Monthly Volcanic Activity Report (December, 2010)
Japan Meteorological Agency
Meakandake[ Alert Level : 1]
Tremors with small amplitudes were observed four times from 12am to 10pm on 17 December. No remarkable
changes in plume, infrasonic and tilt data were observed during the occurrence of these tremors. The previous
tremor was observed on 18 March 2009.
Seismic activity has returned to the background level, after a temporal increase of volcanic earthquakes
with small amplitude during 17 December through 19 December.
According to the observation by Kakioka Magnetic Observatory of J MA, geomagnetic total intensity at
Meakandake has been increasing since July 2009, which reflects the cooling process beneath the
south slope of 96-1 crater, and its trend has been declining since July 2010.
No remarkable changes in both plume activity and crustal deformation were observed.
Asamayama[ Alert Level : 1]
Seismic activity was at low level, with a slight temporal activation during 28-31 December.
White plume was been rising to an altitude of 100-300m above the crater.
The sulfur-dioxide flux was measured as an average of 100-300 t/d in December (Fig.1 ).
No remarkable changes by both GPS and tiltmeter were observed.
Fig.1 Emission rate of SO2 at Asamayama. Closed circle and Open circle show the observation by JMA and
GSJ (Geological Survey of Japan), respectively.
Izu-Oshima[ Alert Level : 1]
Landwide inflation, which has been detected since late May 2010 by GPS and strainmeter observation, has been
declining since September. GPS network of GSI (Geospatial Information Authority of Japan) and tiltmeter
network of NIED (National Research Institute for Earth Science and Disaster Prevention) have also shown the
volcano inflation since May 2010 (Fig. 2).
Seismicity in the shallow parts in and around Izu-Oshima has been at low level in this period except when small
earthquakes temporally increased at the western offshore areas of Izu-Oshima on 22 December.
No remarkable change in surface phenomenon was observed.
Fig.2
Daily earthquake frequency and volume strain change in micro-strain (Dilatation positive).
Miyakejima [Alert Level : 2]
Gas-and-steam plumes rose to a height of 100-400m above the crater rim. The sulfur-dioxide flux varied from
500 to 900 t/d in December 2010 (cf. 700-900 t/d; November 2010; Fig.3). According to the report from Miyake
village, high SO2 concentration was sometimes recorded in some inhabited areas.
Seismicity has persisted at low level since early September 2010.
There was no geomagnetic change reflecting inner heat state beneath Miyakejima.
GPS observation shows continuous deflation of the volcano originated from the shallow source.
Fig.3
Emission rate of SO2 at Miyakejima.
Ioto [Near-crater Warning]
According to the observation by NIED, seismicity has stayed at low level.
According to the GPS observation by GSI, landwide upheaval resumed in May 2010 that was first observed
from August 2006 and ceased around October 2009, but slowed down since middle November. The extension of
the baseline in NS direction is still continuing.
Fukutoku-Oka-no-Ba [Near-sea-area Warning]
According to the information from the JMSDF (Japan Maritime Self-Defense Force) on 18 December,
discolored blue-white and green sea water was emitted from multiple active vents, and drifted south with 280
meters width and 1800 meters long (photo. 1).
Discolored water has frequently been observed around Fukutoku-Okano-Ba in recent years. The latest
submarine eruption occurred on 3 February 2010.
Photo.1 Discolored sea water at Fukutoku-Oka-no-Ba taken on 18 December 2010. Minami-Iwoto is at the
upper-left of this photo. Courtesy of JMSDF.
Kirishimayama（Shinmoedake）[Alert Level : 2]
Seismic activity at Shinmoedake was relatively high during December, with 203 earthquakes observed (cf. 150;
November 2010). Tremors with small amplitudes and short duration were occasionally observed. Gas-and-steam
plumes rose to a height of 100m above the crater rim (Maximum; 200m). GPS observation revealed no signs of
crustal deformation caused by volcanic activity.
Sakurajima[Alert Level : 3]
Explosive eruptions increased from late November till early December. Small eruptions intermittently occurred
since middle December. In this period, eruptions occurred 62 times (cf. 59; November 2010), of which 52 times
(cf. 50; November 2010) were explosive eruptions. Volcanic projectile reached to about 1300m from the
Showa-crater. No pyroclastic flow was observed.
There was no eruption at Minamidake summit crater.
Volcanic seismicity has remained at relatively low level.
The sulfur-dioxide flux elevated with an average of 2600 t/d in December 2010 (cf. 1100-1900 t/d; November
2010).
According to GPS measurement, the dilatation of the Sakurajima island turned into contraction or static state in
about June 2010. According to GPS measurement by the GSI, extension of the baselines that traverse Aira-Caldera
( at closed-off section of Kagoshima bay) decelerated in about July 2010. The water-tube tiltmeter by
MLIT( Ministry of land Infrastructure, Transport and Tourism; 2.5km SE of Minamidake summit crater )
suggested that the subsidence of summit has been slowing down since late November (Fig. 4). A temporal small
tilt change, which has been related to the increased magma supply beneath Sakurajima island, was confirmed on
early December.
Fig. 4 Tilt change observed by water-tube tiltmeter at station Arimura from January 2009 to December 2010,
corrected for tidal response and eruptions. Summit upheaval corresponds to positive tilt. In the upper figure,
red bars denote monthly frequencies of explosions from Showa-Crater.
Satsuma-Iojima [Alert Level : 2]
White-plume activity at Iodake summit crater remained above background levels, and rose 100 meters
(maximum; 300m) above the crater rim in this period. Seismicity has stayed at low level. An aerial observation
was conducted in corporation with the JMSDF on 14 December. No change of the distribution on thermal
anomalies was detected in and around the center of summit crater, as well as the last observation on 22 December
2009.
Suwanosejima [Alert Level : 2]
Mainly inferred from seismic records, possible ash explosions occurred intermittently through this period. 17
explosive eruptions (cf. 94; November 2010) occurred in this period. Volcanic earthquakes and tremors remained
at high level.
An aerial observation was conducted in corporation with the JMSDF on 14 December. High temperature areas
were confirmed both at the center of summit crater bottom and at the lower part of outer rim.