Quaternary Volcanoes > Active Volcanoes > Hachijojima

5: Historical eruptions - 6: Present activities

5: Historical eruptions
   The record of eruptions from Hachijojima is limited, from after the 15th century to the early 17th century, and not complete (Sugihara and Shimada, 1998). All recorded eruptions occurred in the Nishiyama Volcano (Table 2). There are records of eruptions at the summit of the Nishiyama Volcano on December 7, 1487 (year 1 of Chokyo Era) and during 1518–1523 (year 15 of Eisho Era–year 3 of Daie Era). On October 27, 1605 (year 10 of Keicho Era), there was an eruption from a fissure that occurred on the southeastern flank of the Nishiyama Volcano (Fujitozando Volcanic Chain), erupting scoria and lava flows from the lower part of the fissures (Sugihara and Shimada, 1998). As described earlier, volcanic deposits with carbon-14 ages of around 400 yr BP are Osarigahana Pyroclastic Flow Deposits and associated lava flows, Idesarigahana Lava, Fujitozando Scoria Cone deposit, and associated lava flows on the southeastern flank of the Nishiyama Volcano and Funatsukihana Scoria Cone Deposit on the southwestern flank. These historical records and stratigraphic sequence of younger deposits establish that the Nishiyama Volcano underwent frequent summit eruptions and fissure eruptions on the southeast to southwest flank during the Muromachi Period to the early Edo Period. There is no firm record of subsequent eruptions. Thus, it is assumed that there were no eruptions after the early 17th century.

6: Present activities
6.1 Seismic activities
   Seismic activities are associated with magma intrusions in the Nishiyama Volcano. In August 2002, there was an earthquake swarm near the Nishiyama Volcano and extenstion was observed around it. Analysis of a series of seismic activities and crustal movements indicated that these movements were caused by a dike that intruded from the center of Nishiyama, expanding into the northwestern shore (Kumagai et al., 2003).

6.2 Hot springs
   All hot springs in use in Hachijojima were found in the Kashidate, Nakanogo and Sueyoshi areas on the southern foot of the Higashiyama Volcano. Most hot springs contain sodium and chloride, and the temperature of the spring is 40–65 ºC. The majority of source springs are pumped.

6.3 Geothermal power plants
   In the Nakanogo area on the southern flank of the Higashiyama Volcano, a geothermal power plant with rated output of 3300 kW has been in operation since 1999. Two steam wells with depths of 1650 and 960 m exist.

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