Japan is home to 108 of the world’s 1,500 or so active volcanoes, including more than 10 percent of the active volcanoes that are a threat to human populations. Volcanoes in Japan are ranked A to C in accordance with the degree of their volcanic activity, with A being the most active. Some A volcanoes have erupted 400 times a year. Mt. Fuji is classified as an active volcano even though it hasn't erupted since 1707.

Worst recorded volcanic eruptions (number of dead): 1) Mt, Tambora, Sumbawa, Indonesia, Apr. 10-12, 1815 (92,000); 2) Krakatoa, Indonesia, Aug. 26-28, 1883 (36,000); 3) Mt. Pelée, Martinique, May 8, 1902 (28,000); 4) Nevado del Ruíz, Columbia, Nov. 13, 1985 (23,000); 5) Mt. Vesuvius, Italy, Aug 24, 79 AD (16,000); 6) Mt. Unzen Japan , May 21, 1792 (14,500). [Source: World Almanac]

The world's dangerous volcanoes (as judged by their potential for a dangerous eruption and nearness to major population areas): 1) Merapi (Indonesia); 2) Taal (Philippines); 3) Unzen (Japan); 4) Sakurajima (Japan); 5) Ulawun (Papua New Guinea); 6) Mauna Loa (the United States); 7) Rainier (the United States); 8) Colima (Mexico); 9) Santa Maria/ Santiaguito (Guatemala); 10) Galeras (Columbia); 11) Teide (Canary Islands); 12) Vesuvius (Italy); 13) Etna (Italy); 14) Santorini (Greece); 15) Niragongo (Zaire). [Source: International Association of Volcanology and Chemistry of the Earth's Interior]

Two supervolcanoes erupted in Japan in the last 2 million years.

Bandai, a volcano in northeast Honshu near Fukushima, erupted with a huge catastrophic explosion in 1888 like that on Mt. St. Helens. Almost 1.6 billion cubic meters of the volcano’s summit collapsed, producing 1.5-kilometer-wide crater and releasing a high-speed avalanche that reached seven miles, engulfing several villages, killing 461 people and leaving behind huge piles of debris that blocked rivers and streams, turning valleys into large lakes. The whole process was similar to what occured on Mt. St. Helens in 1981.

Hikers have died on volcanoes in Japan after taking a wrong turn on a trail and being overcome by volcanic gases, In April 2009, a U.S. poet, Craig Arnold, disappeared after setting off on a hike on the volcanic island of Kuchinoerabujima, 50 kilometers off the cost of southern Kyushu.

The southern Kyushu prefectures of Kagoshima and Miyazaki are home to shirasu tablelands created by pyroclastic flows and layers of ash during the last 25,000 years. Shirasu is a type of volcanic ash and pumice peculiar to southern Kyushu. It is very fertile but because it can retain a lot of moisture it is associated can trigger landslides and mudslides in heavy rains.

Websites and Resources


Volcano Information in Japan: Volcano Research Center at Tokyo University ; Volcano Information from Japan Meteorological Agency Japan Meteorological Agency ; Tectonics and Volcanoes of Japan ; Laboratory of Volcano Physics at the University of Hokkaido ; Hayakawa Paleovolcanology Laboratory (last updated in 2000) ; Wikipedia List of Volcanoes in Japan Wikipedia ; USGS Volcanoes of Japan and ; Volcano and Earthquake Map ; U.S. Professor Disappears During Volcano Hike ; Earthquakes in Japan

Mount Asama: ; Wikipedia Wikipedia ; Asama Volcano Museum (Japanese language site) ; strong> Unzen Government National Park Site National Parks of Japan ; Unzen Volcano University of Tokyo ; Unzen Tourism Unzen Tourism ; Mt Aso: Aso Volcano Disaster Prevention Council Aso Volcano Disaster Prevention Council Government National Park Site National Parks of Japan ; Aso Fan site Aso Fan Aso Tourist pamphlet (PDF) Aso Caldera Tourism ; Map Japan National Tourism Organization JNTO Japan National Tourism Organization (PDF) JNTO Aso Hiking Map

