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Earth-Science Reviews

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Recent progress of geophysical and geological studies of Mt. Fuji Volcano,Japan

Yosuke Aokia,⁎, Kae Tsunematsub,c, Mitsuhiro Yoshimotob

a Earthquake Research Institute, The University of Tokyo, Tokyo, JapanbMount Fuji Research Institute, Yamanashi Prefectural Government, Fujiyoshida, Yamanashi, JapancNow at Department of Earth and Environmental Sciences, Yamagata University, Yamagata, Japan

A R T I C L E I N F O

Keywords:Mt. FujiVolcanic eruptionMagma plumbing systemVolcano monitoringForecasting an eruption

A B S T R A C T

Mt. Fuji, located in central Japan near the triple junction of the Philippine Sea, Eurasia (or Amurian), and NorthAmerican (or Okhotsk) plates, is one of the arc volcanoes associated with the subduction of the Pacific plate. Mt.Fuji has unique features including an average eruption rate in the last 100,000 years of 4–6 km3/ka, which ismuch higher than that of other volcanoes along the same arc (0.01 and 0.1 km3/ka). Basaltic rocks dominate inMt. Fuji, while other arc volcanoes are dominated by intermediate and felsic compositions, and Mt. Fuji haserupted both explosively and effusively, with the two largest eruptions in the last 2000 years having differentstyles; the 864–866 CE Jogan eruption was effusive, while the 1707 Hoei eruption, the most recent eruption, wasexplosive. Mt. Fuji is not only interesting from a scientific point of view, but also important from a societal pointof view because it is only 100 km from the Tokyo metropolitan region, one of the biggest cities in the worldhosting more than 30 million people. The Hoei eruption resulted in more than a few tens of millimeters of ashfallin Tokyo by more than 150mm. With this background, Mt. Fuji has been studied intensively using geological andgeophysical methods to understand the evolution, magma plumbing system, and current activity of the volcano.This article synthesizes the current knowledge about Mt. Fuji. In particular, we provide background informationrequired to understand the Jogan and Hoei eruptions, and discuss how to assess the size, timing, and style of thenext eruption. Statistical insights suggest that the next eruption of Mt. Fuji is more likely to be voluminous with along precursor, given a repose time of more than 300 years.

1. Introduction

Mt. Fuji is one of the arc volcanoes associated with the subductionof the Pacific plate (Fig. 1). Mt. Fuji (3776m) stands out from othervolcanoes in Japan by at least five aspects: volume, composition,eruption style, vent location, and hazard. It has a large volume of about400–500 km3 despite being active only in the last80,000–100,000 years, corresponding to the average ejection rate of4–6 km3/ka. This ejection rate is significantly larger than that of otherarc volcanoes along the same arc, between 0.01 and 0.1 km3 (Tsukuiet al., 1986; Yoshimoto et al., 2010).

Second, the chemical composition of Mt. Fuji is distinct from otherarc volcanoes. Intermediate and felsic magmas such as andesite, dacite,or rhyolite dominate in arc volcanoes, whereas Mt. Fuji has mainlyejected basaltic rocks. For example, the 864–866 CE Jogan eruption,one of the two largest eruptions in the last 2000 years, ejected a total ofabout ~1.4 km3 of basaltic materials (Miyaji et al., 2006). The complex

tectonic setting of Mt. Fuji (Fig. 1) might play a role, but the prevalenceof basaltic magmas has not been explained.

Third, Mt. Fuji has erupted in various styles from effusive to ex-plosive eruptions. While the Jogan eruption was mainly effusive, the1707 Hoei eruption, another one of the largest eruptions in the last2000 years, was an explosive eruption which ejected a total of about1.6 km3 of basaltic and dacitic materials (Miyaji et al., 2011).

Fourth, Mt. Fuji has erupted both from the summit and the flank.Since the ambient stress field around Mt. Fuji is dominated by north-west-southeast compression due to the collision with the Philippine Seaplate (e.g., Ukawa, 1991; Araragi et al., 2015), the vents are mainlydistributed on the northwestern and southeastern flanks. In fact, all theeruptions of Mt. Fuji in the last 2200 years, including the Jogan andHoei eruptions, are from the flank rather than the summit. This eruptivehistory indicates that large areas are under potential threat from lavaflows.

Finally, Mt. Fuji is only about 100 km from the Tokyo metropolitan

https://doi.org/10.1016/j.earscirev.2019.05.003Received 2 April 2018; Received in revised form 11 April 2019; Accepted 2 May 2019

⁎ Corresponding author.E-mail address: yaoki@eri.u-tokyo.ac.jp (Y. Aoki).

Earth-Science Reviews 194 (2019) 264–282

Available online 11 May 20190012-8252/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).

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area with a population of more than 30 million. The area is thus po-tentially at risk from volcanic hazards. Indeed, the most recent Hoeieruption was so explosive that the Tokyo metropolitan region receivedup to 100mm of ash (Miyaji et al., 2011). The same or similar eruptionnow would cause severe volcanic hazards in Tokyo and the surroundingareas. The Hoei eruption started 49 days after a nearby M∼ 8.5earthquake, indicating that the region was affected by volcanic hazardsless than two months after the seismic activity.

Therefore, understanding the potential location, style, size, andtiming of the next eruption of Mt. Fuji is important not only from ascientific standpoint but also for the hazard assessment. This articlereviews insights into understanding how Mt. Fuji was formed and po-tentially assesses its next eruption of Mt. Fuji. Section 2 summarizes thetectonic setting and stress field around Mt. Fuji. We have reviewed theevolution of Mt. Fuji during the last 400,000 years in Sections 3.Sections 4 and 5 describe insights into the internal structure and currentactivity of Mt. Fuji. Based on the discussion between Sections 2 and 5,Sections 6 and 7 summarize how we can address the research questionsposed in this section and assess the next eruption.

2. Tectonic background

2.1. Plate motions around Mt. Fuji

Mt. Fuji is located near the triple junction of the Philippine Sea,Eurasian (or Amurian), and North American (or Okhotsk) plates, underwhich the Pacific plate subducts at a convergence rate of ~85mm/yr(Argus et al., 2010; Fig. 1). From the south, the Philippine Sea platesubducts beneath the North American (or Okhotsk) and Eurasian (orAmurian) plates from the Suruga and Sagami troughs with convergence

rates of about 25 and 15mm/yr, respectively (e.g., Argus et al., 2010).The Philippine Sea plate collides at the northern tip near Mt. Fuji(Fig. 1). While the Philippine Sea plate is an oceanic plate, the collidingsection in it is part of an island arc with lower average density thanoceanic plates. The island arc on the Philippine Sea plate thus cannotsubduct as smoothly as oceanic plates, resulting in a collision at theplate boundary.

Seismicity at the subducting and colliding plate boundaries aroundthe northern tip of the Philippine Sea plate exhibit a marked difference(Ishida, 1992). The subducting plate boundary exhibits abundant seis-micity including large earthquakes of M∼8 such as the 1854 Ansei and1923 Kanto earthquakes in the Suruga and Sagami troughs, respec-tively. On the other hand, the colliding part of the plate boundary lacksmajor seismicity. Although seismic reflectors were detected to the northof Mt. Fuji (Iidaka et al., 1990), it lacks widespread seismic reflectorsassociated with plate subduction. The subducting plate boundary hostsobvious seismic reflectors corresponding to the Moho of the subductingPhilippine Sea plate (Arai and Iwasaki, 2015).

2.2. Regional and local stress field

The plate configuration described above results in a regional stressfield with northwest-southeast compression and northeast-southwestextension around Mt. Fuji (Ukawa, 1991). Mt. Fuji and Izu-Oshimavolcanoes (Fig. 1) are elongated in a northwest-southeast direction (Ida,2009; Fig. 2), with dominant strikes of volcanic fissures (Takada et al.,2007), and focal mechanisms of shallow earthquakes (Ukawa, 1991;Araragi et al., 2015) confirming the stress field. The shape of volcanicislands becomes more rounded (Fig. 2), and the orientation of volcanicfissures becomes radial with distance from the plate boundary (Ida,

Fig. 1. Tectonic setting around Mt. Fuji. PAC, PHS, EUR, AMR, NA, and OKH denote Pacific, Philippine Sea, Eurasian, Amurian, North American, and Okhotsk plates,respectively. Red triangles represent active volcanoes, in which Mt. Fuji is represented by the biggest triangle. Gray dash lines represent depth contours of thesubducting Philippine Sea plate with an interval of 10 km given by Hirose et al. (2008) and Nakajima et al. (2009). Rupture areas of the 1854 Ansei and 1923 Kantoearthquakes are also shown. Yellow rectangles denote the areas shown as close-up views in Fig. 2. (For interpretation of the references to colour in this figure legend,the reader is referred to the web version of this article.)

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2009). These observations confirm the collision and subduction of thePhilippine Sea plate control the regional stress field.

The local stress field on the edifice of Mt. Fuji is not only controlledby the collision and subduction of the Philippine Sea plate but also bythe stress field exerted by the loading of the volcano itself. Araragi et al.(2015) investigated seismic anisotropy around Mt. Fuji at depths shal-lower than ∼4 km, and found that while the fast direction of theseismic wavespeed is radially distributed near the summit of Mt. Fuji, itroughly strikes northwest-southeast (Fig. 3). The differential stress,orientation of cracks, or lattice preferred orientation of rocks generateanisotropy of seismic velocity. In this case, the origin of seismic

anisotropy is likely the differential stress. Their study suggests that thestress field around Mt. Fuji at shallow (≤4 km) depths is, at least, acombination of the regional stress field and the stress from volcanoloading.

3. Evolution of Mt. Fuji and recent eruptions

The evolution and geology of Mt. Fuji have been extensively in-vestigated since pioneering studies by Prof. Hiromichi Tsuya in the1930s (e.g., Tsuya, 1955, 1962), leading to the most recent version ofthe geological map (Takada et al., 2016). Thus, we do not attempt to

Fig. 2. Close-up views of (a) Mt. Fuji, (b) Izu-Oshima, and (c) Miyakejima volcanoes, whose locations are shown in Fig. 1. The shape of Mt. Fuji and Izu-Oshimavolcanoes are more elliptical than Miyakejima because the ambient stress fields around them are more deviatoric than the stress field around Miyakejima.

Fig. 3. Rose diagrams of fast polarization directions obtained from a shear-wave splitting analysis for each seismic site. Gray lines indicate directions of the maximumcompression at a depth of 2.0 km that fits with the obtained fast polarization directions; they are obtained by a combination of the point load at the summit of Mt. Fujiand an appropriate ambient stress field (see Araragi et al., 2015, for details). Modified from Araragi et al. (2015).

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give a comprehensive review of the evolution and previous eruptions ofMt. Fuji. Instead, here we briefly summarize the eruptions in chron-ological order, focusing on the recent Jogan and Hoei eruptions, whichrepresent diverse eruptive styles of Mt. Fuji.

