Japan's volcanic alert levels: climbing active volcanoes and dealing with ashfall

Japan has 111 active volcanoes, according to the Japan Meteorological Agency (JMA). JMA monitors 51 of them around the clock, and uses a five-step Volcanic Alert Level at 49 (as of March 2026). Many are also hiking destinations. Here is how to read the alert levels and what Japanese agencies advise for climbing volcanoes and dealing with ashfall.

Volcanic Alert Levels

JMA says there are five Volcanic Alert Levels "based on the target area and action to be taken." The English keywords are from JMA's English leaflet; the summaries of what they mean are ours, based on JMA's Japanese explanation.

JMA's English page notes that warnings cover residential areas when the level is 4 or 5. Two cautions from JMA's Japanese pages: a volcano can erupt without any abnormality being observed first, and the level will not necessarily rise one step at a time. In 2014, a sudden steam explosion at Mount Ontake left 63 people dead or missing (JMA); the Cabinet Office notes that many of the victims were hikers near the crater.

Climbing an active volcano

Japan's Cabinet Office (disaster management) advises:

• Submit a climbing notification (tozan todoke) where the volcano has such a system. Japan strengthened the duty to submit one in a 2023 legal revision (Prime Minister's Office).
• Carry the volcano's hazard map, a phone and spare battery, rain gear, a towel, a headlamp, goggles for ash, a helmet, food and water.
• Check the alert level and JMA's information for climbers before and during the climb.
• If it erupts, shelter in a mountain hut or behind rocks, put on your helmet and goggles, cover your mouth with a mask or a damp towel, and descend as soon as the eruption calms.

JMA's "eruption flash report" (funka sokuho) gives only the volcano's name and the time of eruption. JMA asks people who receive it to protect themselves immediately: descend, take refuge in a shelter or hut, or hide behind nearby rocks.

When ash falls

The Prime Minister's Office explains that volcanic ash is made of tiny, hard, jagged particles that can scratch eyes and lungs.

• Wear a dust mask; if ash gets in your eyes, rinse with water rather than rubbing, and switch from contact lenses to glasses.
• Ash makes roads slippery and brakes less effective.
• Don't wash ash into gutters or drains; it clogs them.
• When clearing ash from a roof, wear a dust mask and goggles, secure the ladder, use a safety rope and helmet, and always work in pairs.
• JMA's ashfall forecasts suggest staying indoors and not driving when ashfall is "heavy" (1 mm or more), protecting yourself with a mask and driving slowly when it is "moderate," and closing windows when it is "light."
• The Cabinet Office's guideline for wide-area ashfall around Tokyo recommends, where possible, stocking more than one week of supplies, plus dust masks and goggles; the 1707 Hoei eruption of Mount Fuji lasted two weeks.

Related: Hiking in Japan, The Ten Essentials. Our Japanese edition has a fuller guide: 噴火警戒レベルと火山灰への備え.