Jakarta. Mount Anak Krakatau’s 25-hour continuous eruption has ended, but the volcano remains highly active and could erupt again in the near future, the Geological Agency’s Volcanology and Geological Hazard Mitigation Center (PVMBG) said Monday.

The continuous eruption began on Sept. 4 and ended in the early hours of Sept. 6, after lasting about 25 hours. Anak Krakatau has since returned to its characteristic Strombolian eruption pattern, in which volcanic material is intermittently ejected from the crater.

PVMBG Head Siti Sumilah Rita Susilawati said the end of the continuous eruption did not mean the volcano had become inactive.

“Volcanic activity remains high, and the possibility of another eruption in the near future remains,” Siti said in an official statement Monday.

During monitoring from Sept. 6-7, Anak Krakatau continued to produce Strombolian eruptions, with black volcanic ash columns reaching a maximum height of 300 meters above the summit.

Instrumental monitoring also recorded 93 low-frequency earthquakes, 98 hybrid or multiphase earthquakes, as well as other eruption and emission-related seismic activity over the two-day period.

PVMBG has therefore kept Anak Krakatau at Level III, or Alert, and maintained a 3-kilometer exclusion zone around the volcano’s activity center.

The agency warned that potential hazards include incandescent rock fragments, heavy ashfall, hot clouds and lava flows if continuous eruptions resume.

Residents, tourists and shipping operators are prohibited from entering the 3-kilometer radius around the volcano’s activity center.

No current tsunami threat
Despite the ongoing volcanic activity, PVMBG said Anak Krakatau’s current eruptions are not triggering a tsunami.

Siti urged residents along the Banten and Lampung coasts to remain calm and avoid unverified information about a potential tsunami.

“Residents in the coastal areas of Banten and Lampung are urged to remain calm. Current eruptive activity is not triggering a tsunami, so people can continue their normal activities while following official information and directions from local authorities,” she said.

The reassurance comes amid memories of the December 2018 Sunda Strait tsunami, which struck coastal areas of Banten and Lampung after a large section of Anak Krakatau collapsed into the sea.

Volcanologist Surono said the current eruptions should not automatically be interpreted as a sign that Anak Krakatau is heading toward a major eruption.

He explained that frequent eruptions are part of the natural development of the young volcano, as volcanic material accumulates around its eruption center and gradually builds up its body.

“A young volcano like Anak Krakatau needs to erupt frequently to build its body so that it becomes taller and larger,” Surono said.

Surono said Anak Krakatau had also experienced prolonged eruptive activity in the past, including in 2007, when the volcano almost continuously erupted throughout the year.

He said the current activity does not necessarily indicate that excessive energy is building up underground.

“As long as the system remains open, there is no excessive buildup of energy. Eruptions will occur frequently, but the material falls around the summit,” he said.

Surono also said the current eruptions do not directly pose the same tsunami mechanism as the 2018 disaster. The 2018 tsunami was caused by the collapse of part of Anak Krakatau’s volcanic body into the sea, rather than the eruption itself directly generating the waves.

Why the eruptions continue
Surono said that Anak Krakatau is essentially still building itself. Material released during eruptions accumulates around the crater, gradually adding to the volcano’s height and size. Frequent eruptions are therefore part of the volcano’s natural growth process.

However, he stressed that the volcano still needs to be closely monitored and that residents and fishermen operating around the Sunda Strait should comply with the authorities’ safety recommendations.

The loud booming sounds heard from Anak Krakatau in areas far from the volcano can also vary depending on atmospheric conditions and the direction in which sound waves travel, Surono said.

PVMBG continues to monitor Anak Krakatau through visual and instrumental observations around the clock and will reassess its activity level if significant changes occur.

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