Editing Mount Fuji (section)

== Geology ==
{{Further|Historic eruptions of Mount Fuji|List of volcanoes in Japan|Triple junction}}
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[[File:Geologycal cross-section of Fuji.png|upright=1.45|thumb|Geological cross-section of Fuji volcano. [[Key (map)|Key]]: N<sub>2</sub> = [[Tertiary]] [[sedimentary rock]]s; αN<sub>2</sub> = Tertiary volcanic rocks; αQ<sub>1</sub> = [[Komitake volcano]]; α-δQ<sub>1</sub> = [[Ashitaka volcano]]; βQ<sub>2</sub> = Older Fuji volcano; αβQ<sub>2</sub> = Younger Fuji volcano.<ref name="VRC_ERI">{{cite web |url=http://www.eri.u-tokyo.ac.jp/VRC/vrc/others/fujigeol.html |title=Geology of Fuji Volcano |publisher=Hokkaido National Agricultural Experiment Station|via=Volcano Research Center, Earthquake Research Institute (ERI), University of Tokyo|access-date=November 17, 2023|last=Miyaji|first=Naomichi|archive-date=January 16, 2021|archive-url=https://web.archive.org/web/20210116061501/http://www.eri.u-tokyo.ac.jp/VRC/vrc/others/fujigeol.html |url-status=live}}</ref>]]

Mount Fuji is located at a [[triple junction]] [[Oceanic trench|trench]] where the [[Amurian Plate]], [[Okhotsk Plate]], and [[Philippine Sea Plate]] meet.<ref name=MooresTwiss1995>{{cite book |last1=Moores |first1=Eldridge M. |last2=Twiss |first2=Robert J. |title=Tectonics |date=2014 |publisher=Waveland Press |isbn=978-1-4786-2199-7 |page=208}}</ref><ref name=NatGeogFuji>{{cite web |title=Mount Fuji |date=December 6, 2011 |publisher=[[National Geographic Society]] |access-date=18 May 2018 |url=https://www.nationalgeographic.org/media/mount-fuji/ |archive-date=June 12, 2018 |archive-url=https://web.archive.org/web/20180612143949/https://www.nationalgeographic.org/media/mount-fuji/ |url-status=dead}}</ref> These three plates form the western part of Japan, the eastern part of Japan, and the [[Izu Peninsula]] respectively.<ref name=Piotr/> The [[Pacific Plate]] is being [[subducted]] beneath these plates, resulting in volcanic activity. Mount Fuji is also located near three [[island arc]]s: the [[Southwestern Japan Arc]], the [[Northeastern Japan Arc]], and the [[Izu–Bonin–Mariana Arc|Izu-Bonin-Mariana Arc]].<ref name=Piotr>{{cite book |last1=Oguchi |first1=Takashi |last2=Oguchi |first2=Chiaki |editor1-last=Migon |editor1-first=Piotr |chapter=Mt. Fuji: The Beauty of a Symmetric Stratovolcano|title=Geomorphological Landscapes of the World |date=2010 |publisher=[[Springer Netherlands]]|isbn=9789048130542 |pages=303–309}}</ref> The Fuji triple junction is only {{convert|400|km}} from the [[Boso triple junction]].

Fuji's main crater is {{cvt|780|m}} in diameter and {{cvt|240|m}} deep. The bottom of the crater is {{cvt|100|-|130|m}} in diameter. Slope angles from the crater to a distance of {{cvt|1.5|–|2|km}} are 31°–35°, the [[angle of repose]] for dry gravel. Beyond this distance, slope angles are about 27°, which is caused by an increase in [[scoria]]. Mid-flank slope angles decrease from 23° to less than 10° in the [[foothills|piedmont]].<ref name=Piotr/>

