Mount Agung is unambiguously active. Bali’s highest and most sacred volcano ended a 53-year quiet spell in 2017 with an intense seismic crisis followed by explosive eruptions and lava effusion, and intermittent activity continued into at least 2019. The volcano sits above a deep, multi-level magma plumbing system that has fueled eruptions for thousands of years, and Indonesia’s volcano monitoring agency maintains continuous surveillance of the mountain. For anyone living on Bali, planning travel there, or simply curious about one of Southeast Asia’s most closely watched volcanoes, the short answer is that Agung is very much alive.
Why Agung Exists in the First Place
Mount Agung owes its existence to the collision of two tectonic plates. The Indo-Australian Plate dives beneath the Eurasian Plate along the Sunda Arc, and the partial melting triggered by that subduction generates the magma that feeds Agung and its neighbors across the Indonesian archipelago.1IOP Conference Series: Earth and Environmental Science. Tectonic Setting of Mount Agung, Bali: Insight From Petrology and Geochemistry Analysis This is the same basic engine that drives volcanic arcs around the Pacific Ring of Fire.
Beneath Agung specifically, magma does not simply rise in a single pipe from the mantle to the surface. Mineral studies of erupted rocks reveal at least two major storage levels: a deep reservoir roughly 18 to 22 kilometers below the surface, near the boundary between the crust and the mantle, and a shallower zone between about 3 and 7 kilometers depth, around the transition from sedimentary rocks to harder basement rock.2PubMed Central. Multi-level magma plumbing at Agung and Batur volcanoes increases risk of hazardous eruptions This multi-level plumbing matters because magma can stall, accumulate, and interact at different depths before it finally reaches the surface, making eruption behavior harder to predict.
The Catastrophic 1963 Eruption
Agung’s most devastating eruption in recorded history began in March 1963 and remains one of the best-documented volcanic climate experiments in modern science. The eruption killed more than a thousand people on Bali, destroyed villages with pyroclastic flows and lahars, and blanketed the island in ash. But its effects reached far beyond Indonesia.
Massive quantities of sulfur dioxide injected into the stratosphere created an aerosol veil that reduced the amount of solar radiation reaching Earth’s surface. Tropospheric temperatures dropped by up to about 1°C, with the peak cooling occurring roughly a year and a half after the eruption, between August 1964 and August 1965.3Journal of Volcanology and Geothermal Research. Further studies of the atmospheric temperature change produced by the Mt. Agung volcanic eruption in 1963 The mechanism involved stratospheric aerosol particles absorbing incoming solar radiation before it could warm the lower atmosphere, essentially putting a thin sunshade over the planet.
The event became a benchmark for climate science. Researchers used the eruption’s well-measured aerosol output as input for atmospheric models, and the computed temperature changes matched observations closely in both the stratosphere and the troposphere. That agreement provided early evidence that volcanic eruptions can measurably alter global climate, and that theoretical models could reproduce those effects.4PubMed. Mount agung eruption provides test of a global climatic perturbation Later work revisiting the 1963 forcing found that the details of how many distinct eruptive phases occurred can shift estimates of peak radiative forcing by 10 to 20 percent, a reminder that even well-studied eruptions still hold uncertainties.5Atmospheric Chemistry and Physics. Revisiting the Agung 1963 volcanic forcing – impact of one or two eruptions
The 2017 Reawakening
After more than half a century of quiet, Agung began stirring again in mid-2017. Unusual fumarolic activity appeared in the summit crater, and seismicity started climbing. By mid-September, earthquake rates were rising from tens per day to hundreds per day, with the events concentrated between Mount Agung and the neighboring Batur Caldera to the northwest. Seismicity peaked on 22 September with more than 800 earthquakes above magnitude 1 recorded in a single day, and a magnitude 4.2 event struck on 26 September.6Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Seismicity
Advanced seismic analysis later revealed the swarm was even more intense than routine catalogs captured. By applying waveform-matching techniques that detect smaller events missed by standard methods, researchers identified roughly 5,800 earthquakes between August and December 2017, about fourteen times more than the 407 in the routine catalog.7EarthArXiv. Seismic swarm preceding the 2017 Mount Agung eruption in Bali (Indonesia) enhanced by the matched filter approach The swarm’s peak came in late September, but the volcano did not actually erupt until late November, a roughly two-month gap that made forecasting the eruption’s onset extremely difficult for authorities and scientists.
