Progress in Earth andPlanetary Science

Nishikawa et al.
Progress in Earth and Planetary Science(2023) 10:21
https://doi.org/10.1186/s40645-023-00552-4

Open Access

RESEARCH ARTICLE

Simulated distributions of pumice rafts
in Japan following eruptions at volcanic islands
and submarine volcanoes
Haruka Nishikawa1* , Tatsu Kuwatani2, Noriko Tada2 and Hiromi Kayama Watanabe3

Abstract
Voluminous pumice rafts produced by the 2021 phreatomagmatic eruption of Fukutoku-Oka-no-Ba, a submarine
volcano located in the Izu-Bonin Islands, reached many Japanese ports and islands, damaging fisheries and hinderingmarine traffic and trade. This event emphasized the necessity for governments and stakeholders to develop plans inadvance and prepare disaster mitigation measures before an eruption. To investigate when and to what extent pumice might intersect trade routes and arrive at islands after future eruptions, we conducted particle tracking simulationsof eruptions at major volcanic islands and submarine volcanoes near Japan using the velocity field from the ocean
reanalysis dataset. Seven major volcanoes that have produced pumice rafts in the past century were selected: thesubmarine volcano NNE of Iriomote Island, Izu-Tobu Volcanoes, Miyakejima, Bayonnaise Rocks, Nishinoshima, Kaitoku
Seamount, and Fukutoku-Oka-no-Ba. We partly reproduced the distribution of pumice arrivals recorded after the 1986
Fukutoku-Oka-no-Ba eruption, demonstrating the potential effectiveness of the simulations. We report likely pumiceraft arrivals and drifting durations for the investigated eruptive scenarios, which may aid future risk assessments forpumice arrivals.
Keywords Pumice, Submarine volcano, Fukutoku-Oka-no-Ba, Particle tracking experiment, Dispersion, Natural hazard
1 Introduction
Pumice is generated by the vesiculation and quenchingof silicic magma during volcanic eruptions. Due to its
low density, pumice is often buoyant in water, and pumice erupted from volcanic islands or submarine volcanoes is occasionally found adrift at sea (Kato 2009; Bryan*Correspondence:
Haruka Nishikawa
harukan@jamstec.go.jp
1
Research Institute for Value‑Added‑Information Generation (VAiG),
Japan Agency for Marine-Earth Science and Technology, 3173‑25
Showa‑Machi, Yokohama, Kanagawa 236‑0001, Japan
2
Research Institute for Marine Geodynamics (IMG), Japan Agency
for Marine-Earth Science and Technology, 2‑15 Natsushima‑Cho,
Yokosuka, Kanagawa 237‑0061, Japan
3
Institute for Extra‑Cutting‑Edge Science and Technology
Avant‑Garde Research (X‑Star), Japan Agency for Marine-Earth Scienceand Technology, 2‑15 Natsushima‑Cho, Yokosuka, Kanagawa 237‑0061,
Japan

et al. 2012), often in large (a few square meters to several hundreds of square kilometers), mobile accumulations called pumice rafts (e.g., Jutzeler et al. 2014, 2020).
Some pumice rafts drift several thousands of kilometers
over months to years, whereas others sink to the seafloor
or become stranded on shorelines (Jutzeler et al. 2014;
Fauria et al. 2017; Fauria and Manga 2018; Whitham andSparks 1986). These rafts have been recognized as natural
hazards impacting human life, local industries (impeding
marine traffic and operations in harbors and ports), andcoastal ecosystems (Hurlbut and Verbeek 1887; Jutzeler
et al. 2014, 2020; Oppenheimer 2003; Sigurdsson et al.
1987).
The 13 August 2021 phreatomagmatic eruption of Fukutoku-Oka-no-Ba submarine volcano (the Izu-Bonin islands,
Japan) erupted a large volume of pumice that accumulated
in rafts (e.g., Yoshida et al. 2022a; Maeno et al. 2022; Fauria et al. 2023) and drifted to the Ryuku Islands ~ 1400 km© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/.

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to the west, arriving about two months after the eruption(Japan Coast Guard 2021; Geological Survey of Japan 2021;
Tada et al. 2021). The pumice rafts impeded local activities
and industries and damaged ecosystems for several months
after arrival, with some local effects persisting until the present day (e.g., Yoshida et al. 2022a, b, c; Ohno et al. 2022),
becoming a temporary societal problem in Japan thatwas widely reported in various media. For example, pumice rafts blocked harbors by covering coasts and surface
waters, and individual pumice clasts obstructed the water
intakes of motor vessels and damaged hulls and propellers,
hindering the operation of fishing boats and maritime traffic. In addition, the pumice rafts impacted the fish farming and tourism industries by killing fish and rendering
beaches inaccessible due to abundant flotsam, respectively.
Some papers also reported significant impacts on coastal
ecosystems (e.g., Akiyama et al. 2022; Ohno et al. 2022;
Sato et al. 2022).
To reduce the damage caused by pumice rafts, advanced
preparation is essential, including numerical simulations
predicting their movements. Jutzeler et al. (2014, 2020)
demonstrated that combining satellite observations ofpumice raft movements with real-time predictive simulations is effective for predicting raft drift directions. Morerecently, Asami and Takahashi (2023) presented a simulation model that predicts pyroclast behavior in the marine
environment with practical accuracy. Because it takes time
for local government agencies and stakeholders to prepare
mitigation measures, it is important to estimate the likelihood, magnitude, and drift duration of pumice rafts fora target location using predictive numerical simulations
before a potential eruption.
Here, we conducted numerical simulations of drifting
pumice rafts to clarify the likelihood and duration of drift
to important areas along the Japanese coast. We focused on
volcanic islands and submarine volcanoes near Japan thathave produced giant pumice rafts in past eruptions. We
first conducted a numerical drifting simulation for the 1986
Fukutoku-Oka-no-Ba eruption to validate the effectivenessof our simulation by comparing the results to observationsof pumice raft arrivals at several locations in Japan. Then,
we conducted the same drifting simulations for potential
future eruptions at seven volcanoes known to have produced pumice rafts. By dissipating the tracked particles
from the starting point each month over several tens ofyears, we incorporated seasonal and annual ocean current
variations into the analysis.

