(2) Geography and geology of the Koushin region
There are many mountains in Nagano and Yamanashi prefectures whose peaks are higher than 3000 m in altitude,
while land that is over 1000 m in altitude accounts for more
than 50% of the area of these prefectures. There are some
flatlands between mountains, such as the Nagano (Zenkohji)
Basin, Saku Basin, Matsumoto Basin, Suwa Basin, Kofu
Basin, and Ina Basin. Additionally, the prefectures contain
several active volcanoes, such as Mt. Fuji, Mt. Asama, Mt.
Yatsugatake, and Mt. Ontake. Relatively small alluvial
plains have been formed by rivers in these prefectures, such
as the Sai, Chikuma, Tenryu, and Kiso Rivers. These plains
are used as paddy field.
The Itoigawa–Shizuoka Tectonic Line runs from north to
southeast through the middle of Nagano Prefecture, dividing
an area of the prefecture into two geomorphological regions.
The western side of the line consists mainly of igneous rocks
formed from the Paleozoic Era to the Mesozoic Era. (In fact,
all the mountains of the northern, central, and southern
Japanese Alps are made of igneous rocks.) To the east of the
Itoigawa–Shizuoka Tectonic Line is the Fossa Magna
(“Great Rift Belt”), where the basement rocks are mainly
marine strata formed in the Neogene and some kinds of
igneous rocks. Quaternary eruption products of volcanoes
such as Mt. Asama, Mt. Yatsugatake, and Mt. Ontake have
accumulated and covered these basement rocks.
(3) Geography and geology of Niigata Prefecture
Niigata Prefecture, which faces the Sea of Japan side of
central Honshu, is an elongated area that stretches for about
240 km along the Sea of Japan coast from the northeast to
the southwest, with an area of 12,584 km
2 (making it the
fifth largest prefecture in Japan). Along the prefectural border are mountains ranging from 1500 to 3000 meters in
height, and the Agano River and Shinano River, which
originate from these mountains (Fig. 7.1). The Echigo Plain,
the largest plain in the prefecture, lies between these
mountains and coastal dunes. The Kashiwazaki Plain lies in
the downstream part of the Sabaishi River, and the Takada
Plain lies in the downstream part of the Seki River. Other
areas in this prefecture are hilly and mountainous areas. On
Sado Island, the Kuninaka Plain spreads between the
Oosado Mountains and the Kosado Hills.
The geological features of Niigata Prefecture can be
divided into four parts: (1) in the eastern part of the Kasiwazaki–Chiba Tectonic Line, rigid rocks (sedimentary rocks
and granitoids) of Paleozoic and Mesozoic formations are
mainly distributed and are widely covered by a green tuff
layer of Neogene strata; (2) the central part of Niigata Prefecture contains an area called Fossa Magna between the
Kasiwazaki–Chiba and Itoigawa–Shizuoka Tectonic Lines,
where sedimentary rocks (soft stones such as sandstone and
mudstone) of Neogene and Quaternary strata are thickly
distributed; (3) in the western part of the Itoigawa–Shizuoka
Tectonic Line, sedimentary and metamorphic rocks of
Paleozoic and Mesozoic formations are distributed; and
(4) in the mountains of Sado Island, volcanic rocks and
volcanic sedimentary rocks (green tuff), mainly deposited in
Paleogene to Neogene formations, are distributed.
Coastal sand dunes are connected to the plains of Niigata
Prefecture along the coastline. About 9000 to 7000 years
ago, after the Holocene glacial retreat, sediments were carried by rivers, and these coastal dunes are estimated to have
formed about 1000 years ago. As the mouth of the rivers
was blocked by the sand dunes, a vast wetland zone was
formed between the mountains and the coastal dunes, which
became the current Echigo plain. Alluvial plain deposits
(unsolidified sediments) are thickly distributed in the plains
of Niigata Prefecture, and in the Niigata Plain the thickness
reaches 160 m. The area close to the coast is mainly composed of sand and viscous soil, and the ground in the
upstream area close to the mountains is mainly composed of
gravel and sand.
7.1.3 Climate Condition
of the Kanto-Koushinetsu Region
(1) Climate condition of the Kanto region
The climate of Japan is influenced by a monsoonal flow that
carries moist air from the Indian Ocean and Pacific Ocean. In
general, Japan has four distinct seasons, namely, spring
(March to May), summer (June to August), autumn
(September to November), and winter (December to
February). In the Kanto region, it is usually warm
year-round, being rainy in the summer and dry in the winter
with dry winds. The summer rain is due to seasonal rains
(called “Tsuyu”) which occur from mid-June to mid-July), as
well as typhoons.
Mean annual precipitation in the Kanto region ranges
from 1000 to 3000 mm (in Tokyo the value is 1528 mm),
with the Kanto Plain receiving relatively little precipitation.
The southwest area of the Kanto region is a common pathway for typhoons, and this area therefore receives especially
high rainfall. The annual mean air temperature is 16.3 °C in
Tokyo, and is higher in southern coastal areas than in
mountainous zones.
