Earthquakes and tsunami Japan is substantially prone to earthquakes, tsunamis, and volcanoes because of its location along the Pacific Ring of Fire. It has the
15th highest natural disaster risk as measured in the 2013 World Risk Index. As many as 1,500 earthquakes are recorded yearly, and magnitudes of 4 to 6 are common. More recent major quakes are the 1995
Great Hanshin earthquake and the
2011 Tōhoku earthquake, a 9.1-magnitude quake that hit Japan on March 11, 2011. It triggered a large tsunami and the
Fukushima Daiichi nuclear disaster, one of the worst disasters in the history of nuclear power. The 2011 Tōhoku earthquake was the largest ever recorded in Japan and is the world's fourth largest earthquake to strike since 1900, according to the U.S. Geological Service. It struck offshore about northeast of Tokyo and east of the city of
Sendai and created a massive tsunami that devastated Japan's northeastern coastal areas. At least 100 aftershocks registering a magnitude of 6.0 or higher have followed the main shock. At least 15,000 people died as a result. Researchers found the source of great thrust earthquakes and associated tsunamis in the
Greater Tokyo Area at the
Izu-Ogasawara Trench. Reclaimed land and human-made islands are particularly susceptible to
liquefaction during an earthquake. As a result, there are specific earthquake resistance standards and ground reform work that apply to all construction in these areas. In an area that was possibly reclaimed in the past, old maps and land condition drawings are checked, and drilling is carried out to determine the strength of the ground. However, this can be very costly, so for a private residential block of land, a Swedish weight sounding test is more common. In 1991, Japan's
Unzen Volcano on Kyushu, about east of Nagasaki, awakened from its 200-year slumber to produce a new
lava dome at its summit. Beginning in June, repeated collapse of this erupting dome generated
ash flows that swept down the mountain's slopes at speeds as high as .
Unzen erupted in 1792 and killed more than 15,000 people. It is the worst volcanic disaster in the country's recorded history. Mount Fuji is a
dormant stratovolcano that last erupted on 16 December 1707 till about 1 January 1708. The
Hōei eruption of Mount Fuji did not have a lava flow, but it did release some of
volcanic ash. It spread over vast areas around the volcano and reached
Edo almost away. Cinders and ash fell like rain in
Izu,
Kai,
Sagami, and
Musashi provinces. In Edo, the volcanic ash was several centimeters thick. The eruption is rated a 5 on the
Volcanic Explosivity Index. 4 pyroclastic flow and the spread of Aso 4 tephra (90,000 to 85,000 years ago). The pyroclastic flow reached almost the whole area of Kyushu, and volcanic ash was deposited of 15 cm in a wide area from Kyushu to southern Hokkaido. There are three VEI-7 volcanoes in Japan. These are the
Aira Caldera, the
Kikai Caldera, and the
Aso Caldera. These giant calderas are remnants of past eruptions.
Mount Aso is the largest active volcano in Japan. 300,000 to 90,000 years ago, there were four eruptions of Mount Aso that emitted huge amounts of volcanic ash that covered all of Kyushu and up to
Yamaguchi Prefecture. • The Aira Caldera is 17 kilometers long and 23 kilometers wide, located in south Kyushu. The city of
Kagoshima and the
Sakurajima volcano are within the Aira Caldera. Sakurajima is the most active volcano in Japan. • The Aso Caldera stretches 25 kilometers north to south and 18 kilometers east to west in
Kumamoto Prefecture, Kyushu. It has erupted four times: 266,000 and 141,000 years ago with 32 DRE km3 (
dense-rock equivalent) each; 130,000 years ago with 96 DRE km3; and 90,000 years ago with 384 DRE km3. • The Kikai Caldera is a massive, mostly submerged caldera up to 19 kilometres (12 mi) in diameter in the Ōsumi Islands of Kagoshima Prefecture, Japan. It is the remains of the ancient eruption of a colossal volcano. Kikai Caldera was the source of the
Akahoya eruption, one of the largest eruptions during the
Holocene (10,000 years ago to present). About 4,300 BC,
pyroclastic flows from that eruption reached the coast of southern Kyūshū up to away, and ash fell as far as Hokkaido. The eruption produced about 150 km3 of
tephra, giving it a Volcanic Explosivity Index of 7. The Jōmon culture of at least southern Kyushu was destroyed, and it took nearly 1,000 years to recover. According to a 2014 study by KOBEC of
