Monthly Volcanic Activity Report (February, 2011)

Transcription

1 Monthly Volcanic Activity Report (February, 2011) Japan Meteorological Agency Izu-Oshima[ Alert Level : 1] Earthquakes at the western offshore areas of Izu-Oshima increased on 9 th temporarily in this period. Landwide inflation, which has been detected since late May 2010 by GPS and strainmeter observation, has been declining since September, and has tuned into static state since January GPS network of GSI (Geospatial Information Authority of Japan) has also shown the volcano inflation since May No remarkable change in surface phenomenon was observed. Miyakejima [Alert Level : 2] Gas-and-steam plumes rose to a height of m above the crater rim. The sulfur-dioxide flux was 1000 t/d in February 2011 (cf t/d; January 2011; Fig.1). 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 There was no geomagnetic change reflecting inner heat state beneath Miyakejima. GPS observation shows continuous deflation of the volcano originated from the shallow source.

2 Fig.1 Emission rate of SO2 at Miyakejima. Ioto [Near-crater Warning] According to the observation by NIED (National Research Institute for Earth Science and Disaster Prevention), seismicity in shallow parts in Ioto has been higher than before since August 2010, and is furthermore on the increase in this period. According to the GPS observation by GSI, landwide upheaval that was first observed from August 2006 slowed down since middle November 2010, but has been on the increase since late January The extension of the baseline in NS direction is still continuing and recently southward displacement has been remarkably seen in the south end. Fukutoku-Oka-no-Ba [Near-sea-area Warning] According to the information from the JCG(Japan Coast Guard) on 8 February, discolored milky, blue, blue-white and green sea water was drifted northeast with 50 meters width and 1,000 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 Photo.1 Discolored sea water at Fukutoku-Oka-no-Ba taken on 8 February Minami-Ioto is at the upper-left of this photo. Courtesy of JMSDF.

3 Kirishimayama(Shinmoedake)[Alert Level : 3] On 26 th January, a phreatomagnetic eruption started at Shinmoedake in the Kirishimayama volcano group, accompanying the emission of large amount of volcanic ash. Lava accumulated in the crater and explosive eruptions occurred repeatedly, emitting volcanic ash near-continuously. Since 9 th February, it had consisted of the intermittent ash eruptions. After that, small eruptions with explosive ones sometimes occurred, but became less frequent. Since 28 th February, newly small scale of eruptions had occurred. The maximum plume height in February rose as high as 3,000 m above the crater rim on 1 st, 2 nd, 4 th, and 18 th February. In this period, explosive eruptions ocurred 9times. No pyroclastic flow was observed( Photo.2 ). Photo.2 Explosive eruptions occurred in February (A high-sensitivity camera is installed at approximately 7 km SW from the summit crater) 1 st (07:54) ash plume to 2 km altitude, drifting SE, ballistics projecting up to 3.2 km-maximum distance. 2nd(15:53) ash plume to 3 km altitude, drifting E, ballistics projecting up to 1 km-maximum distance. 3rd(08:09) ash plume to 1.5 km altitude, drifting E. 4th(09:02) ash plume to 3 km altitude, drifting E, ballistics projecting around the summit crater. 18th(18:16) ash plume to 3 km altitude, drifting S, ballistics projecting up to 1 km-maximum distance.

4 An explosive eruption on 1 st February at 07:54 threw ballistics(major axis; 70cm, minor axis; 50cm) up approximately 3.2 kilometers away in a south-western direction, accompanying the maximum amplitude of 458Pa at Yunono (approximately 3 kilometers away in a south-western direction). This air-shock damaged many window glasses.at Kirishimaya-city in Kagoshima prefecture. An explosive eruption on 1 4th February at 05:07 threw small ballistics, with a diameter of 1.5-5cm to the north-eastern direction with maximum distance of 16km of Kirishimayama due to the strong wind, which damaged some sliding roofs and all that. Night-time glow was visible by a high-sensitivity camera from 26 January to 10 February, and on 28 th February. Seismic activity remained above background level, and a temporal increase in seismicity just before and after explosive eruptions was observed. Seismic events occurred 2,506 times (cf. 2,037 times; January 2011). Volcanic tremor started on 26 th January, decreased in amplitude after 29 th January, and ceased on 7 th February. After that, they occurred intermittently, but a small volcanic tremor had occurred consecutively since 28 th February (Fig. 2). Fig.2 Seismicity and plume activity at Shinmoedake from 2003 to February 2011.

