750,000 people leaving their homes in 14 municipalities in Shizuoka and Yamanashi due to lava and pyroclastic flows, as indicated in March 2013. In addition, 470,000 people, mainly in Kanagawa, would need to evacuate because of volcanic ash in the air, according to the latest plan.Just a Matter of Years Since the Great Tohoku Earthquake of March 2011, scientists have been watching Mt Fuji for signs of activity.

The new readings, taken by the National Research Institute for Earth Science and Disaster Prevention, reveal that the pressure is at 1.6 megapascals, nearly 16 times the 0.1 megapascals it takes to trigger an eruption. Therefore the pressure in Mount Fuji's magma chamber is now higher than it was in 1707, the last time the nearly 4,000-metre-high Japanese volcano erupted, causing volcanologists to speculate that a disaster is imminent. According to retired professor Masaaki Kimura ( Professor Emeritus from the Faculty of Science of the University of the Ryukyus, Okinawa, Japan ) this and other recent phenomena indicate an eruption of Mt Fuji should have taken place in 2011 with a four-year margin of error ending in 2015. In 2000 and 2001 a series of low-frequency earthquakes were recorded beneath the volcano, leading to widespread predictions of an imminent blow.

Since the March 2011 tsunami and the 6.4 magnitude earthquake that followed four days later, Japan has been on tenterhooks, and in May 2012 Masaaki Kimura warned that a massive eruption within three years would be likely because of several major factors: steam and gases are being emitted from the crater, water eruptions are occurring nearby, massive holes emitting hot natural gases are appearing in the vicinity and finally, the warning sign that pushed the professor to make the announcement, a 34km-long fault was found underneath the volcano. The fault, experts suggested, could indicate a total collapse of the mountainside if there is another significant shift, and it would probably cause a collapse in the event of an eruption, leading to huge mud and landslides. Professor Toshitsugu Fujii, the head of Japan's volcanic eruption prediction panel, says an eruption could cause chaos and carnage all the way to Tokyo. "Mount Fuji has been resting for 300 years now, and this is abnormal. It usually erupts in some form every 30 years. So the next eruption could be a big-scale explosive eruption If there is a large eruption, the government fears it could cause more than $30 billion in damage to public health and agriculture. Volcanic rocks will fall near the mountain.

Ash accumulations in some areas could be as high as 60 centimetres. Even Tokyo, 100 kilometres to the north-east, could be coated in volcanic ash. Tokyo will be covered in a few centimetres of ash. Yokohama will be under 10 centimetres. Trains will stop, planes won't fly and crops will fail. Millions will be affected", said Professor Toshitsugu Fujii.Geology Mount Fuji is located at the triple junction where the Amurian Plate, the Okhotsk Plate, and the Philippine Sea Plate meet. Those plates form the western part of Japan, the eastern part of Japan, and the Izu Peninsula respectively. Scientists have identified four distinct phases of volcanic activity in the formation of Mount Fuji. The first phase, called Sen-komitake, is composed of an andesite core recently discovered deep within the mountain.

Sen-komitake was followed by the "Komitake Fuji," a basalt layer believed to be formed several hundred thousand years ago. Approximately 100,000 years ago, "Old Fuji" was formed over the top of Komitake Fuji. The modern, "New Fuji" is believed to have formed over the top of Old Fuji around 10,000 years ago. The volcano is currently classified as active with a low risk of eruption. The last recorded eruption was the Hōei eruption which started on December 16, 1707 (Hōei 4, 23rd day of the 11th month) and ended about January 1, 1708 (Hōei 4, 9th day of the 12th month) during the Edo period. The eruption formed a new crater and a second peak (named Hōei-zan after the Hoei era) halfway down its side. Fuji spewed cinders and ash which fell like rain in Izu, Kai, Sagami, and Musashi. Since then, there have been no signs of an eruption. In the evening of March 15, 2011, there was a magnitude 6.2 earthquake at shallow depth a few kilometres from Mount Fuji on its southern side. But according to the Japanese Meteorological Service there was no sign of any eruption. In September 2012, mathematical models created by the National Research Institute for Earth Science and Disaster Prevention suggest that the pressure in Mount Fuji's magma chamber could be at 1.6 megapascals higher than it was in 1707. However, since there is no known way to directly measure the pressure of a volcano's magma chamber, such research is only speculative.

