Anak Krakatau ash keeps Jakarta's airports shut and 2,300 flights off the board

Seven Indonesian airports, including both of Jakarta's commercial fields, remained closed on Monday morning after volcanic ash from Anak Krakatau drifted across the Sunda Strait. Transport Minister Dudy Purwagandhi said about 2,300 flights had been delayed, diverted or cancelled and that more than 270,000 passengers were affected. One South Sumatra airport had reopened. Jakarta's Soekarno-Hatta was scheduled to stay shut until 6 p.m. local time.

The volcano sits in the strait between Java and Sumatra, on the caldera left by the 1883 Krakatoa eruption. It began a strong eruptive phase late on Friday. A 25-hour burst that threw lava and a boom heard 700 kilometres away ended on Sunday, the Geology Agency said. Moderate eruptions, dark ash and small earthquakes continued on Monday. Visual checks were poor because of weather.

How high the ash went

Indonesia's meteorological agency, BMKG, reported ash to about 20,000 feet on the Java side and as high as 50,000 feet on the Sumatra side and over parts of Banten. AirNav Indonesia said tests still found ash in the airspace around Jakarta and several other cities, which is why the closures held even after the loudest phase stopped.

Airports kept shut on Monday included Soekarno-Hatta and Halim Perdanakusuma in the capital region, Husein Sastranegara in Bandung and Radin Inten II near Bandar Lampung. Semarang and Surabaya were prepared as alternate landing fields. Airlines were told to inspect engines before returning any aircraft to service. Ash is glass. It melts in a turbine and can stop an engine in minutes.

Sunday's earlier tally from the ministry put 1,558 delayed flights and 170,000 stranded passengers, with more than 900 of those flights tied to Soekarno-Hatta. Monday's higher figures reflect the extra night of closure and the knock-on cancellations for aircraft that were in the wrong city.

Schools, ships and the 2018 memory

Jakarta moved classes online on Monday. The same order covered parts of West Java, Banten and Lampung so that children would not walk through ash. Some shipping in the strait was disrupted. Lana Saria, head of the Geology Agency, said the chance of further eruptions in the coming days remained high. The listed hazards were volcanic bombs, heavy ashfall and lava if the column built again.

Anak Krakatau collapsed in December 2018 and sent a tsunami that killed more than 400 people. That history is why a plume over the strait is treated as a national transport event rather than a local tourism story. The present eruption has not produced a comparable wave. The present cost is in terminals and classrooms.

When the clocks restart

Purwagandhi would not give a firm reopening time beyond the 6 p.m. Monday hold at the main airport. "We cannot ascertain when this will end due to the dynamic weather," he said. Ash does not follow a press schedule. A shift in wind can clear Soekarno-Hatta and still close Lampung, or the reverse.

For passengers the practical facts are simple. Tickets through Jakarta on Monday morning were not flying. Engine inspections will slow the recovery even after the airspace is declared clean. Schools will stay remote until local governments say the ash on streets and in gutters is no longer a health issue.

The next official markers are the Geology Agency's next eruption bulletin and AirNav's next ash test around the capital. Those two notes, not the passenger count, will decide when the 2,300-flight hole in the timetable starts to close.