Report on Sinabung (Indonesia) — 16 September-22 September 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 September-22 September 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Sinabung (Indonesia). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 16 September-22 September 2015. Smithsonian Institution and US Geological Survey.
3.17°N, 98.392°E; summit elev. 2460 m
All times are local (unless otherwise noted)
PVMBG reported that during 8-14 September foggy weather sometimes prevented visual observations of Sinabung and the growing lava dome in the summit crater. Lava flows on the flanks were incandescent as far as 2 km ESE. As many as six pyroclastic flows per day were detected, traveling as far as 3.5 km ESE and SE. Ash plumes rose as high as 2.5 km. Seismicity consisted of avalanche signals, low-frequency and hybrid events, tremor, tectonic events, and volcanic earthquakes. Seismicity fluctuated, although it had declined compared to the previous week. Deformation measurements showed deflation. The Alert Level remained at 4 (on a scale of 1-4), indicating that people within 7 km of the volcano on the SSE sector, and within 6 km in the ESE sector, should evacuate. Based on information from PVMBG, the Darwin VAAC reported that on 18 September an ash plume from a pyroclastic flow rose to an altitude of 3.3 km (11,000 ft) a.s.l. On 21 September an ash plume rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted SW. Later that day a pilot observed an ash plume drifting 45 km SW at an altitude of 5.8 km (19,000 ft) a.s.l.
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. The youngest deposit is a SE-flank pyroclastic flow 14C dated by Hendrasto et al. (2012) at 740-880 CE. 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.