Abstract
After 53 years of quiescence, Mount Agung awoke in August 2017, with intense seismicity, measurable ground deformation, and thermal anomalies in the summit crater. Although the seismic unrest peaked in late September and early October, the volcano did not start erupting until 21 November. The most intense explosive eruptions with accompanying rapid lava effusion occurred between 25 and 29 November. Smaller infrequent explosions and extrusions continue through the present (June 2019). The delay between intense unrest and eruption caused considerable challenges to emergency responders, local and national governmental agencies, and the population of Bali near the volcano, including over 140,000 evacuees. This paper provides an overview of the volcanic activity at Mount Agung from the viewpoint of the volcano observatory and other scientists responding to the volcanic crisis. We discuss the volcanic activity as well as key data streams used to track it. We provide evidence that magma intruded into the mid-crust in early 2017, and again in August of that year, prior to intrusion of an inferred dike between Mount Agung and Batur Caldera that initiated an earthquake swarm in late September. We summarize efforts to forecast the behavior of the volcano, to quantify exclusion zones for evacuations, and to work with emergency responders and other government agencies to make decisions during a complex and tense volcanic crisis.
Highlights
Mount Agung is sacred to the Hindu population of Bali, and is a great tourist attraction on the island
⋅ increase in fumarolic activity ⋅ increase in felt earthquake freq. and M ⋅ increase in VT seismicity
⋅ modeling showed that large Pyroclastic density currents (PDCs) could travel >10 km in
Summary
Mount Agung is sacred to the Hindu population of Bali, and is a great tourist attraction on the island. While earthquake rates decreased during this time period, RSAM ratios of the closest two stations showed an indication of magma migration toward the summit crater and RSAM values showed a subtle but persistent long-term trend increase, a trend that continued into the initial phreatomagmatic eruptions in late November (Fig. 3). The onset of magmatic eruption was preceded by a swarm of 22 larger LF earthquakes on the morning of November 25 local time, the onset of lava effusion, which was first detected in satellite data the same day, was not recorded seismically. Mount Agung began producing regular, discrete explosions early on in the effusive phase, none of the explosions were recorded seismically on the CVGHM network until 23 December. The date of alert-level change is denoted in the header for each entry, though key events and observations begin prior to and after that date
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