VOLCANOES IN JAPAN: GEOLOGY, SAFETY, MONITORING, RESEARCH

VOLCANOES IN JAPAN

null
Japan is home to 7.2 percent (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.

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]

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. In June 2010, a 13-year-old girl died and three others were hospitalized after inhaling volcanic gasses near Sukayu hot springs in the Mt. Hakkoda area of Aomori.

There are 15 active volcanoes on Hokkaido. 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.

Websites and Sources on Volcanoes: USGS Volcanoes volcanoes.usgs.gov ; Volcano World volcano.oregonstate.edu ; Volcanoes.com volcanoes.com ; Wikipedia Volcano article Wikipedia , Smithsonian Global Volcanism Program <a href=https://volcano.si.edu/"> volcano.si.edu operated by the Smithsonian has descriptions of volcanoes around the globe and a catalog of over 8,000 eruptions in the last 10,000 years. Volcano Information in Japan: Volcano Research Center at Tokyo University eri.u-tokyo.ac.jp ; Wikipedia List of Volcanoes in Japan Wikipedia ;; U.S. Professor Disappears During Volcano Hike cnn.com/2009 Mount Asama: ; Wikipedia Wikipedia ; Asama Volcano Museum (Japanese language site) asamaen.tsumagoi.gunma.jp ; Mt Aso: Aso Volcano Disaster Prevention Council Aso Volcano Disaster Prevention Council

Geology of Japan's Volcanoes

null
Usu March 2000 eruption Japan has numerous active volcanoes. This is a consequence of the country's location along several converging tectonic plate boundaries in the western Pacific. Japan has two major volcanic fronts, where chains of volcanoes are concentrated. One extends from the Chishima Islands through the Izu and Ogasawara Islands, while the other extends from the Chugoku region to the Satsunan Islands. Both volcanic zones run roughly parallel to major oceanic trenches. [Source: Yomiuri Shimbun, October 7, 2014]

Japan’s volcanoes are part of the "Ring of Fire," 40,000-kilometer (a 25,000-mile) horseshoe stretching from the southern tip of South America, running along the coasts of South and North America, across the Bering Strait, past Japan, and down to New Zealand. The 452 volcanoes and the underwater trenches — such as the Japan Trench, the Ryuku Trench, and the Middle America Trench that make up the Ring of Fire — are produced by the sinking of geological plates under other geological plates — a process called subduction. This melts rock in the upper parts of Earth's mantle, creating magma that pushes back to the surface of Earth through cracks in the crust.

The movement and friction between the plates can generate powerful earthquakes along their boundaries. Subduction also carries water and other volatile materials deep into Earth's mantle. Under the high temperatures and pressures at depth, the addition of water lowers the melting point of mantle rocks and contributes to the formation of magma. Magma generated above the subducting plate can rise through the Earth's crust. When it reaches the surface, it can erupt as lava, ash, and volcanic gases, forming and enlarging volcanoes over time

Relationship Between Volcanoes and Earthquake in Japan

The same tectonic processes that produce Japan's volcanic chains also create conditions for frequent earthquakes. Japan's position along multiple active plate boundaries makes earthquakes and volcanic activity closely associated features of its geology. Japan has experienced several major earthquakes in recent decades, including the 1995 Great Hanshin Earthquake and the 2011 Great East Japan Earthquake. Seismic activity has also been detected beneath numerous volcanoes, including areas where earthquakes may indicate changes in volcanic systems. Such activity does not necessarily mean that an eruption is imminent, but it is closely monitored because changes in earthquake frequency, depth, and location can provide information about conditions beneath a volcano. [Source: Yomiuri Shimbun, October 7, 2014]

Mount Fuji is one of the volcanoes monitored for seismic and volcanic activity. The volcano has been dormant since its last eruption in 1707, but earthquakes and other underground changes are periodically observed in the surrounding region. Japan maintains extensive monitoring networks for earthquakes and volcanoes because of the country's tectonic setting. These systems provide data used to assess seismic hazards, monitor volcanic activity, and prepare communities for possible earthquakes and eruptions.

After the Great East Japan Earthquake in 2011, Mount Ontake, located near a volcanic front, remained dormant for several years but them erupted violently in 2024. Other nearby volcanoes, including Mount Norikura and Mount Yake, which straddle the border between Gifu and Nagano prefectures, experienced a series of magnitude 3 and 4 earthquakes. These events drew attention to the possible relationship between major earthquakes and subsequent volcanic activity. [Source: Japan Times, September 30, 2014]

Masaaki Churei, a former Japan Meteorological Agency official who studied the relationship between earthquakes and volcanoes, said: "When a huge earthquake occurs off the Sanriku coastline, volcanoes that have remained dormant tend to erupt two or three years after the earthquake. It’s possible the Great East Japan Earthquake instigated the eruption of Mount Ontake."

However, the relationship between large earthquakes and volcanic eruptions remains complex. A major earthquake can alter stresses and pressures within Earth's crust and may influence a volcanic system, but an eruption cannot necessarily be predicted from an earthquake alone. The 2011 earthquake therefore prompted increased scientific attention to volcanic activity in central Japan.

