Northeastern Japan Arc

The Northeastern Japan Arc, also Northeastern Honshū Arc, is an island arc on the Pacific Ring of Fire. The arc runs north to south along the Tōhoku region of Honshū, Japan. It is the result of the subduction of the Pacific Plate underneath the Okhotsk Plate at the Japan Trench. The southern end of the arc converges with the Southwestern Japan Arc and the Izu-Bonin-Mariana Arc at the Fossa Magna (ja) at the east end of the Itoigawa-Shizuoka Tectonic Line (ITIL). This is the geologic border between eastern and western Honshū. Mount Fuji is at the point where these three arcs meet. To the north, the Northeastern Japan arc extends through the Oshima Peninsula of Hokkaidō. The arc converges in a collision zone with the Sakhalin Island Arc and the Kuril arc in the volcanic Ishikari Mountains of central Hokkaidō. This collision formed the Teshio and Yūbari Mountains.

The Ōu Mountains form the volcanic part of the inner arc. The volcanic front consists of Quaternary volcanoes, which extend the length of the range. It also includes the Quaternary volcanoes of southwestern Hokkaidō. The Dewa Mountains and the Iide Mountains are non-volcanic uplift ranges that run parallel to the west of the Ōu Mountains.

The outer arc ranges are the Kitakami and the Abukuma Mountains. These mountains are made from pre-tertiary rock. The mountains rose in the Cenozoic and have since been worn smooth by erosion.

Japan trench topographic
The Japan Trench, where the Pacific Plate slides beneath the Okhotsk Plate is the cause of the Northeastern Japan Arc


  • glgarcs, An Introduction to the Landforms and Geology of Japan, 2006, last access 2008-09-11.
Hokkaido Koma-ga-take

Hokkaidō Koma-ga-take (北海道駒ヶ岳, Hokkaidō Koma-ga-take), also Oshima Koma-ga-take (渡島駒ヶ岳), Oshima Fuji (渡島富士), or just Koma-ga-take (駒ヶ岳) is a 1131-meter adesitic stratovolcano on the border between Mori, Shikabe, and Nanae, all within the Oshima Subprefecture of Hokkaidō, Japan.

Occurrence of volcanic activity started some 30000 years ago. Following roughly 5000 years of dormancy, volcanic activity at Mount Koma-ga-take restarted at the start of the 17th century, triggering the Kan'ei Great Famine in 1640. Since then, there have been at least 50 recorded volcanic events at Mount Koma-ga-take.

Japan Trench

The Japan Trench is an oceanic trench part of the Pacific Ring of Fire off northeast Japan. It extends from the Kuril Islands to the northern end of the Izu Islands, and is 8,046 meters (26,398 ft) at its deepest. It links the Kuril-Kamchatka Trench to the north and the Izu-Ogasawara Trench to its south with a length of 800 km (500 miles). This trench is created as the oceanic Pacific plate subducts beneath the continental Okhotsk Plate (a microplate formerly a part of the North American Plate). The subduction process causes bending of the down going plate, creating a deep trench. Continuing movement on the subduction zone associated with the Japan Trench is one of the main causes of tsunamis and earthquakes in northern Japan, including the megathrust Tōhoku earthquake and resulting tsunami that occurred on 11 March 2011. The rate of subduction associated with the Japan Trench has been recorded at about 7.9-9.2 cm/yr.

Japanese archipelago

The Japanese archipelago (日本列島, Nihon Rettō) is a group of 6,852 islands that form the country of Japan. It extends over 3,000 km (1,900 mi) from the Sea of Okhotsk northeast to the Philippine Sea south along the northeastern coast of the Eurasia continent. It consists of islands from the Sakhalin island arc, the Northeastern Japan arc to the Ryukyu islands and the Nanpō Islands.

The term Home Islands was used at the end of World War II to define the area of Japan to which its sovereignty and the constitutional rule of the Emperor would be restricted. The term is also commonly used today to distinguish the archipelago from Japan's colonies and other territories in the first half of the 20th century.

Mount Aka (Yatsugatake)

Mount Aka (赤岳, Aka-dake) is a 2,899m mountain on the border of Chino, Hara of Nagano, and Hokuto of Yamanashi in Japan. This mountain is the tallest mountain of Yatsugatake Mountains.