Kobe University, in a worst-case scenario, if there is a VEI-7 eruption of the Aso Caldera and if the volcanic ash is carried by westerly winds, then pyroclastic flows would cover the 7 million population near the Aso Caldera within two hours. The pyroclastic flows could reach much of Kyushu. Beyond the pyroclastic area is volcanic ash that falls from the sky. If the volcanic ash continuously flows northward, then the
ash fall would make it impossible to live normally in large parts of the main islands of Japan due to the paralysis of traffic and lifelines for a limited period (a few days to 2 weeks) until the eruption subsides. In this scenario, the exception would be eastern and northern Hokkaido (the Ryukyu Islands and southern Nanpo Islands would also be excluded). Professor Yoshiyuki Tatsumi, head of KOBEC, told the
Mainichi Shimbun that "the probability of a gigantic caldera eruption hitting the Japanese archipelago is 1 percent in the next 100 years" with a death toll of many tens of millions of people and wildlife. The potential exists for tens of millions of humans and other living beings to die during a VEI-7 volcanic eruption with significant short-term effects on the global climate. Most casualties would occur in Kyushu from the pyroclastic flows. The potential damage from the volcanic ash depends on the
wind direction. If, in another scenario, the wind blows in a western or southern direction, then the volcanic ash could affect the East Asian continent or South-East Asia. If the ash flows eastward, then it will spread over the Pacific Ocean. Since the Kikai Caldera is submerged, it is unclear how much damage the
hot ash clouds would cause if large quantities of volcanic ash stayed beneath the ocean surface. The underwater ash would be swept away by
ocean currents.
Paektu Mountain on the
Chinese–North Korean border had a
VEI-7 eruption in 946. Paektu Mountain is mainly a threat to the surrounding area in
North Korea and
Manchuria. The west coast of Hokkaido is about away. However, a temple in Japan reported "white ash falling like snow" on 3 November 946 AD. So strong winds carried the volcanic ash eastward across the Sea of Japan. An average of of ashfall covered about of the Sea of Japan and northern Japan (
Hokkaido and
Aomori Prefecture). It took the ash clouds a day or so to reach Hokkaido. In October 2021, large quantities of pumice pebbles from the
submarine volcano Fukutoku-Okanoba damaged fisheries, tourism, the environment, 11 ports in Okinawa, and 19 ports in
Kagoshima prefecture. Improving technology and methods to predict volcano and giant caldera eruptions would help to prepare and evacuate people earlier. Technology is needed to accurately capture the state of the
magma chamber, which spreads thinly with a thickness of less than several kilometers around the middle of the crust. The underground area of Kyushu must be monitored because it is a dangerous area with the potential for a caldera eruption. The most protective measure is to stop the hot ash clouds from spreading and devastating areas near the eruption so that people don't need to evacuate. There are currently no protective measures to minimize the spread of millions of tons of deadly hot ash during a VEI-7 eruption. In 2018,
NASA published a theoretical plan to prevent a volcanic eruption by pumping large quantities of cold water down a borehole into the hydrothermal system of a supervolcano. The water would cool the huge body of magma in the chambers below the volcano so that the liquid magma would become semi-solid. Thus, enough heat could be extracted to prevent an eruption. The heat could be used by a geothermal plant to generate
geothermal energy and electricity.
Typhoons Since recording started in 1951, an average of 2.6 typhoons reached the main islands of Kyushu, Shikoku, Honshu, and Hokkaido per year. Approximately 10.3 typhoons approach within the 300-kilometer range near the coast of Japan. Okinawa is, due to its geographic location, most vulnerable to typhoons, with an average of 7 storms per year. The most destructive was the
Isewan Typhoon, with 5,000 casualties in the
Tokai region in September 1959. In October 2004,
Typhoon Tokage caused heavy rain in Kyushu and central Japan, resulting in 98 casualties. Until the 1960s, the death toll was hundreds of people per typhoon. Since the 1960s, improvements in construction, flood prevention, high tide detection, and early warnings have substantially reduced the death toll, which rarely exceeds a dozen people per typhoon. Japan also has special search and rescue units to save people in distress. Heavy snowfall during the winter in the
snow country regions causes
landslides, flooding, and
avalanches. ==Environmental issues==