The eruption itself began on 21 November 2017 with a small explosive burst that sent ash about 700 meters above the summit. A lava flow appeared in the crater by 25 November, and by the 26th, the ash column reached roughly 6 kilometers above the summit, high enough to force the closure of the airport in Lombok, about 95 kilometers to the southeast.8Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Scientific Observations The most intense explosive activity and rapid lava effusion occurred between 25 and 29 November 2017. Smaller, less frequent explosions and lava extrusions continued through at least June 2019.9PubMed Central. The 2017-19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption
How Scientists Monitor Agung
Keeping watch over an active volcano like Agung requires overlapping technologies, each capturing different signals. As of 2017, the ground-based seismic network included two short-period stations on Agung’s south and southwest flanks, positioned roughly 4 and 5 kilometers from the summit, plus four additional stations in the Batur Caldera nearby.8Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Scientific Observations These stations detect the earthquakes that signal magma movement underground and are the first line of defense for early warning.
Satellite-based radar has become increasingly important. Researchers used Sentinel-1 satellite data to track ground deformation around Agung during the 2017-2018 crisis. Atmospheric interference initially confused the signal, with strong weather effects being misidentified as true ground movement at one point. But refined analysis showed that surface uplift, a hallmark of magma intruding beneath the surface, could have been detected with 95 percent confidence by October 2017, about 15 days after the seismic swarm began and a full month before the eruption started.10Journal of Geophysical Research: Solid Earth. Automated Methods for Detecting Volcanic Deformation Using Sentinel‐1 InSAR Time Series Illustrated by the 2017–2018 Unrest at Agung, Indonesia That finding is encouraging for future crises, though it came retrospectively.
Thermal monitoring from space adds another layer. During the December 2017 eruptive episodes, researchers combined data from the Sentinel-2A and ASTER satellites to map the temperature distribution within the lava filling the crater, distinguishing hotter and cooler zones within the flow.11IOP Conference Series: Earth and Environmental Science. Thermal model of lava in Mt. Agung during December 2017 episodes derived from Integrated SENTINEL 2A and ASTER remote sensing datasets Longer-term thermal tracking using Landsat-8 data from 2013 through 2019 showed a sharp rise in crater surface temperatures during the 2017-2018 eruptions, confirming that satellite-detected thermal changes can serve as a precursor to eruptions.12Journal of Physics: Conference Series. Surface temperature changes of the crater of Agung Volcano from Landsat-8 TIRS during 2017-2018 eruption
The Alert System and Evacuation Response
Indonesia uses a four-level alert system for its volcanoes, managed by the Center for Volcanology and Geological Hazard Mitigation, known by its Indonesian acronym CVGHM. During the 2017 crisis, Agung’s alert level escalated rapidly. It rose to Level 2 (Waspada) on 14 September as unusual fumarolic activity and increasing seismicity appeared. Four days later, as earthquakes accelerated, it jumped to Level 3 (Siaga). On 22 September, when seismicity peaked, the level was raised to Level 4 (Awas), the highest, which triggered mass evacuations.13Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Summary of Basic Timeline
The timeline created a painful dilemma. Seismicity peaked in late September, but the eruption did not begin until late November. With evacuees displaced for over a month and no eruption materializing, authorities lowered the alert to Level 3 on 29 October to allow some return. When the eruption finally began on 21 November, the level was raised back to Awas on the 26th. It was later lowered again to Level 3 on 10 February 2018. This sequence illustrates a fundamental tension in volcano crisis management: evacuating too early strains communities and erodes trust, while evacuating too late risks lives.
CVGHM is responsible for setting both alert levels and hazard zone maps, while Indonesia’s national and regional disaster management agencies handle the logistics of evacuation and emergency response. Exclusion zones during the 2017 crisis were defined using computer models that simulated pyroclastic density currents, lahars, and ash dispersal, layered on top of existing hazard maps.14Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Crisis Response
Lahars and Ongoing Hazards Beyond Eruptions
Even after explosive activity winds down, Agung remains dangerous. Loose volcanic debris blanketing the slopes can be remobilized by heavy rain, generating lahars: fast-moving slurries of water, mud, rock, and ash that follow river channels downhill. Just days after the November 2017 eruption, a debris flow surged down the Yeh Sah River after rainfall of about 32 millimeters in a day was recorded at a nearby station.15E3S Web of Conferences. Estimation of debris flow using Curve Number analysis for The Mount Agung Volcanic event, Bali, Indonesia These secondary lahars can continue for years after an eruption, especially during the rainy season, as long as loose material remains on the volcano’s slopes.