The Kanto Plain is drained by the Kuji, Naka, Tone, Ara,
Tama, and Sagami river systems (Fig. 7.1). The Tone river
system has the largest drainage area of any river system in
Japan (16,840 km
2 ) and is also the country’s second longest
248
H. Sumida et al.
There are many mountains in Nagano and Yamanashi prefectures whose peaks are higher than 3000 m in altitude,
while land that is over 1000 m in altitude accounts for more
than 50% of the area of these prefectures. There are some
flatlands between mountains, such as the Nagano (Zenkohji)
Basin, Saku Basin, Matsumoto Basin, Suwa Basin, Kofu
Basin, and Ina Basin. Additionally, the prefectures contain
several active volcanoes, such as Mt. Fuji, Mt. Asama, Mt.
Yatsugatake, and Mt. Ontake. Relatively small alluvial
plains have been formed by rivers in these prefectures, such
as the Sai, Chikuma, Tenryu, and Kiso Rivers. These plains
are used as paddy field.
The Itoigawa–Shizuoka Tectonic Line runs from north to
southeast through the middle of Nagano Prefecture, dividing
an area of the prefecture into two geomorphological regions.
The western side of the line consists mainly of igneous rocks
formed from the Paleozoic Era to the Mesozoic Era. (In fact,
all the mountains of the northern, central, and southern
Japanese Alps are made of igneous rocks.) To the east of the
Itoigawa–Shizuoka Tectonic Line is the Fossa Magna
(“Great Rift Belt”), where the basement rocks are mainly
marine strata formed in the Neogene and some kinds of
igneous rocks. Quaternary eruption products of volcanoes
such as Mt. Asama, Mt. Yatsugatake, and Mt. Ontake have
accumulated and covered these basement rocks.
(3) Geography and geology of Niigata Prefecture
Niigata Prefecture, which faces the Sea of Japan side of
central Honshu, is an elongated area that stretches for about
240 km along the Sea of Japan coast from the northeast to
the southwest, with an area of 12,584 km
2 (making it the
fifth largest prefecture in Japan). Along the prefectural border are mountains ranging from 1500 to 3000 meters in
height, and the Agano River and Shinano River, which
originate from these mountains (Fig. 7.1). The Echigo Plain,
the largest plain in the prefecture, lies between these
mountains and coastal dunes. The Kashiwazaki Plain lies in
the downstream part of the Sabaishi River, and the Takada
Plain lies in the downstream part of the Seki River. Other
areas in this prefecture are hilly and mountainous areas. On
Sado Island, the Kuninaka Plain spreads between the
Oosado Mountains and the Kosado Hills.
The geological features of Niigata Prefecture can be
divided into four parts: (1) in the eastern part of the Kasiwazaki–Chiba Tectonic Line, rigid rocks (sedimentary rocks
and granitoids) of Paleozoic and Mesozoic formations are
mainly distributed and are widely covered by a green tuff
layer of Neogene strata; (2) the central part of Niigata Prefecture contains an area called Fossa Magna between the
Kasiwazaki–Chiba and Itoigawa–Shizuoka Tectonic Lines,
where sedimentary rocks (soft stones such as sandstone and
mudstone) of Neogene and Quaternary strata are thickly
distributed; (3) in the western part of the Itoigawa–Shizuoka
Tectonic Line, sedimentary and metamorphic rocks of
Paleozoic and Mesozoic formations are distributed; and
(4) in the mountains of Sado Island, volcanic rocks and
volcanic sedimentary rocks (green tuff), mainly deposited in
Paleogene to Neogene formations, are distributed.
Coastal sand dunes are connected to the plains of Niigata
Prefecture along the coastline. About 9000 to 7000 years
ago, after the Holocene glacial retreat, sediments were carried by rivers, and these coastal dunes are estimated to have
formed about 1000 years ago. As the mouth of the rivers
was blocked by the sand dunes, a vast wetland zone was
formed between the mountains and the coastal dunes, which
became the current Echigo plain. Alluvial plain deposits
(unsolidified sediments) are thickly distributed in the plains
of Niigata Prefecture, and in the Niigata Plain the thickness
reaches 160 m. The area close to the coast is mainly composed of sand and viscous soil, and the ground in the
upstream area close to the mountains is mainly composed of
gravel and sand.
7.1.3 Climate Condition
of the Kanto-Koushinetsu Region
(1) Climate condition of the Kanto region
The climate of Japan is influenced by a monsoonal flow that
carries moist air from the Indian Ocean and Pacific Ocean. In
general, Japan has four distinct seasons, namely, spring
(March to May), summer (June to August), autumn
(September to November), and winter (December to
February). In the Kanto region, it is usually warm
year-round, being rainy in the summer and dry in the winter
with dry winds. The summer rain is due to seasonal rains
(called “Tsuyu”) which occur from mid-June to mid-July), as
well as typhoons.
Mean annual precipitation in the Kanto region ranges
from 1000 to 3000 mm (in Tokyo the value is 1528 mm),
with the Kanto Plain receiving relatively little precipitation.
The southwest area of the Kanto region is a common pathway for typhoons, and this area therefore receives especially
high rainfall. The annual mean air temperature is 16.3 °C in
Tokyo, and is higher in southern coastal areas than in
mountainous zones.
The Kanto Plain is drained by the Kuji, Naka, Tone, Ara,
Tama, and Sagami river systems (Fig. 7.1). The Tone river
system has the largest drainage area of any river system in
Japan (16,840 km
2 ) and is also the country’s second longest
248
H. Sumida et al.