Historic Eruptions Of Mount Fuji Mou nt Fuji is the highest volcano in Japan. The mountain as it appears now is the "New Fuji volcano", which began to erupt about 10,000 years ago. Under the "New Fuji volcano" lies the "Old Fuji volcano", which was active between 100,000 years ago and 10,000 years ago and the "Komitake volcano", which became active 700,000 years ago. Komitake There has been much volcanic activity in the vicinity of Mount Fuji for several million years. In the location occupied by the current Mount Fuji, a volcano known as Mount Komitake (小御岳火山), literally meaning "small mountain volcano", became active 700,000 years ago. Around this time, another volcano, Mount Ashitaka (愛鷹山), in the area to the south-east of Mount Fuji, was also highly active. The peak of the ancient volcano, Komitake, can be seen from the north face of Mount Fuji at the fifth station, about 2,300 meters (7,500 ft) above sea-level. Old Fuji Around 100,000 years after becoming inactive, Komitake entered another period of activity. The volcano in this period is known as Old Fuji (古富士 kofuji).

Older Fuji was known as to have explosive eruptions, throwing out large quantities of scoria, volcanic ash and lava, forming a large mountain which reached a height of 3,100 meters (10,200 ft). New Fuji Following the Old Fuji period, there were about 4,000 years of inactivity, ending at around 5,000 years ago, when Mount Fuji became active again; this period is known as New Fuji (新富士 shinfuji), and continues to the present day. Eruptions of New Fuji exhibit phenomena such as lava flows, magma, scoria, volcanic ash, collapses and side eruptions, leading it to be called "a department store of eruptions".

Ash from New Fuji is often black, and eruptions are new in terms of geological layers. Valuable data on the activity of Mount Fuji is recorded in Japanese historical documents dating from the 8th century onwards. It exhibits a range of representative eruptions. Explosive eruptions before the activity 3005 years ago There were four explosive eruptions in the Jōmon era, which are known by the names Sengoku scoria (Sg), Ōsawa scoria (Os), Ōmuro scoria (Om) and Sunazawa scoria (Zn). As the wind normally blows from the west in the area of Mount Fuji, most ejectants fall to the east, but in the case of the Ōsawa scoria, they were carried on the east wind, as far as the vicinity of Hamamatsu. The Gotemba mud flows About 2,300 years ago the east face of the volcano collapsed and liquid mud flowed down to the Gotemba area as far as the Ashigara plain in the east and the Suruga bay across Mishima city in the south. This incident is now called the Gotemba mudflow (御殿場泥流 Gotemba deiryū). Liquid mud piled up over an area as wide as the city area of Mishima. Jōgan eruption In 864 (the 6th year of the Jōgan era) there was an eruption on the north-east side of Mount Fuji, which produced a great amount of lava. 864 (Jōgan 6, 5th month): Mount Fuji erupted for 10 days, and it ejected from its summit an immense quantity of cinders and ash which fell back to earth as far away as the ocean at Edo bay.

Many people perished and great numbers of homes were destroyed. The volcanic eruption began on the side of Fuji-san closest to Mount Asama, throwing cinders and ash as far away as Kai province. Some of the lava-filled up a large lake Senoumi (せの海) which existed at the time, dividing it into two lakes, Saiko (西湖) and Shōjiko (精進湖). This is known as the Aokigahara lava (青木ヶ原溶岩), and at present is covered by the dense Aokigahara forest. Hōei eruption The latest eruption, in 1707 (the 4th year of the Hōei era), was known as the great Hōei eruption.

It followed several weeks after the Great Hōei earthquake:

• November 11, 1707 (Hōei 4, 14th day of the 10th month): The city of Osaka suffers tremendously because of a very violent earthquake.
• December 16, 1707 (Hōei 4, 23rd day of the 11th month): An eruption of Mt. Fuji; the cinders and ash fell like rain in Izu, Kai, Sagami, and Musashi. This eruption was remarkable in that it spread a vast amount of volcanic ash and scoria over a region as far away as Edo.

Records of eruption Sixteen eruptions of New Fuji have been recorded since 781. Many of the eruptions occurred in the Heian era, with twelve eruptions between 800 and 1083. Sometimes inactive periods between eruptions lasted for hundreds of years, as in the period between 1083 and 1511, when no eruptions were recorded for over 400 years.

At present, there have been no eruptions since the Hoei eruption in 1707-1708, around 300 years ago. Who's Professor Masaaki Kimura? Masaaki Kimura graduated in science at the Faculty of Fisheries of the University of Tokyo (1963) and obtained a Doctorate in marine geology (1968). He has worked for the University of Tokyo's Ocean Research Institute, the Geological Survey of Japan, the Agency of Industrial Science and Technology of the Ministry of International Trade and Industry of Japan, and Columbia University's Lamont-Doherty Earth Observatory. He taught at the University of the Ryukus from 1977 to 2002. He has since retired from that University and is now general director of Marine Science and Culture Heritage Research Association.