3.1. Evolution before 100 ka

Scientific drilling revealed that the evolution of Mt. Fuji is dividedinto several stages (Yoshimoto et al., 2010; Fig. 4). First, Ashitake

volcano to the south of the current Mt. Fuji started to grow about 400 kaago. Pre-Komitake volcano, located to the north of current Mt. Fuji,started to grow with effusions of basaltic lava flows at around 270 ka,ending up with explosive eruptions of basaltic andesite and dacitemagmas at around 160 ka. Komitake volcano grew, by effusions ofbasaltic lavas, on top of Pre-Komitake volcano between around 160 kaand 100 ka, when the youngest part of Mt. Fuji started to grow.Yoshimoto et al. (2010) proposed that a change in regional tectonicsaround 150 ka ago might have been responsible for a change in the rockchemistry from Pre-Komitake volcano to subsequent volcanoes, but thisconjecture has not been proved yet.

3.2. Evolution after 100 ka

Basaltic volcanism dominates in the current Fuji volcano, and itsactivity can be divided into two periods, the older Fuji between 100 kaand 10 ka and the younger Fuji since 10 ka. Eruptions of the older Fujimay have been explosive considering that extensive deposits from oldFuji eruptions cover an area of ∼250 km2 mainly to the east of Mt. Fuji(Miyaji et al., 1992; Yoshimoto et al., 2010). Basaltic lava flows dom-inate the eruptions of younger Fuji, but explosive eruptions of daciticand andesitic magmas such as the Zunasawa eruption ∼3 ka ago andthe 1707 Hoei eruptions also exist.

After a dominance of sub-Plinian explosive eruptions of basalticmagma, widespread scoria falls, and lahar deposits between 100 and17 ka (Uesugi, 1990; Yamamoto et al., 2007) made volcanic fans on thelowlands of the volcano.

Voluminous lava flows dominated the volcanic activity between17 ka and 8 ka, but the insufficient number of measurements does notpermit an evaluation of the ejected volume during this period.

Explosive eruptions and lava flows from the summit and flank until1500 BCE (stage 3: see Fig. 5) followed a relatively mild activity be-tween 10,000 BCE, and 3500 BCE. It is during this period that the maingrowth of the volcano occurred due to voluminous ejections of magma;the size of the volcano was already as large as that in the present by3500 BCE. The current summit of Mt. Fuji is composed of rocks ejectedduring this period.

Mt. Fuji erupted explosively between 1500 BCE and 1300 BCE fromthe summit with ejections of scoria and pyroclastic flows (e.g.,Yamamoto et al., 2005a). One of the most notable ejecta is the Zuna-sawa deposit, ejected around 1300 BCE from the eastern flank, where itis distributed (e.g., Machida, 1977; Yamamoto et al., 2005b). The Zu-nasawa deposit contains rocks with SiO2 content of up to 70%, similarto the scoria ejected by the Hoei eruption.

The debris deposit associated with a flank collapse in the easternflank around 900 BCE cover 53 km2 with a volume of 1.05 km3 (Miyajiet al., 2004; Miyaji, 2007). Whether a phreatic eruption or the shakingfrom an earthquake triggered the collapse is unknown.

The flank collapse 2.9 ka ago was followed by a series of summiteruptions, one of the most significant of which occurred 2.2 ka ago, asub-Plinian eruption with an eruptive volume of ∼0.5 km3 (Suzuki andFujii, 2010). The eruption 2.2 ka ago was the latest summit eruption of

Fig. 4. A schematic north-south cross section through Mt. Fuji. After Yoshimoto et al. (2010).

Fig. 5. (top) Cumulative volume of eruptive products of Mt. Fuji over the last11,000 years. (bottom) Cumulative volume of eruptive products over the last2200 years. After Miyaji (2007).

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Mt. Fuji.After this summit eruption in 2.2 ka, small-scale flank eruptions

occurred until the 8 th century, after which Mt. Fuji erupted at least tentimes in 781, 800–802, 864–866, 937, 999, 1033, 1083, 1435–1436,1511, and 1707 (Fig. 5). Dating of these eruptions is difficult, and thushistorical accounts and mapping of eruptive products are the only waysfor constraining the exact dates of these eruptions.

The 800–802 eruption ejected massive tephras from the north-western and northeastern flanks. Historical accounts suggest that Mt.Fuji might have erupted in 834–848, 853, 858, and 859 as well(Koyama, 1998a) but a more careful examination of the documents isnecessary to confirm the dates.

3.2.1. The 864–866 Jogan eruptionThe 864–866 Jogan eruption is one of the largest eruptions in last

2200 years with more than 1.4 km3 of lavas from vents aligned on thenorthwestern flank with a horizontal extent of ∼6 km. The lavas buriedmost of a lake that existed at that time. The interaction between thelava and lake water triggered a secondary phreatic eruption, generatingpillow lavas (Miyaji et al., 2006).

3.2.2. Eruptions between the Jogan and Hoei eruptionsThe 937 eruption was originated from three fissures aligned and

located on the northern flank between 1800 and 2900m above sealevel. Some lavas reached up to 17 km to the northeast from the vent(Fujita et al., 2002). Yamamoto et al. (2005b) suggested that the 937eruption was from the southern flank as well as the northern flank,although the volume of the eruptive product from the southern flank isestimated to be only 0.01 km3 compared with 0.06 km3 from thenorthern flank.

The 1033 eruption also originated from the northern and southernflanks (Yamamoto et al., 2005b). On the northern flank, a 3 km-longfissure between 2150 and 3450m above sea level and a vent at 2050mabove sea level were responsible for the eruption. Lavas flowednortheastward for up to 7 km from the vent (Fujita et al., 2002).

Details of the 1083 eruption are not well known, but Koyama(1998b) suggested that the eruption was explosive based on a historicalaccount that the eruption was heard in Kyoto, ∼270 km from Mt. Fuji.Details of the 1435–1436 and 1511 eruptions are not also well knownbut historical accounts suggest that lava effusion might have dominatedthe 1435–1436 eruption (Koyama, 1998b). The 1511 eruption might

Fig. 6. Isopach of the tephra ejected from the 1707 Hoei eruption. a) Location of Fuji Volcano. b) Reginal isopach of the total Hoei tephra. c) Local isopach. Solid dotsand stars indicate outcrops and locations where historical documents are available. Thickness is shown in centimeters. Squares indicate cities and villages; N, Narita;S, Sawara; E, Edo or present Tokyo; Y, Yokohama, H; Hiratsuka; Od, Odawara; O, Oyama; G, Gotemba; Sb, Subashiri; Sn, Susono; Sy, Suyama. After Miyaji et al.(2011).

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have originated from the northern flank (Koyama, 1998b).

3.2.3. The 1707 Hoei eruptionThe 1707 Hoei eruption, the most recent one, is one of the most

explosive eruptions in Mt. Fuji in historical time. The eruption startedon 16 December 1707, 49 days after the 1707 Hoei earthquake(M=8.7) occurred in the Nankai trough, southwest Japan. This tem-poral coincidence and static stress changes in Mt. Fuji by the Hoeiearthquake led Chesley et al. (2012) to suggest that the extensionalstress changes of about 0.1MPa by the Hoei earthquake might havetriggered the eruption. The Hoei eruption lasted for 16 days until 1January 1708.

The eruption has been reconstructed in detail by Miyaji et al.(2011). The total ejected volume is estimated to be 1.6 km3 with aVolcano Explosivity Index (Newhall and Self, 1982) of 5. The eruptionstarted by two energetic eruptive pulses with an ash column higher than20 km. The energetic pulses gave way to discrete sub-Plinian basalticeruptions before sustained activity with column heights of more than13 km, during which there were at least two heightened phases with

column heights of more than 16 km. A sudden process such as conduitcollapse, rather than a gradual process such as decompression of themagma chamber, halted the eruption.

The Hoei eruption accumulated more than a meter of ash within afew kilometers from the vent, and more than 100mm of ash accumu-lated 100 km away from the vent in the downwind direction (Fig. 6).The Japanese government predicts an economic loss of ∼2.5 trillionyen (or 25 billion US dollars) if a Hoei-type eruption would occur redtoday (Aramaki, 2007).

3.2.4. Modern activityWhile Mt. Fuji has not erupted since 1707, deep low-frequency

earthquakes have been persisting at least since the first seismic ob-servations in the 1980s (Kanjo et al., 1984; Ukawa, 2005). The numberof deep low-frequency earthquakes increased in 2000–2001 but thisunrest did not result in surficial expressions (Ukawa, 2005). The EastShizuoka earthquake (Mw 6.0) four days after the 2011 Tohoku-okiearthquake was located right beneath Mt. Fuji but did not trigger thevolcanic activity of Mt. Fuji. Also, the earthquake did not trigger any

Fig. 7. (a) Distribution of hypocenters around Mt.Fuji between 1 January 1995 and 31 December 2018with depths shallower than 30 km and M=1.0.Focal mechanisms are also shown. Focal mechanismsin red correspond to earthquakes with significantnumber aftershocks in 2011 and 2012. Large andsmall green triangles indicate the location of thesummit of Mt. Fuji and Hakone Volcano, respec-tively. (b) The cumulative number of earthquakes ofM≥ 1 between 1 January 1995 and 31 December2018. The earthquake rate is stationary except whenaftershocks of the East Shizuoka earthquake on 15March 2011 and a M=5.4 earthquake on 27January 2012 occurred. A significant increase ofseismicity in 2015 is due to elevated volcanic activityin Hakone Volcano (e.g., Mannen et al., 2018). (Forinterpretation of the references to colour in thisfigure legend, the reader is referred to the web ver-sion of this article.)

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deformation or increase in seismic activity around Mt. Fuji. (Fujitaet al., 2013). Fig. 7(a) denotes the distribution of hypocenters ofearthquakes shallower than 30 km between 1995 and 2018 with focalmechanisms. Seismic activity is not spatially uniform but concentratedto the east of Mt. Fuji. Aftershocks of the East Shizuoka earthquake andseismicity related to volcanic activity in Hakone Volcano, shown by asmall green triangle in Fig. 7(a), are also seen. Focal mechanisms arerather diverse, but they are dominated by thrust and strike-slip faultingwith compressional axes striking roughly northwest-southeast. Fig. 7(b)depicts the cumulative number of earthquakes exceeding M=1.0. Itdemonstrates that the seismicity is temporally stationary except whenaftershocks of the East Shizuoka earthquake and a M=5.4 earthquake

on 27 January 2012 occurred and when the Hakone Volcano was activein 2015 (e.g., Mannen et al., 2018).

4. Geophysical view of the dmagma plumbing system

The magma plumbing system of an active volcano can be inferredfrom both petrological and geophysical insights. Petrology can providethe information about the depth of magma reservoirs as well as thedecompression rate, but not about the horizontal extent of the magmareservoir. On the other hand, seismic and electromagnetic imaging candetect magma reservoirs as bodies of low seismic velocity and low re-sistivity, but the images provide no information on how the magmamigrated toward the surface.

