Anak Krakatau erupts continuously since Sept. 4; ash reaches 50,000 ft, aviation warnings issued

Anak Krakatau, the active cone of the Krakatau volcano complex, has been in continuous eruption since late Sept. 4 local time in Indonesia, sending ash high enough to trigger Orange aviation alerts and ash warnings for the Jakarta flight region. Aviation and disaster-monitoring bulletins use the name Krakatau for the volcano, which sits in the Sunda Strait between Java and Sumatra.

Indonesia’s volcanology agency, PVMBG, also known as Badan Geologi, said the eruption began at 23:07 WIB on Sept. 4, or 16:07 UTC, and was still ongoing in the early hours of Sept. 5. In a special report published via MAGMA Indonesia, the agency said, “Kondisi terkini Gunung Anak Krakatau erupsi menerus, berlangsung sejak tanggal 04 September 2026 pukul 23:07 WIB hingga saat laporan ini dibuat.” PVMBG described the activity as “erupsi menerus,” or continuous eruption, including lava-fountain-style activity. The volcano remained at Alert Level III, known as Siaga, and authorities advised the public to stay outside a 3-kilometer, or roughly 2-mile, radius.

The eruption’s most immediate wider impact was on aviation. The Darwin Volcanic Ash Advisory Centre issued multiple ash advisories on Sept. 4, with cloud tops in some advisories reaching as high as FL500, or about 50,000 feet. That altitude is well within airspace used by commercial aviation, and volcanic ash can damage aircraft engines and interfere with flight operations. One Darwin VAAC advisory said, “HIGH LEVEL EMISSION IN PROGRESS. HEIGHT BASED ON IR TEMP OF -64 DEGREES AT 04/1640Z.” Aviation warnings also included SIGMETs for the Jakarta FIR, or flight information region, signaling ash hazards in controlled airspace used by commercial flights. The Global Disaster Alert and Coordination System, or GDACS, listed the event as VO 1000148 with an overall Orange alert on Sept. 5.

As of Sept. 5 at 15:29 UTC, research found no verified reports of deaths, injuries, structural damage or a tsunami tied to the eruption. PVMBG said local observations included audible booming heard in parts of Java and Sumatra, underscoring how widely the eruption was being noticed even without confirmed reports of direct harm.

The volcano is closely watched because of where it sits: in the Sunda Strait, near densely populated coastlines and beneath important regional air routes. Anak Krakatau is also closely monitored because a partial flank collapse in 2018 triggered a deadly tsunami in the Sunda Strait. But PVMBG said the rebuilt cone is currently relatively small and is not judged to have the potential to collapse at a scale that would trigger a tsunami. That assessment is specific to the current eruption, based on the agency’s latest monitoring.

For now, the clearest hazards are the ongoing eruption itself, the ash cloud risk to aviation and the exclusion zone around the volcano. Indonesian authorities have kept the alert at Level III while monitoring continues.