Growth process of the lava dome/flow complex at Sinabung Volcano during 2013–2016

Mount Sinabung, North Sumatra, Indonesia, erupted for the first time in 2010 and reactivated again in 2013. The eruption started with a phreatic phase, changed to phreatomagmatic, and then andesite lava appeared at the summit crater in late December 2013. Lava effusion continued and has been associated with partial to complete collapses of the lava complex, which successively generated pyroclastic density currents (PDCs). The lava complex grew first as a lava dome and then developed into a lava flow (lava extension stage). It extended up to about 3 km in horizontal runout distance by late 2014. When the front of the lava complex moved onto the middle and lower slope of the volcano, PDC events were initially replaced by simple rock falls. Inflation of the upper part of the lava complex began in mid-2014 when the movement of the lava flow front stagnated. The inflation was associated with hybrid seismic events and frequent partial collapses of the upper part of the lava complex, generating PDC events with long travel distances. From mid-September 2014, new lobes repeatedly appeared near the summit and collapsed. Cyclic vulcanian events began in August 2015 when hybrid events peaked, and continued > 1.5 years (vulcanian stage). These events sometimes triggered PDCs, whose deposits contained vesiculated lava fragments. The distribution of PDC deposits, which extended over time, mostly overlapped in areal extent with that of the 9th–10th century eruption. Eruption volumes were estimated based on measurements with a laser distance meter during 6 periods, digital surface model (DSM) analysis of satellite images during one period, and the cumulative number of seismically detected PDC events, assuming a constant volume of each PDC event. The total volume of eruption products reached about 0.16 km3 DRE as of the end of 2015. The lava discharge rate was largest during the initial stage (> 7 m3/s) and decreased exponentially over time. The discharge rate during the vulcanian stage was ≪ 1 m3/s. The trend of decreasing discharge rate is in harmony with that of ground deflation recorded by a GPS measurement. The chemical composition of lava slightly evolved with time. Cyclic vulcanian events may have been triggered by limited degassing conditions in the upper conduit and by unloading of the conduit by lava dome collapses