Jakarta. A prolonged eruption of Mount Anak Krakatau earlier this month added an estimated 32.8 hectares of land to the volcanic island in the Sunda Strait, the Geological Agency said Thursday, citing an analysis of Sentinel satellite imagery.

The newly formed land was detected along the northwestern, western and southwestern sectors of Anak Krakatau following continuous eruptive activity on Sept. 4-6.

Siti Sumilah Rita Susilawati, head of the Center for Volcanology and Geological Hazard Mitigation (PVMBG) at the Geological Agency, said the expansion was believed to have resulted from the accumulation of pyroclastic material and lava flows produced during the eruption.

“Additional land can be seen on the body of Mount Anak Krakatau in the northwest-west-southwest sectors as a result of deposits of pyroclastic material and lava flows from the Sept. 4-6, 2026 eruption,” Rita said in a statement posted on the Geological Agency's X account.

The agency calculated the increase in land area at approximately 32.8 hectares.

Satellite imagery also revealed two small mounds resembling islets northwest and southeast of Anak Krakatau.

The Geological Agency said their appearance may be associated with the same continuous eruptive episode, which lasted for approximately 25 hours.

Instrumental monitoring showed that the continuous eruption began at 11:07 p.m. on Sept. 4 and ended at 12:04 a.m. on Sept. 6. A brief Strombolian eruption occurred several hours later.

Under the agency's preliminary interpretation, relatively fluid magma may have reached the surface through an elongated opening extending from northwest to southeast. Erupted material then accumulated at separate locations, producing the two features visible in the satellite imagery.

However, the agency stressed that the interpretation remains preliminary and must be confirmed through direct observations.

The Geological Agency plans to compare satellite imagery from before and after the eruption and conduct field verification to determine the precise nature of the morphological changes.

The public has been urged to remain calm and avoid approaching the newly detected features.

Anak Krakatau is currently at Level II, or Waspada (Advisory), after its alert status was lowered from Level III, or Siaga (Watch), on Sept. 21.

At the current alert level, people are prohibited from conducting activities within a 2-kilometer radius of the active crater.

The Geological Agency has also advised people to stay away from the two newly detected mounds and maintain a distance of at least 1 kilometer from them while their nature and stability are assessed.

Further analysis of satellite imagery and field observations will be used to determine how the September eruption reshaped Anak Krakatau and the surrounding area.

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