Sakurajima Tokyo University volcano site Volcano Research Center Wikipedia Wikipedia Geological map Geological Survey of Japan ; Mt. Usu Toya Usu Geopark Toya Usu Geopark ; Izu Islands Tokyo Islands ; Wikipedia Wikipedia ; Wikitravel Wikitravel

Mt. Fuji: Good Photos of Mt. Fuji at Japan-Photo Archive ; Mount Fuji Guide; Wikipedia Wikipedia ; Picture Tokyo ; Wikitravel Wikitravel ; Sacred Destinations ; Fuji-Hakone-Izu National Park Government National Park Site National Parks of Japan ; Fuji Volcano / ; 1707 Eruption PDF ; National Geographic article ; Getting to Mt. Fuji: Lonely Planet Lonely Planet Maps and Links ; Maps: Japan National Tourism Organization JNTO ; ; Volcanic Fuji: Fuji Volcano / ; 1707 Eruption PDF ; National Geographic article

Unzen Eruptions

Unzen, a large volcano on Kyushu near Nagasakai, erupted catastrophically in 1792. An earthquake triggered by the eruption and the collapse of a lava dome sent an entire mountain side sliding into the ocean. The ensuing 100-meter-high tsunami submerged coastal villages, killing about 15,000 people.

Tsunamis engulfed the city of Shimabara with water reaching as far inland as the gates of the city castle. More than 43 square miles of the Shimabara peninsula was covered by water. The waves then traveled across the bay, washing away nearly 6,000 houses and 1,600 fishing boats along another 75-miles section of coastline.

Unzen, whose main peak is Mt. Fugendake, was mostly quiet for the next two centuries then it erupted suddenly on November 17, 1990. A total of 44 people died and 2,500 houses were crushed from pyroclastic flows and mudslides. The eruption wasn't declared over until May, 1996.

Trouble began in May 1991 as tons of ash piled up in the crater producing a swelling lava dome that was capable of causing a huge explosion if it collapsed. The 40,000 people in Shimabara, a coastal resort near Unzen, didn't seem too worried. One resident told Reuters, "We actually thought, 'Aha, a new tourist attraction.' We all brought our kids out to see it, things like that."

Unzen Eruption, Earthquake and Tsunami in 1792

In 1792, the collapse of one of its several lava domes of Mt. Unzen—a volcano near present-day Nagasaki in Kyushu—triggered a megatsunami that killed about 15,000 people in Japan’s worst-ever volcanic-related disaster. The volcano was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow that killed 43 people, including three volcanologists. [Source: History of Tsunamis in Japan, *+*]

Activity from 150,000 years ago to the present has occurred at a number of sites around the volcanic complex, building four main domes at different times: the No-dake (70–150,000 years old), Myo-ken-dake (25–40,000 years old), Fugen-dake (younger than 25,000 years old) and Mayu-yama (4,000 years old) volcanic peaks. Fugendake has been the site of most eruptions during the past 20,000 years and lies about 6 kilometers (3.7 miles) from the center of Shimabara, a town in the Shimabara Peninsula of Nagasaki Prefecture, Japan. *+*

Unzen’s deadliest eruption occurred in 1792, with a large dacitic lava flow coming from Fugen-dake. The east flank of the Mayu-yama dome collapsed unexpectedly following a post-eruption earthquake, creating a landslide. This caused a megatsunami that reached a height of 100 metres (330 feet), and killed an estimated 15,000 people. As of 2011 it is the worst volcanic related eruption in Japan. *+*

1792 Unzen earthquake and tsunami resulted from volcanic activities of Mount Unzen on May 21. The southern flank of the Mayuyama dome in front of Mount Unzen collpased, resulting in a tremendous tsunami. Many people were killed by this tsunami in Higo (Kumamoto Prefecture, situated 20 kilometers away across the Ariake Sea). The coastline of the Ariake Sea in area was dramatically changed by the event. [Source: Wikipedia +]

Towards the end of 1791, a series of earthquakes occurred on the western flank of Mount Unzen which gradually moved towards Fugen-dake (one of the Mount Unzen's peaks). In February 1792, Fugen-dake started to erupt, triggering a lava flow which continued for two months. Meanwhile, the earthquakes continued, shifting nearer to the city of Shimabara. On the night of 21 May, two large earthquakes were followed by a collapse of the eastern flank of Mount Unzen's Mayuyama dome, causing a landslide which swept through the city of Shimabara and into Ariake Bay, triggering a great tsunami. +

