mountainous areas by the action of running water, waves,
wind, mass movement and so forth, and the eroded material
is deposited in the plain. Therefore, the sediments constituting the plains include clastics and weathered materials
derived from the basement geology upstream. As these
sediments are exposed near the surface of lowland plains or
redeposited as wind dust, materials derived from the basement geology also affect soil parent materials.
2.2.2 Meso- to Mini-landforms in the Mobile
Zone: Arrangement of Mountains, Basins,
Plains and Volcanoes
(1) Arrangement of mountains, basins and plains as
features of the island arc
The Japanese Islands comprise the Eastern Japan island arc
system (Kuril arc, Northeast Japan arc and Izu-Ogasawara
arc), which is active in connection with the subduction of
Pacific Plate, and the Western Japan island arc system
(Southwest Japan arc and Ryukyu arc), which is active in
connection with the subduction of the Philippine Sea Plate.
The ongoing tectonic movement manifests as earthquakes
and geodetic crustal movements. Earthquakes repeatedly
occur over a long period, crustal deformation is ongoing,
uplift or subsidence accumulates at each place, and landforms and geological structures such as basins, mountain
ranges, island arcs and trenches have been formed. Mountains are areas of relative uplift, and plains are areas of relative subsidence.
In areas where arcs meet other arcs, unique geological
structures and topographical arrangements arise due to
mutual collision and the duplication of properties
(Figs. 2.12, 2.13 and 2.14). The terrestrial area of the
Japanese Islands consists mainly of an outer arc (fore-arc)
and an inner arc (back-arc). The lowland between the outer
and inner arcs is an area of relative subsidence and in places
consists of marine areas, such as the Seto Inland Sea.
The outer arc is located outside the volcanic front and is a
broad zone of slow uplift with large, long-wavelength
undulations. The terrestrial area of this zone is a mainly
mountainous area composed of basement rocks of
pre-Paleogene age; the Neogene formation is barely distributed inside the mountains. This area was generally subjected to land erosion through the Late Cenozoic. The
terrestrial areas of the outer arc are as follows: Shikotan;
Habomai Island; the Nemuro Peninsula; Kushiro and the
Kitakami Mountains; the Abukuma Mountains; the Ogasawara Islands included in the Eastern Japan island arc
system; the Akaishi Mountains; the Kii Mountains; the
Shikoku Mountains and Amami Islands; the Okinawa
Islands; and the Sakishima Islands included in the Western
Japan island arc system (Fig. 2.13).
The inner arc is located inside the volcanic front and is a
region with marked crustal activity characterized by volcanic
activity. Uplift and subsidence with short wavelengths are
dominant, and faults and folds are prominent. Long north–
south uplift parts include the Ou Mountains and Dewa
Mountains, and alternating areas of subsidence occur
between them, which is visible in the topography
(Fig. 2.15). In the subsidence basin, thick Neogene and
Quaternary materials are deposited. A part of the formation
afterward became a constituent of the uplifted mountains.
From the northeastern part of Hokkaido, the main part of the
Kuril Islands, including Kunashiri Island and Etorofu Island,
and the Tohoku region west of the Ou Mountains, constitutes the inner arc of the Eastern Japan arc system. In the
Southwest Japan arc, like in the Eastern Japan arc system,
volcanic activity and the topographical and geological features are not distinct. In the Ryukyu arc, volcanic islands
such as Iōjima, Kuchinoerabu-jima and the Tokara Islands
are inner arc islands.
At the meeting point of the island arcs, the band structure
of the island arcs is disturbed by plate collision and lateral
movement of the land-side plate, resulting in topography and
structure characterized by compression and extension toward
different directions (Fig. 2.13). In the central part of Hokkaido, the collision of the Okhotsk Plate with the Northeast
Japan arc formed a folding mountain range in the central
axis of Hokkaido in the mid-Cenozoic Era, stretching from
the Teshio Mountains to the Yubari Mountains. Later, the
westward movement of the outer arc of the Kuril Island arc
formed the Hidaka Mountains by fault movement. In the
central part of Honshu, the collision of the Southwest Japan
arc with the Philippine Sea Plate formed the flexible
arrangement of Akaishi Mountains and the Kanto Mountains
in the Late Cenozoic Era. In Kyushu, the Ryukyu arc and the
Southwest Japan arc are in contact with each other, and the
characteristics of the inner arc of the Ryukyu arc (Beppu–
Shimabara rift belt crossing the central part of Kyushu)
overlap with the old belt structure of the Southwest Japan arc
(Fig. 2.13).
(2) Geographical distribution of volcanoes
In the Japanese Islands, the occurrence and rise of magma
that manifests as volcanic activity are caused by the subduction of the oceanic plate at the convergent boundary, and
the volcanic line is connected to the shaft of the island arc. In
the process of the massive penetration of felsic magmas to
the upper crust, which creates formations of acidic rocks, a
wide area of uplift in the rock mass distribution area
sometimes forms mountains. The wide area of uplift in the
2 Soil-Forming Factors
27
wind, mass movement and so forth, and the eroded material
is deposited in the plain. Therefore, the sediments constituting the plains include clastics and weathered materials
derived from the basement geology upstream. As these
sediments are exposed near the surface of lowland plains or
redeposited as wind dust, materials derived from the basement geology also affect soil parent materials.