4.1. Petrological and geochemical insights

The FeO*/MgO ratio of the volcanic products from Mt. Fuji is stableover time, leading Togashi and Takahashi (2007) to suggest that themagma reservoir of Mt. Fuji has been receiving magma more or lessconstantly over the last ∼100,000 years. Considering a high eruptionrate during that time (Tsukui et al., 1986), the rate of magma supply tothe magma reservoir is high. Togashi and Takahashi (2007) suggestedthat this magma supply does not allow magma to reside in the magmareservoir long enough to be differentiated, resulting in a dominance ofbasaltic rocks.

An investigation of volcanic products by Yoshimoto et al. (2004)and a melt inclusion study by Kaneko et al. (2010) of the Hoei eruptiondeposits suggests the existence of two magma reservoirs beneath Mt.Fuji, the deeper one being at ∼20 km and the shallower one at 8–9 kmbelow sea level (Fig. 8). Kaneko et al. (2010) proposed that magmas inthe deeper and shallower reservoir would be basaltic and felsic, re-spectively. An accumulation of magma in the conduit left behind byprevious eruptions forms the shallower magma reservoir. Differentia-tion over time makes the accumulated magma more felsic. This modelwith two magma reservoirs can explain why felsic eruptions sometimesoccur in a volcano dominated by basaltic rocks like Mt. Fuji, and thechronology of the 1707 Hoei eruption which started by silicic eruptionsfollowed by basaltic eruptions (Miyaji et al., 2011). The deeper magmareservoir is deeper than that of other volcanoes along the Izu-Bonin arcsuch as Izu-Oshima whose magma reservoir is at around 10 km (e.g.,Mikada et al., 1997). Fujii (2007) suggested that this deep magma re-servoir is produced because of the underplating of the Philippine Seaplate, making the crust thicker. (Fig. 9). Togashi and Takahashi (2007)also suggested the presence of a deep magma reservoir to explain theHoei explosive eruption. They suggested that, during the Hoei eruption,the magma rose up from the magma reservoir quickly enough not toallow time to degas. The Togashi and Takahashi (2007) model issomewhat different from Kaneko et al. (2010) because it does not re-quire the presence of a shallow magma reservoir.

Shibata et al. (2015) suggested from Sr and Nd isotope ratio that themagmas of Pre-Komitake (≥270–160 ka; Fig. 4) share a similar mantlesource with those of subsequent volcanoes, Komitake and Fuji (Fig. 4).They also argued, using the major element content data, that the Pre-Komitake magmas could have experienced fractionation at a pressure of≥1.2 GPa or ≥35 km, greater than that of subsequent magmas, ∼500MPa or ∼15 km. It may imply the existence of a fossil magma reservoirthat has been active during the Pre-Komitake era at ∼35 km beneathMt. Fuji.

Migration of magma during the eruption 2.2 ka ago, the latestsummit eruption of Mt. Fuji, has been reconstructed from groundmassmicrolite textures by Suzuki and Fujii (2010) who inferred that theeruption was preceded by a magma decompression at a rate of0.005–0.012MPa/s (Stage 1 of Fig. 10), which can be roughly trans-lated as a magma ascent rate of 0.17–0.40m/s when the density of thehost rock is assumed to be 3000 kg/m3. The earliest stage of the erup-tion involves widening of the vent, conduit, or both with an increasing

Fig. 8. A schematic model of the magma plumbing system of Mt. Fuji inferredfrom melt inclusions. The magma plumbing system consists of relatively deep(∼20 km) basaltic and shallow SiO2-rich magma reservoirs (∼8–9 km). AfterKaneko et al. (2010).

Fuji

10

20

30

40

50

Izu arc

Granitic rock

Depth

(km)

PHS

Gabbro

Peridotite

EU

Fig. 9. A schematic cross-section beneath Mt. Fuji and a volcano along the Izuarc, indicating that the location of granitic mid-crust controls the depth of themagma reservoir, shown in gray. The granitic mid-crust beneath Mt.Fuji isdeeper than the Izu arc because the crustal materials of the Izu arc underplatethe Eurasian plate, denoted as EU in the figure, through subduction of thePhilippine Sea plate, denoted as PHS in the figure. Modified from Fujii (2007).

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rate of magma decompression (Stage 2 in Fig. 10). The decompressionrate further increased up to 0.13–0.22MPa/s (Stage 3 in Fig. 10) withan increased eruption rate and decreasing outgassing rate. Variabledecompression rates of magma characterize the later stage (Stages 4and 5 in Fig. 10) because of a variable flow rate of magma between thecentral and marginal parts of the conduit. The eruption 2.2ka ago is alsocharacterized by a decrease of overpressure at the reservoir after themajor eruption in Stage 3. In the last stage, the magma velocity has aspatial gradient, with a low velocity at the margin and high at thecenter of the conduit. An overall increase of outgassing from the con-duit margin is inferred in this stage (Stage 5 in Fig. 10).

4.2. Seismic imaging

Seismic imaging has contributed to the delineation of the magmaplumbing system of Mt. Fuji. Lees and Ukawa (1992) found an extendedregion of low seismic velocities at depths of 20 km or deeper beneathMt. Fuji. Since the depth of low seismic velocities is consistent with thedepths of the magma reservoir inferred from petrology as describedabove, they were interpreted as evidence of a magma reservoir beneathMt. Fuji. However, the spatial resolution of their imagery is not goodenough to confirm the interpretation. Recent studies (e.g., Kamiya andKobayashi, 2007; Matsubara et al., 2008; Nakajima et al., 2009) alsofound similar low-velocity anomalies in their datasets, but the spatialresolution is still not good enough to delineate the magma plumbingsystem in detail.

Nakamichi et al. (2007) applied local seismic tomography to imagea seismic structure around Mt. Fuji from a densely deployed temporaryseismic network (Fig. 11). They found that low P-wave velocities andlow Vp/Vs ratios characterize the area around hypocenters of low-fre-quency earthquakes, interpreting the low-velocity zone as indicative ofthe presence of volatiles such as H2O or CO2. However, they failed toimage 20 km or deeper, where the magma reservoir is likely to exist.

Scattering attenuation investigated by Chung et al. (2009) foundthat the crust beneath Mt. Fuji is more inhomogeneous than that insurrounding regions; the mean free path of seismic waves around Mt.Fuji is about 1 km at 2–8 Hz, a typical value seen in active volcanoes.

Intrinsic attenuation in the crust beneath Mt. Fuji, however, is notsignificantly different from that in surrounding regions (Chung et al.,2009), indicating that partial melt beneath Mt. Fuji is not as abundantas that in hot spot volcanoes.

Kinoshita et al. (2015) used receiver functions to image the seismicstructure down to about 80 km. They found a low- velocity zone at13–26 km below Mt. Fuji, the bottom of which is characterized by asharp velocity contrast (Fig. 12). The low velocity likely marks amagma reservoir beneath Mt. Fuji. They also found that a velocitycontrast at 40–50 km associated with underplating of basaltic materials,which volcanic arcs ubiquitously host (e.g., Takahashi et al., 2009),disappears beneath Mt. Fuji. It might reflect a pathway of magma fromthe subducting Pacific plate. Also, a geochemical insight by Nakamuraet al. (2008) suggested that volcanic fluids in Mt. Fuji are dominantlyfed from the Pacific plate instead of the overriding Philippine Sea plate.These studies indicate that the magma of Mt. Fuji is fed from the Pacificplate through the region marked by a lack of velocity contrast at depthsof 40–50 km that Kinoshita et al. (2015) found.

A seismic exploration experiment with five active sources and 469temporary seismometers was conducted in 2003 (Oikawa et al., 2006;Tsutsui et al., 2007) to infer the seismic structure beneath Mt. Fuji inthe upper crust. The active sources and seismometers were linearlyaligned to delineate a two-dimensional seismic velocity structure acrossMt. Fuji. Tsutsui et al. (2007) found a reflector dipping to the southwestat depths of around 15 km to the northeast and 25 km to the southwest(Fig. 13). This reflector corresponds to the top of subducting PhilippineSea plate. They also identified a series of short and horizontal reflectorswith lengths of a few kilometers at depths 8–15 km (Fig. 13). One of thereflectors is located near the shallowest part of low-frequency earth-quakes (Nakamichi et al., 2004), so these reflectors probably reflectvelocity discontinuities due to the presence of volcanic materials.

4.3. Electromagnetic imaging

The seismic structure discussed so far can be compared with re-sistivity structure. Aizawa et al. (2004) derived the resistivity structurebeneath Mt. Fuji down to 50 km from a campaign-mode

Fig. 10. A schematic view of the evolution of the eruption 2.2 ka ago, the last summit eruption of Mt. Fuji as reconstructed from groundmass microlite textures. Theearlier and later stages are shown in the left and right panels, respectively. After Suzuki and Fujii (2010).

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electromagnetic survey. A prominent feature derived from their study isa high resistivity body corresponding to the subduction of the Phi-lippine Sea plate (R1 in Fig. 14) which is ubiquitous in subductionzones. Another prominent feature is a low resistivity body below depthswhere low-frequency earthquakes occur. Although the spatial resolu-tion is not good enough, the low resistivity they found might corre-spond to the magma reservoir or magma pathway discussed byKinoshita et al. (2015). A more sophisticated analysis by Aizawa et al.(2016) shows that the low resistivity region extends up to a depth ofabout 7 km with a slight offset from the summit to the southwest(Fig. 15). This low resistivity body roughly corresponds to the

hypocenter of the East Shizuoka earthquake (Mw6.0) on 15 March 2011,four days after the 2011 Tohoku-oki earthquake. Aizawa et al. (2016)combined this resistivity structure and isotopic properties of ground-water in the area to interpret that the Mw 6.0 earthquake was triggeredwithin a fracture zone through which magmatic gases penetrate.

Another electromagnetic survey revealed that there is an area re-presented by low resistivity at the shallowest level, 500–2000m abovesea level (Fig. 16; Aizawa et al., 2005). This low resistivity is inter-preted as a confined hydrothermal system with a spatial extent of a fewkilometers rather than spreading over the whole edifice. Aizawa et al.(2005) suggested that the confined hydrothermal system resulted from

Fig. 11. (a) Distribution of epicenters (gray dots) and grid locations (open red squares) of the inversion by Nakamichi et al. (2007). Spacing of the open red squaresserves as a proxy of the spatial resolution of the seismic tomography. Blue lines A–A' and B–B′ show the cross sections in (b)–(g). (b) P-wave velocities, (c) S-wavevelocities, and (d) Vp/Vs ratio along the profile A–A′ in (a). The red arrow in (b) indicates the location of Mt. Fuji. The contour intervals for P and S wave velocities are0.5 km/s and 0.25 km/s, respectively. Black and red dots represent hypocenters of tectonic and deep low-frequency earthquakes, respectively. Note that velocities aregiven only in areas where the resolution is sufficiently high. (e)(f)(g) Similar to (b)(c)(d) but along the B–B′ profile in (a). The thick white line shows the location of areflector inferred by Tsumura et al. (1993). Modified from Nakamichi et al. (2007). (For interpretation of the references to colour in this figure legend, the reader isreferred to the web version of this article.)