Mount Asama

Mount Asama (浅間山, Asama-yama) is an active complex volcano in central Honshū, the main island of Japan. The volcano is the most active on Honshū. The Japan Meteorological Agency classifies Mount Asama as rank A. It stands 2,568 metres (8,425 ft) above sea level on the border of Gunma and Nagano prefectures. It is included in 100 Famous Japanese Mountains.

Mount Eniwa

Mount Eniwa (恵庭岳, Eniwa-dake) is an active volcano located in Shikotsu-Toya National Park in Hokkaidō, Japan. It sits opposite Mount Tarumae and Mount Fuppushi on the shores of Lake Shikotsu, the caldera lake that spawned the volcanoes. Mount Eniwa is the tallest of the three volcanoes.

Mount Fuji

Mount Fuji (富士山, Fujisan, IPA: [ɸɯꜜdʑisaɴ] (listen)), located on Honshū, is the highest volcano in Japan at 3,776.24 m (12,389 ft), 2nd-highest peak of an island (volcanic) in Asia, and 7th-highest peak of an island in the world. It is a dormant stratovolcano that last erupted in 1707–1708. Mount Fuji lies about 100 kilometers (60 mi) south-west of Tokyo, and can be seen from there on a clear day. Mount Fuji's exceptionally symmetrical cone, which is snow-capped for about 5 months a year, is a well-known symbol of Japan and it is frequently depicted in art and photographs, as well as visited by sightseers and climbers.Mount Fuji is one of Japan's "Three Holy Mountains" (三霊山, Sanreizan) along with Mount Tate and Mount Haku. It is also a Special Place of Scenic Beauty and one of Japan's Historic Sites. It was added to the World Heritage List as a Cultural Site on June 22, 2013. According to UNESCO, Mount Fuji has "inspired artists and poets and been the object of pilgrimage for centuries". UNESCO recognizes 25 sites of cultural interest within the Mount Fuji locality. These 25 locations include the mountain and the Shinto shrine, Fujisan Hongū Sengen Taisha, as well as the Buddhist Taisekiji Head Temple founded in 1290, later immortalized by Japanese ukiyo-e artist Katsushika Hokusai.

Mount Fuppushi

Mount Fuppushi (風不死岳, Fuppushi-dake) is dormant volcano located in Shikotsu-Toya National Park in Hokkaidō, Japan. It sits adjacent to Mount Tarumae and opposite Mount Eniwa. Mount Fuppushi is on the south shore of Lake Shikotsu, the caldera lake that spawned the volcanoes.

Mount Fure

Mount Fure (フレ岳, Fure-dake) is a mountain in the Nasu Volcanic Zone. It is located in Chitose, Hokkaidō, Japan. The mountain is the source of the Shiribetsu River.

Mount Mekunnai

Mount Mekunnai (目国内岳, Mekunnai-dake) is an andesitic volcano in the Mount Raiden Volcanic Group on the border between Iwanai and Rankoshi, Hokkaidō, Japan. Mount Mekunnai is a pyroclastic cone. The mountain consists of primarily non-alkali, mafic, volcanic rock. The rock is younger than that of neighboring Mount Raiden, being categorized at 700,000 to 13,000 years old. The rock is older than that of the Niseko Volcanic Group.

Mount Morappu

Mount Morappu (モラップ山, Morappu-san) is a mountain located in Shikotsu-Toya National Park in Hokkaidō, Japan. It sits on the shore of Lake Shikotsu, a caldera lake. It also hosts a nationally established ski slope.

Mount Raiden

Mount Raiden (雷電山, Raiden-yama) is an andesitic volcano in the Mount Raiden Volcanic Group on the border between Iwanai and Rankoshi, Hokkaidō, Japan. Mount Raiden is a pyroclastic cone. The mountain consists of primarily non-alkali, mafic, volcanic rock.

Mount Tarumae

Mount Tarumae (樽前山, Tarumae-zan) is located in the Shikotsu-Toya National Park in Hokkaidō, Japan. It is located near both Tomakomai and Chitose towns and can be seen clearly from both. It is on the shores of Lake Shikotsu, a caldera lake. Tarumae is a 1,041 metre active andesitic stratovolcano, with a lava dome.

