Sinabung Volcano (Sumatra, Indonesia) awoke from over 1200 years of dormancy with multiple phreatic explosions in 2010. After a period of quiescence, Sinabung activity resumed in 2013, producing frequent explosions, lava dome extrusion, and pyroclastic flows from dome collapses, becoming one of the world's most active volcanoes and displacing over 20,000 citizens. This study presents a compilation of the geochemical datasets collected by the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) from 2010 - current (2016), which provides insights into the evolution of the eruption. Based on observations of SO2 emissions, ash componentry, leachate chemistry, and bulk ash geochemistry, the eruption can be split into five distinct phases. The initial stage of phreatic summit explosions occurred from August - October 2010, during which background SO2 emissions averaged ~550 ± 180 t/d (1 s.d.). An eruptive pause (phase two) starting in October 2010 abruptly ended in September 2013 with a resumption of conduit-clearing eruptions. This third phase had a relatively modest background SO2 emission rate (avg. ~410 ± 275 t/d) and produced ash consisting entirely of accidental ejecta with high S/Cl leachate ratios (up to 30), suggestive of deep-sourced magma and the incorporation of hydrothermal sulfur-bearing phases. The most intense phase of the eruption (phase four) occurred from December 2013 to February 2014, when juvenile magma first reached the surface. This period included dozens of large eruptions per day, high SO2 emission rates (average: 1,120 ± 1,030 t/d, peak: ~3,800 t/d), the onset of lava dome extrusion, and a dramatic drop in S/Cl ash leachates to ratios < 5, all reflecting increased degassing from shallow magma and the clearing out of sulfurous phases from the old hydrothermal system. From late February 2014 through the time of writing (September 2016), Sinabung settled into a relatively steady state of lower activity (phase five). Ash emissions now consist of dominantly juvenile material, and background SO2 emission rates have been progressively decreasing to an average of ~250 - 300 t/d. Starting August 2016, SO2 emissions started being measured in a continuous manner using a network of permanent scanning DOAS instruments. We find that long-term SO2 emission rates have been gradually declining at Sinabung since early 2014, consistent with an apparent decrease in magma supply. Our degassing model suggests that large explosions and pyroclastic flows could continue in the near-term owing to conduit plugging and dome collapses, remaining a major threat until the magma supply rate decreases further and the eruption ends.
Additional publication details
Gas and ash emissions associated with the 2010–present activity of Sinabung Volcano, Indonesia