[[File:Hasshinpo of Mt.Fuji 40.jpg|thumb|[[Volcanic crater|Crater]] with the [[Eight Sacred Peaks]] (''Hasshin-po'')]]
Scientists have identified four distinct phases of volcanic activity in the formation of Mount Fuji. The first phase, called ''Sen-komitake'', is composed of an [[andesite]] core recently discovered deep within the mountain. ''Sen-komitake'' was followed by the "''Komitake'' Fuji", a [[basalt]] layer believed to have formed several hundred thousand years ago. Approximately 100,000&nbsp;years ago, "Old Fuji" was formed over the top of ''Komitake'' Fuji. The modern, "New Fuji" is believed to have formed over the top of Old Fuji around 10,000&nbsp;years ago.<ref>{{cite news |url=https://www.japantimes.co.jp/news/2004/04/04/national/third-ancient-volcano-discovered-deep-inside-fuji/|title=Third ancient volcano discovered within Mount Fuji |work=[[Japan Times]] |date=April 4, 2004|access-date=November 17, 2023|archive-date=March 11, 2014|archive-url=https://web.archive.org/web/20140311111128/https://www.japantimes.co.jp/news/2004/04/04/national/third-ancient-volcano-discovered-deep-inside-fuji/#.Ux7vYXbP32c|url-status=live}}</ref>

Pre-Komitake started erupting in the [[Middle Pleistocene]] in an area {{cvt|7|km|mi|frac=2|spell=in}} north of Mount Fuji. After a relatively short pause, eruptions began again, which formed Komitake Volcano in the same location. These eruptions ended 100,000 years ago. Ashitaka Volcano was active from 400,000 to 100,000 years ago and is located {{cvt|20|km}} southeast of Mount Fuji. Mount Fuji started erupting 100,000 years ago, with Ko-Fuji (old-Fuji) forming 100,000 to 17,000 years ago, but it is now almost completely buried. A large [[volcanic landslide|landslide]] on the southwest flank occurred about 18,000 years ago. Shin-Fuji (new-Fuji) eruptions in the form of [[lava]], [[lapilli]], and [[volcanic ash]] have occurred between 17,000 and 8,000 years ago, between 7,000 and 3,500 years ago, and between 4,000 and 2,000 years ago. Flank eruptions, mostly in the form of parasitic [[cinder cone]]s, ceased in 1707. The largest cone, [[Mount Ōmuro (Mount Fuji)|Omuro-Yama]], is one of more than 100 cones aligned NW-SE and NE-SW through the summit. Mt. Fuji also has more than 70 [[lava tunnel]]s and extensive lava tree molds. Two large landslides are at the head of the Yoshida-Osawa and Osawa-Kuzure valleys.<ref name=Piotr/>

{{As of|2002|12}}, the volcano is classified as active with a low risk of eruption. The last recorded eruption was the [[Hōei eruption]] which started on December 16, 1707 (''[[Hōei]] 4, 23rd day of the 11th month''), and ended about January 1, 1708 (''Hōei 4, 9th day of the 12th month'').<ref name="1707 eruption"/> The eruption formed a new [[Volcanic crater|crater]] and a second peak, named [[Mount Hōei]], halfway down its southeastern side. Fuji spewed cinders and ash which fell like rain in [[Izu Province|Izu]], [[Kai Province|Kai]], [[Sagami Province|Sagami]], and [[Musashi Province|Musashi]].<ref>{{cite book|author-link=Hayashi Gahō|last=Gahō|first=Hayashi|orig-year=Originally published 1652|title=[[Nihon Ōdai Ichiran|Nipon o daï itsi ran; ou, Annales des empereurs du Japon]]|trans-title=Nipon o daï itsi ran; or, Annals of the Emperors of Japan|language=fr|translator-last=Titsingh|translator-first=Isaac|translator-link=Isaac Titsingh|editor-last=von Klaproth|editor-first=Julius|year=1834|location=Paris |publisher=[[Royal Asiatic Society|Oriental Translation Society of Great Britain and Ireland]]|page=416}}
</ref> Since then, there have been no signs of an eruption. However, on the evening of March 15, 2011, there was a [[Richter magnitude scale|magnitude]] 6.2 earthquake at shallow depth a few kilometres from Mount Fuji on its southern side.

