(Photo by Karuizawa Weather Station, 15 September 2004)
Revised on 23 June 2005
Asama volcano, which is one of the most active volcanoes in Japan, erupted at 20:02 JST, 1 September 2004.
Fresh lava emerged in mid-September and continuous eruption took place in 15-18 September. Coordinating Committee for Prediction of Volcanic Eruption (CCPVE) was appealing cautions by saying that there is the possibility of more explosions.
Since the spring of 2005, seismicity and thermal activity have gradually declined, JMA updated the Level as 2 (Active) on 23 June. However, CCPVE commented "There is a possibility of eruptive activity in future, therefore, careful watch is still necessary" on the same day.
Major eruption of Asamayama in 2004
Tilt change preceding explosionIn the present activity of Asama volcano, very small tilt changes were observed preceding some explosions.
At a tiltmeter set 2.5km distant from the summit, very small tilt changes were observed several hours to one day before some explosions. They are indicated as expansion of a pressure source beneath the active crater.
Tilt change and hourly number of volcanic earthquakes. Small tilt change (the white arrow) was detected just before the explosion (the arrow). Please click the figure to see other examples.
Definition of Volcanic Activity Level of Asama of JMA
Sequence of the Level of Asama by JMA2003.11. 4 / LEVEL 2 / Start of announcement of the Volcanic Activity Level by JMA
2004. 7.20 / LEVEL 1 / Low level of seismicity
2004. 7.31 / LEVEL 2 / High level of seismicity and volcanic gas emission
2004. 9. 1 / LEVEL 3 / Explosive eruption
2005. 6.21 / LEVEL 2 / Seismicity and volcanic gas emission declined
2006. 9.22 / LEVEL 1 / Seismicity and volcanic gas emission declined
LINKSAsama page of Earthquake Research Institute, Tokyo Univ.
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