It is not known to this day whether the collapse occurred as a result of an eruption of the dome or as a result of the earthquakes. The tsunami struck Higo Province on the other side of Ariake Bay before bouncing back and hitting Shimabara again. Out of an estimated total of 15,000 fatalities, around 5,000 are thought to have been killed by the landslide, around 5,000 by the tsunami across the bay in Higo Province, and a further 5,000 by the tsunami returning to strike Shimabara. The waves reached a height of 33–66 feet (10–20 meters), classing this tsunami as a small megatsunami. At the Osaki-bana point Futsu town, the waves locally grew to a height of 187 feet (57 meters) due to the effect of sea bottom topography.

Lake Shirachi is a pond in Shimabara city, Nagasaki Prefecture which was created after the landslide at Mayuyama created by the inpouring of underground water. Its size was first 1 kilometers (south-north) and 300 meters to 400 meters (east to west), but the production of a water exit river made it smaller and it is now 200 meters by 70 meters. As a result of the destruction, Tsukumojima or 99 islets or rocks were distributed near Shimabara city. In the same Nagasaki Prefecture, there are 99 islands or Kuju-kushima distributed from Sasebo city to Hirado city. These islands are different from Tsukumojima.

After 1792, the volcano remained dormant until an earthquake swarm began about 20 kilometers (12 miles) underneath and 10 kilometers (6.2 miles) west of Fugendake in November 1989. Over the following year, earthquakes continued, their hypocentres gradually migrating towards the summit. The first phreatic eruptions began in November 1990, and after inflation of the summit area, fresh lava began to emerge on May 20, 1991.

Deadly Pyroclastic Flow on Mt. Unzen in 1991

Unzen lava dome
On June 3rd, 1991, a violent volcanic eruption produced a pyroclastic flow---a huge fire-ball-like wall of incandescent gas---that killed 43 people including two of the world's most famous volcanologists, the French husband and wife team, Maurice and Katia Krafft.

Despite warnings to evacuate, the mountain was filled with firemen, police, scientists, journalists and farmers. The Kraffts ascended the mountain from Shimabara to film small pyroclastic flows breaking loose from the lava dome on the peak of Unzen. On June 3rd they, an American volcanologist and several members of the Japanese media walked up an eroded valley on the side of the volcano, which had just begun erupting a few days before.

Witnesses said around 4:00pm the sky turned pitch black and houses on the slopes were swallowed up by black clouds, with occasional flashes of lightning. When the pyroclastic flow (PF) occurred there was a loud crack like the sound of a lightning bolt coming from the mountain. One farmer told Reuters, "There was a rain of fire from the sky---burning ash and rock---and I was afraid the car might explode. The air smelled burned. It was hard to breath."

Noel Grove wrote in National Geographic,"Lava on the top---gray on the surface but red hot underneath---broke loose and hurled down the mountain with hurricane force. The tumbling movement energized the lava into fragmentized clouds of killer heat. The three volcanologists plus journalists, cab drivers and farmers died instantly as the heat rolled over them...A subdivision evacuated just hours before the eruption began, was wiped out by flowing mud." [Source:Noel Grove, National Geographic, December 1992]

Describing another pyroclastic flow in the valley, viewed from about two miles way, Grove wrote "a grey ball grew just below Unzen's peak. We watch it blossom into a billowing PF cloud 200 feet high and race down slope...The cloud bottomed out at the foot of the mountain, glanced off a slope, then climbing a thousand feet into the air. Later, on a helicopter ride, I saw the cloud had scorched spring foliage to a dirty brown and set homes on fire." [Source: Noel Grove, National Geographic, December 1992]

During the four years that followed the violent eruption, 200 million cubic meters of lava poured out of Unzen’s crater, creating a lava dome that increased the height of Mt. Fugendake from 1,359 meters to 1,486 meters.


