Two new island-like formations have emerged in the Sunda Strait near Mount Anak Krakatau following a continuous 25-hour eruption in September 2026, according to Indonesia’s Geological Agency. Satellite imagery also revealed the volcano expanded by nearly 33 hectares as officials maintain an alert status.
The formations sit hundreds of meters off opposite sides of the active volcano, aligned almost on a straight line through the crater. Indonesia’s Geological Agency places one about 760 meters off the northwest coast and the other roughly 495 meters to the southeast. Officials first spotted the features in satellite data following a relentless eruption that began late on September 4 and ran for 25 hours non-stop.
Volcanologists and remote sensing experts are currently examining how the landmasses formed. Researchers are evaluating whether relatively fluid magma reached the surface through an elongated conduit or if the mounds simply represent massive piles of loose debris swept together by ocean currents and gravity.
Satellite Data and the 32.8-Hectare Expansion of Anak Krakatau
Earth observation data captured by the European Space Agency’s Sentinel fleet of spacecraft provided the first clear look at the changing geography in the water-filled caldera. Beyond the two offshore mounds, the satellite scans documented significant changes to the main volcanic body itself.
An analysis of imagery conducted on September 15 showed that Anak Krakatau’s landmass expanded by 32.8 hectares. That growth followed pyroclastic material and lava flows cascading down the northwest, west, and southwest sectors during the September blast.
The transformation extended to neighboring islands in the archipelago as well. Vegetation and moisture indexes recorded by remote sensing satellites showed that Sertung Island, located just west of the crater, lost most of its green signature in barely a month as ash blanketed the surface.
Scientific Debate Over New Vents Versus Loose Volcanic Debris
Whether the two offshore mounds represent permanent geological shifts or transient piles of sand remains an open question among researchers. Rita Susilawati, head of the PVMBG Centre for Volcanology and Geological Hazard Mitigation, cautioned that further field verification is required.
Other researchers point to oceanographic factors and the mechanics of underwater deposits. Happy Christin Natalia, a lecturer at the Lampung Institute of Technology, noted that ejecta sliding into the sea can easily be transported by currents and piled up elsewhere. Because the materials are loose rather than solid rock, she warned that the new landmasses behave much like shifting sand dunes.
If field teams eventually confirm that magma is erupting directly from new underwater openings, it could signal a major structural shift. Dini Nurfiani, a researcher at the National Research and Innovation Agency, suggested that such a confirmation might point toward an evolution toward a distributed eruptive system reminiscent of the volcano’s architecture prior to the catastrophic 1883 blowout.
Alert Levels, Travel Disruptions, and Ongoing Safety Restrictions
The intense September activity brought widespread disruption to the Sunda Strait region. The continuous eruption grounded flights for days and left more than 300,000 passengers stranded as cities were covered in thick ash.
Search and recovery efforts also unfolded alongside the geological investigations. Five journalists and three boat crew members went missing while covering the eruption, leading authorities to declare them presumed dead after a weeks-long search of the waters failed to locate their vessel.
Following a decline in activity, the Geological Agency lowered the volcano’s alert status from Level III to Level II on September 21. Officials continue to enforce safety radiuses around the caldera.
- The public and fishers must stay at least two kilometers away from the main eruption center.
- Visitors and locals are advised to maintain a distance of at least one kilometer from the two newly detected formations.