pumice clasts’. In the first experiment, virtual pumice
clasts were tracked from Fukutoku-Oka-no-Ba to Iriomote Island, Okinawa, Genkainada, Bungo Channel, offCape Shionomisaki, and Hahajima Island (Table 1). The
purpose of this experiment was to validate our simulation by comparing the simulated pumice raft arrival
dates at the six target locations with those that followed the January 1986 Fukutoku-Oka-no-Ba eruption,
which produced floating pumice during 18–21 January(Ossaka 1991). Pumice clasts produced by that eruption
were observed at Hahajima on 15 March, Okinawa andIriomote Island in late May, Bungo Channel on 26 June,
off Cape Shionomisaki in August, and at Genkainada in
October (Yoshida et al. 1987; Kato 1988).
In the second set of experiments, virtual pumice clasts were tracked from major volcanic islands
and submarine volcanoes near Japan known to haveproduced pumice rafts in the past few decades. We
selected seven volcanoes: the submarine volcano NNE
of Iriomote Island (V1); the Izu-Tobu volcanic range(V2); Miyakejima (V3); Bayonnaise Rocks (V4); Nishinoshima (V5); Kaitoku Seamount (V6); and Fukutoku-Oka-no-Ba (V7; Table 2). From these volcanoes,
we released virtual pumice clasts to 16 target areas(Table 3) to estimate pumice raft arrivals. We selected
11 areas important to sea traffic based on the shiptracking site https://​w ww.​marin​etraf​fi c.​com/: Osumi
Strait; Koshiki Strait; Bungo Channel, off Cape Shionomisaki, Irago Channel; off Izuoshima Island; off Cape
Omaezaki; off Onahama; off Sakaiminato; Wakasa
Bay; and Tsugaru Strait. We selected Iriomote Island,
Minami-Daito Island, Okinawa, and Amami OshimaIsland because their economies depend on marine
activities and beach tourism, and Chichijima Island
because the only transportation to the island is by sea.
The locations of the selected volcanoes and target areas
are shown in Fig. 1. Figure 1 also shows the paths of
the Kuroshio Current and the Kuroshio Recirculation,
which are known to affect pumice dispersals (e.g., Tada
et al. 2021).

2 Data and methods

Table 1 Target areas selected for the first particle tracking
simulation experiments
Name

Latitude, longitude

Iriomote Island

23.98–24.58°N, 123.55–124.15°E

Okinawa

26.00–27.00°N, 127.47–128.47°E

2.1 Volcanic islands, submarine volcanoes, and target
areas

Genkainada

33.30–34.00°N, 129.35–130.35°E

Bungo Channel

32.87–33.27°N, 131.83–132.53°E

We conducted two particle simulation experiments.
Hereafter, we call the simulated particles ‘virtual

Off Cape Shionomisaki

33.20–33.50°N, 135.46–136.06°E

Hahajima Island

26.35–26.95°N, 141.85–142.45°E

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Table 2 Volcanic island and submarine volcano pumice sources used in this study. Descriptions are based on Ossaka (1991)
Name

Code

Abbrev.

Latitude, longitude

Years in whichpumice rafts were
produced

Submarine volcano NNE of Iriomote
IslandV1

IR

24.5°N, 123.8°E

1924

Izu-Tobu Volcanoes

V2

IZ

35.0°N, 139.1°N

1989

Miyakejima

V3MI

34.1°N, 139.5°E

1983

Bayonnaise Rocks

V4

BA

31.9°N, 140.0°E

1952–1953, 1970

Nishinoshima

V5NI

27.2°N, 140.9°E

1973–1974

Kaitoku SeamountV6

KA

26.1°N, 141.1°E

1981

Fukutoku-Oka-no-Ba

V7

FU

24.3°N, 141.5°E

1917, 1986, 2021

Table 3 Target areas selected for the second particle tracking
simulation experiments
Name

Latitude, longitude(A) Iriomote Island

23.98–24.58°N, 123.55–124.15°E(B) Okinawa

26.00–27.00°N, 127.47–128.47°E(C) Amami Oshima

27.64–28.64°E, 128.82–129.82°E(D) Minami-Daito Island

25.57–26.17°N, 130.92–131.52°E(E) Koshiki Strait

31.54–32.14°N, 129.88–130.18°E(F) Osumi Strait

30.73–31.23°N, 130.70–131.20°E(G) Bungo Channel

32.87–33.27°N, 131.83–132.53°E(H) Off Cape Shionomisaki

33.20–33.50°N, 135.46–136.06°E(I) Irago Channel

34.07–34.67°N, 136.88–137.38°E(J) Off Cape Omaezaki

34.40–34.70°N, 137.94–138.34°E(K) Off Izuoshima Island

34.60–35.10°N, 138.86–139.86°E(L) Off Onahama

37.10–37.70°N, 141.00–141.30°E(M) Off Sakaiminato

35.48–35.88°N, 132.75–133.35°E(N) Wakasa Bay

35.46–35.86°N, 135.20–136.10°E(O) Tsugaru Strait

41.20–41.80°N, 139.92–141.07°E(P) Chichijima Island

26.77–27.37°N, 141.91–142.51°E

2.2 Particle tracking experiments

In our particle tracking simulations, we used horizontal
velocities, sea temperatures, and salinities from the ocean
reanalysis dataset, a daily dataset with a horizontal resolution of 0.1° × 0.1° provided by the operational numerical
weather prediction of the Japan Meteorological Agency
(JMA
2013;
http://​www.​jma.​go.​jp/​jma/​jma-​eng/​jma-​
center/​nwp/​outli​ne2019-​nwp/​index.​htm). The dataset
region is 117°E–160°W, 15°N–65°N. We released virtual
pumice clasts at 0.5 m depth in all simulations because
pumice clasts are usually observed drifting on the sea
surface.
Virtual pumice locations were tracked using theformulae:xn+1 = xn + un t + x

