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High-level eruption at Anak Krakatau ejects ash over 15 km (50 000 feet) a.s.l., Indonesia

ByRishav Kothari

A high-level eruption at Anak Krakatau, Indonesia, ejected volcanic ash up to 15 km (50 000 feet) above sea level at 00:50 WIB on September 5, 2026 (17:50 UTC on September 4). Darwin Volcanic Ash Advisory Center (VAAC) later tracked the ash moving west at approximately 74 km/h (46 mph), while a second layer to about 5.5 km (18 000 feet) extended south. SIGMETs were issued for the Jakarta and Melbourne flight information regions.

Darwin VAAC recorded a rapid increase in reported ash altitude late on September 4. Advisory 2026/163 placed ash at FL070, equivalent to approximately 2 km (7 000 feet) above sea level (a.s.l), at 23:00 WIB (16:00 UTC).

Advisory 2026/164 identified a high-level eruption to approximately 14 km (45 000 feet) a.s.l., at 23:30 WIB (16:30 UTC). Ten minutes later, Advisory 2026/165 noted ash at approximately 15 km (48 000 feet), moving west at about 93 km/h (58 mph).

Darwin VAAC said the high-level emission was continuing and based the altitude estimate on an infrared cloud-top temperature of −68°C (−90.4°F). Ash movement and subsequent forecasts were based on Himawari-9 satellite imagery and consensus model guidance.

Advisory 2026/167, issued at 19:10 UTC, identified two ash layers in satellite imagery at 01:50 WIB on September 5 (18:50 UTC on September 4). Ash extending from the surface to 15 km (48 000 feet) was moving west at approximately 74 km/h (46 mph), while a second layer extending to about 5.5 km (18 000 feet), was moving south at approximately 19 km/h (12 mph).

As of 19:58 UTC on September 4, official sources had not reported airport closures, flight cancellations or delays.

The South Lampung Regency Disaster Management Agency (BPBD), citing a September 3 evaluation by the Geological Agency of Indonesia’s Ministry of Energy and Mineral Resources, reported that Anak Krakatau remained at Level III (Siaga).

The evaluation described shallow or near-surface magma dynamics as very high and maintained a 3 km (1.9 miles) exclusion zone around the active crater.

During the August 22–31 monitoring period, the Geological Agency recorded eruption columns rising 50–400 m (164–1 312 feet) above the crater. Sulfur dioxide emissions ranged from 715 to 2 922 tonnes (788–3 221 short tons) per day.

The monitoring network recorded 174 eruption earthquakes, 714 emission events, 336 low-frequency earthquakes, 32 harmonic events, 851 hybrid or multiphase earthquakes and 30 periods of continuous tremor.

BPBD said potential hazards identified in the September 3 evaluation included incandescent ejecta and heavy ashfall near the volcano. Under the Geological Agency’s Level III recommendations, fishermen, tourists and climbers were instructed to remain outside the 3 km (1.9 miles) exclusion zone and follow official information.

References:

1 Krakatau Volcanic Ash Advisories 2026/163–167 — Darwin VAAC — September 4, 2026

Featured image credit: Sumatera Adil & Federal

Rishav Kothari is Editor-in-Chief of The Watchers, where he runs the newsroom and covers earthquakes, volcanoes, severe weather and space weather.

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