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the limited circulation of hydrothermal fluids beneath Mt. Fuji, con-sistent with a lack of fumaroles, shallowest seismicity, and natural hotspring in and around Mt. Fuji.

5. Geophysical monitoring of Mt. Fuji

Mt. Fuji has been monitored most extensively by seismic methodssince the 1980s when low-frequency earthquakes were observed for thefirst time there (e.g., Kanjo et al., 1984). Enhancement of seismic net-work in the 1990s allowed us to investigate details of the low-frequencyearthquakes. Ukawa (2005) compiled the cumulative number ofearthquakes and wave energy generated by the low-frequency

earthquakes between 1980 and 2004 to indicate that both number andradiated energy of low-frequency earthquakes are more or less constantover time except when a swarm of low-frequency earthquakes wasobserved between 2000 and 2001 (Fig. 17).

Ukawa (2005) also relocated low-frequency earthquakes since the1980s to show that they are concentrated a few kilometers to thenortheast of the summit with depths around 15 km (Fig. 18). Nakamichiet al. (2004) focused on more recent low-frequency earthquakes be-tween 1998 and 2003, leading to a similar conclusion (Fig. 19). Fur-thermore, they found that the swarm seismicity aligns along a linestriking from northwest to southeast, consistent with regional stressfield. This seismicity suggests that the generation of low-frequency

Fig. 12. Cross sections of receiver function amplitude with a cut off frequency of 1.0 Hz along eleven lines in the upper left panel. Lines A, B, C, and D are denoted inblue and lines a, b, c, d, e, f, and g are denoted in red, respectively. Red indicates a velocity boundary, the bottom of which has higher velocity, and blue indicates viceversa. Gray dots and white circles in each panel are hypocenters with a magnitude larger than 0.1 between 2002 and 2005. White circles represent low-frequencyearthquakes. Pink circles represent hypocenters of low-frequency earthquakes relocated by Nakamichi et al. (2007). Green triangles show the location of the summitof Mt. Fuji. Black solid lines denote velocity boundaries from receiver functions inferred by Kinoshita et al. (2015). White arrows indicate the gap in the velocityboundary inferred by Kinoshita et al. (2015). Modified from Kinoshita et al. (2015). (For interpretation of the references to colour in this figure legend, the reader isreferred to the web version of this article.)

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earthquakes beneath Mt. Fuji might be related to dike intrusion at depth(Nakamichi et al., 2004).

Comparing these earthquake locations with seismic velocities de-rived from seismic tomography indicates that the hypocenters of low-frequency earthquakes are characterized by low P-wave velocities andhigh Vp/Vs ratios (Nakamichi et al., 2007; Fig. 11). This led Nakamichiet al. (2007) to suggest that volatiles such as supercritical H2O or CO2,rather than partial melt of magmas, are responsible for generating thelow-frequency earthquakes.

Mt. Fuji is now monitored by more than 20 seismic stations, many ofwhich are broadband sensors, with five and 18 seismic stations withinfive and 15 km from the summit, respectively. The most notableearthquakes recorded with the current seismic network are probablythe 2011 Tohoku-oki earthquake (Mw=9.0) and the East Shizuokaearthquake (Mw=6.0) that occurred near Mt. Fuji 4 days after theTohoku-oki earthquake. Geodetic data and aftershock distribution showthat the East Shizuoka earthquake is an earthquake with a left-lateralslip with some thrust component on a fault striking NNE-SSW (Fujitaet al., 2013; Fig. 20). The static stress change induced by the earthquakeis on the order of 0.1–1MPa at the magma reservoir of Mt. Fuji, largerthan that due to the Tohoku-oki earthquake, which was0.001–0.01MPa (Fujita et al., 2013).

Although these earthquakes did not trigger any volcanic activity,

they changed seismic velocities. Brenguier et al. (2014) inferred thatthe Tohoku-oki earthquake reduced the seismic velocity of Mt. Fuji atdepths shallower than ∼10 km by about 0.1%, which is larger thansurrounding areas. They also found that velocity changes of Mt. Fuji areparticularly susceptible to either static or dynamic stress changes as inother volcanic regions. The cause of this heterogeneous susceptibility isnot understood yet. Araragi et al. (personal communication) recentlyfound that the East Shizuoka earthquake also resulted in a velocityreduction. Comparing the spatial distribution of the velocity drops dueto the Tohoku-oki and East Shizuoka earthquakes will gain insights intothe mechanics of seismic velocity changes induced by static and dy-namic stress changes.

Mt. Fuji has not been only monitored by seismometers, but also bygeodetic instruments such as Global Navigation Satellite System (GNSS)and tiltmeters. Fig. 21 depicts the distribution of GNSS sites. The GNSSmeasurements revealed an expansion of the volcano from late 2005 to2010 with a total extensional strain of about 2× 10−6 (Harada et al.,2010). The observed deformation, however, did not accompany anyseismic activity. Tiltmeters did not record any signals associated withthis expansion because it is too slow to be detected by tiltmeters.However, they would be able to record signals if the deformation wouldhas a shorter timescale.

6. Recommendations for further understanding

Previous geological and geophysical studies have revealed muchabout how Mt. Fuji works, but our understanding is not comprehensiveenough to forecast the time and style of the next eruption. Here wemake some suggestion that might lead to better understanding of Mt.Fuji. It starts from how to forecast the location of the future vents(Section 6.1). We then discuss how to forecast the timing, style, and sizeof the next eruption (Sections 6.2 and 6.3). Finally, we try to suggestfuture directions in Section 6.4 to address research questions specific tounderstand the volcanism of Mt. Fuji.

6.1. Location of future vents

Since Mt. Fuji has exclusively erupted from its flanks over the last2200 years, it is important to assess the location of the next eruption notonly from a scientific but also from a practical viewpoint. A reasonableway to assess the location is to assume that since the stress state of avolcano does not change much over time, the next eruption will occurmore likely at a previous vent. Spatial distribution of previous fissureeruptions compiled by Takada et al. (2007) indicates that the fissures

Fig. 13. Spatial distribution of seismic reflectors identified by Tsutsuiet al. (2007). Labels j, g, and m correspond to the upper surface of thesubducting Philippine Sea plate. Labels, a, b, c, d, e, and f correspondto reflectors that are probably due to the presence of volcanic fluids.Solid ellipsoids represent the location of mid-crustal low-frequencyearthquakes (MLF; Nakamichi et al., 2004). S1, S2, S3, S4, and K1represent the location of active sources. K and M denote layersbounded by solid and broken lines and defined by Oikawa et al.(2006).FJF, SKF, and SGF denote the location of Fujigawa, Shibakawa,and Agoyama faults. After Tsutsui et al. (2007).

Fig. 14. A two-dimensional resistivity structure beneath Mt. Fuji. Black dotsrepresent hypocenters between 1998 and 2002. Starts indicate hypocenters oflow-frequency earthquakes. After Aizawa et al. (2004).

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are distributed radially around the summit and distributed more on thenorthwestern and southeastern flanks with fissures striking northwest-southeast (Fig. 22). This distribution is consistent with the notion thatthe stress field around Mt. Fuji can be represented by a combination of aregional stress field with northwest-southeast compression and a local

stress field generated by the loading of Mt. Fuji itself (e.g., Ukawa,1991; Araragi et al., 2015). It qualitatively suggests that the location ofthe next eruption will more likely be on the northwestern or

Fig. 15. (a) Plan view of the resistivity distribution around Mt. Fuji at 1, 3, 6, and 10 km below sea level. Areas where reliable resistivity was not obtained are maskedby black. Black dots represent where the magnetotelluric measurements were made. (b) Vertical view of resistivity across a profile A–A′ shown (a). Black circlesdenote hypocenters after the 2011 Tohoku-oki earthquake. Inverted triangles represent where the magnetotelluric measurements were made. After Aizawa et al.(2016).

Fig. 16. Two-dimensional shallow resistivity structure beneath Mt. Fuji. AfterAizawa et al. (2005).

Fig. 17. Cumulative number of the DLF events (dotted curve) and cumulativewave energy (solid line) between 1980 and 2004. After Ukawa (2005).

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southeastern flank.Then how can we assess the vent opening probability more quan-

titatively? A number of previous studies have proposed methods toinvestigate spatial distribution of the vent opening probability in aquantitative way (e.g., Marti and Felpeto, 2010; Connor et al., 2012;Cappello et al., 2012; Selva et al., 2012) with a number of applications(e.g, Del Negro et al., 2013; Cappello et al., 2013, 2015; Bevilacquaet al., 2015; Tadini et al., 2017a, 2017b). While these methods arevariable in mathematical details, most of the studies assess the ventopening probability by assuming that the next vent opening is mostlikely located around preexisting geological structures such as vents,faults, or fractures. In the case of Mt. Fuji, the spatial distribution ofvent opening probability can be assessed from the spatial distribution ofvents of previous eruptions (Takada et al., 2007; Fig. 22). As the am-bient stress field around Mt. Fuji is highly anisotropic (Ukawa, 1991:Araragi et al., 2015), an improvement of the methodology to take theambient stress field into account might be necessary to better assess thevent opening probability.

Vent locations in Mt. Fuji are, in fact, temporally variable (e.g.,Takada et al., 2007). They started to be removed from the summit sinceabout 2000 BCE with the farthest vent located at approximately

13.5 km from the summit in about 1500 BCE. These flank eruptionswere followed by eruptions around the summit by 1000 BCE. Vent lo-cations became far removed from the summit once again, with vents asfar as 13.5 km in 800–900 CE. They became contained within ∼6 km inaround 1000 CE (Takada et al., 2007). Takada (1997, 1999) explainedthis variability as resulting from stress perturbation due to a series ofdike intrusions during the episodes. Taking this temporal variability ofvent locations into account will further refine the forecast of the loca-tion of the next eruption, and so a more quantitative assessment is re-quired to precisely understand the current state of the stress beneathMt. Fuji, leading to a more sophisticated forecast of the location of thenext eruption.