(1)

(2)

yn+1 = yn + vn t + y√
x , y = PN 2t

AxH ,

y

AH

(3)

where (xn, yn) is the horizontal virtual pumice location(x and y being the east–west and north–south coordinates, respectively) at time step n; un and vn are the eastward and northward velocities, respectively; and Δt is thetime step, taken here to be 20 min. (λx, λy) is the random
walk displacement represented by Eq. (3), in which ( AxH,yAH) and PN are the horizontal eddy diffusion coefficientsand the probability function of the normal distribution,
respectively. The magnitude of the lateral diffusivity is100–10,000 ­m2⁄s (Nummelin et al. 2021). We conducted
tests using various diffusivities within that range andcompared the results with the record of pumice raftarrivals from the 1986 Fukutoku-Oka-no-Ba eruption.
Based on the results of those tests, we set both AxH andy
AH to be 1,000 ­m2⁄s in all experiments.
In the first experiment, batches of 49,000 virtual pumice clasts were released from Fukutoku-Oka-no-Ba once
per day during 18–21 January 1986. In the second setof experiments, batches of virtual pumice clasts werereleased from the seven selected volcanoes on the 15th
day of each month from 1982 to 2015. Batch sizes were
49,000 virtual pumice clasts for V1 (the submarine volcano NNE of Iriomote Island), V3 (Miyakejima), V4(Bayonnaise Rocks), V5 Nishinoshima), V6 (Kaitoku
Seamount), and V7 (Fukutoku-Oka-no-Ba), and 18,000
virtual pumice clasts for V2 (the Izu-Tobu range). We
defined a square area (each side measuring 0.7°) containing 49 grid squares centered at each volcano. The grid
spacing was 0.1°, the same as the horizontal resolutionof the ocean dataset. One thousand virtual pumice clasts
were put in each grid. We selected only 18 grids near V2(Izu-Tobu), because that volcano is close to land, thus
the batch size was 18,000 virtual pumice clasts for V2. In

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Fig. 1 Submarine volcano and volcanic island sources (blue stars) and target areas (red squares) used in our particle tracking simulations. Greensquares are target areas that were only used in our simulation of the 1986 Fukutoku-Oka-no-Ba pumice raft. Major ocean currents around Japan are
also shown

both experiments, the virtual pumice clasts were assigned
drift duration of 365 days, because drifting pumice clasts
tend to weather into smaller fragments that are no longer
buoyant within a year (Kuroda 1987). The location ofeach virtual pumice clast was recorded every day, and thefirst day that any virtual pumice clast arrived in a target
area was recorded as a pumice raft arrival. Some virtual
pumice clasts continue to drift, and they might arrive atanother target area. The others stop as landing when thesurface horizontal velocity of the nearest grid of them iszero. In this study, we did not consider the remobilization
process that the landing pumices restart to drift.
We calculated the monthly and yearly mean values of
the number of virtual pumice clasts arriving at each target
location and their drift durations. Monthly means weretaken as the average from 1982 to 2015 for each month,and yearly means as the average monthly mean value
from January to December. We considered the mean drift
duration and the shortest drift duration (i.e., the shortest recorded time during all tracking experiments). We

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confirmed that the mean drift durations roughly correspond with the median value of the drift durations fromits distributions for all paths. Thus, the particles that aretransported to the target area in the mean drift duration
could be considered as a large majority. The question ofwhether disaster mitigation measures should focus on
the shortest or mean drift duration is apt, because an
amount of pumice large enough to impede marine traffic will not always reach a port along the shortest route.
Thus, we regard both the mean and shortest times asapproximate times to be alert for pumice arrivals. For
the first experiment, in which we validated our particle
tracking simulation method, we compared the mean andshortest drift durations with the dates on which pumice
clasts were reported in the target areas for the first time,
because those are the only records of pumice arrivals.

(reported in August) for Cape Shionomisaki, 8 November (reported in October) for Genkainada, and 15 March(reported 15 March) for Hahajima Island. The virtual
pumice paths from Fukutoku-Oka-no-Ba to the arrival
locations are shown in Fig. 3. These are the paths in which
the pumice arrived at the nearest date to the record date.
Except for Iriomote Island and Genkainada, the discrepancies between the simulated and recorded arrival dates
are less than 1 month, although the actual discrepancy at
Genkainada might also be less than 1 month because only
the arrival month was recorded. Of the 49,000 virtual
pumice clasts released from Fukutoku-Oka-no-Ba every
day during the period 18–21 January 1986, 117 (0.060%)
arrived at Iriomote Island, 215 (0.110%) at Okinawa, 7(0.004%) at Genkainada, 22 (0.011%) at Bungo Channel,
140 (0.071%) at Cape Shionomisaki, and 14,756 (7.53%) at
Hahajima Island.