2.2.2 Meso- to Mini-landforms in the Mobile
Zone: Arrangement of Mountains, Basins,
Plains and Volcanoes
(1) Arrangement of mountains, basins and plains as
features of the island arc
The Japanese Islands comprise the Eastern Japan island arc
system (Kuril arc, Northeast Japan arc and Izu-Ogasawara
arc), which is active in connection with the subduction of
Pacific Plate, and the Western Japan island arc system
(Southwest Japan arc and Ryukyu arc), which is active in
connection with the subduction of the Philippine Sea Plate.
The ongoing tectonic movement manifests as earthquakes
and geodetic crustal movements. Earthquakes repeatedly
occur over a long period, crustal deformation is ongoing,
uplift or subsidence accumulates at each place, and landforms and geological structures such as basins, mountain
ranges, island arcs and trenches have been formed. Mountains are areas of relative uplift, and plains are areas of relative subsidence.
In areas where arcs meet other arcs, unique geological
structures and topographical arrangements arise due to
mutual collision and the duplication of properties
(Figs. 2.12, 2.13 and 2.14). The terrestrial area of the
Japanese Islands consists mainly of an outer arc (fore-arc)
and an inner arc (back-arc). The lowland between the outer
and inner arcs is an area of relative subsidence and in places
consists of marine areas, such as the Seto Inland Sea.
The outer arc is located outside the volcanic front and is a
broad zone of slow uplift with large, long-wavelength
undulations. The terrestrial area of this zone is a mainly
mountainous area composed of basement rocks of
pre-Paleogene age; the Neogene formation is barely distributed inside the mountains. This area was generally subjected to land erosion through the Late Cenozoic. The
terrestrial areas of the outer arc are as follows: Shikotan;
Habomai Island; the Nemuro Peninsula; Kushiro and the
Kitakami Mountains; the Abukuma Mountains; the Ogasawara Islands included in the Eastern Japan island arc
system; the Akaishi Mountains; the Kii Mountains; the
Shikoku Mountains and Amami Islands; the Okinawa
Islands; and the Sakishima Islands included in the Western
Japan island arc system (Fig. 2.13).
The inner arc is located inside the volcanic front and is a
region with marked crustal activity characterized by volcanic
activity. Uplift and subsidence with short wavelengths are
dominant, and faults and folds are prominent. Long north–
south uplift parts include the Ou Mountains and Dewa
Mountains, and alternating areas of subsidence occur
between them, which is visible in the topography
(Fig. 2.15). In the subsidence basin, thick Neogene and
Quaternary materials are deposited. A part of the formation
afterward became a constituent of the uplifted mountains.
From the northeastern part of Hokkaido, the main part of the
Kuril Islands, including Kunashiri Island and Etorofu Island,
and the Tohoku region west of the Ou Mountains, constitutes the inner arc of the Eastern Japan arc system. In the
Southwest Japan arc, like in the Eastern Japan arc system,
volcanic activity and the topographical and geological features are not distinct. In the Ryukyu arc, volcanic islands
such as Iōjima, Kuchinoerabu-jima and the Tokara Islands
are inner arc islands.
At the meeting point of the island arcs, the band structure
of the island arcs is disturbed by plate collision and lateral
movement of the land-side plate, resulting in topography and
structure characterized by compression and extension toward
different directions (Fig. 2.13). In the central part of Hokkaido, the collision of the Okhotsk Plate with the Northeast
Japan arc formed a folding mountain range in the central
axis of Hokkaido in the mid-Cenozoic Era, stretching from
the Teshio Mountains to the Yubari Mountains. Later, the
westward movement of the outer arc of the Kuril Island arc
formed the Hidaka Mountains by fault movement. In the
central part of Honshu, the collision of the Southwest Japan
arc with the Philippine Sea Plate formed the flexible
arrangement of Akaishi Mountains and the Kanto Mountains
in the Late Cenozoic Era. In Kyushu, the Ryukyu arc and the
Southwest Japan arc are in contact with each other, and the
characteristics of the inner arc of the Ryukyu arc (Beppu–
Shimabara rift belt crossing the central part of Kyushu)
overlap with the old belt structure of the Southwest Japan arc
(Fig. 2.13).
(2) Geographical distribution of volcanoes
In the Japanese Islands, the occurrence and rise of magma
that manifests as volcanic activity are caused by the subduction of the oceanic plate at the convergent boundary, and
the volcanic line is connected to the shaft of the island arc. In
the process of the massive penetration of felsic magmas to
the upper crust, which creates formations of acidic rocks, a
wide area of uplift in the rock mass distribution area
sometimes forms mountains. The wide area of uplift in the
2 Soil-Forming Factors
27