6.2. Style of the next eruption

It is important to assess whether the next eruption is effusive orexplosive not only from a scientific but also a practical point of viewbecause effusive and explosive eruptions cause different hazards (e.g.,Schmincke, 2004; Parfitt and Wilson, 2008). While volcanic productsfrom Mt. Fujiare dominated by basaltic rocks, previous records showthat the volcano has experienced both effusive and explosive eruptions

Fig. 18. Distribution of seismic stations (as of 2001). Numbers inparentheses represent station corrections for P-wave and S-wave arri-vals, where positive numbers indicate that the observed arrivals aresystematically late. (b) Distribution of hypocenters of low-frequencyearthquakes since 1987. Only earthquakes with reliable locations werechosen. Hypocenters in three intervals are shown in different colors;green for those between 1987 and March 1995; blue for those betweenApril 1995 and July 2000; red for those between August 2000 and May2001. (c) Distribution of hypocenters of deep low-frequency earth-quakes considering station corrections. As in (b), only hypocenterswith good quality were chosen. Dashed lines indicate boundaries ofprefectures. The topographic contour interval in (b) and (c) is 300m.After Ukawa (2005). (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of thisarticle.)

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with significant hazards from both types of eruptions, as discussed inSection 3. It is difficult to forecast the style of the next eruption becausevarious factors such as degassing rate, discharge rate, composition, orvolatile content of magma control the eruption style (e.g., Kozono et al.,2013). Volcano monitoring, however, could help forecast the style be-cause whether an eruption is explosive or effusive depends on magmadischarge rate, thus potentially on the supply rate of magma (e.g.,Kozono et al., 2013) that can be assessed by geodetic measurements.

It is also important to assess the possible volcanic hazards from the

eruptions. There are a number of sophisticated simulations of the lavaflows which take topography and temperature-dependent rheology oflava into account (e.g., Crisci et al., 2004; Vicari et al., 2007; Connoret al., 2012; Kelfoun and Vargas, 2016; Dietterich et al., 2017 and re-ferences therein), pyroclastic density currents (e.g., Dufek, 2016;Gueugneau et al., 2017; Dioguardi and Mele, 2018, and referencestherein) and the dispersion of volcanic ash (e.g., Costa et al., 2016;Suzuki et al., 2016, and references therein). These simulations indicatethat a probabilistic assessment of the location, style, or magnitude of an

Fig. 19. Distribution of deep low-frequency earthquakes between 1998 and 2003. (a) Map view of relocated hypocenters. The source mechanism of the largestearthquake with M 2.3 is also shown. (b) Cross-section A-A′ in (a). (c) Cross-section B-B′ in (a). After Nakamichi et al. (2004).

Fig. 20. A fault model of the 2011 East Shizuoka earthquake. A grayrectangle represents the modeled fault. Gray circles depict the after-shock distribution. Black and red vectors denote observed and calcu-lated displacements, respectively. After Fujita et al. (2013). (For in-terpretation of the references to colour in this figure legend, the readeris referred to the web version of this article.)

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eruption can lead to a probabilistic hazard assessment.

6.3. Timing and size of the next eruption

Mt. Fuji has been dormant for more than 300 years. This repose timeis anomalously long compared with the previous repose time in Mt.Fuji. We thus expect that the next eruption will occur soon, but it isimpossible to predict the precise time of it; previous records of erup-tions of Mt. Fuji suggest that the eruptions are neither time-predictablenor size-predictable (Fig. 5). Then, how does this long repose time af-fect the next eruption? A compilation of eruptions in Indonesia after1800 suggests that a longer repose time tends to lead to a more ex-plosive eruption (Bebbington, 2014). Although the maximum reposetime investigated by Bebbington (2014) is a little more than 100 years,in contrast to the current repose time of Mt. Fuji of more than300 years, extrapolation suggests that the next eruption of Mt. Fuji willmore likely be an explosive one. In addition to the statistical assess-ments, the current lack of degassing from the surface leads Togashi andTakahashi (2007) to suggest that the current magma of Mt. Fuji con-tains a large amount of volatiles. The exsolution of the volatiles wouldmake the next eruption explosive.

Seismic imaging seems to lack a large magma reservoir with hun-dreds of cubic kilometers in the crust and upper mantle (Nakamichiet al., 2007; Kinoshita et al., 2015; Figs. 11, 12) as seen in caldera-forming volcanoes like Yellowstone, western United States (e.g., Huanget al., 2015) or Toba, Indonesia (Jaxybulatov et al., 2014). The lack ofsuch large magma reservoirs is consistent with a general lack of largevolcanoes in stratovolcanoes (e.g., Lin et al., 2014; Kiser et al., 2016).Therefore it is reasonable to conclude that Mt. Fuji is not capable ofgenerating a catastrophic eruption with a volume of hundreds orthousands of cubic kilometers, consistent with a lack previous recordsof such eruptions there. However, considering that seismic imaging isnot capable of imaging smaller magma reservoirs, Mt. Fuji is capable ofgenerating smaller but still hazardous eruptions with a volume on theorder of up to cubic kilometers like the Jogan and Hoei eruptions.

An eruption of a longer repose time tends to be preceded by a longerrun-up time between the onset of activity and the eruption. A global

compilation by Passarelli and Brodsky (2012) shows that the run-uptime and repose time roughly have a linear relation, in which the run-up time after a repose time of 300 years is expected to be around100 days. Furthermore, the next eruption could be preceded by criseswithout an eruption well before the actual eruption. The next eruptionof Mt. Fuji should be then preceded by detectable unrest. Indeed, theHoei eruption was preceded by two weeks of intense seismicity (Tsuya,1955; Koyama, 1998b; Hayashi and Koyama, 2002; Miyashita et al.,2007). A compilation of seismic activity preceding eruptions in Mt. St.Helens, Bezymianny and Alsakan volcanoes show that more intenseseismic activity precedes an eruption after a longer repose time. Thelenet al. (2010) found the repose time and cumulative seismic momentroughly has a linear relation. They found that the 1980 Mt. St. Helens,western United States, eruption, after a dormancy of 123 years, and the1956 Bezymianny, Kamchatka, eruption, after a dormancy of about1000 years, were preceded by earthquakes with a cumulative momentmagnitude exceeding 6.0. Sizable earthquake will likely precede thenext eruption of Mt. Fuji. Indeed, many people felt earthquakes, someof which exceeded magnitude 4.0, before the Hoei eruption (Hayashiand Koyama, 2002).

6.4. Why is Mt. Fuji different from other volcanoes?

The recommendations described above are more or less applicableto volcanoes in general. In other words, vent location, time, size, andstyle of the next eruption need to be well assessed to better understandthe volcanism and forecast the next eruption of any volcanoes. Here wemake suggestion to better address research questions specific to Mt.Fuji, which are, as described in the Introduction, 1) why is Mt. Fujilarger than other volcanoes along the same arc?, 2) why has Mt. Fujidominantly ejected basaltic rocks?, 3) why has Mt. Fuji erupted invarious styles from effusive to explosive eruptions?, and 4) why has Mt.Fuji erupted both from the summit and flank?

Questions 1) and 2) are, in fact, interrelated. A high rate of magmasupply from depth makes Mt. Fuji large. Also, high rate of magmasupply does not allow magma to reside in the magma reservoir longenough to differentiate and make the ejected magma a more evolvedchemical composition like andesite or dacite (e.g., Togashi andTakahashi, 2007). Then why is the rate of magma supply of Mt. Fujimuch higher than other volcanoes along the same arc? Ichihara et al.(2017) hypothesized that a volcano along the Izu-Bonin arc on thePhilippine Sea plate (we hereby call it “Volcano X”) subducted to reachbeneath Mt. Fuji ∼100,000 years ago, after which the eruption rate ofMt. Fuji is 50–500 times larger than that of volcanoes along the samearc (Tsukui et al., 1986). Here we explain why this hypothesis can solvethe mysteries of Mt. Fuji as described above following Ichihara et al.(2017).

When Volcano X starts to subduct, the magma reservoir of VolcanoX is expanded because the vent of Volcano X becomes plugged. WhenVolcano X reaches the magma conduit of the original Mt. Fuji, thenmagma reservoirs of the two volcanoes merge to increase the volume ofmagma beneath Mt. Fuji. Both magmas originate from the Pacific plate,consistent with Nakamura et al. (2008) who showed that the fluid in themagma of Mt. Fuji is dominated by that from the Pacific plate. Themagma reservoir of Volcano X, is originally at a depth of ∼10 km be-fore subduction, but it gets deeper when it reaches beneath Mt. Fujibecause of subduction, consistent with the depth of the magma re-servoir inferred from petrological (Fujii, 2007; Kaneko et al., 2010) andseismological (e.g., Lees and Ukawa, 1992; Kinoshita et al., 2015)evidence.

A hypothesis proposed by Ichihara et al. (2017), as described above,seems to be consistent with many features Mt. Fuji has qualitatively. Aquantitative assessment of whether the hypothesis is plausible or not isrequired from thermo- and fluid-dynamic point of view. Also, it is de-sirable to detect the subducted Volcano X from seismic or electro-magnetic imaging to confirm the hypothesis.

Fig. 21. Distribution of GNSS sites. Squares and circles denote those operatedby Geospatial Information Authority and National Research Institute for EarthScience and Disaster Resilience, respectively.

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The mechanics of the Hoei eruption give insights into how to ad-dress Question 3). Kaneko et al. (2010) proposed that a mixture ofbasaltic magma intruded from a depth and differentiated silicic magmaat a shallower depth made the Hoei eruption explosive (Fig. 8). Ex-plosive eruptions of Mt. Fuji in the past (see, for example, Section 3.2)might have been triggered similarly. To confirm this hypothesis, meltinclusion studies to investigate the magma mixing during past eruptionsare required.

A transition between the summit and flank eruptions (Question 4)can be discussed in a general context. Takada (1997) found that manyvolcanoes change the location of their eruptions over time in which thelocation of flank eruptions converges toward the summit or the centralvolcano before the period of summit eruptions. The mechanics for thiscyclic pattern can be understood by considering the stress perturbationby each dike intrusion (Takada, 1997). A dike intrusion makes thesurrounding rock more compressive. This stress field leads to the nextintrusion taking place away from the previous intrusion. In otherwords, if a dike intrusion takes place away from the summit, the nextintrusion takes place closer to the summit. The location of dike intru-sions converges toward the summit after a series of intrusions. Takada(1997) suggested that viscoelastic relaxation of the host rock relaxes thestress field perturbed by dike intrusions, making an intrusion at the

same location as a previous intrusion possible after the stress changedue to the previous intrusion is relaxed.

Takada (1997) suggested that the duration of flank and summiteruption periods are controlled by the strain rate and the supply rate ofmagma, however, the factors controlling the durations are not clearlyunderstood. Previous records show that Mt. Fuji has repeated flank andsummit eruptions every ∼1000 years, where summit eruptions domi-nated between 1000 BCE and 1 CE and flank eruptions were dominatedbetween 1 CE and 1000 CE (see Fig. 7 of Takada, 1997). An extra-polation of this trend suggests that the summit eruptions dominatedbetween 1000 CE and 2000 CE and is now in a transition period fromthe summit to flank eruptions. However, this interpolation cannot bejustified because of the relative inactivity of Mt. Fuji after 1000 CE.

