river system, at 322 km in length. The Tone river system
divides the Kanto region into northern and southern parts. Its
annual gross discharge is 4500–7000 Â 10
6 m
3 . The Naka
river system basin has an area of 3270 km
2 , and its annual
gross discharge is 1500–3000 Â 10
6 m
3 . The areas of the
basins of the Ara, Sagami, Kuji, and Tama Rivers are 2940,
1660, 1490, and 1240 km
2 , respectively, and all of these
four rivers have annual gross discharges of 500–1500 Â
10
6 m
3 (Takamura et al. 1981).
(2) Climate condition of the Koushinetsu region
In the Sea of Japan area of the Koushinetsu region, northwestern winter winds bring heavy snowfall. In the summer,
the region receives less rain than the Pacific area, though it
sometimes experiences extremely hot temperatures because
of the foehn wind. The annual average temperature in Niigata Prefecture is 13.6–13.9 °C, and the annual average
precipitation is 1500–2800 mm. In winter, there is snowfall
of about 1 m on the plains and of over 3 m in the mountains
due to the influence of westerly wind from the Sea of Japan.
There is more precipitation in winter than summer, and from
spring to autumn, there is a relatively high number of sunshine hours.
The climate of the Koshin region varies greatly with
altitude, with annual mean temperatures ranging from 6.4–
15.0°C and mean annual precipitation ranging from 900–
2500 mm. The annual mean air temperature in the foothills
of the high mountains is approximately 10 °C. The climate
in the northern part of Nagano Prefecture belongs to the
climate type of the Sea of Japan, and that in the south of the
Koshin region belongs to the typical inland humid continental climate, with large temperature differences between
summer and winter and between day and night.
7.1.4 Soils of the Kanto-Koushinetsu Region
(1) Soil map of the Kanto-Koushinetsu region
The soil map of the Kanto-Koushinetsu region is shown in
Fig. 7.2. In terms of soil great group, Andosols are distributed over the largest area (40% of the total land area) in
this region, covering the terrace of the Kanto Plain and the
mountainous area in the northeast. Allophanic Andosols
(Silandic Andosols) account for approximately 75% of these
Andosols, making them one of the most representative soils
in the Kanto-Koushinetsu region. Regosolic Andosols
(Vitric Andosols) have the second largest distribution area of
the Andosol great group in the region, and cover volcanic
landforms. Non-Allophanic Andosols, whose distribution
area is limited to the western part of the Kanto-Koushinetsu
region, are the third most widely distributed Andosol in the
region.
Soils belonging to the Brown Forest soil great group have
the second largest distribution by area in this region. These
soils are mainly distributed in the Koushinetsu region, which
is characterized by a temperate climate and
hilly-mountainous areas without volcanic ash deposition.
The third most widely distributed soil great group by area in
this region is Fluvic soil, which mainly covers alluvial plains
in the Kanto region and Niigata Prefecture. In the Japanese
Soil Classification System, Fluvic soils are subdivided by the
condition of the groundwater table into Gley Fluvic soils,
Gray Fluvic soils, and Brown Fluvic soils. Gley Lowland
soils and Gray Lowland soils are mainly used for rice cultivation in this region.
(2) Volcanic ash soil in the northern Kanto region
The northern Kanto region, which includes Ibaraki, Tochigi,
and Gunma Prefectures, is located near Tokyo, which has a
huge consumer market for agricultural products. Eight active
volcanoes (Mt. Nasu, Mt. Takahara, Mt. Nantai, Mt.
Nikko-Shirane, Mt. Kusatsu-Shirane, Mt. Akagi, Mt. Haruna, and Mt. Asama) are located in the western part of this
region (Fig. 7.1). These volcanoes are located on the volcanic front line and accordingly are among the most active
volcanoes in this area. Therefore, an enormous amount of
volcanic ash has been generated from these volcanoes,
which has covered the plains in the northern Kanto region
with layers of tephra.
Tephra layers, both fallout-deposited and flow-deposited,
play an important role in characterizing soils and landscapes
in the northern Kanto region. In the early stage of stratigraphic studies in Japan, tephra sequences were studied in
conjunction with geomorphic surfaces and paleontological
and geomagnetic studies. For instance, the Pleistocene terraces in Utsunomiya City, in the central part of the northern
Kanto region, had been divided into the Hoshakuji Terrace,
the Takaragi Terrace, and the Tawara Terrace (Fig. 7.3). The
higher terrace (i.e., Hoshakuji) contains thicker deposits of
aeolian volcanic ash (so-called loam) lying on top of fluvial
and/or marine deposits. These aeolian weathered Pleistocene
volcanic ash layers were divided into three stratigraphic
formations, namely the Tawara loam, the Takaragi loam, and
the Hoshakuji loam. Developments in characterization
techniques for tephra identification and dating methods
revealed the presence of “marker” tephras spread across the
whole of Japan, and have placed regional tephra stratigraphies on a more solid framework (Machida 1999). Based on
recent results, this type locality has been divided into eight
geomorphic surfaces (Suzuki and Koike 2000), namely, the
Tobiyama-Kamiketsu surface (terrace age = 370–380 ka),
7 Kanto-Koushinetsu Region
249
divides the Kanto region into northern and southern parts. Its
annual gross discharge is 4500–7000 Â 10
6 m
3 . The Naka
river system basin has an area of 3270 km
2 , and its annual
gross discharge is 1500–3000 Â 10
6 m
3 . The areas of the
basins of the Ara, Sagami, Kuji, and Tama Rivers are 2940,
1660, 1490, and 1240 km
2 , respectively, and all of these
four rivers have annual gross discharges of 500–1500 Â
10
6 m
3 (Takamura et al. 1981).
