Overview of the eruptions of Sinabung Volcano, 2010 and 2013–present and details of the 2013 phreatomagmatic phase

A small phreatic eruption of Sinabung Volcano, North Sumatra on 28 August 2010, at 18:30 local time marked the first eruption in the past ~ 1200 years. The eruption took place from two small vents in the south crater area. Explosions and ash emissions from these vents generated multiple ash plumes that reached altitudes of up to 5 km during early- to mid-September. By the end of September 2010, only low level steam plumes were visible and the alert level was reduced from Level 4 (highest) to Level 3. The 2010 eruption effectively ended at this time. Beginning two days after the initial 2010 eruption, activity of the eruption has been monitored continuously by a telemetered seismic network surrounding the volcano and by remotely sensed observations. This monitoring system was supplemented with a near-field continuous GPS network, beginning in February 2011. Persistent fumarolic emissions continued for almost 3 years following the 2010 eruption, before a new eruption began on 15 September 2013. This eruption continues to the present. The ongoing eruption is divided into 5 major phases: 1) phreatomagmatic phase (July 2013–18 December 2013); 2) first dome and collapse phase with pyroclastic density currents (PDCs; block-and-ash flows and related surges) to south (18 December 2013–10 January 2014); 3) lava-flow and collapse phase (10 January 2014–mid-September 2014); 4) second lava dome and collapse phase with PDCs to south (mid-September 2014–July 2015); 5) lava dome collapse and ash explosion phase with PDCs to southeast and east (August 2015–present). The volcano erupted intermittently during the early phreatomagmatic phase with small vertical ash explosions. Then the eruption became increasingly vigorous with more repetitive and intense vertical ash explosions during late October through November. The first small pyroclastic density currents (PDCs) began on November 1. These pyroclastic flows descended the southeastern flank to a distance of 2 km. Swarms of volcano-tectonic (VT) earthquakes and volcanic tremor lasting hours occurred repeatedly during the phreatomagmatic phase and some of these VT-swarms were followed by explosions. In early December 2013, during the transition between phreatomagmatic and dome-collapse phases, swarms of hybrid earthquakes took place preceding and accompanying dome growth. The first lava dome was observed in satellite images on 18 December near the main crater rim. Partial collapses of the dome produced PDCs beginning on 30 December. Growth of this first lava dome continued into January and was accompanied by additional collapses and PDCs. By about 10 January, the lava had transitioned from a summit dome morphology into a lava flow morphology. The resulting lava flow descended the southeast flank of the volcano, producing flow-front and marginal collapses with associated PCDs. One such flow-flank collapse on 2 February 2014 resulted in a PCD that killed 16. The lava flow phase continued through mid-September 2014, when a second summit lava dome began to grow and collapse, producing PDCs initially to the south and southeast, and then beginning in July 2015 to the east and southeast. The eruption of Sinabung resulted in major impacts on the population of the resort and farming area near the volcano and in the Ginting and Karo Regencies of North Sumatra. Local residents, having not experienced eruptions in their lifetimes, were initially curious and eager to receive any information about the eruption regardless of its source. Various institutions provided information with little coordination, resulting in confusion. With time communications have improved and communities and the responsible governments have become better prepared in dealing with the persistent eruption. The Government of Indonesia has provided funding to support villagers who lived within a 5 km radius danger zone to stay in relocation camps as a permanent relocation area is being identified. Unfortunately, on 21 May 2016, 9 additional fatalities took place in the village of Gamber, within the danger zone, when a dome collapse sent a pyroclastic density current into the area. Throughout the eruption, the volcano has been monitored by the Indonesian Center for Volcanology and Geologic Hazard Mitigation (CVGHM) in partnership with the USGS-USAID Volcano Disaster Assistance Program and the Disaster Prevention Research Institute of Kyoto University. Monitoring techniques have included seismic, geodetic, gas, satellite and field observations, as well as occasional sampling of ash and lava for geochemical analyses. In this paper, we summarize key aspects of the monitoring data, their interpretations and their use in forecasting eruptive behavior and in issuance of alerts and warnings. More detailed interpretations of the monitoring data and their use are found in other papers of this special issue.