Mt. Fuji

null
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.

Monitoring Volcanoes in Japan

The Coordinating Committee for the Prediction of Volcanic Eruptions monitors 108 volcanoes, with 41 of these receiving 24-hour attention. The Japanese Meteorological Agency observes 30 of the most active volcanoes. A total of 20 volcanoes — including Asama, Sakurajima, Mt. Unzen, Mt. Usu, and the Miyakejima islands — are monitored around the clock by the Meteorological Agency. Data collected from sites round these volcanoes is used to predict eruptions and estimate the amount of damage they may cause.

null
pyroclastic flows on Unzen Volcanic activity in Japan is monitored mainly by national universities across Japan as part of their research. Sakuramjima in Kagoshima Prefecture, for example, is monitored by the Tokyo Institute of Technology and Kagoshima University using 19 observation sites that monitor various things associated with volcanic eruptions. Tokyo University does the same with Mt. Asama in Nagano Prefecture and Mt. Mihara on Iz-Oshima Island. In recent years a lack of funding as a result of government budget cuts has meant that it has become difficult to maintain the monitoring stations in the way they were meant to be maintained.

In 2014, Japan had 110 active volcanoes, of which 47 were identified by the Japan Meteorological Agency’s Coordinating Committee for Prediction of Volcanic Eruptions as having the potential to erupt within about 100 years and requiring enhanced monitoring. These volcanoes are monitored around the clock by the Japan Meteorological Agency and volcanic monitoring and information centers at meteorological observatories in Sapporo, Sendai, and Fukuoka.[Source: Masatsugu Sonoda, Yomiuri Shimbun, October 1, 2014]

Monitoring includes changes in the number of volcanic earthquakes and movements or expansion of volcanic mountains. Seismographs and Global Positioning System equipment were among the tools used to detect these changes. The agency provided prefectural governments with information relevant to disaster preparedness.

Volcano Preparedness in Japan

Volcanic activity is rated with five levels; 1 (calm), 2 (slight activity), 3 (small to medium activity), 4 (large activity) and 5 (catastrophic activity). A great amount of resources has been put into predicting eruptions. Scientists were able to predict the Mt. Usu eruption in 2000 and the Miyakejima eruption in 2000 but not the Asama eruption in 2004.

To control mudflows, like the one that killed 23,000 villagers in 1985 in Columbia, the Japanese government has erected steel and concrete silt dams along likely mud flow routes to halt, or a least, slow down their advance so people have enough time to be evacuated. Television cameras and sensitive instruments that take 11 different readings are also used for research and detection.

Scientists in Japan have installed global positioning system (GPS) devices at 30 locations particularly active volcanoes and monitor changes in positions to predict eruptions. The instrument are so sensitive that scientists can gage activity in a magma chamber seven kilometers below the surface. The are mainly looking for swelling on the mountains that occurs before an eruption.

Volcanic eruptions can disrupt transportation and other infrastructure far beyond the immediate eruption zone. Volcanic ash can interfere with roads, railways, vehicles, and electronic equipment. Preparedness therefore needs to include evacuation planning, public communication, emergency shelters, monitoring, transportation measures, and coordination among local governments and volcanic experts.

Improving Volcano Safety in Japan

null
Sakurajima observation center The 2014 eruption of Mount Ontake, which killed 63 people, exposed significant gaps in Japan’s volcanic disaster preparedness. Despite the high number of active volcanoes in Japan, most municipalities located near these volcanoes had not prepared detailed evacuation plans. Of 130 municipalities near volcanic vents, 110 had no evacuation preparations, while only seven had completed evacuation plans by the end of March 2014. [Source: Yomiuri Shimbun, October 27, 2014; Taiji Yasuda and Masahiro Sakita, Japan News/Asia News Network, October 1, 2014; Yomiuri Shimbun, October 27, 2014]

Evacuation planning: The central government planned to help local governments develop plans covering restrictions on access to volcanoes, warnings, evacuation routes, and the evacuation of residents, climbers, and tourists. Disaster management councils, made up of local governments and volcanic experts, were responsible for developing these plans. However, 14 active volcanoes had no such councils, partly because some volcanoes had not erupted recently and local governments lacked personnel with specialized volcanic knowledge.

Emergency shelters: The Ontake eruption also demonstrated the importance of sturdy shelters. Mountain lodges and other structures provided protection for some climbers from falling rocks and ash, but many were wooden buildings that were not designed to withstand an eruption. Ontake had no reinforced-concrete shelters specifically designed to protect people from volcanic projectiles and heavy ash. Officials subsequently recognized that stronger shelters and other emergency facilities could have reduced injuries.

Warning and communication systems: Japan also needed faster and clearer ways to warn people on volcanoes. Before the Ontake eruption, the Japan Meteorological Agency had issued information indicating increased volcanic activity, but many climbers were unaware of it. Proposed improvements included mobile-phone alerts, electronic signboards at mountain lodges and trailheads, and simpler explanations of volcanic activity that could be understood by visitors without technical knowledge.