(2) Climate condition of the Koushinetsu region
In the Sea of Japan area of the Koushinetsu region, northwestern winter winds bring heavy snowfall. In the summer,
the region receives less rain than the Pacific area, though it
sometimes experiences extremely hot temperatures because
of the foehn wind. The annual average temperature in Niigata Prefecture is 13.6–13.9 °C, and the annual average
precipitation is 1500–2800 mm. In winter, there is snowfall
of about 1 m on the plains and of over 3 m in the mountains
due to the influence of westerly wind from the Sea of Japan.
There is more precipitation in winter than summer, and from
spring to autumn, there is a relatively high number of sunshine hours.
The climate of the Koshin region varies greatly with
altitude, with annual mean temperatures ranging from 6.4–
15.0°C and mean annual precipitation ranging from 900–
2500 mm. The annual mean air temperature in the foothills
of the high mountains is approximately 10 °C. The climate
in the northern part of Nagano Prefecture belongs to the
climate type of the Sea of Japan, and that in the south of the
Koshin region belongs to the typical inland humid continental climate, with large temperature differences between
summer and winter and between day and night.
7.1.4 Soils of the Kanto-Koushinetsu Region
(1) Soil map of the Kanto-Koushinetsu region
The soil map of the Kanto-Koushinetsu region is shown in
Fig. 7.2. In terms of soil great group, Andosols are distributed over the largest area (40% of the total land area) in
this region, covering the terrace of the Kanto Plain and the
mountainous area in the northeast. Allophanic Andosols
(Silandic Andosols) account for approximately 75% of these
Andosols, making them one of the most representative soils
in the Kanto-Koushinetsu region. Regosolic Andosols
(Vitric Andosols) have the second largest distribution area of
the Andosol great group in the region, and cover volcanic
landforms. Non-Allophanic Andosols, whose distribution
area is limited to the western part of the Kanto-Koushinetsu
region, are the third most widely distributed Andosol in the
region.
Soils belonging to the Brown Forest soil great group have
the second largest distribution by area in this region. These
soils are mainly distributed in the Koushinetsu region, which
is characterized by a temperate climate and
hilly-mountainous areas without volcanic ash deposition.
The third most widely distributed soil great group by area in
this region is Fluvic soil, which mainly covers alluvial plains
in the Kanto region and Niigata Prefecture. In the Japanese
Soil Classification System, Fluvic soils are subdivided by the
condition of the groundwater table into Gley Fluvic soils,
Gray Fluvic soils, and Brown Fluvic soils. Gley Lowland
soils and Gray Lowland soils are mainly used for rice cultivation in this region.
(2) Volcanic ash soil in the northern Kanto region
The northern Kanto region, which includes Ibaraki, Tochigi,
and Gunma Prefectures, is located near Tokyo, which has a
huge consumer market for agricultural products. Eight active
volcanoes (Mt. Nasu, Mt. Takahara, Mt. Nantai, Mt.
Nikko-Shirane, Mt. Kusatsu-Shirane, Mt. Akagi, Mt. Haruna, and Mt. Asama) are located in the western part of this
region (Fig. 7.1). These volcanoes are located on the volcanic front line and accordingly are among the most active
volcanoes in this area. Therefore, an enormous amount of
volcanic ash has been generated from these volcanoes,
which has covered the plains in the northern Kanto region
with layers of tephra.
Tephra layers, both fallout-deposited and flow-deposited,
play an important role in characterizing soils and landscapes
in the northern Kanto region. In the early stage of stratigraphic studies in Japan, tephra sequences were studied in
conjunction with geomorphic surfaces and paleontological
and geomagnetic studies. For instance, the Pleistocene terraces in Utsunomiya City, in the central part of the northern
Kanto region, had been divided into the Hoshakuji Terrace,
the Takaragi Terrace, and the Tawara Terrace (Fig. 7.3). The
higher terrace (i.e., Hoshakuji) contains thicker deposits of
aeolian volcanic ash (so-called loam) lying on top of fluvial
and/or marine deposits. These aeolian weathered Pleistocene
volcanic ash layers were divided into three stratigraphic
formations, namely the Tawara loam, the Takaragi loam, and
the Hoshakuji loam. Developments in characterization
techniques for tephra identification and dating methods
revealed the presence of “marker” tephras spread across the
whole of Japan, and have placed regional tephra stratigraphies on a more solid framework (Machida 1999). Based on
recent results, this type locality has been divided into eight
geomorphic surfaces (Suzuki and Koike 2000), namely, the
Tobiyama-Kamiketsu surface (terrace age = 370–380 ka),
7 Kanto-Koushinetsu Region
249