Mechanisms of lava flow emplacement during an effusive eruption of Sinabung Volcano (Sumatra, Indonesia)

The ongoing effusive phase of the eruption of Sinabung Volcano (Sumatra, Indonesia) began in late December 2013, and has produced a 2.9 km long andesitic lava flow with two active secondary summit lobes, frequent pyroclastic density currents (PDCs) (with ≤5 km runout distance), and associated plumes up to 5 km in height. Large intermediate to silicic composition lava flows of the type documented here are common at volcanoes around the world, but they are infrequently observed while active. This eruption provides a special opportunity to observe and study the mechanisms of emplacement and growth of an active andesitic lava flow. We use visible and thermal satellite images to document the flow and describe the dominant processes driving emplacement of the lava over the course of the eruption. Effusion and flow advance rates were at their highest in January–March 2014. A decrease in flow advance rate in late March 2014 from 20 to 70 m d⁻¹ to <5 m d⁻¹ was the result of a decrease in effusion rate from ~9 m³ s⁻¹ to ~3 m³ s⁻¹. Initial flow emplacement was most likely controlled by the yield strength of the flow crust, which we estimate to have increased in thickness from 1 to 4 m during January–June 2014, calculated from average flow surface temperatures that decreased from ~60 °C to <30 °C during this period. Further decrease in flow advance rate in June 2014 to ~1 m d⁻¹ suggests that the flow's interior had cooled, and that propagation was limited by the yield strength of the flow's interior (core). Inflation of the flow during this period of core-controlled slow advance eventually caused lava to overtop ridges bounding the flow near the summit, and created significant gravitational instabilities. These instabilities led to collapse of the upper portions of the lava flow and generated PDCs, followed by breakout of new flow lobes from the collapse scars in October 2014 and June 2015. Effusion continues as of June 2017 and presents a significant hazard for collapse and generation of PDCs. This ongoing activity appears to represent a typical eruption of Sinabung, with flow length and area similar to numerous older flows observed around the volcano.