Bali disaster officials: volcanic eruptions not a countdown to megathrust

Denpasar — — Bali’s disaster agency is stressing that recent volcanic eruptions in Indonesia do not serve as a countdown to a megathrust earthquake, and that volcanic and tectonic earthquakes arise from different processes that must be assessed separately.

On 7 September 2026, Bali Provincial Disaster Management Agency (BPBD Bali) head I Gede Agung Teja Bhusana Yadnya responded to online concern that several eruptions, including at Anak Krakatau, might signal a looming megathrust event in the region, according to local outlet NusaBali.

Teja explained that volcanic earthquakes are linked to magma movement and pressure inside a volcano, while tectonic earthquakes are caused by energy release along faults and plate boundaries. He said eruptions can trigger volcanic earthquakes around the volcano but are not directly associated with megathrust earthquakes, which occur in the shallow part of a subduction zone where one tectonic plate dives beneath another.

Volcanic eruptions and megathrust fears

Public anxiety intensified after Anak Krakatau in the Sunda Strait erupted repeatedly at the end of August and early September, part of a broader pattern of heightened volcanic activity at several Indonesian volcanoes. NusaBali reported that social media users began linking these eruptions to a possible large megathrust earthquake.

Both BPBD Bali and independent experts have pushed back against that narrative. Teja said associating current eruptions with an imminent megathrust earthquake is not accurate, emphasising that the eruptions generate volcanic earthquakes local to the volcano rather than large regional tectonic events. Separately, disaster expert Daryono of the Indonesian Association of Disaster Experts (IABI) told national media that increased volcanic activity “does not automatically” trigger a megathrust earthquake and that multiple eruptions occurring close together are better understood as a spatial and temporal coincidence.

According to Daryono, volcanic earthquakes generally do not have enough energy or the right mechanism to initiate major tectonic ruptures in megathrust zones, which are driven by long-term plate convergence. He added that scientific monitoring has not produced evidence that synchronous eruptions across Indonesia are a reliable precursor to a megathrust event.

Earthquake sources around Bali

The BPBD Bali clarification does not imply that the island has no earthquake hazard. Teja and BMKG analysts note that Bali is bordered to the south by a subduction-zone megathrust and to the north by the Flores Back-arc Thrust system. The northern structure is the same regional back-arc thrust that recently produced a damaging magnitude 7.7–7.8 earthquake and tsunami off Flores, according to BMKG and international seismological reporting.

BMKG regional bulletins for Bali describe earthquake epicentres both on land and offshore, with clusters near the Lombok Strait associated with a strike-slip fault and to the north along the Flores Back-arc Thrust. These mapped sources illustrate why Bali remains exposed to tectonic shaking even when local volcanoes are quiet.

However, BPBD Bali and BMKG officials underline that recorded small and moderate earthquakes around the island cannot be used as a precise countdown to a future megathrust event. Indonesia’s public broadcaster RRI notes that megathrust zones run offshore south of Sumatra, Java, Bali, Nusa Tenggara and onward to Maluku, forming a long-term tsunami and earthquake hazard that must be managed through preparedness rather than prediction of exact dates.

Status of Bali’s volcanoes and monitoring

Teja said there was no ongoing volcanic eruption in Bali at the time of his 7 September remarks and that local volcano conditions were normal. Bali’s best-known active volcanoes are Mount Agung in Karangasem and Mount Batur in Bangli, both classified as active by Indonesia’s Geological Agency. Recent eruptive episodes elsewhere in the country do not imply that these volcanoes are about to erupt purely because other peaks are active, according to the Volcano Disaster Mitigation Agency (PVMBG).

BPBD Bali coordinates with the Geological Agency and PVMBG on volcanic monitoring, while BMKG is responsible for national earthquake and tsunami monitoring. A BMKG national catalogue of magnitude 5.0 and above earthquakes lists recent events across Maluku, Java, Nusa Tenggara and other regions, but does not provide any forecast of a specific megathrust strike affecting Bali.

Officials and experts urge residents and visitors to focus on practical preparedness rather than speculative links between unrelated hazards. BPBD Bali calls on the public to follow official information channels, learn the characteristics of volcanic and tectonic risks, and implement mitigation measures such as safe building practices, evacuation planning and awareness of tsunami-prone coastlines.

In a country with more than a hundred active volcanoes and multiple major fault systems, simultaneous eruptions and frequent small earthquakes are to be expected. The presence of megathrust and back-arc thrust faults near Bali confirms that the region faces long-term geological risk, but current eruptions and routine seismicity do not in themselves show that a megathrust earthquake is imminent.

Sources

• NusaBali
• IDN Times
• CNBC Indonesia
• Gobaligo Bali News Blog
• BeritaSatu
• BMKG – Press release on Flores Back-Arc Thrust earthquake
• RRI