Our last Bulletin report (BGVN 36:01), covered the interval from 6 August 2010 to late-March 2011. This report covers activity for 21 March 2011 through 9 February 2014. During this interval, eruptions clearly took place in March and April 2011, in May 2012, and in April 2013. Crater glow was seen in July, and again during late August to early September 2013, suggesting eruptions. The next report came 9 February 2014, again indicating an eruption then. MODVOLC data discussed at the end also supplements this eruptive information. Highlights include several episodes of abundant alerts and several intervals with pauses, including a 10 month pause that ended on 17 May 2012.

2011. The Center of Volcanology and Geological Hazard Mitigation (CVGHM) reported that during 21-23 March incandescent material from Karangetang was ejected 50-75 m above the crater. Lava flows traveled as far as 2 km and collapses from the lava-flow fronts generated avalanches that moved down the flanks at most another 300 m. On 24 March lava was incandescent in areas 1.5 km away from the crater. Incandescent material from the lava-flow fronts rolled an additional 200-500 m down the flanks. Incandescent material was again ejected 75 m above the crater. Later that day, due to decreased seismicity and a decline in the rate of lava flows, the Alert Level was lowered to 3 (on a scale of 1-4).

CVGHM reported that during 30-31 March incandescence emanated from Karangetang's main crater as well as bluish and white gas plumes. Lava flows originating from the main crater traveled 2 km down the flanks. Incandescent avalanches from the main crater and from the lava-flow fronts traveled up to 1.8 km down the flanks. On 31 March a thunderous sound was accompanied by a gray plume that rose 200 m above the crater. The Alert Level remained at 3 (on a scale of 1-4). During 1 May and at least into August, lava flows remained active. News indicated 600 people evacuated in August.

2012. Based on analyses of satellite imagery, the Darwin Volcanic Ash Advisory Centre (VAAC) reported that on 14 May 2012 an ash plume rose to 3.7 km a.s.l. and drifted 130 km SE. On 16 May an ash plume again rose to an altitude of 3.7 km a.s.l. then drifted about 110 km SE. The VAAC also described a 16 December ash plume to an altitude of 3.7 km drifting 110 km SE.

2013. Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that on 9 April an ash plume rose to an altitude of 4.3 km a.s.l. and drifted over 45 km WNW. According to a (Kompas) news article, pahoehoe lava flows traveled 150 m and rock avalanches traveled 2 km on that same day.

Based on reports from the observation post in Salili, CVGHM stated on 26 July that the occurrence of rock avalanches descending Karangetang's flanks decreased during 2013; the last one occurred on 7 July, and traveled 2 km down the Batuawang and Kahetang (E) drainages. Although fog often prevented visual observations, white plumes were sometimes seen rising up to 500 m from two craters. Incandescence from the lava dome was reflected in the plume at night. Seismicity fluctuated, but signals indicating avalanches declined. Based on the cessation of avalanches, visual observations, and decreasing seismicity, the Alert Level was lowered to 2 (on a scale of 1-4) on 26 July.

Based on observations from the post in Salili, CVGHM reported that although Karangetang was sometimes covered in fog during 1 August-2 September white plumes were seen rising up to 500 m above the main crater and up to 300 m above Crater II. Incandescence from the crater was often observed at night. Avalanches began traveling down the Batuawang drainage on 2 September and then intensified the next day. The Alert Level was raised to 3 (on a scale of 1-4) on 3 September.

2014. Based on analyses of satellite imagery and wind data, the Darwin VAAC reported that on 9 February an ash plume rose to an altitude of 4.3 km a.s.l. and drifted over 80 km W.

MODVOLC thermal alerts. In BGVN 36:01 we reported thermal alerts derived from the Hawai'i Institute of Geophysics and Planetology Thermal Alerts System (MODVOLC), discussing the presence or absence of thermal alerts through the last available posted alert, 12 March 2011. During this report's duration, the alerts sometimes continued and were typically abundant, usually on the order of one or more per week or two, but in some cases several alerts per day, until pausing after 15 May 2011. They resumed during the days 8 and 13 August 2011 and then stopped.

When the alerts resumed on 17 May 2012, they had undergone a pause of 10 months. Alerts were again abundant during 17 May until 18 June 2012. A pause ensued until 9 September 2012 and the alerts were common until 26 January 2013. The subsequent pause ended and alerts resumed during 4 April-5 June 2013. The subsequent pause took place during 6 June-2 September 2013, and then the pause ended with a few alerts during 3-5 September 2013 but an absence of alerts for the remainder of 2013. When checked on 1 July 2014, only one alert for 2014 had been posted: 8 June 2014.

Geological Summary. Karangetang (Api Siau) volcano lies at the northern end of the island of Siau, about 125 km NNE of the NE-most point of Sulawesi. The stratovolcano contains five summit craters along a N-S line. It is one of Indonesia's most active volcanoes, with more than 40 eruptions recorded since 1675 and many additional small eruptions that were not documented (Neumann van Padang, 1951). Twentieth-century eruptions have included frequent explosive activity sometimes accompanied by pyroclastic flows and lahars. Lava dome growth has occurred in the summit craters; collapse of lava flow fronts have produced pyroclastic flows.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Kompas (URL: http://nasional.kompas.com/read/2013/04/09/08311241/Guguran.Lava.Karangetang.Hingga.2.km); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).