3 Results
3.1 Pumice arrivals from Fukutoku‑Oka‑no‑Ba in 1986

The number of virtual pumice clasts that arrived at eachtarget area during each month and the month in whichpumice clasts were reported in the area for the first time
are illustrated in Fig. 2. Virtual pumice clasts reached
Iriomote Island, Okinawa, and Genkainada later than therecorded arrivals, whereas virtual pumice clasts reached
Cape Shionomisaki and Hahajima earlier than therecorded arrivals. The closest arrival dates to the record
are 19 July (first reported pumice arrival late May) for Iriomote Island, 6 June (reported in late May) for Okinawa,
22 June (reported 28 June) for Bungo Channel, 5 August

3.2 Pumice drift paths for potential eruptions from 7
volcanoes

Figure 4 shows example drift paths for 50 randomly
selected virtual pumice clasts released from V1 (the submarine volcano NNE of Iriomote Island) in March 2004;
similar examples for other volcanoes are provided in the
Appendix. The yearly mean number of virtual pumice
clasts released from each source volcano that arrived ateach target area and their yearly mean drift durations(i.e., numbers and durations averaged over the entire
study period) are illustrated in Fig. 5.

Fig. 2 Number of virtual pumice clasts that arrived at each target area from the Fukutoku-Oka-no-Ba 1986 eruption. The red stars represent thedates on which the first pumice clasts were reported at each location

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Fig. 3 Simulated trajectories and arrival dates of virtual pumice clasts released during 18–21 January 1986 from Fukutoku-Oka-no-Ba (black star).
The illustrated paths are those of the virtual pumice clasts that arrived nearest the date that pumice clasts were reported for the first time. Simulated
and recorded arrival dates are denoted by ‘SIM’ and ‘REC,’ respectively

Fig. 4 Simulated drift paths of 50 randomly selected virtual pumice clasts released from V1 (the submarine volcano NNE of Iriomote Island,
indicated by the black star) on 15 March 2004. Blue rectangles indicate target areas

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Fig. 5 The average number of virtual pumice clasts arriving at each target area after being released from (V1) the submarine volcano NNE of
Iriomote Island, (V2) the Izu-Tobu volcanic range, (V3) Miyakejima, (V4) Bayonnaise Rocks, (V5) Nishinoshima, (V6) Kaitoku Seamount, and (V7)
Fukutoku-Oka-no-Ba. In each frame, the black star represents the location of the volcano source. The numbers reported were averaged over all
simulations; for example, an average of 7318 of the total 49,000 virtual pumice clasts released from the submarine volcano NNE of Iriomote Island
were transported to Okinawa per simulation. The radii of the pie charts are proportional to the logarithm of the average number of virtual pumice
clasts that arrived at each target area. The color scale of the pie charts indicates the average drift duration of each proportion of the virtual pumice
clasts that arrived. If the mean number of virtual pumice clasts was below 1, a value of 0 is reported

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Greater numbers of virtual pumice clasts arrived attarget areas along or in the Pacific Ocean than at target
areas along or in the Sea of Japan because, other thanV1 (the submarine volcano NNE of Iriomote Island), allinvestigated volcanoes are in the Pacific Ocean. To arrivein the Sea of Japan, virtual pumice clasts must become
entrained in the Tsushima Warm Current (Fig. 1).
Because the submarine volcano NNE of Iriomote Island
is located south of the divergence of the Kuroshio Current and Tsushima Warm Current, virtual pumice clasts
released there are more easily transported to targets in
the Sea of Japan (M, Sakaiminato; N, Wakasa Bay; andO, Tsugaru Strait) than are virtual pumice clasts released
from other volcanoes (Figs. 1, 4, 5a).
Virtual pumice clasts released from V2 (Izu-Tobu
range), V3 (Miyakejima), and V4 (Bayonnaise Rocks)
mainly arrived at eastern target areas (H, Cape Shionomisaki; I, Irago Channel; K, Izuoshima Island; and L,
Onahama; Fig. 5b–d). These virtual pumice clasts wererarely transported to the Sea of Japan because theirsource volcanoes are near the mainstream of the Kuroshio Current. Larger numbers of virtual pumice clasts
were transported to western target areas (A, Iriomote
Island; B, Okinawa; C, Amami Oshima; D, Minami-Daito
Island; and H, Cape Shionomisaki) from V4 (Bayonnaise
Rocks) than from V2 (Izu-Tobu range) and V3 (Miyakejima), seemingly due to their locations relative to the axisof the Kuroshio Current: V2 and V3 are on the inshoreside of the Kuroshio axis, whereas V4 is on the offshoreside (Fig. 1). Some virtual pumice clasts released fromV4 became entrained in the Kuroshio Recirculation, awestward current on the offshore side of the mainstream
Kuroshio Current (Fig. 1). Westward transport by the
Kuroshio Recirculation is also notable for virtual pumice clasts released from V5 (Nishinoshima), V6 (Kaitoku
Seamount,) and V7 (Fukutoku-Oka-no-Ba) (Fig. 5e–g).
Some virtual pumice clasts transported from these volcanoes by the Kuroshio Recirculation arrived near A(Iriomote Island) and were transferred to the Tsushima
Warm Current, ultimately reaching M (Sakaiminato). A
large proportion of the virtual pumice clasts from thesethree volcanoes was transported to nearby P (Chichijima
Island).
The yearly and monthly means and standard deviations of the number of virtual pumice clasts that
arrived at each target area from each volcano source
are illustrated in Fig. 6. The range of interannual variations (black symbols) are within an order of magnitude
except for virtual pumice clasts from V3 (Miyakejima)arriving at A (Iriomote Island), H (Cape Shionomisaki),I (Irago Channel), and J (off Cape Omaezaki) (Fig. 6A,
H–J); virtual pumice clasts from V2 (Izu-Tobu range)
arriving at C (Amami Oshima), I (Irago Channel),and J (off Cape Omaezaki) (Fig. 6C, I, J); and virtual

