Report on Sinabung (Indonesia) — March 2011

Bulletin of the Global Volcanism Network, vol. 36, no. 3 (March 2011)
Managing Editor: Richard Wunderman

Sinabung (Indonesia) Decreased activity following August-September 2010 eruption

Please cite this report as:

Global Volcanism Program, 2011. Report on Sinabung (Indonesia). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 36:3. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN201103-261080.

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Sinabung

Indonesia

3.17°N, 98.392°E; summit elev. 2460 m

All times are local (unless otherwise noted)


Sinabung, which sits 80 km NNW of Toba caldera, produced its first confirmed historical eruption in August 2010 (BGVN 35:07). We present clarifications on our previous report, some seismic data from the interval 2-4 September 2010 that included large local tectonic earthquakes, episodes of continuous volcanic tremor, and the return of calm after mid-September 2010.

Clarifications. Kus Hendratno (of the Center of Volcanology and Geological Hazard Mitigation, CVGHM) provided additional information about the first figure in our last Sinabung report (BGVN 35:07), which we had captioned as undated.

The upper photo, taken from the SW, showed the second eruption on 3 September (in the evening) and shows a plume he considered to be deflected down the E flank by strong winds blowing down-slope. The lower photo was taken on 30 August from the NE. Hedratno did not know the date that the eruption ended.

In addition, we described the 27 August 2010 eruption as the "first Holocene eruption" in BGVN 35:07. There was an unconfirmed historical eruption in 1881, and there may yet emerge evidence for other Holocene eruptions. Thus, we now prefer to refer to the 27 August eruption as the first confirmed historical eruption.

Additional information about 2-4 September 2010 activity. Table 2 presents some basic data on 2 to 4 September seismicity. These data are but a portion of a 4 September report by Agus Budianto (head of a geophysical team that responded to the crisis). The seismic data reflect both the presence of volcanic earthquakes, earthquakes interpreted as associated with emissions, far tectonic earthquakes, and tremor. The latter continued in all but one 6-hour time slot on the table, and in two cases, 1800-2400 on the 3rd and 0000-0600 on the 4th, tremor reached dominant amplitudes of 50 mm.

Table 2. Details about seismicity observed at Sinabung during 2-4 September 2010. Terminology as follows: "12@3-63 mm" refers to 12 earthquakes with amplitudes of 3-63 mm; "5-15 s," to duration times. Courtesy of Agus Budianto (affiliation listed in Information contacts).

Date (2010)TimeVolcanic earthquakesShallow volcanic earthquakesEmission earthquakeTremor amplitudes
02 Sep 0000-0600 12 at 3-63 mm; 5-15 s; S & P 0.5-4 s 7 at 3.5-10 mm; 3.5-6 s 2 at 2-6 mm; 48-53 s  
  0600-1200 12 at 6-44 mm; 4.5-16 s; S&P 1-4 s 6 at 2-4 mm; 5-11 s Continous (3 mm)
  1200-1800 5 at 9-75 mm; 5-11 s; S&P, 0.5-4s Continous (3 mm)
  1800-2400 Continous
 
03 Sep 0000-0600 Continous
 
  0600-1200 Continous
 
  1200-1800 Continous
 
  1800-2400 21 at 10-30 mm; 10-30 s; S&P 0.5-1.5 s Continous
 
04 Sep 0000-0600 2 at 21.5-25 mm;14-15 s; S&P 2.5-3 1 at 18.5 mm; 5 s Continous
 
  0600- 1200 6 at 9-100 mm; 10-32.5 s; S&P 1.5-2 4 at 2.5 mm; 7.5-9.5 s Continous (7 mm)
  1200-1800 1 at 50mm; 17 s;S&P 1.5s Continous (8 mm)

During 2-4 September, fog often obscured the view.

An eruption at 0438 on 3 September was accompanied by a roaring sounds and vibrations that were felt up to 8 km SE. A thick black plume erupted up to 3 km above the crater and drifted E. An eruption on the same day during the hours 1759 to 1801 also caused a roaring sound and weak vibrations that were felt up to 8 km away.

Visual observations showed several periods of the eruption; early in the eruption, a black plume soared as high as 1 km above the crater and drifted E. Then, a plume that appeared "clotted" moved approximately 2 km down the E slopes, with most of the ash falling on the E slope. Finally, a plume rose vertically and took the shape of a mushroom.

Electronic distance measurements after the eruption at 1759 on 3 September 2010 showed deflation (up to 4.5 mm).

On 4 September, the weather was clear, and a thick white plume was visible reaching up to 50 m above the crater and drifting as far as 100 m down the E slope.

Activity during mid- to late-September 2010. CVGHM reported a few noteworthy eruptions, emissions, and changes occurred after early September. During 8-11 September observers saw white-to-gray plumes rising 30-100 m above the crater and generally drifting E. Deformation measurements during 8-14 September showed a slow rate of inflation. Based on analyses of satellite imagery and the CVGHM web camera, the Darwin VAAC reported that on 12 and 14 September ash plumes rose to altitudes of 4.3-4.6 km altitude.

During 15 September-21 September 2010, based on information from CVGHM and views through a web camera, the Darwin VAAC reported ash plumes rising to an altitude of 4.3 km and drifting W. CVGHM reported a slow rate of inflation during 15-18 September followed by deflation during 19-21 September. Fog mostly prevented visual observations. On 20 September diffuse white plumes rose 30 m above the crater and drifted NE.

On 22 September a white plume rose as high as 100 m above the crater. The decrease in activity based on visual observations, seismicity, deformation, and SO2 concentration prompted CVGHM to lower the Alert Level to 3 (on a scale of 1-4) on 23 September, where it remained through at least mid-March 2011.

Geologic Background. Gunung Sinabung is a Pleistocene-to-Holocene stratovolcano with many lava flows on its flanks. The migration of summit vents along a N-S line gives the summit crater complex an elongated form. The youngest crater of this conical andesitic-to-dacitic edifice is at the southern end of the four overlapping summit craters. An unconfirmed eruption was noted in 1881, and solfataric activity was seen at the summit and upper flanks in 1912. No confirmed historical eruptions were recorded prior to explosive eruptions during August-September 2010 that produced ash plumes to 5 km above the summit.

Information Contacts: Kus Hendratno, Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://portal.vsi.esdm.go.id/joomla/; Camera URL: http://merapi.bgl.esdm.go.id/aktivitas_merapi.php?page=aktivitas-merapi&subpage=kamera-g-sinabung); Agus Budianto, Kementerian Energi Dan Sumber Daya Mineral, Republik Indonesia, Badan Geologi, Jalan Diponegoro No. 57 Bandung 40122 Indonesia.