Chapter 2    Basic Knowledge about Natural Disasters in Japan

§1: Earthquake

An earthquake is a phenomenon in which the bedrock is pushed or pulled by the surroundings, causing the bedrock to shift suddenly along a certain plane. The shaking caused by this sudden displacement of the bedrock is transmitted to the surroundings, and when it finally reaches the surface of the Earth, the surface of the Earth "shakes." We know from this "shaking" that an earthquake has occurred underground.

Earthquake disaster example #1: 1995 Great Hanshin-Awaji Earthquake (1995 Kobe Earthquake)

The 1995 Great Hanshin-Awaji Earthquake (magnitude 7.3) struck Kobe City at 5 a.m. on January 17, 1995, with strong tremors occurring directly beneath the city. Many buildings collapsed, resulting in a high number of casualties. More than 6,400 people were killed or reported missing, the highest number since World War II. Not only were many buildings severely damaged, but hundreds of meters of highway were overturned. The fire that broke out after the earthquake continued to spread for several days, leaving some areas in burnt ruins. Those who escaped the damage caused by the building collapse had to live in evacuation shelters for a long time as the lifelines around Kobe City, such as electricity, water, and gas supplies, became unusable.

Earthquake disaster example #2: 2024 Noto Peninsula Earthquake

The Noto Peninsula earthquake (magnitude 7.6) struck on January 1, 2024, prompting the issuance of a major tsunami warning. Strong tremors caused many houses to collapse and triggered landslides. Major roads were damaged and became unusable, which impacted rescue efforts. As with the Great Hanshin-Awaji earthquake, lifelines such as electricity, gas, and water supplies became unavailable. The fact that this earthquake occurred in winter made life in the evacuation shelters very difficult. It took about six months to restore the water supply and sewage lifelines.

§2: Tsunami 

When an earthquake occurs, the ground is lifted or pushed down near the epicenter. If an earthquake occurs in the ocean and the hypocentre is shallow beneath the seafloor, the seafloor will move vertically, causing the seawater to move from the seafloor to the sea surface. It also causes the sea level to fluctuate. A tsunami is a phenomenon in which changes in the seawater brought about in this way spread out as a wave. Tsunamis can also happen due to submarine earth movement, subsidence, or volcanic eruption.  

Tsunami disaster example: 2011 Great East Japan Earthquake

The huge tsunami caused by the Great East Japan Earthquake on March 11, 2011 (magnitude 9.0) destroyed and washed away many buildings along the Pacific coast in the Tohoku region. More than 22,200 people were killed or missing, mainly in the coastal areas of the Tohoku region. It took several months to restore the lifelines.

§3: Volcanic Eruption

A volcanic eruption is a natural phenomenon involving the eruption of magma (molten rock) from a crater in the form of volcanic gas, lava, and fragments. An eruption also occurs when volcanic gases, primarily heated water vapour emerge from the volcano without any magma reaching the surface. The former is called a magmatic eruption, and the latter a steam explosion. Additionally, when magma erupts and comes into contact with water, such as seawater, on or near the Earth's surface, it can cause an explosion known as a phreatomagmatic eruption.

Volcanic eruption disaster example #1: 2014 Mt. Ontake Volcano eruption

Mt. Ontake (3,067 m high), at the border between Nagano and Gifu, experienced a phreatic explosion at 11:52 am on September 27, 2014. Large cinders were scattered over an area extending 1 km from the crater. 58 climbers near the crater were killed, and five remain missing.

Volcanic eruption disaster example #2: Unzen Volcano pyroclastic flow disaster

On November 17, 1990, Unzen Volcano in Nagasaki Prefecture began erupting for the first time in 198 years, forming a lava dome at its summit crater. 43 people died, including members of the press and firefighters who were within the hazard warning zone. On June 8, 1991, a pyroclastic flow reached 5.5 km from the crater, but this time, more than 200 people were saved in time to evacuate from the hazard warning zone that had been designated the day before.

§4: Landslide

Landslides are terrifying disasters that can take many lives and destroy property, including houses, in an instant. A debris flow occurs when rocks and sand on a mountainside or riverbed are swept downstream by heavy rain. A landslide is the sudden collapse of a mountain slope, naturally occurring cliff, or artificially constructed embankment.

Examples of heavy rain and landslides disasters: 2018 heavy rains in western Japan

From June 28 to July 8, 2018, torrential rains occurred nationwide, mainly in western Japan, due to the influence of Typhoon No. 7 and the seasonal rain front.

In the 2018 western Japan heavy rains, damages from river overflows, floods, and landslides occurred in various places. 263 dead, 8 missing, 6,783 houses completely destroyed, 11,346 buildings partially destroyed, and 6,982 buildings flooded above the floor.

§5: Typhoon

Low atmospheric pressure that forms over the tropical ocean is called a "tropical cyclone." Of these, in the northwestern Pacific Ocean or the South China Sea, a "tropical cyclone" with a maximum wind speed of about 17 m/s or more is called a "typhoon.” Developed cumulonimbus clouds are gathering near the typhoon, resulting in heavy rainfall. In addition, the closer to the center of the typhoon, the stronger the winds and storms. 

These storms, accompanied by heavy rainfall, can cover areas of up to 800 km (500 miles) in diameter and generate winds up to 80 m/s (180 miles an hour). The typhoon season in Japan runs from May through October, with the majority of activity from July to September. Typhoons that hit Japan are often accompanied by damaging high tides, leaving residents living close to the ocean at risk. Landslides are also a serious concern during periods of heavy rain. Conditions for a landslide are particularly dangerous after rain has fallen at a rate of 20 mm or more an hour, or when 100 mm of rain falls nonstop. 

§6: Flood

A flood is a phenomenon in which a river rises due to heavy rain or melting snow and overflows outside the embankment. In Japan, it is often caused by torrential rain during the typhoon season and the rainy season.

Typhoon and flood disaster example: 1959 Isewan Typhoon

The Isewan Typhoon on September 26, 1959 made landfall at Cape Shionomisaki, Wakayama Prefecture. It caused extensive damage across most of the country, including the Kii Peninsula to the Tokai region. According to the Japan Meteorological Agency, the typhoon was powerful and had a wide storm area. Aichi Prefecture recorded maximum wind speeds of 45.4 m/s (102 miles/hour) in Irago, Atsumi Town, and 37.0 m/s (83 miles/hour) in Nagoya. The coastal areas of the Kii Peninsula and Ise Bay suffered extensive damage from storm surge, strong winds, and river flooding. In Aichi Prefecture, in particular, the storm surge caused large-scale flooding in Nagoya, Yatomi Town, and the Chita Peninsula in a short period of time under severe storms, resulting in significant damage with many people killed or missing. The number of people killed and missing exceeded 5,000.