8.1 Soils of the Chubu Region
8.1.1 Soil-Forming Factors
1. Topography and geology
The Chubu region is located approximately in the center of
Honshu, facing the Sea of Japan in the north and the Pacific
Ocean in the south (Fig. 8.1). Highlands, including the Hida
Mountains, Kiso Mountains, and Akaishi Mountains, spread
inland, and the elevation of the region ranges from 0 m
above sea level (a.s.l.) on the coastal plain to 3000 m at the
mountain tops. The region contains two large faults, namely
the Itoigawa–Shizuoka Tectonic Line and the Median Tectonic Line, and its geology is largely divided by these two
faults. Eastward from the Itoigawa–Shizuoka Tectonic Line,
rocks from the Neogene Period are mainly distributed. West
of the Itoigawa–Shizuoka tectonic line, the region is divided
north and south by the Median Tectonic Line. In the
northern part (inner zone), plutonic rocks such as granite,
low-pressure metamorphic rocks, and middle Paleozoic
rocks are mainly distributed, and in the southern part (outer
zone), high-pressure metamorphic rocks and superbasic
rocks are distributed (Kato 2002). Most of the Hida and Kiso
Mountains located in the inner zone consist of granitic rocks.
Mt. Norikura and Mt. Ontake, two volcanoes located on the
south side of the Hida Mountains, consist of Quaternary
andesitic volcanic rocks. On the southern side of these
volcanoes, along the boundary between Gifu and Nagano
Prefectures, a mountainous area (the Atera Mountains) that
extends up to Aichi Prefecture consists of felsic volcanic
rocks of the Late Cretaceous (Nohi Rhyolite). The Akaishi
Mountains, which are part of the outer zone, consist mainly
of metamorphic rocks (the Sanbagawa belt) and sedimentary
rocks (the Chichibu belt) (Sakai 2007). From Mt. Fuji to the
Izu Peninsula, volcanic ejecta derived from the activity of
Holocene volcanoes such as Mt. Fuji, Mt. Hakone, and Mt.
Amagi are widely distributed, including volcanic ash,
pumice stone, and scoria. Additionally, many volcanic rocks
erupted to the ocean floor in the Neogene Period are distributed in the Izu Peninsula (Wakasawa and Takahashi
2012).
The depositional area of Holocene tephra erupted from
the active volcanoes in the Chubu region (e.g. Mt. Ontake,
Mt. Haku, Mt. Tateyama) is not very clear, but the amount of
Holocene tephra in the region could be relatively lower than
in other regions. Machida (1999) reported that the Chubu
region is also affected by nationally distributed Holocene
marker tephras, such as the U-Oki tephra (ca. 9.3 ka) from
the Ulleung Island volcano and the K-Ah tephra (ca. 6.3 ka)
from Kikai, a major caldera largely submerged off the coast
of southern Kyushu. However, these Holocene volcanoes are
far from the Chubu region. Machida (1999) also reported
that several nationally spread Quaternary tephras, such as the
Aso-4 tephra (ca. 84–89 ka) from the Aso Caldera in
southern Kyushu and the AT tephra (ca. 24–25 ka) from the
Aira Caldera, are observed in the Chubu region. Furthermore, on the Sea of Japan side of the region, the DKP tephra
(ca. 43–55 ka), erupted from Daisen volcano, is distributed.
In the Chubu region, alluvial fans are distributed between
the mountains and the plain (Fig. 8.2) (Yoshikawa et al. 1981).
The Kurobe River alluvial fan, in the eastern part of Toyama
Prefecture, approaches the ocean with the uplifting Hida
Mountains behind (Kamishima and Takeuchi 2016). From the
Middle to Late Pleistocene, alluvial fans and terraces were
extensively formed in the northwestern part of Mie Prefecture
(Yoshida 1983). In the west, from Cape Omaezaki in Shizuoka
Prefecture, hilly lands, diluvial uplands, and alluvial fans
developed at the southern foot of the mountains belonging to
the outer zone (Wakasawa and Takahashi 2012).
2. Climate
The Chubu region is affected by the Asian monsoon and is
struck by typhoons in the summer months. Due to these effects,
the climate of the Chubu region is divided into the following
three distinctive regions (Fig. 8.3): Hokuriku region, on the Sea
of Japan side; the Tokai region, on the Pacific Ocean side; and
the Hida region, in the Central Highlands.
(1) Hokuriku region: During the winter months, moist
monsoon wind blowing from the Sea of Japan, which is
stopped by high mountains, brings large amounts of
precipitation. The precipitation usually falls as snow,
making this one of the snowiest areas in Japan. The
snow melts in spring.
(2) Central Highlands: These contain 3000-m-high mountains (the Hida Mountains and Kiso Mountains). In
winter, the temperature is low due to lower amounts of
atmospheric water vapor, and the temperature difference
between day and night is large. This region has a
so-called continental climate.
(3) Tokai region: In winter, dry and sunny days continue
due to foehn wind. This area is warm even in winter.