7. Summary

Mt. Fuji is a young volcano which started to grow only around400 ka ago. Rock chemistry suggests that it has been divided into a fewstages, the most recent of which started around 10 ka. The eruption ratewas high between 10 ka and 8 ka when the eruptive volume was morethan 30 km3 DRE only in ∼2000 years, compared with a total of a littlemore than 40 km3 in the last 10,000 years. Mt. Fuji was relatively

Fig. 22. Location of fissure eruptions after 15000 BCE. Red, yellow, green, blue lines denote eruptive fissures dated after 300 BCE, between 1500 BCE and 300,between the Kikai-Akahoha eruption (K-Ah; 7300 BCE) and 1700 BCE, and between 15,000 BCE and the Kikai-Akahoya eruption, respectively. After Takada et al.(2007). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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dormant between 8 ka and 5 ka after which it was reactivated.The eruptions of Mt. Fuji over the last 2000 years have exclusively

been from northwestern and southeastern flanks, consistent with theregional stress of northwest-southeast compression. Some vents arelocated radially with respect to the summit, consistent with an isotropicstress field near the summit due to the loading of the volcano. Thelargest eruptions during the last 2000 years include the 864 Jogan and1707 Hoei eruptions which ejected 2.1 km3 and 1.6 km3 of magma,respectively. The Jogan eruption mainly emitted basaltic lavas, whilethe Hoei eruption was an explosive eruption triggered by the intrusionof a basaltic magma into a dacitic magma chamber. The Hoei eruptionstarted 49 days after a nearby M∼8.5 earthquake so that the eruptionwas likely triggered by the change of static stress, dynamic stress, orboth, due to the M∼8.5 earthquake. Mt. Fuji has been dormant since1707, but low-frequency earthquakes have been observed at depthsaround 15 km. The activity of the low-frequency earthquakes becamehigh in 2000, but no associated surficial anomalies were observed. TheEast Shizuoka earthquake (Mw 6.0) right beneath Mt. Fuji on 15 March2011, four days after the 2011 Tohoku-oki earthquake, did not triggerany volcanic activity.

To understand the characteristics of Mt. Fuji, the magma plumbingsystem of Mt. Fuji has been studied intensively by geological and geo-physical methods. Geological considerations suggest that the magmareservoirs of Mt. Fuji are located at 20 km and 8–9 km beneath thevolcano (Kaneko et al., 2010). The depth of the magma reservoir at20 km is deeper than that in other volcanoes along the same arc becauseof the underplating of the Philippine Sea plate, resulting in an appar-ently thicker crust (Fujii, 2007). The shallower reservoir consists ofmore evolved magma, to which basaltic magma was injected, andsubsequently triggered the 1707 Hoei eruption (Kaneko et al., 2010).Seismic studies also suggest a magma reservoir at around 20 km, rightbeneath where low-frequency earthquakes occur (Nakamichi et al.,2007; Kinoshita et al., 2015). Electromagnetic studies suggest a con-ductive body at depths more than 20 km, which is likely to represent amagma reservoir (Aizawa et al., 2004). Seismic observations revealedthat low-frequency earthquakes in 2000 were aligned with a strike ofnorthwest-southeast a few kilometers to the northeast of the summit(Nakamichi et al., 2004; Ukawa, 2005).

For a better understanding of the Mt. Fuji magma plumbing systemand improved forecasting of the evolution of future eruptions, we needto combine geophysical and petrological insights about the location andproperties of the magma reservoir of Mt. Fuji. Geophysical insightsgained from seismic, geodetic, and electromagnetic measurements candetermine the location of the magma reservoir. However, these esti-mations have uncertainties. Petrological measurements do not provideany information on the horizontal location of the magma reservoir butcan constrain the depth of the magma reservoir with some uncertaintiesindependently from geophysical measurements. Also what is uniqueabout the petrological measurements is that they can assess the magmaascent rate, which helps assess the magma movement preceding aneruption. With this point of view, it is important to combine thesecomplementary measurements to gain more insights into the magmadynamics beneath Mt. Fuji during its activity to and better forecast aneruption.

Acknowledgments

This project was initiated as a field trip guide for The 3rdInternational Summer School of Earthquake Science “Monitoring phy-sical properties associated with tectonic processes” in September 2015organized by Earthquake Research Institute, The University of Tokyoand Southern California Earthquake Center and The 1st field camp ofAsian Consortium of Volcanology in November 2015. Detailed andconstructive reviews by Fidel Costa and three anonymous reviewerssubstantially improved the manuscript. We thank Richard Jordan forlanguage editing which also substantially improved the manuscript.

Some figures are created with Generic Mapping Tools (Wessel andSmith, 1998; Wessel et al., 2013).

References

Aizawa, K., Yoshimura, R., Oshiman, N., 2004. Splitting of the Philippine Sea Plate and amagma chamber beneath Mt. Fuji. Geophys. Res. Lett. 31, L09603. https://doi.org/10.1029/2004GL019477.

Aizawa, K., Yoshimura, R., Oshiman, N., Yamazaki, K., Uto, T., Ogawa, Y., Tank, S.B.,Kanda, W., Sakanaka, S., Furukawa, Y., Hashimoto, T., Uyeshima, M., Ogawa, T.,Shiozaki, I., Hurst, A.W., 2005. Hydrothermal system beneath Mt. Fuji volcano in-ferred from magnetotelurics and electric self-potential. Earth Planet. Sci. Lett. 235,343–355. https://doi.org/10.1016/j.epsl.2005.03.023.

Aizawa, K., Sumino, H., Uyeshima, M., Yamaya, Y., Hase, H., Takahashi, H.A., Takahashi,M., Kazahaya, K., Ohno, M., Rung-Arunwan, T., Ogawa, Y., 2016. Gas pathways andremotely triggered earthquakes beneath Mount Fuji, Japan. Geology 44, 127–130.https://doi.org/10.1130/G37313.1.

Arai, R., Iwasaki, T., 2015. Transition from collision to subduction and its relation to slabseismicity and plate coupling. Earth Planets Space 67, 76. https://doi.org/10.1186/s40623-015-0247-6.

Aramaki, S., 2007. Volcanic disaster mitigation maps of Fuji Volcano and overview ofmitigation programs. In: Aramaki, S. (Ed.), Fuji Volcano, Yamanashi Institute ofEnvironmental Sciences, pp. 451–475 (in Japanese with English abstract).

Araragi, K.R., Savage, M.K., Ohminato, T., Aoki, Y., 2015. Seismic anisotropy of the uppercrust around Mount Fuji, Japan. J. Geophys. Res. 120, 2739–2751. https://doi.org/10.1002/2014JB011554.

Argus, D.F., Gordon, R.G., Heflin, M.B., Ma, C., Eanes, R.J., Willis, P., Peltier, W.R., Owen,S.E., 2010. The angular velocities of the plates and the velocity of Earth's Centre fromspace geodesy. Geophys. J. Int. 180, 913–960. https://doi.org/10.1111/j.1365-246X.2009.04463.x.

Bebbington, M.S., 2014. Long-term forecasting of volcanic explosivity. Geophys. J. Int.197, 1500–1515. https://doi.org/10.1093/gji/ggu078.

Bevilacqua, A., Isaia, R., Neri, A., Vitale, S., Aspinall, W.P., Bisson, M., Fiandoli, F.,Baxter, P.J., Bertagnini, A., Esposti Ongaro, T., Iannuzzi, E., Pistolesi, M., Rosi, M.,2015. Quantifying volcanic hazard at Campi Flegrei caldera (Italy) with uncertaintyassessment: 1. Vent opening maps. J. Geophys. Res. Solid Earth 120, 2309–2329.https://doi.org/10.1002/2014JB011775.

Brenguier, F., Campillo, M., Takeda, T., Aoki, Y., Shapiro, N.M., Briand, X., Emoto, K.,Miyake, H., 2014. Mapping pressurized volcanic fluids from induced crustal seismicvelocity drops. Science 345, 80–82. https://doi.org/10.1126/science.1254073.

Cappello, A., Neri, M., Acocella, A., Gallo, G., Vicari, A., Del Negro, C., 2012. Spatial ventopening probability map of Etna volcano (Sicily, Italy). Bull. Volcanol. 74,2083–2094. https://doi.org/10.1007/s00445-012-0647-4.

Cappello, A., Bilotta, G., Neri, M., Del Negro, C., 2013. Probabilistic modeling of futurevolcanic eruptions at Mount Etna. J. Geophys. Res. Solid Earth 118, 1925–1935.https://doi.org/10.1002/jgrb.50190.

Cappello, A., Geshi, N., Neri, M., Del Negro, C., 2015. Lava flow hazards – an impedingthreat at Miyakejima volcano, Japan. J. Volcanol. Geotherm. Res. 308, 1–9. https://doi.org/10.1016/j.jvolgeores.2015.10.005.

Chesley, C., LaFemina, P.C., Puskas, C., Kobayashi, D., 2012. The 1707 Mw 8.7 Hoeiearthqukae triggered the largest historical eruption of Mt. Fuji. Geophys. Res. Lett.39, L24309. https://doi.org/10.1029/2012GL053868.

Chung, T.W., Lees, J.M., Yoshimoto, K., Fujita, E., Ukawa, M., 2009. Intrinsic and scat-tering attenuation of the Mt. Fuji Region, Japan. Geophys. J. Int. 177, 1366–1382.https://doi.org/10.1111/j.1365-246X.2009.04121.x.

Connor, L.J., Connor, C.B., Meliksetian, K., Savov, I., 2012. Probabilistic approach tomodeling lava flow inundation: a lava flow hazard assessment for a nuclear facility inArmenia. J. Appl. Volcanol. 1, 3. https://doi.org/10.1186/2191-5040-1-3.

Costa, A., Suzuki, Y.J., Cerminara, M., Devenish, B.J., Esposti Ongaro, T., Herzog, M., VanEaton, A.R., Denby, L.C., Bursik, M., de'Michieli Vitturi, M., Engwell, S., Neri, A.,Barsotti, S., Folch, A., Macedonio, G., Girault, F., Carazzo, G., Tait, S., Kaminski, E.,Mastin, L.G., Woodhouse, M.J., Phillips, J.C., Hogg, A.J., Degruyter, W., Bonadonna,C., 2016. Results of the eruptive column model inter-comparison study. J. Volcanol.Geotherm. Res. 325, 2–25. https://doi.org/10.1016/j.jvolgeores.2016.01.017.

Crisci, G.M., Rongo, R., Di Gregorio, S., Spataro, W., 2004. The simulation model SCIARA:the 1991 and 2001 lava flows at Mount Etna. J. Volcanol. Geotherm. Res. 132,253–267. https://doi.org/10.1016/S0377-0273(03)00349-4.

Del Negro, C., Cappello, A., Neri, M., Bilotta, G., Herault, A., Ganci, G., 2013. Lava flowhazards at Mount Etna: constraints imposed by eruptive history and numerical si-mulations. Sci. Rep. 3, 3493. https://doi.org/10.1038/srep03493.

