Izu-Tobu

Izu-Tobu
Izu-Tobu volcano field

Mount Ōmuro, a symbolic pyroclastic cone of　the Izu-Tobu volcano field
Highest point
Elevation 1,406 metres (4,613 ft)
Coordinates 34°53′59″N 139°05′52″E / 34.89972°N 139.09778°E / 34.89972; 139.09778Coordinates: 34°53′59″N 139°05′52″E / 34.89972°N 139.09778°E / 34.89972; 139.09778
Naming
Native name 伊豆東部火山群
Geography
Location Izu Peninsula, Shizuoka Prefecture, Japan
Geology
Mountain type Pyroclastic cones
Last eruption July 1989

Izu-Tobu (伊豆東部火山群 Izu Tōbu Kazangun) is a large, dominantly basaltic range of volcanoes on the east side of the Izu Peninsula which lies on the Pacific coast of the island of Honshu in Japan. The field covers a total area of 400 km2. The only recorded activity was a submarine phreatic eruption, between the city of Ito and Hatsushima island, that lasted for just 10 minutes in 1989. Ito, home to 74,000 people, is known for its hot springs.

Morphology

The field covers the east side of the Izu Peninsula. It consists of several small stratovolcanoes (mostly Pleistocene in age) and overlapping pyroclastic cones, which covers 400 km2 in area. There are 70 young monogenetic volcanoes on land. Kawagodaira maar, which is about 3,000 years old, produced a large Holocene eruption that sent pyroclastic flows over a wide area.

Eruptions

Distribution map

1989 Eruption

The only recorded eruption was an event on 13 July 1989. Two earthquakes, on 30 June and 9 July took, place on the Izu-Tobu Volcano. On 13 July, a seismometer recorded seisimity, a research vessel, the RV Takuyo reported hearing an explosion sound from the sea floor followed by a 30 second vibration at 18:33 pm. At 18:40 pm the crew reported that the sea domed up 500 m from the vessel, then a grey-black plume rose from the area, five more domes were reported in the next 5 minutes which caused the ship to vibrate. After that seisimity declined.

This marks the only known eruptive activity at Izu-Tobu. The next day a survey using an unmanned vessel discovered a new cone 100 metres underwater. The cone was around 450 Metres wide with a summit crater 200 m in diameter. The height of the cone above the sea floor was only 10 m in height.

The University of Tokyo monitors Izu-Tobu 24 hours a day.

Distinct cones

Image Name Location Type[1][2] Height Eruption[1][2] Coordinates Comments
Mount Ōmuro
(大室山)		 Itō Cinder cone 580 m 4 ka 34°54′11″N 139°05′40″E / 34.9031°N 139.0945°E / 34.9031; 139.0945 Lava flow formed the Jōgasaki coast.

(Right)
 Mount Komuro
(小室山)		 Itō Cinder cone 321 m 15 ka 34°56′21″N 139°07′52″E / 34.9391°N 139.131°E / 34.9391; 139.131
Mount Io
(伊雄山)		 Itō Cinder cone 459 m 2.7 ka 34°52′18″N 139°04′46″E / 34.8717°N 139.0795°E / 34.8717; 139.0795
Mount Tōgasa
(遠笠山)		 Izu &
Higashizu		 Cinder cone 1,197 m 14 ka - 15 ka 34°52′43″N 139°01′57″E / 34.8786°N 139.0325°E / 34.8786; 139.0325 Oldest volcano in Izu-Tobu volcano field
 Kawagodaira
(皮子平)		 Izu Volcanic crater approx. 1,090 m 3.2 ka 34°51′36″N 138°58′55″E / 34.860°N 138.982°E / 34.860; 138.982
Mount Maruno
(丸野山)		 Izu Cinder cone 697 m 107 ka 34°54′40″N 139°01′26″E / 34.911°N 139.024°E / 34.911; 139.024
Mount Sukumo
(巣雲山)		 Izu Cinder cone 581 m 132 ka 35°00′18″N 139°02′13″E / 35.005°N 139.037°E / 35.005; 139.037
Mount Hachikubo
(鉢窪山)		 Izu Cinder cone 674 m 17 ka 34°51′43″N 138°55′44″E / 34.862°N 138.929°E / 34.862; 138.929 Lava flow from Mount Hachikubo formed Jōren Falls.
Mount Maru
(丸山)		 Izu Cinder cone 938 m 17 ka 34°51′18″N 138°56′20″E / 34.855°N 138.939°E / 34.855; 138.939
Mount Takatsuka
(高塚山)		 Izunokuni Cinder cone 369 m 132 ka 35°00′59″N 138°58′48″E / 35.0165°N 138.98°E / 35.0165; 138.98 Cinder cone was halved by quarrying.
Mount Hachino
(鉢ノ山)		 Kawazu Cinder cone 619 m 36 ka 34°47′35″N 138°58′16″E / 34.793°N 138.971°E / 34.793; 138.971

(Left)
 Mount Yahazu
(矢筈山)		 Itō Lava dome 816 m 2.7 ka 34°53′42″N 139°03′25″E / 34.895°N 139.057°E / 34.895; 139.057

(Right)
 Mount Anano
(孔ノ山)		 Itō Lava dome 660 m 2.7 ka 34°54′00″N 139°03′11″E / 34.9°N 139.053°E / 34.9; 139.053
Mount Iwano
(岩ノ山)		 Izu Lava dome 602 m 2.7 ka 34°54′47″N 139°02′20″E / 34.913°N 139.039°E / 34.913; 139.039
Ippeki lake
(一碧湖)		 Itō Maar Surface elevation
185 m[3]		 103.5 ka 34°55′48″N 139°06′18″E / 34.93°N 139.105°E / 34.93; 139.105
Jōgasaki coast

(城ヶ崎海岸)

 Itō Lava flow
-
 4 ka
 34°53′24″N 139°08′17″E / 34.89°N 139.138°E / 34.89; 139.138 This coast was mostly formed by lava flow from Mount Ōmuro.
Teishi knoll
(手石海丘)		 Sagami Sea (off Itō) Volcanic crater 81 m below sea level 13 July 1989 34°59′06″N 139°07′08″E / 34.985°N 139.118889°E / 34.985; 139.118889 Youngest volcano in Izu-Tobu volcano field. Eruption video by Japan Coast Guard

References

  1. 1 2 Shizuoka University - Masato Koyama's website
  2. 1 2 Izu Shimbun newspaper article　"伊豆の大地の物語"
  3. ↑ 環境省自然環境局生物多様性センター 1980年の第2回自然環境保全基礎調査 陸水域関係調査報告書 （湖沼） 全国版 PDF
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