Fig. 5 continued

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Fig. 6 Means and standard deviations (SDs) of the number of virtual pumice clasts that arrived at each target area from (V1) submarine volcano
NNE of Iriomote Island (IR), (V2) Izu-Tobu volcanic range (IZ), (V3) Miyakejima (MI), (V4) Bayonnaise Rocks (BA), (V5) Nishinoshima (NI), (V6) Kaitoku
Seamount (KA), and (V7) Fukutoku-Oka-no-Ba (FU). Black symbols and error bars are yearly means and SDs from 1982 to 2015; colored symbols anderror bars are monthly means and SDs from 1982 to 2015

pumice clasts from V4 (Bayonnaise Rocks) arriving at
I (Irago Channel), J (off Cape Omaezaki), K (off Izuoshima Island), and M (off Sakaiminato) (Fig. 6I–K, M).
We expected the number of virtual pumice arrivals tochange depending on the season because the seasonalmonsoon should affect the flow field. For all paths, theyearly and monthly means of the number of virtual
pumice arrivals are within an order of magnitude ofeach other; however, the monthly standard deviationsof some paths are markedly larger than the yearly standard deviations, meaning that the interannual variation
was large in specific months. We selected the paths
and months for which the yearly mean virtual pumice
number was larger than 100 and the monthly standard
deviation was more than twice as large as the yearlystandard deviation (Table 4). For the paths from V2(Izu-Tobu Volcanoes), V3 (Miyakejima), and V4 (Bayonnaise Rocks) to H (off Cape Shionomisaki), I (Irago

Channel), J (off Cape Omaezaki), and K (off IzuoshimaIsland), the standard deviations are large except during July–August. For the paths from V3 (Miyakejima)
and V4 (Bayonnaise Rocks) to A (Iriomote Island), B(Okinawa), C (Amami Oshima), and D (Minami-Daito
Island), and for the paths from V5 (Nishinoshima), V6(Kaitoku Seamount), and V7 (Fukutoku-Oka-no-Ba) to
A (Iriomote Island), the standard deviations are large
from October to December.
As we expected, the virtual pumice drift durations
generally depended on the distance between the volcanoes and the target areas (Fig. 7). The virtual pumicedrift durations also showed seasonal effects. Virtual
pumice clasts released from V5 (Nishinoshima), V6(Kaitoku Seamount), and V7 (Fukutoku-Oka-noBa) during the summer generally exhibited notably
shorter drift durations than those released during thewinter. Seasonality is also apparent in the interannual

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Table 4 Paths for which the yearly mean virtual pumice number was larger than 100 and the monthly standard deviation was morethan twice as large as the yearly standard deviation
Volcano (A) Iriomote(B) Okinawa(C) Amami(D) M.Daito(E) Koshiki(F) Osumi(G) Bungo(H) Shionomisaki

Nov

Nov

Mar., Jun., Jul.,
Nov.

May

Dec

Dec

Dec

Feb., Apr., May,
Jun., Sep., Oct.,
Dec.

(J) Omaezaki(K) Izuoshima(L) Onahama(V1) IR(V2) IZ(V3) MI(V4) BA

Jul., Dec.

(V5) NI

Oct(V6) KA

Oct(V7) FU

Oct., Nov.

Volcano (I) Irago

Aug.
(M)
(N) Wakasa (O) Tsugaru (P) Chichijima
Sakaiminato(V1) IR(V2) IZ

Sep., Oct., Nov.,
Dec.

Jun., Sep., Oct.,
Nov., Dec.

May(V3) MI

May, Jun., Jul.,
Sep., Oct., Nov.

Jan., Mar., Jun.,
Sep., Oct., Nov.

Mar., Apr., Jun.

Jan., Jun., Dec.

(V4) BA

Jan., Feb., Apr.,
May, Jul., Sep.

Feb., Mar., Apr.,
Sep., Oct.

Feb., Apr., Aug.,
Sep., Oct., Nov.,
Dec.

Feb., Apr., Nov.

(V5) NI(V6) KA(V7) FUvariation. We selected the paths and months for which
the number of yearly mean virtual pumice arrivals waslarger than 100 and the standard deviation of the duration in a specific month was 2 months greater or lessthan that of the yearly mean (Table 5). Such paths arefrom V2 (Izu-Tobu), V3 (Miyakejima), and V4 (Bayonnaise Rocks) to H (off Cape Shionomisaki), I (Irago
Channel), J (off Cape Omaezaki), and K (off IzuoshimaIsland) and appeared mainly from January to May andfrom October to December, i.e., other than in summer.
This is the same tendency that is apparent in Table 4.
We note that the mean drift durations differed markedly from the shortest drift durations over all particle
tracking experiments from 1982 to 2015 (Fig. 8). For
47.3% of the paths, the shortest drift durations were atleast 6 months shorter than the mean drift durations.

4 Discussion
For the pumice drift, various factors that affect thepumice path are entangled in a complex manner. In
this study, some factors (e.g., remobilization) are notincluded in the particle tracking experiments. Here
we discuss the influence of such potential factors on
our results and discuss how we understand the simulated results. First, we discuss the reproducibility ofthe virtual pumice dispersion from the January 1986
Fukutoku-Oka-no-Ba eruption. Then, we explain thepotential factors, seasonality, and reliability of the drift
duration.
4.1 Reproducibility of the January 1986
Fukutoku‑Oka‑no‑Ba eruption

For this eruption, our simulated pumice raft arrival dates
are generally consistent with the recorded arrival dates
except for A (Iriomote Island). For Iriomote Island, thesimulated arrival date was more than 1.5 months later
than the recorded arrival date. There are two possible
reasons why the simulation cannot reproduce the real
drift duration. One is the uncertainty of the existenceof the non-stational mesoscale eddy and the other is thelack of the remobilization.
All the virtual pumices that were transported from
Fukutoku-Oka-no-Ba to Iriomote Island from January 1986 in our simulation might take a circuitous path,
which might be longer than the direct westward route,due to the existence of the non-stationary mesoscale
eddy. Virtual pumices were trapped by an eddy thatexisted near Fukutoku-Oka-no-Ba and transported tothe south by the eddy. Consequently, all virtual pumices

