Will Mount Anak Krakatau Eruption Trigger Tsunamis? BNPB Assures It Won’t
Mount Anak Krakatau Erupts Again: Authorities Downplay Tsunami Fears as Lava Fountains Light Up the Strait
Kabarsaji.com – The island of Mount Anak Krakatau, sitting in the Sunda Strait between Java and Sumatra, sent plumes of volcanic material skyward through the night and into Saturday morning, sending shockwaves of booming and rumbling noise across nearby waters. For residents along the coasts of Banten province and Lampung province, the spectacle reignited a wound that had barely healed: the memory of a devastating tsunami that struck the same stretch of coastline just over six years earlier.
Yet this time, Indonesia's disaster management apparatus has moved quickly to separate the dramatic visuals from the actual geological risk. The National Disaster Management Agency (BNPB) issued a direct appeal to coastal communities, asking them to hold steady and not allow anxiety to override practical preparedness.
The Shadow of December 22, 2018
The emotional weight behind the current unease is easy to understand. On December 22, 2018, a partial flank collapse of Mount Anak Krakatau's newly built edifice sent a wall of water racing toward the shores of Banten and Lampung within minutes. Hundreds of lives were lost, villages were swept away, and the event became one of the costliest natural disasters in Indonesia's recent history. The tsunami was not caused by a conventional seismic wave but by the sudden gravitational pull of a collapsing volcanic slope displacing the strait's water column. That mechanism made it fast, unpredictable, and extraordinarily lethal.
Because of that episode, any renewed activity at the volcano now carries an outsized psychological charge. Residents who lost homes, livelihoods, and family members in 2018 watch every tremor and every ash cloud with a vigilance that outsiders may find difficult to appreciate.
What the Geologists Actually Found
The Center for Volcanology and Geological Hazard Mitigation (PVMBG), the agency tasked with monitoring Indonesian volcanoes, conducted an assessment of the volcano's current morphology. Its conclusion, relayed through BNPB channels in Jakarta on Saturday, was that the post-2018 growth of Mount Anak Krakatau's edifice remains comparatively modest. In practical terms, the new cone has not yet accumulated enough mass or structural weakness to make a large-scale flank collapse — the kind that generated the 2018 tsunami — a realistic near-term scenario.
Acting Head of the BNPB Disaster Data, Information, and Communication Center, Berton SP Panjaitan, conveyed the agency's position plainly:
"Therefore, the people of Banten and Lampung are advised not to panic."
He acknowledged that the government fully recognizes the community's anxiety, particularly among those whose daily lives unfold within sight of the strait. The reassurance was framed not as dismissal but as an evidence-based reading of the current volcanic geometry.
Nighttime Activity: Lava Fountains and a Prolonged Tremor
The eruption sequence that unfolded overnight and into Saturday morning included a sustained lava fountain visible against the dark sky. Observers recorded at least one associated seismic event with an amplitude of 70 millimetres and a duration of 21,600 seconds — roughly six hours of continuous ground shaking as recorded by local seismometers. Such a long-duration signal typically reflects sustained magma movement through shallow conduits rather than a single discrete rupture.
The physical force of the ejection was sufficient to impair monitoring infrastructure. The BNPB Operations Control Directorate confirmed that surveillance cameras and CCTV units positioned near the active crater were knocked out of service by volcanic debris, temporarily blinding the observation network at the most critical moment.
Alert Level III and the Three-Kilometre Exclusion Zone
With the volcano holding at Alert Level III — the second-highest tier on Indonesia's four-level scale, indicating active eruption with potential for ashfall, lava flows, and pyroclastic activity — authorities directed that all fishing operations, resident movement, and tourist excursions within a three-kilometre radius of the active crater be suspended. The restriction applies equally to local fishers who depend on the strait for daily income and to visitors drawn by the spectacle of glowing lava columns.
Alert Level III does not mean the volcano is at maximum danger, but it does mean that conditions can escalate without long warning. The exclusion zone is a buffer against sudden ballistic ejecta, lahars, or unexpected flank instability.
Three Operational Priorities
BNPB outlined a compact set of actions it expects regional governments and local disaster agencies to execute immediately:
First, systematic patrols of the designated danger zone to confirm that no one remains inside the exclusion radius, whether by accident or by choice. Second, verification that evacuation routes leading to coastal assembly points are clear, signposted, and passable under degraded visibility conditions. Third, a public communication push discouraging residents from approaching the volcano to photograph or livestream the eruption — a behaviour that, while understandable, places individuals within range of hazards that cameras cannot capture.
Why the Distinction Matters
Volcanic tsunamis are rare compared with seismic tsunamis. They require either a sufficiently large volume of material to collapse into water, or a submarine eruption powerful enough to displace the water column. The current eruption at Anak Krakatau, while visually dramatic, has not yet demonstrated the scale of mass failure that produced the 2018 event. PVMBG's morphological reading suggests the new cone is still too small and too structurally coherent for that failure mode. Monitoring will continue, and the alert level will be adjusted if the geometry changes.
For now, the message from Jakarta to the shores of the Sunda Strait is measured: stay informed, respect the exclusion zone, keep evacuation routes clear, and let the seismographs and the geologists do their work before fear does.
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