=== Recorded eruptions ===
About 11,000 years ago, a large amount of lava began to erupt from the west side of the top of the ancient Fuji mountain. This lava formed the new Fuji, which is the main body of Mount Fuji. Since then, the tops of the ancient Fuji and the new Fuji have been side by side. About 2,500–2,800 years ago, the top part of ancient Fuji was destroyed in a large [[sector collapse]] and only the top of Shin-Fuji remained.
Ten known eruptions can be traced to reliable records.<ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/0index.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |title=Database of eruptions and other activities of Fuji Volcano, Japan, based on historical records since AD781 |language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=May 7, 2021 |archive-url=https://web.archive.org/web/20210507121143/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/0index.html |url-status=live }}</ref><ref>{{cite web |url=https://pandoraboss.com/2021/10/08/all-about-mount-fuji/ |title=All about Mount Fuji |language=en |access-date=October 10, 2021 |archive-date=March 5, 2023 |archive-url=https://web.archive.org/web/20230305232643/https://pandoraboss.com/2021/10/08/all-about-mount-fuji/|url-status=usurped|website=pandoraboss.com}}</ref>
{| class="wikitable"
! Date(s) || Notes !! {{Refh}}
|-
| July 31, 781
| The eruption was recorded in the ''[[Shoku Nihongi]]'' and it was noted that "ash fell", but there are no other details.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/781.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:天応元年（781）噴火|title=Ten'nō gan'nen (781) funka|trans-title=Eruption in the first year of Ten'ō (781)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729153559/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/781.html |url-status=live }}</ref>
|-
| April 11 – May 15, 800<br/>February 13, 802
| The ''[[Nihon Kiryaku]]'' states that during the first phase, the skies were dark even during the daytime. The second phase is known from the ''[[Nippon Kiseki]]'', which notes that gravel fell like hail.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/800.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:延暦十九～二十一年（800～802）噴火|title=Nobe-reki jū kyū ~ nijūichinen (800 ~ 802) funka|trans-title=Eruption in the 19th to 21st years of Enryaku (800 to 802)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172559/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/800.html |url-status=live }}</ref>
|-
| June–September 864<br/>December 865 – January 866
| Both phases were recorded in the {{lang|ja-latn|[[Nihon Sandai Jitsuroku]]}}. This eruption created three of the [[Fuji Five Lakes]]: [[Lake Motosu|Motosu]], [[Lake Shōji|Shōji]], and [[Saiko Lake|Saiko]], from a single lake that became separated by lava flow.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/864.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:貞観六～七年（864～866初頭）噴火|title=Jōgan roku ~ nana-nen (864 ~ 866 shotō) funka|trans-title=Eruption in the 6th to 7th years of Jōgan (864 to early 866)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172559/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/864.html |url-status=live }}</ref>
|-
| November 937
| This was recorded in the ''Nihon Kiryaku''.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/937.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:承平七年（937）噴火|title=Jōhei nana-nen (937) funka|trans-title=Eruption in the 7th year of Jōhei (937)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172601/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/937.html |url-status=live }}</ref>
|-
| March 999
| It is noted in the ''[[Honchō Seiki]]'' that news of an eruption was brought to Kyoto, but no other details are known.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/999.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:長保元年（999）噴火|title=Chōhō gan'nen (999) funka|trans-title=Eruption in the first year of Chōhō (999)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172559/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/999.html |url-status=live }}</ref>
|-
| January 1033
| According to the ''Nihon Kiryaku'', news of this eruption was brought to Kyoto two months later.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1033.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:長元五年末（1033初頭）噴火|title=Chō gen go nenmatsu (1033 shotō) funka|trans-title=Eruption at the end of Chōgen 5 (early 1033)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172601/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1033.html |url-status=live }}</ref>
|-
| April 17, 1083
| The only contemporary recording of this was written by a Buddhist monk and can be found in the ''[[Fusō Ryakuki]]''. Later writings indicate that the sound of the eruption may have been heard in Kyoto.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1083.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:永保三年（1083）噴火|title=Nagayasu san-nen (1083) funka|trans-title=Eruption in the third year of Eihō (1083)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172604/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1083.html |url-status=live }}</ref>
|-
| between January 30, 1435, and January 18, 1436
| A record of this appears in the ''[[Ōdaiki]]'', a chronicle kept by the monks at [[Kubo Hachiman Shrine]] in [[Yamanashi, Yamanashi|Yamanashi City]], and it states that a flame was visible on Mount Fuji. As there is no mention of smoke, this appears to have been a [[Hawaiian eruption]] (lava only).
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1435.html|first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:永享七年（1435または1436初頭）噴火|title=Eikyō nana-nen (1435 matawa 1436 shotō) funka|trans-title=Eruption in the seventh year of Eikyō (1435 or early 1436)|language=ja |access-date=November 15, 2023 |df=dmy-all}}</ref>
|-
| August 1511
| The ''[[Katsuyamaki]]'' (or ''Myōhōjiki''), written by monks at Myōhō-ji in [[Fujikawaguchiko]], indicates that there was a fire on Mount Fuji at this time, but as there is no vegetation at the described location, this was almost certainly a lava flow.
| <ref>{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1511.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:永正八年（1511）噴火|title=Eishō hachi-nen (1511) funka|trans-title=Eruption in the eighth year of Eishō (1511)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=May 18, 2021 |archive-url=https://web.archive.org/web/20210518000536/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1511.html |url-status=live }}</ref>
|-
| December 16, 1707
| The [[Hōei eruption]]
| <ref name="1707 eruption">{{cite web |url=https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1707.html |first=Masato |last=Koyama |publisher=[[Shizuoka University]] |script-title=ja:宝永四年（1707）噴火|title=Hōei shi-nen (1707) funka|trans-title=Eruption in the fourth year of Hōei (1707)|language=ja |access-date=2021-07-29 |df=dmy-all |archive-date=July 29, 2021 |archive-url=https://web.archive.org/web/20210729172602/https://sakuya.vulcania.jp/koyama/public_html/Fuji/fujid/1707.html |url-status=live }}</ref>
|}