Dietterich, H.R., Lev, E., Chen, J., Richardson, J.A., Cashman, K.V., 2017. Benchmarkingcomputational fluid dynamics models of lava flow simulation for hazard assessment,forecasting, and risk management. J. Appl. Volcanol. 6, 9. https://doi.org/10.1186/s13617-017-0061-x.

Dioguardi, F., Mele, D., 2018. PYFLOW_2.0: a computer program for calculating flowproperties and impact parameters of past dilute pyroclastic density currents based onfield data. Bull. Volcanol. 80, 28. https://doi.org/10.1007/s00445-017-1191-z.

Dufek, J., 2016. The fluid mechanics of pyroclastic density currents. Annu. Rev. FluidMech. 48, 459–485. https://doi.org/10.1146/annurev-fluid-122414-034252.

Fujii, T., 2007. Magmatology of Fuji volcano. In: Aramaki, S. (Ed.), Fuji Volcano.Yamanashi Institute of Environmental Sciences, pp. 233–244 (in Japanese withEnglish abstract).

Fujita, K., Suzuki, Y., Yoshino, N., Kitagawa, J., Koyama, M., Miyaji, N., Shimoyama, T.,Anyoji, N., 2002. Stratigraphy of the Kenmarubi lavas and associated deposits in the

Y. Aoki, et al. Earth-Science Reviews 194 (2019) 264–282

280

north slope of Fuji Volcacno. In: Japan. Japan Earth and Planetary Science JointMeeting, Abstract V032–P021.

Fujita, E., Kozono, T., Ueda, H., Kohno, Y., Yoshioka, S., Toda, N., Kikuchi, A., Ida, Y.,2013. Stress field change around the Mount Fuji volcano magma system caused bythe Tohoku megathrust earthquake, Japan. Bull. Volcanol. 75, 679. https://doi.org/10.1007/s00445-012-0679-9.

Gueugneau, V., Kelfoun, K., Roche, O., Chupin, L., 2017. Effects of pore pressure inpyroclastic flows: Numerical simulation and experimental validation. Geophys. Res.Lett. 44, 2194–2202. https://doi.org/10.1002/2017GL072591.

Hayashi, Y., Koyama, M., 2002. Estimated magnitudes of the earthquakes preceding the1707 Hoei eruption of Fuji Volcano. Historical Earthquakes 18, 127–132 (in Japanesewith English abstract).

Hirose, F., Nakajima, J., Hasegawa, A., 2008. Three-dimensional seismic velocity struc-ture and configuration of the Philippine Sea slab in southwestern Japan estimated bydouble-difference tomography. J. Geophys. Res. 113, B09315. https://doi.org/10.1029/2007JB005274.

Huang, H.-H., Lin, F.-C., Schmandt, B., Farrell, J., Smith, R.B., Tsai, V.C., 2015. TheYellowstone magmatic system from the mantle plume to the upper crust. Science 348,773–777. https://doi.org/10.1126/science.aaa5648.

Ichihara, M., Adam, C., VIdal, V., Grosse, P., Mibe, K., Orihashi, Y., 2017. Dots-and-linesapproach to subduction volcanism and tectonics. J. Geogr. 126, 181–193 (inJapanese with English abstract).

Ida, Y., 2009. Dependence of volcanic systems on tectonic stress conditions as revealed byfeatures of volcanoes near Izu peninsula, Japan. J. Volcanol. Geotherm. Res. 181,35–46. https://doi.org/10.1016/j.jvolgeores.2008.12.006.

Iidaka, T., Mizoue, M., Nakamura, I., Tsukuda, T., Sakai, K., Kobayasi, M., Haneda, T.,Hashimoto, S., 1990. The upper boundary of the Philippine Sea plate beneath thewestern Kanto region estimated from S–P-converted wave. Tectonophysics 179,321–326. https://doi.org/10.1016/0040-1951(90)90297-L.

Ishida, M., 1992. Geometry and relative motion of the Philippine Sea plate and Pacificplate beneath the Kanto-Tokai district, Japan. J. Geophys. Res. 97, 489–513. https://doi.org/10.1029/91JB02567.

Jaxybulatov, K., Shapiro, N.M., Koulakov, I., Mordret, A., Landès, M., Sens-Schönfelder,C., 2014. A large magmatic sill complex beneath the Toba caldera. Science 346,617–620. https://doi.org/10.1126/science.1258582.

Kamiya, S., Kobayashi, Y., 2007. Thickness variation of the descending Philippine Seaslab and its relationship to volcanism beneath the Kanto-Tokai district, Central Japan.J. Geophys. Res. 112, B06302. https://doi.org/10.1029/2005JB004219.

Kaneko, T., Yasuda, A., Fujii, T., Yoshimoto, M., 2010. Crypto-magma chambers beneathMt. Fuji. J. Volcanol. Geotherm. Res. 193, 161–170. https://doi.org/10.1016/j.jvolgeores.2010.04.002.

Kanjo, K., Karakama, I., Matsu'ura, R.S., 1984. Seismic activities of Mt. Fuji region de-tected by continuous observation of micro-earthquakes. J. Phys. Earth 32, 463–468.https://doi.org/10.4294/jpe1952.32.463.

Kelfoun, K., Vargas, S.V., 2016. VolcFlow capabilities and potential development for thesimulation of lava flows. Geol. Soc. Lond. Spec. Publ. 426, 337–343. https://doi.org/10.1144/SP426.8.

Kinoshita, S.M., Igarashi, T., Aoki, Y., Takeo, M., 2015. Imaging crust and upper mantlebeneath Mount Fuji, Japan, by receiver functions. J. Geophys. Res. 120, 3240–3254.https://doi.org/10.1002/2014JB011522.

Kiser, E., Palomeras, I., Levander, A., Zelt, C., Harder, S., Schmandt, B., Hansen, S.,Creager, K., Ulberg, C., 2016. Magma reservoirs from the upper crust to the Mohoinferred from high-resolution Vp and Vs models beneath Mount St. Helens,Washington State, USA. Geology 44, 411–414. https://doi.org/10.1130/G37591.1.

Koyama, M., 1998a. Reevaluation of the 800–802 A.D. eruption of Fuji Volcano, Japan,and its Influence on the ancient traffic network around the volcano, based on eruptivedeposits and historical records. Bull. Volcanol. Soc. Jpn. 43, 349–371 (in Japanesewith English abstract).

Koyama, M., 1998b. Reevaluation of the eruptive history of Fuji Volcano, Japan, mainlybased on historical documents. Bull. Volcanol. Soc. Jpn. 43, 323–347 (in Japanesewith English abstract).

Kozono, T., Ueda, H., Ozawa, T., Koyaguchi, T., Fujita, E., Tomiya, A., Suzuki, Y.J., 2013.Magma discharge variations during the 2011 eruptions of Shinmoe-dake volcano,Japan, revealed by geodetic and satellite observations. Bull. Volcanol. 75, 695.https://doi.org/10.1007/s00445-013-0695-4.

Lees, J.M., Ukawa, M., 1992. The South Fossa Magna, Japan, revealed by high-resolutionP- and S-wave travel time tomography. Tectonophysics 208, 377–396. https://doi.org/10.1016/0040-1951(92)90436-A.

Lin, G., Shearer, P.M., Matoza, R.S., Okubo, P.G., Amelung, F., 2014. Three-dimensionalseismic velocity structure of Mauna Loa and Kilauea volcanoes in Hawaii from localseismic tomography. J. Geophys. Res. Solid Earth 119, 4377–4392. https://doi.org/10.1002/2013JB010820.

Machida, H., 1977. Tephra Talks: Natural History of Volcanoes and Plains. Soju Shobo,pp. 324 (in Japanese).

Mannen, K., Yukutake, Y., Kikugawa, G., Harada, M., Itadera, K., Takenaka, J., 2018.Chronology of the 2015 eruption of Hakone volcano, Japan: geological background,mechanism of volcanic unrest and disaster mitigation measures during the crisis.Earth Planet. Space 70, 68. https://doi.org/10.1186/s40623-018-0844-2.

Marti, J., Felpeto, A., 2010. Methodology for the computation of volcanic susceptibility:An example for mafic and felsic eruption on Tenerife (Canary Islands). J. Volcanol.Geotherm. Res. 195, 69–77. https://doi.org/10.1016/j.jvolgeores.2010.06.008.

Matsubara, M., Obara, K., Kasahara, K., 2008. Three-dimensional P- and S-wave velocitystructures beneath the Japan Islands obtained by high-density seismic stations byseismic tomography. Tectonophysics 454, 86–103. https://doi.org/10.1016/j.tecto.2008.04.016.

Mikada, H., Watanabe, H., Sakashita, S., 1997. Evidence for subsurface magma bodies

beneath Izu-Oshima volcano inferred from a seismic scattering analysis and possibleinterpretation of the magma plumbing system of the 1986 eruptive activity. Phys.Earth Planet. Inter. 104, 257–269. https://doi.org/10.1016/S0031-9201(97)00060-5.

Miyaji, N., 2007. Eruptive history, eruption rate and scale of eruptions for the FujiVolcano during the last 11,000 years. In: Aramaki, S. (Ed.), Fuji Volcano. YamanashiInstitute of Environmental Sciences, pp. 79–95 (in Japanese with English abstract).

Miyaji, N., Endo, K., Togashi, S., Uesugi, Y., 1992. Tephrochronological history of Mt.Fuji. In: Kato, H., Noro, H. (Eds.), 29 th IGC Field Trip Guide Book. vol. 4. Volcanoesand geothermal fields of Japan, Geol. Surv. Jpn, Tsukuba, pp. 75–109.

Miyaji, N., Togashi, S., Chiba, T., 2004. A large-scale collapse event at the eastern slope ofFuji volcano about 2900 years ago. Bull. Volcanol. Soc. Jpn. 49, 237–248 (inJapanese with English abstract).

Miyaji, N., Kamiji, M., Suzuki, S., Chiba, T., Endo, K., Takahashi, M., Murata, T.,Watanabe, Y., 2006. Phreatic explosion deposit formed by the inflow of Aokigaharalava flows at AD 864 to the lake Shoji of Fuji volcano. In: Japan Geoscience UnionMeeting, Abstract V101-010.

Miyaji, N., Kan'no, A., Kanamaru, T., Mannen, K., 2011. High-resolution reconstruction ofthe Hoei eruption (AD 1707) of Fuji volcano. Japan. J. Volcanol. Geotherm. Res. 207,113–129. https://doi.org/10.1016/j.jjvolgeores.2011.06.013.

Miyashita, M., Churei, M., Uhira, K., Hayashi, Y., Katayama, H., Fujii, T., Murakami, M.,Ukawa, M., Shirato, S., Yamasato, H., Yokota, T., 2007. Surveillance of activity of Fujivolcano, Japan – scenario of the 1707 Hoei Eruption and volcano information. In:Aramaki, S. (Ed.), Fuji Volcano. Yamanashi Institute of Environmental Sciences, pp.441–449 (in Japanese with English abstract).

