Editing Geography of Japan (section)

===Volcanic eruptions===
[[File:Sakurajima_20091003.jpg|thumb|upright|[[Sakurajima]] eruption on October 3, 2009]]
{{see also|List of volcanoes in Japan}}
Japan has 111 active volcanoes. That is 10% of all active volcanoes in the world. Japan has stratovolcanoes near the subduction zones of the tectonic plates. During the 20th century, several new volcanoes emerged, including [[Shōwa-shinzan]] on Hokkaido and [[Myōjin-shō]] off the [[Bayonnaise Rocks]] in the Pacific.<ref name="volcanoes-japan">{{cite web |url=http://volcano.und.edu/vwdocs/volc_images/north_asia/japan_tec.html |archive-url=https://web.archive.org/web/20070204064754/http://volcano.und.edu/vwdocs/volc_images/north_asia/japan_tec.html |archive-date=February 4, 2007 |title=Tectonics and Volcanoes of Japan |publisher=Oregon State University |access-date=March 27, 2007}}</ref>  In 1991, Japan's [[Unzen Volcano]] on Kyushu, about {{convert|40|km|abbr=on}} 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 [[Volcanic ash|ash]] flows that swept down the mountain's slopes at speeds as high as {{convert|200|km/h|abbr=on}}. [[Unzen Volcano|Unzen]] erupted in 1792 and killed more than 15,000 people. It is the worst volcanic disaster in the country's recorded history.<ref name="dynearth">{{USGS|title=Plate tectonics and people|last1=Kious|first1=W. Jacquelyne|last2=Tilling|first2=Robert I.|url=http://pubs.usgs.gov/gip/dynamic/tectonics.html}}</ref>

Mount Fuji is a [[Dormant volcano|dormant]] stratovolcano that last erupted on 16 December 1707 till about 1 January 1708.<ref name=GSJ_active>{{cite web |title=Active Volcanoes of Japan |url=https://gbank.gsj.jp/volcano/Quat_Vol/act_map_e.html |publisher=Geological Survey of Japan |work=AIST |access-date=March 7, 2016 |archive-date=March 8, 2016 |archive-url=https://web.archive.org/web/20160308105251/https://gbank.gsj.jp/volcano/Quat_Vol/act_map_e.html |url-status=live }}</ref><ref name=Britannica>{{cite web |url=https://www.britannica.com/EBchecked/topic/221527/Mount-Fuji |title=Mount Fuji |publisher=Encyclopædia Britannica, inc. |date=11 September 2019 |access-date=21 June 2022 |archive-date=29 October 2009 |archive-url=https://web.archive.org/web/20091029041347/http://www.britannica.com/EBchecked/topic/221527/Mount-Fuji |url-status=live }}</ref> The [[Hōei eruption of Mount Fuji]] did not have a lava flow, but it did release some {{convert|800|e6m3}} of [[volcanic ash]]. It spread over vast areas around the volcano and reached [[Edo (Tokyo)|Edo]] almost {{convert|100|km|-1}} away. Cinders and ash fell like rain in [[Izu Province|Izu]], [[Kai Province|Kai]], [[Sagami Province|Sagami]], and [[Musashi Province|Musashi]] provinces.