mountainous areas is mesic, while that of plain and plateau
areas are thermic (15–22 °C). In subtropical areas of the
Nansei Islands, the soil temperature regime is hyperthermic
( ! 22 °C).
As explained in Sect. 2.2, the topography of Japan has
specific characteristics in contrast to other parts of the world.
It is located in the circum-Pacific orogeny, and 70% of the
land area is composed of steep, mountainous areas or gentle
hilly areas; lowlands only occupy approximately 14% of the
land area. Mountainous areas run through the center of the
Japanese archipelago like a spine, meaning that large portions of the islands are steep mountains, and only small areas
of flat land exist. This also means that Japan’s river systems
have short watercourses and steep slopes, resulting in small
catchment areas. The rainy seasons and typhoons, as well as
melting snow in early spring, cause large changes in river
flow volume, which results in frequent natural disasters such
as flooding. Flooding creates floodplains and natural levees
in the alluvial plains of the lowlands. Behind these natural
levees, back swamps form that contain fine particles such as
clay and silt and are poorly drained.
In Northern Japan, including the Hokkaido and Tohoku
regions, where climatic conditions are cool, hygrophytes,
such as the common reed and Japanese alder, grow, and
Low-moor Peat soils form due to low soil temperature limiting the decomposition of organic material (Fig. 4.8). In
Hokkaido, frigid soil temperature regimes exist, especially in
the eastern and northern parts of the island, but also in the
Ishikari, Teshio, Sarobetsu, and Kushiro River basins, where
large back swamps and marshy ground have formed. Large
areas of Organic soils can be found here. High-moor Peat
soils and Low-moor Peat soils are present in the Ishikari
peatland, whereas low-moor peatland occupies much of the
Sarobetsu and Kushiro peatlands (Sakaguchi 1974). The
Kushiro peatland, one of the largest peatlands in Japan, is
preserved under relatively natural conditions because of its
poor geographical setting. At the base of the peat layer, a
layer containing shell exoskeletons of marine origin has been
found, showing that the area is a large shallow marshy
ground created after the marine regression in the Holocene
Epoch. Subsequently, the Kushiro River drained into the
marshy ground, flooding it repeatedly. In addition, there was
seepage from surrounding hilly areas (diluvial uplands) that
were capes previously under marine transgression supplying
water, resulting in the formation of a paludization-type
peatland (Fig. 4.8).
The abundance of volcanic mountains is also an important characteristic of the topography and geology of Japan.
These not only deposit volcanic ash and other volcanic
ejecta during eruptions, but also occasionally form depressions and gently sloping topography in mountainous and
highland areas as a result of lava and mud flows. Areas
where young volcanoes of Quaternary age are present have
topographical features formed by lava and mud flows that
easily collect water, including dammed basins and/or shallow swale features. Subsequently, abundant seepage water is
supplied from the slope and foot of a volcano, forming lakes
and wetlands. In mountainous and highland areas with high
elevation, the rate of decomposition of plant remains is slow
due to low soil temperature, and terrestrialization-type
peatlands form (Sakaguchi 1974).
The Oze Marshland, in Honshu, is located in the mountainous area of the Gunma–Fukushima–Niigata border at an
elevation of 1400 m a.s.l. It is the largest typical high-moor
Fig. 4.8 Formation of typical paludaization-type peatland in Japan.
a Seepage peatland formed by the growth of hygrophyte in swamp with
seepage water from diluvial upland and terrace cliffs. b Fluvial peatland
formed by the growth of hygrophyte such as common reed in back
swamp of alluvial plain. These types of peatlands are common in
northern Japan in the Hokkaido and Tohoku regions where the climate
is cool, and they are often large scale. (Figures supplied by Masayuki
Tani)
78
Y. Takata et al.
areas are thermic (15–22 °C). In subtropical areas of the
Nansei Islands, the soil temperature regime is hyperthermic
( ! 22 °C).
As explained in Sect. 2.2, the topography of Japan has
specific characteristics in contrast to other parts of the world.
It is located in the circum-Pacific orogeny, and 70% of the
land area is composed of steep, mountainous areas or gentle
hilly areas; lowlands only occupy approximately 14% of the
land area. Mountainous areas run through the center of the
Japanese archipelago like a spine, meaning that large portions of the islands are steep mountains, and only small areas
of flat land exist. This also means that Japan’s river systems
have short watercourses and steep slopes, resulting in small
catchment areas. The rainy seasons and typhoons, as well as
melting snow in early spring, cause large changes in river
flow volume, which results in frequent natural disasters such
as flooding. Flooding creates floodplains and natural levees
in the alluvial plains of the lowlands. Behind these natural
levees, back swamps form that contain fine particles such as
clay and silt and are poorly drained.
In Northern Japan, including the Hokkaido and Tohoku
regions, where climatic conditions are cool, hygrophytes,
such as the common reed and Japanese alder, grow, and
Low-moor Peat soils form due to low soil temperature limiting the decomposition of organic material (Fig. 4.8). In
Hokkaido, frigid soil temperature regimes exist, especially in
the eastern and northern parts of the island, but also in the
Ishikari, Teshio, Sarobetsu, and Kushiro River basins, where
large back swamps and marshy ground have formed. Large
areas of Organic soils can be found here. High-moor Peat
soils and Low-moor Peat soils are present in the Ishikari
peatland, whereas low-moor peatland occupies much of the
Sarobetsu and Kushiro peatlands (Sakaguchi 1974). The
Kushiro peatland, one of the largest peatlands in Japan, is
preserved under relatively natural conditions because of its
poor geographical setting. At the base of the peat layer, a
layer containing shell exoskeletons of marine origin has been
found, showing that the area is a large shallow marshy
ground created after the marine regression in the Holocene
Epoch. Subsequently, the Kushiro River drained into the
marshy ground, flooding it repeatedly. In addition, there was
seepage from surrounding hilly areas (diluvial uplands) that
were capes previously under marine transgression supplying
water, resulting in the formation of a paludization-type
peatland (Fig. 4.8).
The abundance of volcanic mountains is also an important characteristic of the topography and geology of Japan.
These not only deposit volcanic ash and other volcanic
ejecta during eruptions, but also occasionally form depressions and gently sloping topography in mountainous and
highland areas as a result of lava and mud flows. Areas
where young volcanoes of Quaternary age are present have
topographical features formed by lava and mud flows that
easily collect water, including dammed basins and/or shallow swale features. Subsequently, abundant seepage water is
supplied from the slope and foot of a volcano, forming lakes
and wetlands. In mountainous and highland areas with high
elevation, the rate of decomposition of plant remains is slow
due to low soil temperature, and terrestrialization-type
peatlands form (Sakaguchi 1974).
The Oze Marshland, in Honshu, is located in the mountainous area of the Gunma–Fukushima–Niigata border at an
elevation of 1400 m a.s.l. It is the largest typical high-moor
Fig. 4.8 Formation of typical paludaization-type peatland in Japan.
a Seepage peatland formed by the growth of hygrophyte in swamp with
seepage water from diluvial upland and terrace cliffs. b Fluvial peatland
formed by the growth of hygrophyte such as common reed in back
swamp of alluvial plain. These types of peatlands are common in
northern Japan in the Hokkaido and Tohoku regions where the climate
is cool, and they are often large scale. (Figures supplied by Masayuki
Tani)
78
Y. Takata et al.