1991 eruption
Sakurajima---across Kinko-wan Bay from Kagoshima in southern Kyushu---is regarded as one of the world’s most active volcanoes. It belches out dangerous gases and produces ash showers on a regular basis that cover Kagoshima in a snowfall-like blanket of gray. Sakurajima has been producing steam and ash almost continuously since 1955. There were major eruptions in 1914, 1915, 1946, 1955 and 1960. Often the eruption are hard to predict. Alerts for a an eruption in August 2008 were not issued until eruptions and pyroclastic flows were observed.

The first record of a Sakurajima eruption was in A.D. 708. The Sakurajima eruption in 1914 was the largest ever in Japan in historical times. The eruption came as no surprise. The ground around the volcano rumble for days. In Kagoshima 417 earthquakes were recorded in the 30 hours before the mountain exploded. The 1914 eruption produced 3 billion tons of lava, covered many villages and transformed Sakurajima from an island into a peninsula by filling in a 400-meter-wide, 70-meter-deep strait.

In 1987 Sakurajima spewed out molten rock and gases more than 100 times. "It's like a soda bottle with its cap off instead of on," a geologist told Discover magazine. "A small amount of lava is released pretty constantly, rather than a large amount all at once, as at Mt. St Helens." Sakurajima erupts so often that hard hats are mandatory for Japanese students visiting the foot of volcano. Annual volcano drills prepare residents for a disaster.

Sakurajima consist of three peaks: 1,117-meter-high Kita-dake, 1,060-meter-high Naka-dake, and 1,040-meter-high Minami-dake. Minami-dake contains the crater where all the activity takes place. On the slopes of the volcano are deep layers of lava and ash. In some places there is incredibly fertile soil that produces white radishes that weigh 80 pounds.

Mount Usu Eruption

Mt.Usu---south of Tokyako Spa in southwestern Hokkaido---is a 732-meter-high volcano that frequently erupts and has a cable car. An eruption in 1977 destroyed a cab car and rained rocks and 30 centimeters of ash on Toyako Onsens. It also was the source of the Mt. Showa eruption.

In March 2000, Mt. Usu, began erupting. Large amounts of superheated steam and gas were hurled as high as 3,200 meters into the air from craters on the lower slopes of the volcano. No one was hurt. More than 17,000 people were evacuated. Stones from eruptions fell on nearby towns.

Mt. Usu, located on the south of Lake Toya, erupts every 30 to 50 years. In August 1977, Mt. Usu erupted and caught people by surprise. A panicky evacuation ensued when the eruptions began and three people were killed in August 1978 by a mudflow after they returned to their homes, thinking it was safe. The eruption continued until 1982 and formed the 667-meter-tall Usu Shinzan peak on the crater basin.

Mt. Usu is a stratovolcano that emerged between 15,000 and 20,000 years. The summit was torn off by an explosion about 7,000 to 8,000 years ago. A large mudflow in 1822 ripped through a town and killed 59 people. Pyroclastic flows occurred in 1769, 1822 and 1853. The 1822 eruption produced the 671-meter-high Ogarison peak. The 1853 eruption produced the 732-meter-high Ousu peak. In 1910, some 45 craters opened up and one person was killed in a mud slide. There were also huge explosion caused by magma interacting with ground water.

Evacuation Before Mount Usu Eruption

Even though craters opened up on a hill only 300 meters above the hot spring resort of Toyako Onsen during the Usu eruption no one was killed or hurt. This is because scientists were able to accurately predict the eruption and people were ordered to evacuate their homes for gymnasiums in nearby cities before the eruptions began.

Mt. Usu has a history of producing earthquakes before an imminent eruptions. So when a series of strong earthquakes rattled the mountain in 2000 an order was given for all people in the area to evacuate. Particularly urgency was given to moving people who lived along likely paths of mud slides and pyroclastic flows. Four days after the warning was given Mt. Usu erupted.

A total of 17,300 people were evacuated. About 13,039 of them long term. About a third of these people were allowed to return home after a couple of weeks. The others had to wait until the eruptions were largely over about a month later.

Miyakejima Eruptions

MiyakejimaIsland (120 miles south of Tokyo) is a volcanic island with a circumference of 36 kilometers and dominated by Mt. Hyotan and Mt. Oyama volcanoes. My. Hyotan last erupted in 1983, destroying 400 houses with reddish-black lava.

