Anak Krakatau Eruption Sends Ash to 50,000 Feet as Lava Fountains Light Up Sunda Strait

Darwin aviation officials are tracking two continuous ash layers after a powerful overnight eruption produced lava fountains, booming explosions and an upper plume roughly 15 kilometers high.

Published 2026-09-05T13:49:13.324Z

A major eruption of Anak Krakatau sent volcanic ash to approximately 50,000 feet above sea level as a continuous high-altitude cloud spread west from Indonesia's Sunda Strait. The eruption followed hours of repeated explosions and culminated in towering ash, glowing lava fountains, booming sounds and air shockwaves from the active cone between Java and Sumatra.

The Darwin Volcanic Ash Advisory Centre confirmed the high plume in Himawari-9 satellite imagery. Its September 5 advisory tracked two distinct ash layers: an upper cloud reaching flight level 500, about 50,000 feet or 15.2 kilometers, moving west at roughly 30 knots, and a lower cloud reaching flight level 200, about 20,000 feet or 6.1 kilometers, moving south to southeast at approximately 10 knots.

Forecast dispersion maps carried both layers forward for at least 18 hours. The upper cloud was projected to spread far west and southwest over the Indian Ocean while the lower layer expanded south and southeast of Krakatau. Ash at those altitudes is a serious aviation hazard because it can damage aircraft engines, abrade windscreens and contaminate critical systems. The advisory describes the ash cloud's position and expected movement; it does not by itself confirm that a particular airport has closed or that a specific flight has been canceled.

Indonesia's MAGMA monitoring service recorded at least 10 eruptions from Friday, September 4, into early Saturday. The sequence included closely spaced explosions during Friday morning and another cluster late Friday night. A black, dense ash column was seen rising about 300 meters above the summit during one earlier eruption before nighttime activity intensified.

The sustained phase began at approximately 11:07 p.m. local time Friday. Observers interpreted the bright red material rising continuously above the crater as a lava fountain. Explosions and rumbling were heard at the Pasauran observation post, while instruments recorded one prolonged eruption signal with a maximum amplitude of 70 millimeters and a reported duration of 21,600 seconds.

Ejected volcanic material also struck and disabled a monitoring camera near the volcano, according to Indonesia's disaster-management agency, BNPB. Other instruments, remote observations and satellite imagery continued to provide evidence after the camera stopped operating. Cloud and fog sometimes prevented ground observers from measuring the eruption column directly, which explains why some early surface reports said the plume could not be seen even as satellites later detected ash at extreme altitude.

Anak Krakatau remains at Level III, or Siaga, on Indonesia's four-level ground-alert scale. PVMBG and BNPB are enforcing a three-kilometer exclusion zone around the active crater. Residents, fishermen, visitors and tour operators are being told not to enter the restricted area or approach the volcano to record the eruption.

The spectacular eruption has also revived anxiety along the coasts of Banten and Lampung, where memories of the deadly 2018 Sunda Strait tsunami remain strong. BNPB has asked the public to remain calm. PVMBG's present evaluation is that the volcano's post-2018 structure remains relatively small and does not currently show the potential for the type of massive flank collapse that generated that tsunami. That assessment addresses present conditions and should not be interpreted as a permanent guarantee; coastal residents should continue following BMKG, BNPB and local emergency instructions.

Krakatau's history explains the intense attention surrounding any major eruption. The catastrophic 1883 event destroyed much of the former island and generated tsunamis that killed more than 36,000 people. Anak Krakatau—the Child of Krakatau—began growing inside the old caldera in 1927 and has erupted frequently since. In December 2018, collapse of part of the younger cone generated another deadly tsunami around the Sunda Strait.

For now, the immediate story is the scale and persistence of the current ash emission. A plume reaching 50,000 feet rises to the upper tropical troposphere near the tropopause and can affect aviation far beyond the volcano itself. SeismicWatch Pro will continue following Darwin VAAC forecasts, PVMBG observations, changes to the exclusion zone and any updates from Indonesian disaster and tsunami authorities.