Anak Krakatau Still in 'Incubation Phase': What Does It Mean?

September 14, 2026 | 07:34 pm

TEMPO.CO, Jakarta - Mount Anak Krakatau in Indonesia’s Sunda Strait is still in what scientists describe as an “incubation phase,” meaning a major caldera-forming eruption is not considered imminent, according to a researcher at the National Research and Innovation Agency (BRIN).

Aditya Pratama, a researcher at BRIN’s Geological Disaster Research Center, said Anak Krakatau is still far from the stages that precede a large eruption capable of creating a new caldera.

“At Anak Krakatau, it is estimated to still be in the incubation phase. It is still quite far from reaching the fermentation phase before a caldera-forming eruption,” Aditya said during an online disaster-management discussion in Jakarta on Monday, September 14.

The assessment provides context amid renewed attention to Anak Krakatau, the volcano that emerged in the Sunda Strait following the catastrophic 1883 eruption of Krakatau.

What Is the Incubation Phase?

Aditya explained that the volcanic system in the Sunda Strait has historically gone through three main stages: ancient Krakatau, younger Krakatau and Anak Krakatau, which gradually emerged after the 1883 eruption.

According to the research framework cited by Aditya, caldera-forming eruptions generally develop through several stages, beginning with incubation and followed by maturation and fermentation before a major eruption.

In simple terms, the incubation stage indicates that the volcanic system has not yet developed the conditions associated with the later stages of a caldera-forming eruption.

“This is at least the second cycle of caldera formation, in the fifth, fourth, sixth centuries, and in 1883,” Aditya said, referring to evidence of major eruptive cycles in the Krakatau volcanic system.

Where Is Anak Krakatau’s Magma?

Recent research published in Frontiers in Earth Science identified Anak Krakatau’s magma reservoir at depths ranging from about 7.4 to 26.6 kilometers beneath the volcano, Aditya said.

The finding differs from evidence from the older Krakatau volcanic systems. Ancient and younger Krakatau were found to have large magma reservoirs at much shallower depths before their major destructive eruptions.

Researchers analyzed the petrographic and geochemical characteristics of more than a dozen rock samples and found that Anak Krakatau’s magma has continued to evolve, with characteristics that distinguish it from earlier phases of the volcanic system.

The presence of olivine minerals in Anak Krakatau samples also indicates differences in the chemical composition of its current magma system, Aditya said.

Does This Mean Anak Krakatau Is Safe?

The assessment does not mean Anak Krakatau poses no volcanic hazard. The volcano remains active, and its potential for future eruptions persists.

However, Aditya said the current stage suggests that the development toward a major caldera-forming eruption would take a considerable amount of time.

He said a better understanding of Anak Krakatau’s magma system and its long-term volcanic cycles could help authorities improve disaster preparedness and mitigation strategies.

Anak Krakatau remains one of Indonesia’s closely monitored volcanoes because of its location in the Sunda Strait, between the islands of Java and Sumatra.

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