The volcanic island that grew from the crater left by one of modern history’s deadliest eruptions is rebuilding itself at a pace that has scientists worried. Anak Krakatau, which rises from the Sunda Strait between Java and Sumatra, has been erupting intermittently since late 2023, and a peer-reviewed study published in early 2026 in the Bulletin of Volcanology now warns that the speed of its regrowth could set the stage for another catastrophic flank collapse, the same type of event that sent a tsunami crashing into coastal communities in December 2018.
That 2018 disaster killed at least 430 people, injured roughly 14,000, and displaced more than 33,000 along the shores of western Java and southern Sumatra. It happened without a conventional earthquake trigger. The western side of Anak Krakatau’s cone simply slid into the sea during an eruption, displacing enough water to generate waves that struck the coast with almost no warning. The volcano’s parent, Krakatau, produced one of the most violent eruptions in recorded history in 1883, killing more than 36,000 people, the vast majority swept away by tsunamis that radiated across the strait and beyond.
Now, barely seven years after losing roughly two-thirds of its height, Anak Krakatau is putting itself back together.
A volcano that keeps rebuilding itself
Anak Krakatau, whose name translates to “Child of Krakatau,” first broke the ocean surface in 1927, roughly four decades after the caldera-forming blast that destroyed its predecessor. Since then, it has followed a cycle of growth and destruction that the new Bulletin of Volcanology study documents in detail. Using archival records, satellite imagery, and drone surveys, the researchers reconstructed the island’s physical evolution from 1927 through 2023, tracking how repeated eruptions built the cone higher and wider over nearly a century.
The December 2018 collapse interrupted that growth dramatically. In a matter of minutes, the volcano lost an estimated 150 to 180 million cubic meters of material as its southwestern flank slid into the caldera basin. But almost immediately, new eruptions began filling the void. A separate morphological analysis published in Geoscience Letters documents how the post-collapse crater has been steadily filling with fresh volcanic material, reshaping the island’s profile.
The Bulletin of Volcanology study goes further, modeling different growth-rate scenarios to assess when the rebuilt cone might again become structurally unstable. If the volcano continues adding material at the elevated rates observed in the years immediately following the 2018 collapse, the conditions that preceded that flank failure could recur sooner than the century-long buildup that preceded it.
What monitoring shows in 2026
The Smithsonian Institution’s Global Volcanism Program, which maintains the most comprehensive global eruption database, issued a volcanic activity report for Krakatau on 28 April 2026 confirming that Anak Krakatau remains frequently active. NASA Earth Observatory imagery captured thermal anomalies and ash plumes during a period of increased explosions that Indonesian volcanologists reported beginning in late November 2023. The Darwin Volcanic Ash Advisory Centre, operated by Australia’s Bureau of Meteorology, continues to track ash-bearing eruptions from the volcano that could affect aviation routes over the strait, drawing its data from CVGHM (Indonesia’s Center for Volcanology and Geological Hazard Mitigation), the national authority responsible for monitoring and issuing official alert levels.
However, no peer-reviewed quantitative measurements of the volcano’s growth rate covering the period from 2024 through mid-2026 have been published yet. The Bulletin of Volcanology study’s reconstruction ends in 2023, leaving a gap of roughly two and a half years during which the volcano has continued erupting without its output being formally measured and published in the scientific literature. That gap matters because the central hazard question is whether Anak Krakatau is rebuilding faster than its long-term average from 1927 to 2018, a rate that would raise the probability of another sector collapse and tsunami.
Why the 2018 collapse changed the calculus
Before December 2018, Anak Krakatau was treated as a known hazard but not necessarily an imminent one. The volcano had been growing steadily for decades, producing frequent small-to-moderate eruptions that were closely watched but rarely triggered widespread alarm. The flank collapse changed that perception in two ways.
First, it demonstrated that a volcanic tsunami could strike the Sunda Strait’s densely populated coastlines with very little lead time. Unlike tsunamis generated by submarine earthquakes, which can be detected by deep-ocean pressure sensors and seismic networks, a tsunami caused by a volcanic landslide originates much closer to shore and propagates faster than warning systems can typically respond. Indonesia’s tsunami buoy network, which had suffered from chronic underfunding and maintenance failures, was largely non-functional at the time of the 2018 event.
Second, the collapse revealed that Anak Krakatau’s cone was less structurally sound than some hazard assessments had assumed. The volcano sits in a shallow submarine caldera, and its flanks rest partly on loose, water-saturated sediment. When fresh lava and pyroclastic material pile up faster than the underlying structure can support, the risk of gravitational failure increases. The 2026 study’s scenario modeling is built around exactly this dynamic: how quickly does new material accumulate, and at what point does the growing cone exceed the load-bearing capacity of its foundation?
Millions live within the tsunami shadow
The Sunda Strait is one of Indonesia’s busiest waterways, connecting the Java Sea to the Indian Ocean and separating two of the country’s most populated islands. The provinces of Banten (on Java’s western tip) and Lampung (on Sumatra’s southern end) are home to millions of people, many of them living in low-lying coastal areas that were directly affected by the 2018 tsunami. The port city of Merak, a key terminal for ferries crossing the strait, sits roughly 50 kilometers from Anak Krakatau.
For these communities, the practical implications of the new research are concrete. The 2018 tsunami’s inundation footprint and the far larger historical footprint from 1883 provide conservative benchmarks for planning where critical infrastructure like hospitals, power stations, and emergency shelters should be sited. CVGHM remains the authoritative source for official alert levels and evacuation guidance, and its bulletins should be treated as the definitive word on immediate risk.
But communities do not need to wait for precise growth-rate figures to take sensible precautions. A structurally young volcanic cone with a documented history of catastrophic flank collapse, sitting in a shallow caldera beside densely populated coastlines, warrants standing preparedness: regular evacuation drills, clearly marked escape routes, and coordination between local disaster agencies and national monitoring centers.
What scientists are watching next
The next few years of research will be critical for narrowing the uncertainty. High-resolution satellite interferometry (InSAR), which can detect centimeter-scale ground deformation from orbit, could reveal whether the rebuilt cone is developing the internal stress patterns that preceded the 2018 failure. Repeat drone surveys, of the kind used in the Bulletin of Volcanology study, can track volume changes with precision that satellite imagery alone cannot match. Continuous seismic and acoustic monitoring, maintained by CVGHM and supplemented by international networks, provides the real-time data needed to detect changes in eruption frequency or magma movement beneath the edifice.
If future studies document a sustained period of unusually rapid cone growth or detect new zones of flank deformation, that would strengthen the case for enhanced tsunami preparedness across the strait. If growth rates settle back toward the long-term average and the edifice shows signs of stabilizing, the concern would ease modestly, though it would not disappear. Anak Krakatau has collapsed before, and the geological record suggests it will do so again. The question is not whether, but when, and whether the people living in its shadow will have enough warning to get to higher ground.
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*This article was researched with the help of AI, with human editors creating the final content.