In July 2000, 813-meter-high Mt. Oyoma began erupting. One explosion sent smoke 15,000 meters in the air. All the 3,800 residents on the island were evacuated, mostly to neighborhoods in Tokyo. Eleven million cubic meters of volcanic ash fell on the island. In 2004, the island was still evacuated. Residents had been allowed to make short visits but the presence of dangerous volcanic gases made the island dangerous to live on.


In February 2005, people were allowed to return to Miyakejima even though the infrastructure was still damaged and poisonous gases were still being emitted from the volcano. Certain areas of the island were off limits. The residentss were give ¥4.5 million is disaster relief but were only allowed to spend a third of it to rebuild their houses. In April 2005, schools reopened on Miyakejima after 4½ years. Students went to school, carrying special belt bags containing gas masks. Efforts were made to revive the fishing, farming and tourism industries.

By 2007, wild birds and other animals had returned to Miyakejima but poisonous fumes were killing its famous trees and reducing once grand forest to grasslands. The Miyakejima volcano erupted in July 2005 and February 2006. An eruption in 1840 killed 11.

Mt. Asama Eruptions

Mt. Asama (on the border of Gunma and Nagano Prefectures) is a very active 2568-meter-high, three-fold composite volcano that erupted at least 50 times and has a large eruption every four or five centuries. In 1783, pyroclastic flows killed 1,151 people. In 1911 there were sporadic eruptions with numerous deaths. In 1930s there was some volcanic activity. Six died near the crater in 1930. There were three more deaths in 1931. In 1947, 11 mountaineers died after being hit by rocks and cinders from an eruption. In 1721 the same thing happened to 15 mountain climbers

In 1973, Asama erupted after being dormant for more than 11 years. Scientists recorded 4,000 small explosions in a four month period. Eruption in 1982 and 1983 sent ash beyond Tokyo Bat to the Boso Peninsula. There were minor eruptions with some ash fall in 1990 and again in April 2003. Today, tourists check out the blocks of solidified lava produced by eruptions in the Edo period in the 17th to 19th centuries.

Mt. Asama experienced a minor eruption in February 2009,. Smoke billowed more than 2,000 meters into the air and rocks were thrown more than a kilometer from the crater. Ash fell as far as central Tokyo and Chiba Prefecture. A warning of an eruption was issued two days before after swelling at the top of the volcano was detected and people were told not go within four kilometers of the crater. Scientists say there is a possibility of large eruption in the not too distant future as magma has accumulated in shallow area near the peak.

The summit area of Asthma is often closed due to worries about eruptions. Sometimes an area within a four kilometer radius is closed off and guards are posted on the trails to turn back hikers.

Mt. Asama Eruptions in 2004

Asthma came to life in 2004, with four mid-size eruptions between September and November. Smoke and ash was hurled more than a mile into the sky, falling on Tokyo 90 miles away, and damaged crops n the vicinity of the volcano. Hundreds of tremors were recorded. Shocks from the eruption blew out windows at the Asama Volcano Museum near the base of the mountain, set off some forest fires, and forced the evacuation of some houses. A farm 20 kilometers norther of the carte was ht by a shower of rocks. No one was hurt.

Minor eruptions continued for several days, Lava spewed out the crater in fountains and poured down the slopes. A magma dome---first since 1982---was formed. As of December 2004, Asama was still releasing 2,000 to 4,000 tons of gas a day and lava could be seen at the bottom of the crater

Asama erupted off and on until June 2005. A huge andosite boulder that was five meters tall and 5 meters deep and weighed 200 to 300 tons was ejected and came to rest about 200 meters from the crater. Scientist think it was part of a lid at the bottom of the crater that was smashed during the eruption. The boulder flew 170 meters, bounced once, leaving a 13-meter wide hole and stopped.

