Natural hazards in Japan

Japan records thousands of felt earthquakes every year. Most are minor, but large subduction earthquakes along the Japan Trench and the Nankai Trough, and shallow quakes on inland faults, have repeatedly caused great damage: the Great Kanto Earthquake of 1923, the Great Hanshin-Awaji Earthquake that struck Kobe in 1995, the Great East Japan Earthquake and tsunami of 2011, the Kumamoto earthquakes of 2016 and the Noto Peninsula earthquake of 1 January 2024.

The Japan Meteorological Agency measures shaking with its own seismic intensity scale, shindo, from 0 to 7. Levels 5 and 6 are divided into lower and upper, giving ten steps. Unlike magnitude, which describes the energy released, shindo describes how strongly the ground shakes at a particular place. Buildings erected under the stricter seismic standards introduced in 1981 have performed well in major quakes.

Large undersea earthquakes can displace the sea floor and send tsunami waves towards the coast within minutes. Japanese gave the world the word tsunami, 'harbour wave', and the Sanriku coast of Tohoku has been struck many times, most devastatingly in 2011.

The JMA issues tsunami information within about three minutes of a strong earthquake, in three levels: a major tsunami warning, a tsunami warning and a tsunami advisory. Coastal towns have signposted evacuation routes, tsunami evacuation towers and marked safe heights. The rule is simple: after strong or long shaking near the coast, or on any tsunami warning, move to high ground immediately and do not return until the warning is lifted.

Japan's active volcanoes include some of its best-known landmarks: Mount Fuji, Sakurajima in Kagoshima Bay, Aso in Kyushu and Asama on the border of Nagano and Gunma. Around fifty of them are monitored around the clock by the JMA. The eruption of Ontake in September 2014, which killed hikers on the summit, showed that even small steam-driven eruptions can be deadly.

For monitored volcanoes, the JMA issues volcanic alert levels from 1 to 5. Level 1 means potential for increased activity; level 2 restricts access to the crater area; level 3 restricts access to the mountain; levels 4 and 5 call for preparation for evacuation and evacuation of residential areas. Hiking trails and roads are closed accordingly, so checking the current level before climbing a volcano is essential.

Typhoons reach Japan mainly from July to October. They bring destructive winds, storm surges and torrential rain, and routinely halt flights, Shinkansen and ferries. Seasonal rain fronts, especially at the end of the rainy season, can produce 'linear rainbands' that dump extreme amounts of rain on one area for hours.

Because rivers are short and slopes steep, heavy rain quickly leads to floods, debris flows and landslides. Warnings escalate from advisories to warnings and, for rare extreme events, emergency warnings. Municipalities issue evacuation information on a five-level scale; at level 4, everyone in the danger zone should evacuate.

Summer heat is a serious and growing risk: high temperatures combined with humidity cause many cases of heatstroke each year, especially among older people. The Ministry of the Environment and the JMA issue heatstroke alerts based on the wet-bulb globe temperature, which combines heat, humidity and sunshine.

In winter, heavy snow on the Sea of Japan side can block roads and railways, and avalanches threaten backcountry skiers. Along coasts, high waves and rip currents also claim lives.

In an earthquake, protect the head and take cover under a sturdy table, keep away from windows and shelves, and do not rush outside while the shaking lasts. In hotels, follow staff instructions and the evacuation map on the door. Near the coast, head for high ground at once. In a typhoon, stay indoors, avoid rivers and coasts, and expect transport to stop.

The Japan Tourism Agency's Safety tips app sends earthquake early warnings, tsunami warnings, weather warnings and heatstroke alerts in several languages. The JMA website publishes all current warnings, and NHK World broadcasts disaster information in English. Travel insurance and a charged phone are sensible basics.