Indexed on: 23 Apr '17Published on: 09 Apr '17Published in: Journal of Volcanology and Geothermal Research
Most volcanoes worldwide are not monitored in real-time; for those that are, patterns of pre-eruptive earthquakes coupled with conceptual models of magma ascent enable short-term forecasting of eruption onset. Basic event locations, characterization of background seismicity, and recognizing changes in earthquake types and energy release are most important to successful eruption forecasting. During renewed activity at Sinabung Volcano, Indonesia, this approach was used by the Center for Volcanology and Geological Hazards Mitigation (CVGHM) and the USGS Volcano Disaster Assistance Program to forecast eruption onset, identify changes in eruptive styles and raise or lower alert levels and extend or contract evacuation zones. After > 400 years of quiescence, Sinabung Volcano began erupting in August 2010. The volcano was unmonitored at the onset of phreatic eruptions in 2010, but soon had a monitoring network. Patterns of seismicity, primarily increasing swarms of high frequency volcano tectonic (VT) seismicity were used to forecast the continuing phreatic eruptions. Volcanic activity decreased in mid-September 2010, while additional intrusions accompanied by distal VT swarms continued through September 2013, when explosive phreatic eruptions recurred. Explosive eruptions were forecast based on increases in the real-time seismic amplitude measurement (RSAM) and VT seismicity. Seismicity changed markedly in late November and early December 2013 with the occurrence of deep seismicity and an overall transition from low frequency (LF) dominated irregular (in time and magnitude) to regular seismicity – a transition that accompanied the continued rise, eventual emergence and growth of a lava dome in the summit crater. In late December 2013 to early January 2014, the eruptive style changed as additional ascending magma deformed the summit and the dome grew beyond the capacity of the summit crater, resulting in the collapse of the summit lava dome (0.002 km3) on 11 January and producing the largest pyroclastic flow to date. The collapse was forecast by a several order of magnitude increase in RSAM, continued strong distal VT seismicity, an increase in proximal seismicity, and by large-scale observed deformation of the summit area. Similarly a second collapse was forecast based on increases in distal seismicity. We propose a process-based volcano seismicity model, that when applied to real volcanic data, helps to forecast eruption timing, size and changes in eruption style.