23-25 August 2023

Hakone (箱根)Guided by
Shimano, T. (Tokoha Univ.)
Kasama, T. (Hakone geopark)
Uno, M.
(Tohoku Univ.)

Fuji-Hakone field excursion

Overview

Being the highest mountain in Japan (3776 m), Mt. Fuji (富⼠) is the most famous andsymbolic mountain in Japan. It is an active stratovolcano that last erupted during 17071708. Mt. Hakone (箱根) is another active volcano next to Mt. Fuji, and is characterized
by a volcanic caldera and intense hydrothermal activities, and is one of the mostpopular Onsen (hot spring) destination near Tokyo. We will visit the Hoei crater, thevolcanic crater of the 1707-1708 Hoei eruption of Mt. Fuji. You will enjoy traditional
Japanese style Onsen-ryokan (hotel with hot spring) at Hakone, visit the Owakudani
fumarole, and enjoy volcanic excursion around Hakone. Near Odawara (⼩⽥原), youcan also visit some historic castles.
Please check physical requirements in page 6.

Fuji (富⼠)Schedule
Meeting: Odawara JR Station or Hotel (TBD), 15:00, 23rd Aug.
Dismissal: Odawara JR Station,
15:00, 25th Aug.
Day 1 (23rd Wed.) Stay at Odawara
Meeting at Odawara. Optional tour to Odawara castle.
Day 2 (24th Thu.) Fuji volcano excursion
Stop 1 Fujinomiya Trail 5th Station (2400 m height)
Trekking to Hoei Crater (~3 hours)
Stop 2 Tarobo Outcrop
Stop 3 (optional) Komakado Kazaana (Lava cave)
Staying at Onsen Ryokan (hot spring hotel) at Hakone

1Day 3 (25th Fri.) Hakone volcano excursion
Stop 4 Owakudani fumarole
Stop 5 Nagao mountain ridge(view of Caldera Lake and Landslides)
Stop 6 Yamabushi mountain ridge (view of Caldera and Lava Domes)
Stop 7 Daikan mountain(view of Caldera and Lava Domes)
Stop 8 Ishigakiyama castle ruin
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*Schedule above may change due to weather conditions.

Fuji volcano

Fuji &Hakone

Okhotskplate

Eurasia plate

Hoei craters

Pacificplate

III

Philippine sea plate

III
Geological overview of Fuji volcano
Mt. Fuji is the largest active volcanoes in Japan onland standing at a very
unique point along the boundary of several plates in view of plate-techtonics.
It is a young stratovolcano(<100ka) grew up on some older ones, Komitakeand pre-Komitake volcanoes (>100ka; mostly the same as neighbors).
Mt. Fuji is characterized by basaltic magma through most of its life, but isalso famous for its variety in eruption styles. Although whole eruption history
is yet to be understood, the recent activity from 10 ka is classified into
several stages, duration of each stage with some thousand years, in terms ofvent locality and eruption type. Recent stage (<2.2 ka) is dominated byeffusive flank eruptions every some decades in average. But it has been quiet
more than 300 years since 1707-08 when highly explosive Hoei eruption
occurred near the summit that accompanied rare dacitic magma.
Stop 1 Hoei crator
The Hoei eruption occurred on the Southeastern side of Mt. Fuji. The threecraters are formed sequentially from Crater III to I. Crater I is the largest one(~1km in diameter), which is also larger than the summit crater.
Stop 2 Tarobo outcrop
Tarobo(太郎坊) is a 5th step on one of the trails up to the summit of Mt.
Fuji. There used to be a finest outcrop to investigate airfall deposits fromseveral thousand years up to the Hoei eruption, which are now largely buried
by slash avalanches in early 2000’s. You can see the Hoei deposit ~3-4m thickhere with sequential SiO2 decrease in composition upwards.
Stop 3 (optional) Komakado Kazaana (Lava cave)
Komakado kaza-ana is a lava cave formed within the Mishima lava flow that
erupted probably from the summit crater of Mt. Fuji about 10,000 years ago.
The total length of the cave is 243 m. You can observe various flow structureof basaltic lava flow inside the cave.
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https://izugeopark.org/about-izugeo/intro/

HakoneMt. FujiTokyo

Stop 1
Stop 2

Stop 5

Okhotsk plate

Stop 4

OdawaraStop 3

Stop 8Stop 6

Eurasia plater
Suaug

tr o

Stop 7

Sagami t

Mt. Hakone

hugroughIzu peninsula
Philippine sea plate

Google EarthStop 1
Stop 2

Stop 3
Geological map of Fuji volcano (2nd ed., AIST, 2016)
https://gbank.gsj.jp/volcano/Act_Vol/fujisan/map/eng/volcmap_bv3-e.html

4Hakone←Mt.Kanmurigatake

Hakone volcano

May23,2012
A small phreatic eruptionduring June to July,2015
Owakudani
June1,2021

Geological overview of Hakone volcano
Mt. Hakone has a caldera with a diameter of 10 km, which is not particularly
large in Japan, but exists close to plate boundaries, so active faults extend
into the caldera , Tanna(丹那) fault from the south and Hirayama(平⼭) Fault
from the north. Its volcanic activity started 400 ka, and the largest eruption
ejected several dozen km3 of tephra. Tephra deposited several dozen m in theTokyo area due to prevailing westerlies with that of Fuji volcano.
Stop 4 Owakudani(⼤涌⾕) fumarole
Owakudani was once called the Valley of Hell, because of toxic volcanic gases.
Here, you can see traces of the latest activity of the Hakone volcano. The latest
Magmatic activity occurred 3 ka, when Mt. Kamiyama collapsed and Owakudani
formed. Its debris avalanche blocked the Hyakawa(早川) river and formed Lake
Ashinoko(芦ノ湖). The latest phreatic eruption occurred at here in 2015.
Stop 5 Nagao(⻑尾) mountain ridge
Nagao mountain ridge is located on the somma of Hakone volcano and thebest viewpoint of Mt. Kamiyama, Mt. Kanmurigatake and Owakudani. The fanshaped landform is the depositional form of debris avalanche from horseshoe
shaped crater of Mt. Kamiyama.(see photo on page 2 )Stop 6 Yamabushi(⼭伏) mountain ridge
Stop 7 Daikan mountain(⼤観⼭)
These stops are also on the somma of Hakone volcano and viewpoints of central
cones and Lake Ashinoko. Central cones consist thick lava flows and lava domes.
Stop 8 Ishigakiyama(⽯垣⼭) castle ruin
Ishigakiyama castle was built in 1590 to capture Odawara castle. Odawara castle
was surrendered and later rebuilt to became the current Odawara castle, while
Ishigakiyama castle remains as it was at the time. There were several bigearthquake, but many parts have not collapsed.
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Stop 5

Stop 4

Stop 8Stop 6

Geological map of Hakone (Geological Society of Japan, 2007)
Kanagawa Pref. Museum of Natural History (2008)

Stop 7

Physical requirements for the excursion
Capable for 2-3 hours of mountain trekking*. Healthy lung**.
* The excursion at Hoei crater (Stop 1) involves high altitude (2400 m) and 2-3 hours ofmountain trekking. People may stay at local visitor center instead of trekking.
** The air at Owakudani (Stop 4) contains ppm-level H2S and SO2 that is safe for healthy
individuals, but would be not recommended for individuals with lung problems.

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