Two new islands have formed off the coast of Anak Krakatau in Indonesia, representing the first such emergence within the caldera since the volcano’s reappearance in 1930. The geological event followed a 25-hour eruption in early September and was confirmed by Indonesia’s Geological Agency.
The islands are located several hundred meters from Anak Krakatau: one about 760 meters off the north-west coast and the other roughly 495 meters to the south-east, positioned nearly in a straight line that cuts through the volcano’s crater. While satellite imagery and eyewitness accounts have documented the formations, the agency has yet to verify their precise size or elevation above sea level.
The Geological Agency’s preliminary assessment suggests that relatively fluid magma reached the surface through an elongated opening running north-west to south-east during the eruption. This activity deposited volcanic material offshore, creating the two island-like mounds. However, the exact nature and composition of these new landforms remain uncertain. Officials have not ruled out whether they represent new eruption vents or accumulations of erupted material within shallow parts of the caldera.
The presence of the new islands was first noted during a search operation nearly two weeks after the eruption. Yodistara Nugraha, a tourism activist from Kalianda in South Lampung, was flying a drone over the region in an effort to locate missing journalists and others last seen near Anak Krakatau. His drone footage recorded waves breaking over what appeared to be a low, dark mass between Sertung Island and Anak Krakatau, potentially capturing the north-western new island. Nugraha later recognized the significance of the images amid ongoing reports from mariners and volunteers who observed unusual land formations in the area.
Anak Krakatau, meaning "Child of Krakatoa," has been intermittently active since July, with the continuous eruption in early September expanding the island’s land area by approximately 33 hectares through lava flows and pyroclastic deposits. This volcanic activity follows the major destruction caused by Krakatoa’s 1883 eruption, which obliterated most of the original island, resulted in over 36,000 fatalities, and generated global atmospheric effects.
The newly formed islands’ long-term survival will depend on their ability to resist erosion and remain above water during high tides. Anak Krakatau itself underwent multiple cycles of emergence and submersion during its initial formation. Geological experts note that loose volcanic deposits frequently compete with erosive forces, causing significant changes in island morphology over time. For example, Anak Krakatau’s peak height drastically reduced after a major eruption and flank collapse in 2018, illustrating the dynamic nature of volcanic islands in this region.
Further investigation is needed to determine the exact volcanic processes responsible for the new landforms and to monitor ongoing activity in the Sunda Strait between Java and Sumatra, where Anak Krakatau remains an active and evolving volcanic feature.