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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Fig. 7 Means and standard deviations (SDs) of the drift durations of virtual pumice clasts that arrived at each target area from (V1) submarine
volcano NNE of Iriomote Island (IR), (V2) Izu-Tobu volcanic range (IZ), (V3) Miyakejima (MI), (V4) Bayonnaise Rocks (BA), (V5) Nishinoshima (NI), (V6)
Kaitoku Seamount (KA), and (V7) Fukutoku-Oka-no-Ba (FU). Black symbols and error bars are yearly means and SDs from 1982 to 2015; coloredsymbols and error bars are monthly means and SDs from 1982 to 2015

could not take a direct route to Iriomote Island. Although
the eddy had remained there from January to February in1986 in the simulated velocity data, it is likely that there
was no such eddy in the real ocean at that time. This isbecause, although the ocean reanalysis dataset can reproduce this mesoscale eddy, it could not have reproduced
its exact position until corrections based on satellite data
were incorporated in the 1990s (Takatsuki et al. 2017).
The above possibility was suggested by the long-term
simulations for potential eruptions from 1982 to 2015.
As shown in Figs. 7a and 8a, while the mean drift duration from V7 (Fukutoku-Oka-no-Ba) to Iriomote Islandis 9 months, the shortest drift duration is 2 months. The
reason why the drift duration varies in such a range isthat there are two different transport paths. The longer
path is alike the path in Fig. 3. After the start of drift, thepumice initially goes south, then turns west; when the
pumice reaches the Philippines, the Kuroshio transports

the pumice north to Iriomote Island. The shorter path
is similar to that from V7 (Fukutoku-Oka-no-Ba) to B
(Okinawa) (Fig. 3); some pumice goes north after thestart of drift, then turns west and goes straight to Iriomote Island. The path of the pumice with the shortest
drift duration shown in Fig. 8A followed this route, whichtakes only 2 months. According to the record of the 1986
eruption, the real pumice drift took about 4 months,
which indicates that the pumice might be transported in
the shorter path. On the other hand, all virtual pumices
were transported in the longer path by trapping of an
eddy in our simulation for the 1986 Fukutoku-Oka-no-Ba
eruption.
The other factor that possibly caused the discrepancy is remobilization. According to the observationsof the 2021 Fukutoku-Oka-no-Ba eruption, many pumice clasts arrived in the coastal area, but subsequently
left the area and started drifting again (Yoshida et al.

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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Table 5 Paths for which the number of yearly mean virtual pumice arrivals was larger than 100 and the standard deviation of theduration in a given month was 2 months greater or less than the yearly mean
Volcano (A) Iriomote(B) Okinawa(C) Amami(D) M-Daito(E) Koshiki(F) Osumi(G) Bungo(H) Shionomisaki(V1) IR(V2) IZ(V3) MI(V4) BA

Jan., Feb.

(V5) NI(V6) KA(V7) FU
Volcano (I) Irago(J) Omaezaki(K) Izuoshima(L) Onahama (M)(N) Wakasa (O) Tsugaru (P) Chichijima
Sakaiminato(V1) IR(V2) IZ

Feb., Mar., Apr.,
Jun., Dec.

(V3) MIJan., Feb., Mar., Apr., Jan., Feb., Mar., Apr.,
May, Jun., Jul., Aug., May, Jun., Jul., Aug.,
Oct., Nov., Dec.
Oct., Nov., Dec.

(V4) BA

Jan., Feb., Mar., Apr., Jan., Feb., Mar., Apr., Jan., Feb., Mar.,
May, Sep., Oct.,
Oct., Nov., Dec.
Apr., May, Oct.,
Nov., Dec.
Nov., Dec.

(V5) NI(V6) KA(V7) FU

2022b). Such remobilization was not considered in thisstudy. It means that we ignored the indirect path from
Fukutoku-Oka-no-Ba to Iriomote Island. For example, it is possible that pumice once landed at an island
near Iriomote Island (e.g., B: Okinawa) drifted again
and arrived at Iriomote Island. In our simulation, thevirtual pumice arrived at Okinawa on 6 June. If there isa strong southwest current from Okinawa to Iriomote
Island, the remobilized pumice might arrive at Iriomote
Island in June. If we considered such an indirect path,the virtual pumice possibly arrived at Iriomote Island
earlier.
Since our simulation does not incorporate the shortterm wind effect into the reanalyzed ocean current,
wave and tidal mixing, it is difficult to reproduce thedirect landing process and the following remobilization. Why we did not include such factors are explainedin the following subsection.
4.2 Short‑term wind effects on the current, windage, tidal
mixing and Stokes drift

One of the purposes of this study was to reproduce thepumice drift of the 1986 Fukutoku-Oka-no-Ba eruption.
Unfortunately, the ocean environmental dataset that
includes 1986 is not suitable for considering short-term
wind effects, including typhoon, on the current, dragging

by wind, Stokes drift, tidal mixing, and remobilization,
which impact pumice drift (Jutzeler et al. 2014, 2020;
Yoshida et al. 2022a, b; Ohno et al. 2022; Kurogi and
Hasumi 2019).
Before satellite observations, the spatiotemporal resolution of wind data was not sufficiently fine to consider
the effects of typhoons, which alter ocean conditions ona scale of a few hours, or the wind itself, which changes
direction within a few hours. The pumice that wasthought to be transported under the influence of thetyphoon was found after the August 2021 Fukutoku-Okano-Ba eruption. The drift duration was 2.5 months fromV7 (Fukutoku-Oka-no-Ba) to Iriomote Island (Usami andShinjo 2022). This drift path should be the shorter paththat we discuss in 4–1. In addition to the position of theeddies and remobilization, the typhoon could affect thetransport path because summer is typhoon season near
Japan. After the eruption, many typhoons (e.g., Typhoon
Chanthu and Typhoon Mindulle) passed near FukutokuOka-no-Ba. Our simulation cannot reproduce the effectof typhoons perfectly because we used the daily mean
flow field data; thus, the simulation may have missed
abrupt changes (on the scale of a few hours) of the flow
field associated with the passage of a typhoon. However,
the report that the large amounts of pumice were foundat Kita-Daito Island (near D, Minami-Daito Island; Fig. 1)