<ref>{{cite book |language=fr |last1=Titsingh |first1=Isaac |last2=von Klaproth |first2=Julius |author3=Siyun-zai Rin-siyo |date=1834 |url=https://archive.org/details/niponodaitsiran01ringoog |oclc=63259938 |title=Nipon o daï itsi ran; ou, Annales des empereurs du Japon |page=416 |publisher=Paris, Printed for the Oriental Translation Fund; [etc., etc.]}}</ref> In Edo, the volcanic ash was several centimeters thick.<ref>{{cite web |title=18. 噴火災害 |language=ja |website=dil.bosai.go.jp |url=http://dil.bosai.go.jp/library/bousai/funkasaigai/explosion.htm |archive-url=https://web.archive.org/web/20110325062432/http://dil.bosai.go.jp/library/bousai/funkasaigai/explosion.htm |archive-date=March 25, 2011}}</ref> The eruption is rated a 5 on the [[Volcanic Explosivity Index]].<ref name="Fuji — Eruption History">{{cite web |url=http://www.volcano.si.edu/volcano.cfm?vn=283030 |title=Fuji — Eruption History |website=Global Volcanism Program |publisher=Smithsonian Institution |access-date=10 August 2013 |archive-date=11 March 2022 |archive-url=https://web.archive.org/web/20220311110333/https://volcano.si.edu/volcano.cfm?vn=283030 |url-status=live }}</ref>[[File:Aso-4_tephra_90-85ka.svg|thumb|[[Mount Aso]] 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.<ref>{{Cite web |url=https://www.nippon.com/en/features/h00194/ |title=Sakurajima, Japan's Most Active Volcano |date=2018-05-16 |website=nippon.com |publisher=Nippon Communications Foundation |access-date=2018-08-02 |df=mdy-all |archive-date=2018-08-03 |archive-url=https://web.archive.org/web/20180803013956/https://www.nippon.com/en/features/h00194/ |url-status=live }}</ref>
* 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.<ref name="52Aso">[https://www.gsj.jp/data/openfile/no0613/52Aso.pdf 阿蘇カルデラ] 産総研</ref>
* The Kikai Caldera is a massive, mostly submerged caldera up to 19 kilometres (12&nbsp;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&nbsp;years ago to present). About 4,300 BC, [[pyroclastic flow]]s from that eruption reached the coast of southern Kyūshū up to {{convert|100|km|mi|abbr=on}} away, and ash fell as far as Hokkaido. The eruption produced about 150&nbsp;km<sup>3</sup> of [[tephra]],<ref>[http://www.volcano.si.edu/world/volcano.cfm?vnum=0802-06=&volpage=erupt Kikai – Eruptive history] {{Webarchive|url=https://web.archive.org/web/20120820003439/http://www.volcano.si.edu/world/volcano.cfm?vnum=0802-06=&volpage=erupt |date=2012-08-20 }}, Global Volcanism Program. Smithsonian Institution.</ref> giving it a Volcanic Explosivity Index of 7.<ref>Johnston, Eric, "[http://search.japantimes.co.jp/cgi-bin/nn20110301i1.html Latest volcano show: Shinmoe] {{Webarchive|url=https://archive.today/20120715074943/http://search.japantimes.co.jp/cgi-bin/nn20110301i1.html |date=2012-07-15 }}", ''[[The Japan Times]]'', 1 March 2011, p. 3.</ref> The Jōmon culture of at least southern Kyushu was destroyed, and it took nearly 1,000 years to recover.<ref name = "KOBEC Caldera Eruption"/>

