Abstract
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 3km 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 >1.5years (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 0.16km3 DRE as of the end of 2015. The lava discharge rate was largest during the initial stage (>7m3/s) and decreased exponentially over time. The discharge rate during the vulcanian stage was ≪1m3/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.
Highlights
Growth of a lava dome and production of a lava flow are common styles of effusive eruption, which can occur before and after explosive events such as plinian or sub-plinian eruptions (Ogburn et al, 2015).Commonly, in lava dome/flow eruptions, the magma discharge and effusion rates are much smaller than in explosive events, and can continue at a low rate for long durations (Pallister et al, 2013)
Partial collapses that generated pyroclastic density currents (PDCs) events were dominant in the first one month when the lava was moving down the upper slope, and rock falls became dominant instead, when the lava moved to the middle slope (Fig. 5C)
According to Center for Volcanology and Geological Hazard Mitigation (CVGHM) seismic data, low frequency (LF) events that had stopped in the earliest stage of lava dome growth, restarted in early September 2014, and hybrid events increased in late September
Summary
Growth of a lava dome and production of a lava flow are common styles of effusive eruption, which can occur before and after explosive events such as plinian or sub-plinian eruptions (Ogburn et al, 2015). Long-lasting lava dome/flow eruptions produce long-term hazards (months to tens of years) from PDCs to residences around the volcano, in contrast to the heavy but short duration impacts of large explosive eruptions. Such long-lasting lava dome/flow eruptions are well documented at the lava dome/flow eruptions at Unzen and Soufrière Hills volcanoes (Nakada et al, 1999; Kokelaar, 2002). Sinabung entered into an explosive stage at a time when growth of the lava dome/flow had almost stopped This eruption gives us an excellent opportunity to learn new aspects of lava dome/flow eruptions. The lava dome/flow complex formed in this eruption is called the lava complex
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