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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Fig. 8 The shortest drift durations of virtual pumice clasts that arrived at each target area from (V1) submarine volcano NNE of Iriomote Island (IR),(V2) Izu-Tobu volcanic range (IZ), (V3) Miyakejima (MI), (V4) Bayonnaise Rocks (BA), (V5) Nishinoshima (NI), (V6) Kaitoku Seamount (KA), and (V7)
Fukutoku-Oka-no-Ba (FU) from 1982 to 2015

the day after the typhoon had arrived (Yoshida et al.
2022a) suggested that the typhoon affected the pumice
distribution. Thus, it is possible that a typhoon could
markedly change the flow field and it helped to transport pumice northward shorter path. Typhoon would
also affect the pumice in a direct way, windage. However,since the wind data resolution is low, it was not included
in our simulation.
The ocean reanalysis products we used do not include
the tidal mixing and Stokes drift, which strongly affects
near-coast flow fields. This is why we did not count the
number of the virtual pumice clasts that stopped on theland but just count the number of the virtual pumicethat passed the target areas. Sometimes stranded pumice left the beach and drift again especially in the casetyphoon-induced wave overtopping occurred (Yoshida
et al. 2022b). However, due to the lack of reliability forthe exact number of stranded pumice and reproduction of the wave overtopping, we did not consider theremobilization. As we mentioned in the discussion of
the 1986 eruption reproducibility, the lack of remobilization process possibly caused the underestimationof the number of pumice arrival at the target areas.
Wave overtopping is a combined result of astronomic
tide, storm surge and wave run-up and frequently
occurs especially during the typhoon. To reproduce
these processes, a specific model is needed that captures the finer-scale changes of wind and wave dynamics (e.g., 20 min. and 2 km scales used in Amunugama
et al. 2020). The target area of such a finer-scale modelis usually restricted in the coastal area. On the other
hand, while the daily dataset with 10 km horizontal resolution, which we used does not reproduce these processes, the dataset can cover enough wider area to trackthe dispersion of the pumice near Japan. Integration of
the coastal model and offshore model will be an issue inthe future.

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

4.3 Seasonality

While our simulation cannot reproduce the effect of daily
wind change, the simulation did reproduce the effect of
the seasonal monsoon, which influences the flow field
on a scale of a few days. In the Kuroshio region, the winddirection and velocity change seasonally (Nakamura2017). The large interannual variations in the number ofvirtual pumice arrivals or of the drift duration in a specific month arise as a result of such seasonality. For thepaths from V2 (Izu-Tobu Volcanoes), V3 (Miyakejima),
and V4 (Bayonnaise Rocks) to H (off Cape Shionomisaki), I (Irago Channel), J (off Cape Omaezaki), and K (offIzuoshima Island), the interannual variations of arrival
number and drift duration are large, except in summer(Tables 4, 5). As these target areas are located west of
the source volcanoes, the virtual pumice clasts must go
westward (Fig. 1). However, these volcanoes are locatednear the Kuroshio Current. Once the virtual pumice
clasts are trapped by the Kuroshio, it is difficult for themto reach H (off Cape Shionomisaki), I (Irago Channel),J (off Cape Omaezaki), and K (off Izuoshima Island). If
the virtual pumice clasts can escape from the Kuroshio
and transfer to the westward current, it takes additionaltime for them to reach the target areas. Hence, whether
the virtual pumice clasts are trapped by the Kuroshio is
important, and this trapping depends on two factors.
One factor is the variability of the Kuroshio path, which
is not affected by seasonality. The other factor is the seasonal monsoon. Strong monsoonal winds induce Ekman
transport (e.g., Wu and Hsin 2012), which forces virtual
pumice clasts toward or away from the Kuroshio. For
example, the usual wind direction is southwestward in
October near these volcanoes (Nakamura 2017). Suchwind induces southward Ekman transport at the sea surface, which moves virtual pumice clasts near Miyakejima
toward the Kuroshio. In this area, although windy days
continue during winter, spring, and autumn, the wind is
weak during summer (Nakamura 2017). The weak summer monsoon could explain the small interannual variation during summer. For the paths from V3 (Miyakejima)
and V4 (Bayonnaise Rocks) to A (Iriomote Island), B(Okinawa), C (Amami Oshima), and D (Minami-Daito
Island), and for the paths from V5 (Nishinoshima), V6(Kaitoku Seamount), and V7 (Fukutoku-Oka-no-Ba) to
Iriomote Island, the interannual variation of arrival number is large from October to December (Table 4). Thesetarget areas are west of V3 (Miyakejima), V4 (Bayonnaise
Rocks), V5 (Nishinoshima), V6 (Kaitoku Seamount),and V7 (Fukutoku-Oka-no-Ba). Near the target areas,
the autumnal wind direction is southwestward, that is,
the Ekman transport is westward. Thus, when the windspeed is higher, larger numbers of virtual pumice clasts