5 An aerial observation was conducted in corporation with Kagoshima Prefecture, Kyushu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, and JMSDF (Japan Maritime Self-Defense Force) and revealed that the lava accumulated inside the crater after 28 th January grew up to about m in diameter from 1 st through 2 nd February, and the upper part of lava became more flat on the latter day. After that lava remain unchanged (Photo 3). 2011/2/1 10h 2011/2/2 14h 2011/2/3 10h 2011/2/4 10h 2011/2/7 11h 2011/2/9 12h Photo.3(a) Explosive eruptions occurred from 1 st to 9th February st ; Partial erosion of lava, about 500m in diameter. 2nd; Lava with 600m in diameter, and becoming flat at the top of lava. 3 rd and 4th; No change was observed. 7 th ; Slight dint in the center of lava. 18 th ; Partially brown-colored lava, 600m in diameter, unclear boundary between lava and rim wall, Courtesy of Kagoshima Prefecture, Kyushu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, and JMSDF.

6 2011/2/9 09h 2011/2/18 15h 2011/2/21 11h 2011/2/25 11h Photo.3(b) Explosive eruptions occurred from 13rd to25th February 2011 (continued). 13 rd ; No major change was observed. 18 th ; Brown-colored lava with dent in the center, m in diameter. 21 st ; No major change was observed. 25 th ; Accumulating volcanic ash and ballistics and unclear boundary between lava and rim wall, and cracking to N-S direction on the surface of lava. Courtesy of Kagoshima Prefecture, Kyushu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism, and JMSDF. According to the analysis by MRI(Meteorological Research Institute) and NIED from PALSER(Phased Array type L-band Synthetic Aperture Radar) data of the ALOS(Advanced Land Observing Satellite), the amplitude images at Shinmoedake revealed that the lava inside the crater had accumulated, and saturated almost inside the crater on 1 st February. No change was observed after that (Fig.3). The sulfur-dioxide flux decreased with an average of 600 t/d in 25 th February 2011 (cf. 11,000-12,000 t/d; January 2011).

7 Accumulated lava filled lava in the crater No change, compared with 1 st February No change Fig.3(a) The amplitude images of the ALOS/PALSAR acquired after the eruption on 26 th January at Shinmoedake. Taken on ascending orbit with an off-nadir angle of Courtesy JAXA/METI.

8 No change Decrease of lava in the center of crater No change, compared with 18 th February No change, compared with 20 th February Fig.3(b) The amplitude images of the ALOS/PALSAR acquired after the eruption on 26 th Shinmoedake (continued). January at According to GPS measurements, the dilatation of the baselines that traverse the summit crater of Shinmoedake from September 2010 turned into contraction due to the increased ash emission from the summit crater after 26 th January 2011,but slowed down since 2 nd February. According to tilt observation, subsidence in summit area was observed from 26 th January grew stagnant from 2 nd February. According to GPS measurements by GSI, slight dilatation of baselines that traverse deeper magma chamber of Shinmoedake has confirmed within past one month. (*The PALSAR data used in the analysis were prepared by the ALOS Daichi Domestic Demonstration on Disaster Management Application that Volcano Working Group coordinated by the CCPVE (Coordinating Committee for Prediction of Volcanic Eruptions). The PALSAR data belongs to JAXA/METI (Japan Aerospace Exploration agency/ministry of Economy Trade and Industry). We would like to thank Dr.Shimada (JAXA) for the use of his SIGMA-SAR software.)

9 Sakurajima[Alert Level : 3] Explosive eruptions at Showa-crater have increased since middle January In this period, eruptions occurred 144 times (cf. 102; January 2011), of which 110 times (cf. 88; January 2011) were explosive eruptions. Volcanic projectile reached to about m from Showa-crater. Pyroclastic flow at 19:08 on 19 February flew down to southeastern direction with about 500m in length. Explosive eruptions occurred twice on 7 th February at Minamidake summit crater whose last explosive eruption took place on the 3 rd October Volcanic seismicity has remained at relatively low level. The sulfur-dioxide flux was measured with an average of 300 t/d in February 2011 (cf t/d; December 2010). According to GPS measurement, no volcanic change at Sakurajima island was observed this period. 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, but has been accelerating since early February 2011 due to the trend of emitting much volcanic ash (Fig. 4). According to GPS measurement by the GSI, extension of the baselines that traverse Aira-Caldera ( at closed-off section of Kagoshima bay) has been confirmed. Fig. 4 Tilt change observed by water-tube tiltmeter at station Arimura from January 2009 to February 2011, 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. Night-time glow was visible by a high-sensitivity camera on 12 February. Seismicity has stayed at low level. A volcanic tremor with small amplitude and short duration occurred in this period, whose most recent tremor was observed in February Suwanosejima [Alert Level : 2] Mainly inferred from seismic records, possible ash explosions occurred intermittently through this period. 15 explosive eruptions (cf. 26; January 2011) occurred in this period. Volcanic earthquakes and volcanic tremors

10 remained at high level. A 2.9-magnitude earthquake centered around Suwanosejima occurred, and registered 3 on the Japanese seismic intensity scale. Also, seventeen felt earthquake was registered on the Japanese seismic intensity scale. No surface change was observed before and after the earthquakes.