Surveys by KOBEC (Kobe Ocean-Bottom Exploration Center) confirm that a giant lava dome of 23 cubic kilometers formed after the Kikai Caldera erupted in 4,300 BC. There is a 1% chance of a giant caldera eruption in the Japanese archipelago within the next 100 years. Approximately 40 cubic kilometers of magma would be released in one burst and cause enormous damage.<ref name = "Japan's Kikai Caldera">{{cite web |title=Giant lava dome confirmed in Japan's Kikai Caldera |format=website |url=http://www.kobe-u.ac.jp/research_at_kobe_en/NEWS/news/2018_02_09_01.html |archive-url=https://web.archive.org/web/20180727045127/http://www.kobe-u.ac.jp/research_at_kobe_en/NEWS/news/2018_02_09_01.html |archive-date = July 27, 2018 |publisher=Kobe Ocean Bottom Exploration Center (KOBEC) | access-date = 31 March 2019}}</ref>

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 [[Volcanic ash|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.<ref name = "KOBEC Caldera Eruption">{{cite web |title=巨大カルデラ噴火のメカニズムとリスクを発表 (Announce the mechanism and risk of a huge caldera eruption) |format=website |url=http://www.kobe-u.ac.jp/NEWS/info/2014_10_22_01.html |archive-url=https://web.archive.org/web/20190330103442/http://www.kobe-u.ac.jp/NEWS/info/2014_10_22_01.html |archive-date = March 30, 2019 |publisher=Kobe University | access-date = 31 March 2019}}</ref> 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 [[volcanic ash|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 [[China–North Korea border|Chinese–North Korean border]] had a [[946 eruption of Paektu Mountain|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 {{convert|971.62|km|abbr=on}} away. However, a temple in Japan reported "white ash falling like snow" on 3 November 946 AD.<ref name="paektu-sd">{{Cite press release |url=https://www.sciencedaily.com/releases/2017/01/170129111657.htm# |title=Fossilized tree and ice cores help date huge volcanic eruption 1,000 years ago to within three months |website=Science Daily.com |access-date=8 February 2017 |archive-url=https://web.archive.org/web/20201112013611/https://www.sciencedaily.com/releases/2017/01/170129111657.htm |archive-date=November 12, 2020}}</ref> So strong winds carried the volcanic ash eastward across the Sea of Japan. An average of {{convert|5|cm|abbr=on}} of ashfall covered about {{convert|1500000|km2|abbr=on}} of the Sea of Japan and northern Japan ([[Hokkaido]] and [[Aomori Prefecture]]).<ref name=":1">{{Cite journal |title=Volatile emission during the eruption of Baitoushan Volcano (China/North Korea) ca. 969 AD |last=Horn |first=S |date=2000 |journal=Bull Volcanol |doi=10.1007/s004450050004 |volume=61 |issue=8 |pages=537–555 |bibcode=2000BVol...61..537H |s2cid=129624918}}</ref> It took the ash clouds a day or so to reach Hokkaido.<ref name="paektu-sd"/> The total eruption duration was 4 and a half to 14 days (111–333 hours).<ref name="changbaishan">{{Cite book |title=Modern eruption of Changbaishan Tianchi volcano |last=L'iu |first=RX |publisher=China Science Publishing |year=1998}}</ref>

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]].<ref name="pumice"/> Clean-up operations took 2–3 weeks.<ref name="pumice">{{cite web |date=October 30, 2021 |title=Japan ports swamped by pumice spewed from undersea volcano |website=The Guardian |url=https://www.theguardian.com/world/2021/oct/30/japan-ports-swamped-by-pumice-spewed-from-undersea-volcano |archive-url=https://web.archive.org/web/20211030070901/https://www.theguardian.com/world/2021/oct/30/japan-ports-swamped-by-pumice-spewed-from-undersea-volcano |archive-date=October 30, 2021}}</ref>

{| class="wikitable sortable mw-collapsible"
|+VEI 7 eruptions happened in the following locations of Japan.
!Name
!Zone
!Location
!Event / notes
!Years ago before 1950 (Approx.)
!Ejecta volume (Approx.)
|- valign="top"
| '''[[Kikai Caldera]]'''
|
| Japan, [[Ryukyu Islands]]
| [[Akahoya eruption]] 5,300&nbsp;BC
| style="text-align:right;"| 7,300<ref name="Smith2013">{{Cite journal |date=2013 |title=Identification and correlation of visible tephras in the Lake Suigetsu SG06 sedimentary archive, Japan: chronostratigraphic markers for synchronising of east Asian/west Pacific palaeoclimatic records across the last 150 ka |author=Smith|display-authors=etal |journal=Quaternary Science Reviews |volume=67 |pages=121–137 |doi=10.1016/j.quascirev.2013.01.026 |bibcode=2013QSRv...67..121S}}</ref>
| style="text-align:right;"| 170&nbsp;km<sup>3</sup>
|- valign="top"
| '''[[Aira Caldera]]'''
|
| Japan, [[Kyūshū]]
|  Aira-Tanzawa ash
| style="text-align:right;"| 30,000<ref name="Smith2013"/>
| style="text-align:right;"| 450&nbsp;km<sup>3</sup>
|- valign="top"
| '''[[Aso Caldera]]'''
|
| Japan, [[Kyūshū]]
|  Aso-4 pyroclastic flow
| style="text-align:right;"| 90,000
| style="text-align:right;"| 600&nbsp;km<sup>3</sup>
|- valign="top"
| '''[[Mount Aso]]'''
|
| Japan, [[Kyūshū]]
| Four large eruptions between 300,000 and 90,000 years ago.
| style="text-align:right;"| 300,000
| style="text-align:right;"| 600&nbsp;km<sup>3</sup>
|}

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.<ref name=NASA-supervolcano>{{cite news |url=https://www.businessinsider.com/nasa-is-looking-at-how-to-contain-a-volcano-that-may-wipe-out-humanity-2018-10 |title=NASA is trying to figure out how to contain a supervolcano that could destroy humanity |work=[[Business Insider]] |date=October 6, 2018|access-date=January 31, 2019 |url-status=live |archive-url=https://web.archive.org/web/20190111060313/https://www.businessinsider.com/nasa-is-looking-at-how-to-contain-a-volcano-that-may-wipe-out-humanity-2018-10/ |archive-date=2019-01-11}}</ref>