Shinmoedake Eruptions in 2011

On January 26, 2011, 1,421-meter-high Shinmoedake, a volcano on the border of Miyazaki and Kagoshima in Kyushu, began erupting for the first time in 52 years. It shot smoke as high as 3,000 meters into the sky and scattered ash over a fairly large area. No one was hurt but tons of ash smothered downwind towns. It even killed coral about 65 kilometers away from the volcano. The last extended period of activity at the volcano was in the Edo Period when the mountain erupted violently in 1716 and 1717.

Shinmoedake erupted about a dozen times over the course of a month in 2011. Some of the eruptions were caused when the lava dome that formed at the crater became plugged or collapsed. One major eruption---the forth one---produced shock waves and air vibrations more than 300 kilometers away that rattled windows throughout Kyushu and in Kochi and Ehime prefectures in Shikoku. Ash covered more than 7,000 hectares of farmland downwind in Miyaknojo and Nichinan in Miyazaki Prefecture, making things difficult for farmers who could salvage crops only after washing them thoroughly. Volcanic rocks about five centimeters in diameter broke windows in buildings and cars in Miyakanojo.

An eruption on February 1st sent a boulder about 70 centimeters by 50 centimeters flying into the air. It landed three kilometers away in a cedar forest where it made a crater about six meters in diameter and 2.5 meters deep. An off-limits zone covering four square kilometers was set up. No pyroclastic flows were observed on that day.

People who lived in places that received large amounts of ash were kept busy shoveling the ash and putting it in plastic bags that were picked up garbage trucks. Some houses were covered in so much ash that people worried their roofs might collapse. Some train services were halted. A few car accidents were caused by cars sliding on the ash. The Yomiuri Giants, Seibu Lions and Softbank Hawks professional baseball teams managed to keep their training going despite ash falling on their field. When the ash levels were particularly high the teams trained indoors as they would on a rainy day.

A large number of disaster tourists showed up to witness the spectacle. Some defied bans and entered the off-limits zone set up around the volcano. One man who crossed the barrier told the Yomiuri Shimbun, “We want to take some impressive photos.” Another said, “The volcano doesn’t look very active and doesn’t seem to pose any danger now. I don’t thinks its any problem getting closer.”

Pre-Eruption Activity at Shinmoedake

Describing the pre-eruption activity at Shinmoedake, Kyoichi Sasazawa and Takashi Ito wrote in the Yomiuri Shimbun, “Small eruptions caused by phreatic explosions were observed on Shinmoedake from March to May 2010. Phreatic explosions occur when the heat of rising magma causes underground water to boil and steam pressure rises. According to experts, however, the eruptions that took place in 2011 were explosive eruptions characteristic of phreatomagmatic explosions, which are caused when magma and underground water directly interact. [Source: Kyoichi Sasazawa and Takashi Ito, Yomiuri Shimbun, January 30, 2011]

“The Geospational Information Authority of Japan, which has been observing Shinmoedake's crustal movement via the Global Positioning System, said the volcano body began swelling, which indicates an accumulation of magma, in December 2009. During a nine-month period from May 2010, about 6 million cubic meters of magma accumulated in a reservoir about six kilometers underground and about 10 kilometers west-northwest of the Shinmoedake crater. During the same period, about 1 million cubic meters of magma accumulated in a chamber about three kilometers underground just beneath the crater.”

Two weeks after the first eruption “distances between observation points have already changed from expanding to shrinking. Originally 23 kilometers, the distance between two particular points in the Kirishima mountain system expanded by four centimeters during the approximately one year from December 2009 to just before the eruptions. However, the same distance shrank by one centimeter in three days after the eruptions.

Geology and Eruption History of Shinmoedake

Kyoichi Sasazawa and Takashi Ito wrote in the Yomiuri Shimbun, “The magma at Shinmoedake is relatively viscid, according to the experts, as it contains a large amount of silica, a main ingredient of volcanic ash. When the volcano erupts, a great amount of ash is also ejected. Traces of small pyroclastic flows going down 500 to 600 meters have also been observed on the southwestern side of the volcano. [Source: Kyoichi Sasazawa and Takashi Ito, Yomiuri Shimbun, January 30, 2011]