Monitoring and hazard information: The central government planned to reinforce and replace monitoring equipment, including seismometers and cameras, and investigate technologies capable of detecting small movements around volcanic vents. Officials also proposed developing different eruption scenarios and volcanic hazard maps showing areas at risk.

Tourist and climber protection: Safety planning needs to account not only for residents but also for hikers and tourists who may be unfamiliar with volcanic hazards. Registration systems for climbers’ mobile phones, emergency notifications, trail closures, and information boards could help authorities communicate rapidly when conditions change. The experience of Mount Iwo demonstrated that even a relatively small change in volcanic activity can require rapid warnings and evacuation measures.

Alert Level System for 30 Volcanoes in Japan

Local governments have established volcano disaster management councils and introduced the Volcanic Alert Level system for 30 of the 47 closely monitored volcanoes. The system links volcanic activity to recommended actions, including restrictions on access and guidance for climbers. Mount Ontake was added to the alert-level system in March 2008. [Source: Masatsugu Sonoda, Yomiuri Shimbun, October 1, 2014]

Before its September 2014 eruption, Mount Ontake was at Alert Level 1, indicating that residents should be aware that the volcano was active. The level was raised to Level 3 after the eruption. Sakurajima and Kuchinoerabujima in Kagoshima Prefecture were also at Level 3 at the time. Mount Kusatsu-Shirane, on the Gunma-Nagano border, and Mount Aso in Kumamoto Prefecture had been raised from Level 1 to Level 2 earlier in 2014.

To introduce the alert-level system, local governments were required to establish volcano disaster management councils and develop response plans specifying government actions for different levels of volcanic activity.

In 2014, the alert-level system had not been introduced at 17 of the 47 closely monitored volcanoes because the relevant local governments had not established the required disaster management councils. Many of these volcanoes had not experienced recent eruptions. The Japan Meteorological Agency encouraged the remaining local governments to establish the councils and introduce the alert system.

Shortage of Experts and Funding Hampers Volcano Research in Japan

The 2014 eruption of Mount Ontake exposed shortages of funding, monitoring equipment, and specialists in volcanic research in Japan. Although Japan is one of the world’s most seismically active countries, the number of researchers specializing in volcanoes had declined significantly. [Source: Japan Times, September 30, 2014; Yomiuri Shimbun, October 6, 2014]

When Mount Ontake erupted on September 27, 2014, three of the 12 seismographs within 15 kilometers (9 miles) of the summit were not functioning. Two, including one at the summit, had stopped operating during the summer of 2013 and were scheduled for replacement in October 2014. The third operated only during winter because it depended on electricity from a ski resort. Nagoya University volcanologist Koshun Yamaoka said functioning instruments might have detected warning signs before the eruption.

The Japan Meteorological Agency monitored 47 volcanoes around Japan around the clock using 149 seismographs. However, it also relied on observation data from the National Research Institute for Earth Science and Disaster Resilience, universities, municipalities, and other organizations. Two of the agency’s seismographs were located on Mount Ontake.

Funding was another constraint. About ¥20 billion (approximately US$182 million) was allocated to national earthquake and volcano research in fiscal 2013, but only about 10 percent went to volcano research. Most funding supported earthquake research. Researchers argued that volcanic studies require continuous data collection over many years, even when a volcano shows little activity and produces few immediate research results.

Japan also faced a shortage of specialists. There were 696 earthquake and volcano researchers in fiscal 2013, but only a small proportion specialized in volcanoes. Tokyo Institute of Technology professor Kenji Nogami estimated that the number of volcano specialists had fallen below 30. Researchers warned that the shortage could limit Japan’s ability to monitor volcanoes and conduct long-term studies.

The shortage was particularly significant because effective volcanic research depends on continuous observation. University reforms beginning in 2004 placed greater emphasis on institutional efficiency, while government subsidies to universities declined. Researchers said these trends made it more difficult to sustain long-term studies of less active volcanoes.

Mount Sakurajima in Kagoshima Prefecture was an exception. It had 25 seismographs and about 10 people involved in monitoring, including five Kyoto University researchers. Sakurajima recorded 1,097 eruptions in 2013, making it one of Japan’s most intensively monitored volcanoes. The level of staffing and equipment at Sakurajima, however, was not typical of volcano monitoring elsewhere in Japan.

Image Sources: Wikimedia Commons, Volcano Research Center University of Tokyo, United States Geological Survey (USGS)

Text Sources: Volcano Research Center University of Tokyo, United States Geological Survey (USGS), Japan Meteorological Agency New York Times, Washington Post, Los Angeles Times, Yomiuri Shimbun, Japan News, Japan Times, Japan National Tourist Organization (JNTO), National Geographic, The New Yorker, Smithsonian magazine, Encyclopedia.com, Live Science, The Conversation, Time, BBC, CNN, Reuters, Associated Press, AFP, Lonely Planet Guides, Google AI, Wikipedia, The Guardian and various websites, books and other publications.

Last updated August 2026