Mount Yoko (Northern Yatsugatake)

Mount Yoko (横岳, Yoko-dake) also Mount Kita Yoko, is an active lava dome located in the Northern Yatsugatake Volcanic Group of the Yatsugatake Mountains, Honshū, Japan. Mount Yoko has shown the most recent activity and is now considered an active volcano. It last erupted about 800 years ago. The eruption consisted of ash with a lava flow of some 3 million cubic meters. The eruption was dated by corrected radiocarbon dating. The next previous eruption was in or after 400 BCE.

Mount Yoko (Southern Yatsugatake)

Mount Yoko (横岳, Yoko-dake) is located in the Southern Yatsugatake Volcanic Group of the Yatsugatake Mountains, Honshū, Japan.

Sakhalin Island Arc

Sakhalin Island Arc is an ancient volcanic arc dating from the Early Miocene. The arc was a result of the Okhotsk Plate subducting beneath the Eurasian Plate in the convergence zone. The arc runs from mainland Asia through Sakhalin Island into central Hokkaido and the collision zone around the Daisetsuzan Volcanic Group, where the Kuril Island Arc and the Northeastern Japan Arc meet.

Volcanic arc

A volcanic arc is a chain of volcanoes formed above a subducting plate,

positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally, volcanic arcs result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench. The oceanic plate is saturated with water, and volatiles such as water drastically lower the melting point of the mantle. As the oceanic plate is subducted, it is subjected to greater and greater pressures with increasing depth. This pressure squeezes water out of the plate and introduces it to the mantle. Here the mantle melts and forms magma at depth under the overriding plate. The magma ascends to form an arc of volcanoes parallel to the subduction zone.

These should not be confused with hotspot volcanic chains, where volcanoes often form one after another in the middle of a tectonic plate, as the plate moves over the hotspot, and so the volcanoes progress in age from one end of the chain to the other. The Hawaiian Islands form a typical hotspot chain; the older islands (tens of millions of years old) to the northwest are smaller and more lush than the recently created (400,000 years ago) Hawaii island itself, which is more rocky. Hotspot volcanoes are also known as "intra-plate" volcanoes, and the islands they create are known as Volcanic Ocean Islands. Volcanic arcs do not generally exhibit such a simple age-pattern.

There are two types of volcanic arcs:

oceanic arcs form when oceanic crust subducts beneath other oceanic crust on an adjacent plate, creating a volcanic island arc. (Not all island arcs are volcanic island arcs.)

continental arcs form when oceanic crust subducts beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt.In some situations, a single subduction zone may show both aspects along its length, as part of a plate subducts beneath a continent and part beneath adjacent oceanic crust.

Volcanoes are present in almost any mountain belt, but this does not make it a volcanic arc. Often there are isolated, but impressively huge volcanoes in a mountain belt. For instance, Vesuvius and the Etna volcanoes in Italy are part of separate but different kinds of mountainous volcanic ensembles.

The active front of a volcanic arc is the belt where volcanism develops at a given time. Active fronts may move over time (millions of years), changing their distance from the oceanic trench as well as their width.

Yūbari Mountains

Yūbari Mountains (夕張山地, Yūbari-sanchi) is a mountain range of Hokkaidō, Japan.

Part of this range is protected by the Furano-Ashibetsu Prefectural Natural Park (富良野芦別道立自然公園).

Ōu Mountains

The Ōu Mountains (奥羽山脈, Ōu-sanmyaku) are a mountain range in the Tōhoku region of Honshū, Japan. The range is the longest range in Japan and stretches 500 km (311 mi) south from the Natsudomari Peninsula of Aomori Prefecture to the Nasu volcanoes at the northern boundary of the Kantō region. Though long, the range is only about 35 kilometres (22 mi) wide. The highest point in the range is Mount Iwate, 2,038 metres (6,686 ft).The range includes several widely known mountains: Hakkōda Mountains, Mount Iwate, Mount Zaō, Mount Azuma, and Mount Adatara.

Faults and rift zones
Trenches and troughs

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