2024.05.01
Risk5: Volcanic eruption
The horror of an eruption
Looking at the history of Mt. Fuji eruptions, various explosion types had occurred, including lava flows, pyroclastic flows, scoria, volcanic ash, mountain collapse, lateral volcano eruptions, and emission of toxic volcanic gas. Mt. Fuji is known as the "department store of eruptions".
Phenomena related to eruptions
lava flow
In the case of underground magma reaches the surface, it flows down as liquid lava. The flow is slow and you can escape from it by running, but it will burn down everything in its path, whether it is a wooden building or a forest.
pyroclastic flow
In the case of a multiphase flow which includes volcanic debris (volcanic ash, pumice, etc.) and gas components (water vapor, volcanic gas, etc.), the debris and gas flows down mountainsides at high speed. The temperature of the flow reaches several hundred degrees or more, which poses a risk to buildings and cars melting, making such places unsafe as an evacuate shelter. This is the most dangerous phenomenon of all volcanic disasters.
phreatic eruption
In the case subterranean water is heated up by high-temperature magma, it evaporates quickly, becomes high-temperature and high-pressure and leads to an explosion. Although such a phreatic eruption is classified as a small-scale eruption, the 2014 eruption of Mt. Ontake, which falls under this category, caused a large number of casualties. Compared to other types of eruptions, phreatic eruptions are difficult to predict because signs of explosions cannot be detected through movement of magma.
volcanic ash
Volcanic ash is made up of glass and mineral crystal fragments that are crushed and rapidly cooled when magma erupts. Since these particles are often hard and angular in shape, inhaling volcanic ash can damage your lungs.
volcanic toxic gas
Volcanic gas may contain highly toxic chemical compounds such as hydrogen fluoride, hydrogen chloride, and sulfur dioxide that may be released into the atmosphere. Volcanic gases have a strong pungent odor and are easy to detect, but they can be dangerous in zero visibility due to volcanic ash.
Reference
Japan Meteorological Agency's website; Cabinet Office's website about disaster management; Fuji City's website; the history of Mt. Fuji eruption, etc.
Eruptions do not always occur at the summit.
Hoei eruption (1707)
The last eruption from the summit of Mt. Fuji was approximately 2,300 years ago. All the eruptions after that occurred from the middle of Mt. Fuji. This includes the "Jogan Eruption" (864~866), the largest eruption since then which created Aokigahara Jukai Forest, and also the "Hoei Eruption" (1707), the newest eruption that created Hoei crater which is larger than the summit crater.
eruption hazard-map
eruption alert level
At normal times, the volcanic alert level for Mt. Fuji is level 1 (Possible impact zone from an active volcano).
Even if the volcano is at eruption alert level 1, climbers above the 5th station must begin their descent when explanatory information (emergency) regarding the status of the volcano is announced.
If an Volcanic Warning (Near the crater) or a.k.a. Near-crater Warning is issued, the alert level will be raised from 1 to 3 (Restriction on proximity to the volcano). Everyone in the first evacuation zone, including the entire area above the 5th station, must evacuate. Foreign tourists will be asked to evacuate away from the Mt. Fuji vicinity.
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Name |
Volcanic Alert Levels |
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Volcanic Warning(Residential area) |
Level 5 (Evacuation) * |
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Level 4 (Evacuation of the elderly, etc.) * |
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Volcanic Warning(Near the crater) |
Level 3 (Restriction on proximity to the volcano) |
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Level 2 (Restriction on proximity to the crater) *In the process of increasing volcanic activity, there is no alert level 2, and it is only used when it is lowered from level 3. |
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Volcanic Forecast |
Level 1 (Potential for increased activity) |
Prepare for an eruption
helmet
Helmets protect you not only at the time of eruption but also from falling rocks or when you fall down. You can rent a free helmet on the Yoshida trail and Fujinomiya trail. (2,000yen deposit is required on the Yoshida trail.)
Yoshida Trail: Helmet Free Rental
At the 6th Station Safety Guidance Center, you can rent a helmet for free if you pay a deposit of 2,000 yen. (Limited number available)
Fujiyoshida Trail: Helmet Free Rental
At the 5th Station General Guidance Center, you can rent a helmet for free if you fill out the designated documents. (Limited number available)
goggles, mask
Goggles and masks are useful in the event of eruption and against dust when descending the mountain.