Nakajima, J., Hirose, F., Hasegawa, A., 2009. Seismotectonics beneath the Tokyo me-tropolitan area, Japan: effect of slab-slab contact and overlap of seismicity. J.Geophys. Res. 114, B08309. https://doi.org/10.1029/2008JB00610.

Nakamichi, H., Ukawa, M., Sakai, S., 2004. Precise hypocenter locations of midcrustallow-frequency earthquakes beneath Mt. Fuji, Japan. Earth Planets Space 56, e37–e40.https://doi.org/10.1186/BF03352542.

Nakamichi, H., Watanabe, H., Ohminato, T., 2007. Three-dimensional velocity structuresof Mount Fuji and the South Fossa Magna, Central Japan. J. Geophys. Res. 112,B03310. https://doi.org/10.1029/2005JB004161.

Nakamura, H., Iwamori, H., Kimura, J.-I., 2008. Geochemical evidence for enhanced fluidflux due to overlapping subducting plates. Nat. Geosci. 1, 380–384. https://doi.org/10.1038/ngeo200.

Newhall, C.G., Self, S., 1982. The Volcanic Explosivity Index (VEI): an estimate of ex-plosive magnitude for historical volcanism. J. Geophys. Res. 87, 1231–1238. https://doi.org/10.1029/JC087iC02p01231.

Oikawa, J., et al., 2006. Seismic exploration at Fuji volcano with active sources – theoutline of the experiment and the arrival time data. Bull. Earthq. Res. Inst., Univ.Tokyo 81, 71–94.

Parfitt, E.A., Wilson, L., 2008. Fundamentals of Physical Volcanology. Blackwell, pp. 230.Passarelli, L., Brodsky, E.E., 2012. The correlation between run-up and repose time of

volcanic eruptions. Geophys. J. Int. 188, 1025–1045. https://doi.org/10.1111/j.1365-246X.2011.05298.x.

Schmincke, H.-U., 2004. Volcanism. Springer, pp. 324.Selva, J., Orsi, G., Di Vito, M.A., Marzocchi, W., Sandri, L., 2012. Probability hazard map

for future vent opening at the Campi Flegrei caldera, Italy. Bull. Volcanol. 74,497–510.

Shibata, T., Yoshimoto, M., Fujii, T., Nakada, S., 2015. Geochemical and Sr-Nd isotopiccharacteristics of Quaternary magmas from the Pre-Komitake volcano. J. Mineral.Petrol. Sci. 110, 65–70. https://doi.org/10.2465/jmps.141022e.

Suzuki, Y., Fujii, T., 2010. Effect of syneruptive decompression path on shifting intensityin basaltic sub-Plinian eruption: Implication of microlites in Yufune-2 scoria from Fujivolcano, Japan. J. Volcanol. Geotherm. Res. 198, 158–176. https://doi.org/10.1016/j.jvolgeores.2010.08.020.

Suzuki, Y.J., Costa, A., Cerminara, M., Esposti Ongaro, T., Herzog, M., Van Eaton, A.R.,Denby, L.C., 2016. Inter-comparison of three-dimensional models of volcanic plumes.J. Volcanol. Geotherm. Res. 326, 26–42. https://doi.org/10.1016/j.jvolgeores.2016.06.011.

Tadini, A., Bisson, M., Neri, A., Cioni, R., Bevilaqua, A., Aspinall, W.P., 2017a. Assessingfuture vent opening locations at the Somma-Vesuvio volcanic complex: 1. A newinformation geodetabase with uncertainty characterizations. J. Geophys. Res. SolidEarth 122, 4336–4356. https://doi.org/10.1002/2016JB013858.

Tadini, A., Bevilacqua, A., Neri, A., Cioni, R., Aspinall, W.P., Bisson, M., Isaia, R.,Mazzarini, F., Valentine, G.A., Vitale, S., Baxter, P.J., Bertagnini, A., Cerminara, M.,de Michieli Vitturi, M., Di Roberto, A., Engwell, S., Esposti Ongaro, T., Fiandoli, F.,Pistolesi, M., 2017b. Assessing future vent opening locations at the Somma-Vesuviovolcanic complex: 2. Probability maps of the caldera for a future Plinian/sub-Plinianevent with uncertainty quantification. J. Geophys. Res. Solid Earth 122, 4357–4376.https://doi.org/10.1002/2016JB013860.

Takada, A., 1997. Cyclic flank-vent and central-vent eruption patterns. Bull. Volcanol. 58,539–556. https://doi.org/10.1007/s004450050161.

Takada, A., 1999. Variations in magma supply and magma partitioning: the role of tec-tonic settings. J. Volcanol. Geotherm. Res. 93, 93–110. https://doi.org/10.1016/S0377-0273(99)00082-7.

Takada, A., Ishizuka, Y., Nakano, S., Yamamoto, T., Kobayashi, M., Suzuki, Y., 2007.Characteristic and evolution inferred from eruptive fissures of Fuji Volcano, Japan.In: Aramaki, S. (Ed.), Fuji Volcano. Yamanashi Institute of Environmental Sciences,pp. 183–202 (in Japanese with English abstract).

Takada, A., Yamamoto, T., Ishizuka, Y., Nakano, S., 2016. Geological map of Fuji volcano.In: Miscellaneous Map Series 12, Geological Survey of Japan. National Institute ofAdvanced Industrial Science and Technology.

Takahashi, N., Kodaira, S., Tatsumi, Y., Yamashita, M., Sato, T., Kaiho, Y., Miura, S., No,

Y. Aoki, et al. Earth-Science Reviews 194 (2019) 264–282

281

T., Takizawa, K., Kaneda, Y., 2009. Structural variations of arc crusts and riftedmargins in the southern Izu-Ogasawara arc-back arc system. Geochem. Geophys.Geosyst. 10, Q09X08. https://doi.org/10.1029/2008GC002146.

Thelen, W.A., Malone, S.D., West, M.E., 2010. Repose time and cumulative momentmagnitude: a new tool for forecasting eruptions? Geophys. Res. Lett. 37, L18301.https://doi.org/10.1029/2010GL044194.

Togashi, S., Takahashi, M., 2007. Geochemistry of rocks from the Fuji volcano, Japan:constraints for evolution of magmas. In: Aramaki, S. (Ed.), Fuji Volcano. YamanashiInstitute of Environmental Sciences, pp. 219–232 (in Japanese with English abstract).

Tsukui, M., Sakuyama, M., Koyaguchi, T., Ozawa, K., 1986. Long-term eruption rates anddimensions of magma reservoirs beneath Quaternary polygenetic volcanoes in Japan.J. Volcanol. Geotherm. Res. 29, 189–202. https://doi.org/10.1016/0377-0273(86)90044-2.

Tsumura, N., Horiuchi, S., Hasegawa, A., Kasahara, K., 1993. Location of the upperboundary of the Philippine Sea plate beneath the eastern part of Yamanashi pre-fecture estimated from S to P converted waves. J. Seismol. Soc. Jpn. 46, 109–118 (inJapanese with English abstract).

Tsutsui, T., Oikawa, J., Kagiyama, T., Reserch group for seismic exploration of Fuji vol-cano, 2007. Seismic reflection profilings of Fuji volcano, Central Japan. Butsuri-Tansa 131–144 (in Japanese with English abstract), 60.

Tsuya, H., 1955. Geological and petrological studies of Volcano, Fuji, V. 5. On the 1707eruption of Volcano Fuji. Bull. Earthq. Res. Inst., Univ. Tokyo 33, 341–383.

Tsuya, H., 1962. Geological and petrological studies of Volcano Fuji (VI). 6. Geology ofthe Volcano as observed in some borings on its flanks. Bull. Earthq. Res. Inst., Univ.Tokyo 40, 767–804.

Uesugi, Y., 1990. Standard tephra columns for the eastward area of Volcano Fuji, part 1:S-25 – Y-141. Bull. Assoc. Kanto Quat. Res. 16, 3–28 (in Japanese).

Ukawa, M., 1991. Collision and fan-shaped compressional stress pattern in the Izu blockat the northern edge of the Philippine Sea plate. J. Geophys. Res. 96, 713–728.https://doi.org/10.1029/90JB02142.

Ukawa, M., 2005. Deep low-frequency earthquake swarm in the mid crust beneath MountFuji (Japan) in 2000 and 2001. Bull. Volcanol. 68, 47–56. https://doi.org/10.1007/s00445-005-0419-5.

Vicari, A., Alexis, H., Del Negro, C., Coltelli, M., Marsella, M., Proietti, C., 2007. Modelingof the 2001 lava flow at Etna volcano by a Cellular Automata approach. Environ.Model. Softw. 22, 1465–1471. https://doi.org/10.1016/j.envsoft.2016.10.005.

Wessel, P., Smith, W.H.F., 1998. New, improved version of Generic Mapping Tools re-leased. EOS Trans. Am. Geophys. Union 79, 579. https://doi.org/10.1029/98EO00426.

Wessel, P., Smith, W.H.F., Scharroo, R., Luis, J., Wobbe, F., 2013. Generic Mapping Tools:improved version released. EOS Trans. Am. Geophys. Union 94, 409–420. https://doi.org/10.1002/2013EO450001.

Yamamoto, T., Takada, A., Ishizuka, Y., Miyaji, N., Tajima, Y., 2005a. Basaltic pyroclasticflows of Fuji volcano, Japan: characteristics of the deposits and their origin. Bull.Volcanol. 67, 622–633. https://doi.org/10.1007/s00445-004-0398-y.

Yamamoto, T., Takada, A., Ishizuka, Y., Nakano, S., 2005b. Chronology of the products ofFuji Volcano based on new radiometric carbon ages. Bull. Volcanol. Soc. Jpn. 50,53–70 (in Japanese with English abstract).

Yamamoto, T., Takada, A., Ishizuka, Y., Miyaji, N., Tajima, Y., 2007. Basaltic pyroclasticflows of Fuji volcano, Japan: characteristics of the deposits and their origin. In:Aramaki, S. (Ed.), Fuji Volcano. Yamanashi Institute of Environmental Sciences, pp.245–254 (in Japanese with English abstract).

Yoshimoto, M., Fujii, T., Kaneko, T., Yasuda, A., Nakada, S., 2004. Multiple magma re-servoirs for the 1707 eruption of Fuji volcano. Japan. Proc. Japan Acad. Ser. B. 80,103–106. https://doi.org/10.2183/pjab.80.103.

Yoshimoto, M., Fujii, T., Kaneko, T., Yasuda, A., Nakada, S., Matsumoto, A., 2010.Evolution of Mount Fuji, Japan: Inference from drilling into the subaerial oldestvolcano, pre-Komitake. Island Arc 19, 470–488. https://doi.org/10.1111/j.1440-1738.2010.00722.

Y. Aoki, et al. Earth-Science Reviews 194 (2019) 264–282

282