A lava dome about 50 meters in diameter was confirmed in the crater during observations from the air by the University of Tokyo's Earthquake Research Institute. The dome formed as magma rose to the crater and stopped there. "It's already reached the 'magma-eruption' stage, in which magma directly erupts from the volcano," Associate Prof. Ryusuke Imura of Kagoshima University, an expert on volcanic topography, told the Yomiuri Shimbun. He has been conducting on-site research near the volcano. [Ibid]

“The recent eruptions on Shinmoedake peak closely resemble highly destructive blasts that occurred there nearly 300 years ago,” Sasazawa and Ito wrote. “One of more than 20 volcanic peaks in the Kirishima mountain range on the Kagoshima-Miyazaki prefectural border, Shinmoedake is believed to have formed between 7,300 and 25,000 years ago. Most of the recorded eruptions on the Kirishima range have occurred at Shinmoedake and Ohachi peaks.” [Ibid]

“Large eruptions took place at Shinmoedake in 1716 and 1717, during the Kyoho era of the Edo period (1603-1867). Analysis of the volcanic material deposited in the soil by the different eruptions has found that they changed from phreatic to phreatomagmatic explosions and then to magmatic eruptions. According to Imura, the Edo eruptions were 10 times bigger than the current ones, and also involved pyroclastic and mud flows. Although there was no lava flow, intermittent eruptions continued for about 18 months, resulting in the deaths of six people, Imura said.” [Ibid]

“Ash from the eruptions traveled as far as Hachijojima island in Tokyo's Izu Island chain, about 850 kilometers from Shinmoedake. According to analysis by the National Institute of Advanced Industrial Science and Technology on pumice stones from the eruptions through Thursday, the magma is very similar to that ejected in the 1716-17 eruptions. "The eruption process is quite similar to the major eruptions of the Kyoho era, so more violent eruptions could take place," Imura said.” [Ibid]

Mt. Aso

Mt. Aso---halfway between Kumamoto and Beppu on Kyushu---is one of the world's most active volcanoes. Part of Mt. Also National Park, it contains a hissing and steaming crater that can be reached by a road and a cable car.

Mt. Also is double-coned volcano with a huge 10-mile-wide, 15-mile-long caldera that was produced by a catastrophic explosion about 100,000 years ago. The outer rim of the caldera consists of a series of undulating plateaus, which contains towns, roads, and farms with grazing horses and cattle.

Within the caldera are the Five Mountains of Aso: 1) 1337-meter-high Mt. Eboshi-dake, 2) 1238-meter-high Mt. Nishima-dake, 3) 1216-meter-high Mt. Naka-dake, 4) 1408-meter-high Mt. Neko-dake, and 5) 1592-meter-high Mt. Taka-dake.

Most of smoke, high-temperature gases and sulfurous fumes emanate from Mt. Naka-dake. Scattered around the perimeter of Naka-dake's crater are heavily-reinforced concrete structures, where tourists can seek refuge should volcanic bombs suddenly begin flying out of the volcano. These were built after sudden eruptions in 1958 killed 12 visitors near the crater. Another eruption in 1979 killed three people, one kilometer away, in an area thought to safe. In 1989 and 1990 the cable car was closed by a series of eruptions.

The Naka-dake's crater is 100 meters deep and varies in width from 400 meters to 1,100 meters. It is possible to walk along the southern edge.Try to climb to the crater at night. It is spectacular enough during the day with all the smoke spewing out, but at night you can see lava, hidden during the day by smoke, hissing out of fissures inside the crater.

Mt. Fuji

The precursor of Mt. Fuji---Mt. Komitake volcano---was created just north of Mt. Fuji between 200,000 and 700,000 years ago. Old Mt. Fuji erupted with extremely massive explosions about 100,000 years ago and grew out of the south side of Mt. Komitake. New Mt. Fuji emerge from Old Mt. Fuji about 10,000 years ago with eruptions that generated large amounts of lava. The huge lava flows on the flanks of the mountain date to this period.

Today Mt. Fuji is regarded as dormant but still active volcano. It has erupted off and on for the last 2,200 years, with 10 eruptions since A.D. 781 and a large one in 864. Most these eruption spewed large amounts of ash and modest amounts of lava, with eruptions from the summit alternating with eruptions from the slopes. . Eruptions on the slopes occurred on the northwest, northeast and southeast sides.

