Continuous monitoring of SO2 emissions from Sinabung Volcano, Indonesia

Abstract

<p>After more than 800 years of dormancy, phreatic explosions occurred at Sinabung Volcano in North Sumatra, Indonesia, on August 27, 2010. These marked the beginning of a period of unrest at Sinabung that continues through the present. Phreatic activity temporarily ceased in September 2010, however a more explosive phase of the eruption began again in September 2013, sending ash columns as high as 9 km above the volcano’s summit. A lava dome breached the surface on 17-18 December 2013 and subsequent collapses of this dome have produced numerous pyroclastic density currents reaching up to 5 km from the vent. Eruptive activity has waxed and waned since 2013, and the eruption entered period of especially vigorous activity beginning in February 2019 that is continuing through the present.</p><p>Between 2010 and 2013, the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM) significantly ramped up its monitoring efforts at Sinabung by installing seismometers, GPS instruments and electronic distance measuring benchmarks. In August 2016, the volcano observatory then installed a network of 3 scanning Differential Optical Absorption Spectrometers (DOAS) on the eastern side of Sinabung at distances between 4 and 6 km from the volcano’s summit. These DOAS instruments are part of the Network for Observation of Volcanic and Atmospheric Change (NOVAC), and autonomously measure the emission rate of sulfur dioxide (SO<sub>2</sub>) from Sinabung during typical west-wind conditions.</p><p>Since its installation, the DOAS network has provided useful monitoring information at Sinabung. The collected data indicate that the average SO<sub>2</sub> emission rate lies between 100 and 400 metric tons per day (t/d), but emissions up to 2,400 t/d are common throughout the measurement period. The maximum emission rate recorded since 2016 was 4,500 t/d, measured in July 2019. However, the NOVAC instruments are not able to accurately capture the SO<sub>2</sub> emissions associated with large explosive eruptions, and satellite data indicate that plumes associated with such events have sometimes contained significantly more SO<sub>2</sub> than during the more typical passive degassing behavior. Here, we present excerpts of the long-term SO<sub>2</sub> data from Sinabung and compare these with complimentary records of the timing and frequency of explosions, gas exhalations, rockfalls, and pyroclastic flows. These combined datasets provide insights into the active volcanic processes ongoing at Sinabung.</p>