# Izu-Tobu

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 km$^2$. 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 km$^2$ 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
### 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 seismicity, 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 seismicity 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 |
| | 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 and 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 | 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 |