The last eruption occurred in 1707 between the 5th and 8th station. Smoke and ash were thrust 10,000 meters into the sky and an estimated 850 million cubic meters of stone, sand, and ash was hurled out. Three meters of debris accumulated at the foot of Mt. Fuji and six inches of ash blanketed Tokyo. More in the countryside between Mt. Fuji and Tokyo. There were no casualties but hundred of thousands of people fled the area with wooden buckets over their head. The eruption destroyed crops and farming areas. Famines and social upheaval lasted for 10 years.

Future Eruption of Mt. Fuji

falll out from 1707 Fuji eruption
There are concerns that Mt. Fuji may might erupt violently in the not too distant future. Concerns were raised when a series of low frequency temblors began early 2000 and reoccurred in 2001. These tremors sometimes indicate that magma is starting to rise. Some 15,000 people have participated in emergency drills at the foot of Mt. Fuji.

If Mt. Fuji were to erupt like it did in 1707 the damage could be terrible because many more people are living in the area of the mountain than in the 18th century. Such an eruption would produce a huge ash cloud that would blacken the skies over Tokyo and Yokohama. Highways, airports and rail services would be shut down. Lava flows could wipe out large residential areas, block major highways and shut down the railroads. With distribution networks disrupted, food supplies would start to run short and prices sky rocket. If rain falls, soggy ash on transformers could cause short circuits that would cause power failures.

Some geologist speculate that the volcanoes on Iwo Jima are ready to blow any time at the island my be the next Mt. St. Helens or Pinitabu.

The Izu volcano arc is regarded as dangerous. It could produce an explosive eruption that could produce a huge tsunami that could ravage Japan’s densely populated east coast.

Underwater Volcanoes off Japan

There are several underwater volcanoes in the seas off coast of Japan. The Ogasawara undersea volcano six kilometers north of near Minami-Iwojima Island erupted in July, 2005. It produced a kilometer-high plume of steam and a yellowish brown slick of mud and debris on the water surface. Some though it might become an island. The same volcano, also known as Fukutoko, erupted in January 1986 and produced a crescent-shaped 600-meter-in-diameter island that reached 15 meters in height before it was eroded below sea level by ocean waves within three months. Volcanic activity changes the color of the water around the volcano every year.

In February 2009, an underwater volcano erupted near Minami-Iwoto Island in the Ogasawara islands, 1,200 kilometers south of Tokyo, sending a huge cloud of smoke and ash rising in the air and changing the color of the sea to yellowish green. The volcano, known as Fukutokuokanoba, has erupted seven times since 1904. On three occasions land masses were formed that eventually were washed away by the sea.

Kenji Nogami, a volcano expert at Tokyo Institute of Technology, told the Yomiuri Shimbun, “In the 1986 eruption, a new island appeared after lava accumulated. The island was washed away by waves, but seabed upheaval reduced the water depth to 22 meters, It’s possible that this [recent] activity could fore a permanent island.”

Other Eruptions in Japan

beach eruption on Iwo Jima
There are 15 active volcanoes on Hokkaido. An eruption on Mount Takachi in 1926 killed 144 people. In 1995, a volcano named Mt. Komagatake that had been dormant for 54 years erupted six times between 1996 and 2000.

IwoJima---1,250 kilometers south of Tokyo, halfway between the main islands of Japan and Guam--- is where the famous World War II battle took place. Part of a group of volcanic islands called the Bonins, it is also very active volcanically. Some geologists speculate that the volcanoes on Iwo Jima are ready to blow any time and the island my be the next Mt. St. Helens or Pinitabu. Iwo Jima means “Sulfur Island. It rose 46 centimeters June 2006 and January 2007, growing 12 centimeters in one month in November and December 2006. This was more than it rose before it erupted in September 2001. Evidence of a steam explosion was seen late in 2007.

In April 2007, Ogasawara volcano was observed erupting off Minami Iwo Jima island. A fishing crew said it saw the water change color and observed volcanic smoke rising over a five-kilometer stretch of open water.

Image Sources: Volcano Research Center University of Tokyo, USGS

Text Sources: New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

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© 2009 Jeffrey Hays

Last updated January 2014

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