Page 16 of 20

can reach these target areas, and the number of virtual
pumice arrivals depends on interannual wind variations.
Our simulation can reproduce seasonality other thanthat of wind. Virtual pumice clasts released from V5(Nishinoshima), V6 (Kaitoku Seamount), and V7 (Fukutoku-Oka-no-Ba) in summer reached Pacific target areas
relatively quickly (Fig. 7). As the Kuroshio Recirculationthat flows near these volcanoes is strengthened in summer (Yoshida et al. 2022a), these shorter drift durations
reflect the seasonality of ocean currents.
4.4 Reliability of the drift duration

As our final goal was to estimate the risk of pumiceraft arrivals based on the results of our particle tracking experiments, it is important whether the mean or
shortest drift durations are most representative of actual
pumice rafts. We propose that both durations should
be considered for two reasons. (1) The drift duration isvulnerable to the existence of non-stationary mesoscaleeddies. For example, in our experiments, the mean andshortest drift durations from V7 (Fukutoku-Oka-no-Ba)
to B (Okinawa) were 8.5 months (Fig. 7B) and 1.5 months(Fig. 8B), respectively. In comparison, pumice from theAugust 2021 eruption of Fukutoku-Oka-no-Ba arrived at
Okinawa within 2 months, preventing fishing boats fromsailing (e.g., Yoshida et al. 2022a). This case implies thatthe shortest drift duration is reliable. However, in contrast, pumice from the 1986 eruption took 4 months totravel from Fukutoku-Oka-no-Ba to Okinawa. The possible reasons why the 2021 drift time was shorter arethat the pumice erupted that year was not trapped by theeddies that trapped the 1986 raft and/or seasonality. Since
the eruption in 1986 is in winter and 2021 is in summer,
seasonality includes the effect of the seasonal monsoon
and typhoon. This difference suggests that pumice is notalways transported along the shortest route. (2) The initial pumice arrival may not be large enough to impede
marine traffic; this may explain the arrival of virtual pumice clasts at Cape Shionomisaki and Hahajima before real
observations of pumice rafts (Fig. 2): it is possible that thefirst pumice arrival went unrecognized. Thus, following
eruptions, particular attention should be paid during theperiod between the shortest possible drift duration andthe mean duration.
We stress that the amount of pumice that arrives initially will not necessarily be small. A small number ofvirtual pumice clasts in our experiments does not necessarily translate to low real-world risk. We released only
49,000 particles, which is a small number considering thediverse and complex behavior of real pumice rafts. Therefore, warnings of pumice raft arrivals must be basedon specific criteria regarding the number of particles

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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arriving in tracking experiments and careful comparisonswith historical records of pumice arrivals.

these results, we concluded that a period following aneruption that warrants attention is from the shortest drift
record to the mean drift duration, which was estimatedfor each volcano by the simulations from 1982 to 2015.
On the other hand, our results indicate that in order toaccurately predict drift duration within a precision of
1 month or less, we need to take certain factors into consideration, such as remobilization.

5 Concluding remarks
We conducted particle tracking simulations of eruptions
at major volcanic islands and submarine volcanoes near
Japan. In the case of the 1986 Fukutoku-Oka-no-Ba, thesimulated drift durations are consistent with the records
other than Iriomote Island. In addition, all recorded drift
durations fall within the range of the shortest drift record
and the mean drift duration derived from the simulations
for the Fukutoku-Oka-no-Ba from 1982 to 2015. From

Appendix
See Figs. 9, 10, 11, 12, 13 and 14.

Fig. 9 Simulated drift paths of 50 randomly selected virtual pumice clasts released from the (V2) Izu-Tobu volcanic range (black star) on 15 March
2004. Blue rectangles indicate target areas

Fig. 10 Simulated drift paths of 50 randomly selected virtual pumice clasts released from (V3) Miyakejima (black star) on 15 March 2004. Blue
rectangles indicate target areas

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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Fig. 11 Simulated drift paths of 50 randomly selected virtual pumice clasts released from (V4) Bayonnaise Rocks (black star) on 15 March 2004. Blue
rectangles indicate target areas

Fig. 12 Simulated drift paths of 50 randomly selected virtual pumice clasts released from (V5) Nishinoshima (black star) on 15 March 2004. Blue
rectangles indicate target areas

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

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Fig. 13 Simulated drift paths of 50 randomly selected virtual pumice clasts released from (V6) Kaitoku Seamount (black star) on 15 March 2004.
Blue rectangles indicate target areas

Fig. 14 Simulated drift paths of 50 randomly selected virtual pumice clasts released from (V7) Fukutoku-Oka-no-Ba submarine volcano (black star)on 15 March 2004. Blue rectangles indicate target areas

Acknowledgements
The figures were produced using Generic Mapping Tools v4 (Wessel andSmith 1998).
Author contributions
HN conducted particle tracking experiments. TK and NT provided geological
data (pumice transportation and volcanic activity). All co-authors collaborated with the corresponding author in the construction of the manuscript
through several drafts. All authors participated in discussions about the results
and commented on the manuscript. All authors read and approved the final
manuscript.
Funding
TK was supported by CREST Grant Number JPMJCR1761 from the Japan
Science and Technology Agency. NT was supported by a Grant-in-Aid for

Scientific Research (KAKENHI) Number 18H01319. HN was supported by aGrant-in-Aid for Transformative Research Areas (KAKENHI) Number 22H05201
from the Japan Society for the Promotion of Science and PRESTO Grant Number JPMJPR1876 from the Japan Science and Technology Agency.
Availability of data and materials
The ocean reanalysis dataset used in this study is available from the authors
upon request. The request URL is http://​www.​jma.​go.​jp/​jma/​jma-​eng/​jma-​
center/​nwp/​outli​ne2019-​nwp/​index.​htm

Declarations
Competing interests
The authors declare that they have no competing interests.

Nishikawa et al. Progress in Earth and Planetary Science(2023) 10:21

Received: 19 October 2022 Accepted: 26 March 2023

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