=== Current eruptive danger ===
{{Update section|date=November 2022}}
Following the [[2011 Tōhoku earthquake and tsunami|2011 Tōhoku earthquake]], there was speculation in the media that the shock may induce volcanic unrest at Mount Fuji. In September 2012, mathematical models created by the National Research Institute for Earth Science and Disaster Prevention (NRIESDP) suggested that the pressure in Mount Fuji's [[magma chamber]] could be 1.6 [[pascal (unit)|megapascals]] higher than it was before its last eruption in 1707. This was interpreted by some media outlets to mean that an eruption of Mount Fuji could be imminent.<ref>{{cite magazine |url=https://www.wired.co.uk/article/mount-fuji|title=Pressure in Mount Fuji is now higher than last eruption, warn experts |last=Clark |first=Liat |magazine=[[Wired (magazine)|Wired]] |date=September 6, 2012 |access-date=November 17, 2023|archive-date=September 6, 2023|archive-url=https://web.archive.org/web/20230906182958/https://www.wired.co.uk/article/mount-fuji|url-status=live}}</ref> However, since there is no known method of directly measuring the pressure of a volcano's magma chamber, indirect calculations of the type used by NRIESDP are speculative and unverifiable. Other indicators suggestive of heightened eruptive danger, such as active [[fumarole]]s and recently discovered [[fault (geology)|faults]], are typical occurrences at this type of volcano.<ref>{{cite magazine |url=https://www.wired.com/2012/09/doom-volcano-research-media/|title=Doooom! The Perception of Volcano Research by the Media |last=Klemetti |first=Erik |magazine=[[Wired magazine|Wired]] |date=September 10, 2012|access-date=November 17, 2023|archive-date=March 25, 2023|archive-url=https://web.archive.org/web/20230325154058/https://www.wired.com/2012/09/doom-volcano-research-media/|url-status=live}}</ref>

Eruption fears continued into the 2020s. In 2021, a new hazard map was created to help residents plan for evacuation, stoking fears because of its increased estimate of lava flow and additional vents.<ref>{{Cite news|title=Japan: Mount Fuji report doubles estimate of lava flow|last=Ryall|first=Julian|location=Tokyo|date=April 7, 2021|url=https://www.dw.com/en/japan-mount-fuji-report-doubles-previous-estimate-of-lava-flow/a-57119635|access-date=November 19, 2023|publisher=[[Deutsche Welle]]|language=en}}</ref> Soon afterwards, a 4.8 magnitude earthquake hit the area, sending the phrase "Mt Fuji eruption" trending on [[Twitter]].<ref>{{cite news|date=December 2, 2021|title=Japan quells fears of Mt Fuji eruption after earthquake |language=en |publisher=[[Reuters]]|url=https://www.reuters.com/business/environment/japan-quells-fears-mt-fuji-eruption-after-earthquake-2021-12-03/ |access-date=November 19, 2023}}</ref> However, the Japan Meteorological Agency assured the public the earthquake did not increase the eruption risk. In 2023, a new evacuation plan was developed to account for the 2021 hazard map update.<ref>{{cite news|date=March 29, 2023|title=Mount Fuji eruption escape plan calls on residents to evacuate on foot|url=https://www.japantimes.co.jp/news/2023/03/29/national/mount-fuji-eruption-plan/|access-date=November 19, 2023|url-access=limited|work=[[The Japan Times]]|language=en}}</ref>