3. Vegetation
The evergreen broad-leaved forest zone extends to around
800 m a.s.l. on the Pacific Ocean side (400 m a.s.l. on the Sea
of Japan side) and includes plains, hills, and low mountainous
areas. The summer green broad-leaved forest zone extends up
to around 1500 m a.s.l. The subalpine coniferous forest zone
extends up to an altitude of around 2400 m a.s.l. The alpine
zone spreads beyond the subalpine zone (Fig. 8.4) (Numata
274
N. Ogawa et al.
8.1.1 Soil-Forming Factors
1. Topography and geology
The Chubu region is located approximately in the center of
Honshu, facing the Sea of Japan in the north and the Pacific
Ocean in the south (Fig. 8.1). Highlands, including the Hida
Mountains, Kiso Mountains, and Akaishi Mountains, spread
inland, and the elevation of the region ranges from 0 m
above sea level (a.s.l.) on the coastal plain to 3000 m at the
mountain tops. The region contains two large faults, namely
the Itoigawa–Shizuoka Tectonic Line and the Median Tectonic Line, and its geology is largely divided by these two
faults. Eastward from the Itoigawa–Shizuoka Tectonic Line,
rocks from the Neogene Period are mainly distributed. West
of the Itoigawa–Shizuoka tectonic line, the region is divided
north and south by the Median Tectonic Line. In the
northern part (inner zone), plutonic rocks such as granite,
low-pressure metamorphic rocks, and middle Paleozoic
rocks are mainly distributed, and in the southern part (outer
zone), high-pressure metamorphic rocks and superbasic
rocks are distributed (Kato 2002). Most of the Hida and Kiso
Mountains located in the inner zone consist of granitic rocks.
Mt. Norikura and Mt. Ontake, two volcanoes located on the
south side of the Hida Mountains, consist of Quaternary
andesitic volcanic rocks. On the southern side of these
volcanoes, along the boundary between Gifu and Nagano
Prefectures, a mountainous area (the Atera Mountains) that
extends up to Aichi Prefecture consists of felsic volcanic
rocks of the Late Cretaceous (Nohi Rhyolite). The Akaishi
Mountains, which are part of the outer zone, consist mainly
of metamorphic rocks (the Sanbagawa belt) and sedimentary
rocks (the Chichibu belt) (Sakai 2007). From Mt. Fuji to the
Izu Peninsula, volcanic ejecta derived from the activity of
Holocene volcanoes such as Mt. Fuji, Mt. Hakone, and Mt.
Amagi are widely distributed, including volcanic ash,
pumice stone, and scoria. Additionally, many volcanic rocks
erupted to the ocean floor in the Neogene Period are distributed in the Izu Peninsula (Wakasawa and Takahashi
2012).
The depositional area of Holocene tephra erupted from
the active volcanoes in the Chubu region (e.g. Mt. Ontake,
Mt. Haku, Mt. Tateyama) is not very clear, but the amount of
Holocene tephra in the region could be relatively lower than
in other regions. Machida (1999) reported that the Chubu
region is also affected by nationally distributed Holocene
marker tephras, such as the U-Oki tephra (ca. 9.3 ka) from
the Ulleung Island volcano and the K-Ah tephra (ca. 6.3 ka)
from Kikai, a major caldera largely submerged off the coast
of southern Kyushu. However, these Holocene volcanoes are
far from the Chubu region. Machida (1999) also reported
that several nationally spread Quaternary tephras, such as the
Aso-4 tephra (ca. 84–89 ka) from the Aso Caldera in
southern Kyushu and the AT tephra (ca. 24–25 ka) from the
Aira Caldera, are observed in the Chubu region. Furthermore, on the Sea of Japan side of the region, the DKP tephra
(ca. 43–55 ka), erupted from Daisen volcano, is distributed.
In the Chubu region, alluvial fans are distributed between
the mountains and the plain (Fig. 8.2) (Yoshikawa et al. 1981).
The Kurobe River alluvial fan, in the eastern part of Toyama
Prefecture, approaches the ocean with the uplifting Hida
Mountains behind (Kamishima and Takeuchi 2016). From the
Middle to Late Pleistocene, alluvial fans and terraces were
extensively formed in the northwestern part of Mie Prefecture
(Yoshida 1983). In the west, from Cape Omaezaki in Shizuoka
Prefecture, hilly lands, diluvial uplands, and alluvial fans
developed at the southern foot of the mountains belonging to
the outer zone (Wakasawa and Takahashi 2012).
2. Climate
The Chubu region is affected by the Asian monsoon and is
struck by typhoons in the summer months. Due to these effects,
the climate of the Chubu region is divided into the following
three distinctive regions (Fig. 8.3): Hokuriku region, on the Sea
of Japan side; the Tokai region, on the Pacific Ocean side; and
the Hida region, in the Central Highlands.
(1) Hokuriku region: During the winter months, moist
monsoon wind blowing from the Sea of Japan, which is
stopped by high mountains, brings large amounts of
precipitation. The precipitation usually falls as snow,
making this one of the snowiest areas in Japan. The
snow melts in spring.
(2) Central Highlands: These contain 3000-m-high mountains (the Hida Mountains and Kiso Mountains). In
winter, the temperature is low due to lower amounts of
atmospheric water vapor, and the temperature difference
between day and night is large. This region has a
so-called continental climate.
(3) Tokai region: In winter, dry and sunny days continue
due to foehn wind. This area is warm even in winter.
3. Vegetation
The evergreen broad-leaved forest zone extends to around
800 m a.s.l. on the Pacific Ocean side (400 m a.s.l. on the Sea
of Japan side) and includes plains, hills, and low mountainous
areas. The summer green broad-leaved forest zone extends up
to around 1500 m a.s.l. The subalpine coniferous forest zone
extends up to an altitude of around 2400 m a.s.l. The alpine
zone spreads beyond the subalpine zone (Fig. 8.4) (Numata
274
N. Ogawa et al.