Izu-Tobu

Izu-Tobu
Izu-Tobu volcano field
240px Mount Ōmuro, a symbolic pyroclastic cone of　the Izu-Tobu volcano field
Highest point
Coordinates
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

File:Izu-tobu Volcano Group Distribution Map.jpg

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	Height	Eruption	Coordinates	Comments
100px	Mount Ōmuro (大室山)	Itō	Cinder cone	580 m	4 ka		Lava flow formed the Jōgasaki coast.
100px (Right)	Mount Komuro (小室山)	Itō	Cinder cone	321 m	15 ka
50px	Mount Io (伊雄山)	Itō	Cinder cone	459 m	2.7 ka
100px	Mount Tōgasa (遠笠山)	Izu & Higashizu	Cinder cone	1,197 m	14 ka - 15 ka		Oldest volcano in Izu-Tobu volcano field
50px	Kawagodaira (皮子平)	Izu	Volcanic crater	approx. 1,090 m	3.2 ka
100px	Mount Maruno (丸野山)	Izu	Cinder cone	697 m	107 ka
100px	Mount Sukumo (巣雲山)	Izu	Cinder cone	581 m	132 ka
100px	Mount Hachikubo (鉢窪山)	Izu	Cinder cone	674 m	17 ka		Lava flow from Mount Hachikubo formed Jōren Falls.
50px	Mount Maru (丸山)	Izu	Cinder cone	938 m	17 ka
100px	Mount Takatsuka (高塚山)	Izunokuni	Cinder cone	369 m	132 ka		Cinder cone was halved by quarrying.
100px	Mount Hachino (鉢ノ山)	Kawazu	Cinder cone	619 m	36 ka
100px (Left)	Mount Yahazu (矢筈山)	Itō	Lava dome	816 m	2.7 ka
100px (Right)	Mount Anano (孔ノ山)	Itō	Lava dome	660 m	2.7 ka
50px	Mount Iwano (岩ノ山)	Izu	Lava dome	602 m	2.7 ka
100px	Ippeki lake (一碧湖)	Itō	Maar	Surface elevation 185 m	103.5 ka
	Jōgasaki coast (城ヶ崎海岸)	Itō	Lava flow	-	4 ka		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		Youngest volcano in Izu-Tobu volcano field. Eruption video by Japan Coast Guard

References

• Global Volcanism Program
• Volcanolive.com

External links

• Izu-Tobu Volcanoes - Japan Meteorological Agency (Japanese)
• Izu-Tobu Volcanoes : National catalogue of the active volcanoes in Japan PDF - Japan Meteorological Agency
• Izu Tobu Volcano Group - Geological Survey of Japan
• Izu-Tobu: Global Volcanism Program - Smithsonian Institution
• Eruptive history of the Higashi Izu monogenetic volcano field - Shizuoka University