Simulations using high-resolution terrain data collected by drones suggest that the material deposited during the 2017-2019 crisis could generate dangerous lahars in at least 21 drainage channels extending across the northern, northeastern, southern, southeastern, and southwestern flanks of the volcano.16Journal of Volcanology and Geothermal Research. The use of UAV remote sensing for observing lava dome emplacement and areas of potential lahar hazards: An example from the 2017–2019 eruption crisis at Mount Agung in Bali Comparing pre-eruption and post-eruption drone surveys of the terrain allows researchers to estimate the volume of loose material available and model where lahars would travel, achieving about 82 percent agreement with observed lahar footprints in validation tests.17International Journal of Applied Earth Observation and Geoinformation. Determination of potential secondary lahar hazard areas based on pre-and post-eruption UAV DEMs This kind of work helps authorities identify which communities downstream need warning systems and reinforced river infrastructure.
Agriculture, Water, and the Subak System
Understanding why so many people live close to an active volcano requires understanding what the volcano provides. Agung’s south flank is fed by abundant cold springs that emerge at elevations between 300 and 500 meters. These springs are the foundation of the Balinese subak system, a centuries-old communal method of distributing irrigation water that supports terraced rice paddies on the volcano’s lower slopes.18Scientific Reports. The 2017–19 activity at Mount Agung in Bali (Indonesia): Intense unrest, monitoring, crisis response, evacuation, and eruption – Section: Background Volcanic soils are rich in minerals, and the water flowing off Agung sustains some of Bali’s most productive agricultural land. Moving permanently away from the volcano would mean abandoning livelihoods that have supported communities for generations.
Tourism adds another economic layer. Agung is a major draw for hikers and visitors to Bali, and its eruptions directly affect the island’s economy through airport closures, travel cancellations, and reduced tourist arrivals. The 2017 crisis forced the evacuation of tens of thousands of people, disrupted flights across the region, and reminded Bali’s tourism-dependent economy just how vulnerable it is to volcanic unrest.
Cultural Connections to the Volcano
Mount Agung is the most sacred mountain for Bali’s predominantly Hindu population. Pura Besakih, often called Bali’s “mother temple,” sits on its slopes. This spiritual relationship shapes how communities respond to volcanic threats in ways that complement the scientific monitoring system.
Research into disaster communication on Agung’s flanks has found that traditional leaders serve as primary communicators of environmental risk, and that their authority is deeply intertwined with spiritual narratives. Informal learning settings like temple ceremonies, village assemblies, and oral traditions transmit disaster knowledge across generations. This culturally embedded approach creates a form of disaster awareness that blends practical understanding with emotional and spiritual meaning, often motivating community action during crises in ways that official government bulletins alone may not.19Educational Process: International Journal. Communicative Learning in Crisis: How Balinese Local Wisdom Shapes Educational Responses to Mount Agung’s Volcanic Threats
During the 2017 crisis, this dual system of scientific alerts and community-level cultural leadership was tested under pressure. Evacuees had to weigh official orders against spiritual obligations, agricultural schedules, and the practical costs of leaving their homes for an uncertain duration. The experience underscored that effective volcano crisis response on Bali cannot rely solely on instruments and hazard models. It also depends on the trust networks and cultural frameworks that connect people to their landscape, and to the mountain that has shaped Balinese identity for centuries.
What Visitors and Residents Should Know
If you are planning a trip to Bali or live near Agung, the practical reality is straightforward. The volcano is active, it has erupted recently, and it will erupt again. The question is when and how severely, and no one can answer that with precision. Indonesia’s monitoring agencies maintain real-time surveillance using seismometers, satellite radar, and thermal imaging, and the four-level alert system provides structured guidance on when to evacuate and how far.
Between eruptions, the main ongoing risk is lahars during heavy rains. Communities in river valleys draining the volcano’s slopes remain exposed even when the crater is quiet. Travelers should check the current alert level before attempting summit hikes, which are prohibited at elevated alert levels, and should follow local guidance about exclusion zones. The volcano’s flanks are densely populated and intensively farmed precisely because the same geologic processes that make Agung dangerous also make it fertile and water-rich. That tradeoff has defined life on Bali’s eastern slopes for a long time, and it is not going to change.