Anak Krakatau ash keeps Jakarta's airports shut and 270,000 passengers waiting

Seven Indonesian airports, including both of Jakarta's main fields, were still closed on Monday morning because of ash from Mount Anak Krakatau. Transport Minister Dudy Purwagandhi said Soekarno-Hatta would stay shut until at least 6 p.m. local time. Six other airports in Lampung and West Java were held on the same order. One field in South Sumatra had been allowed to reopen. The ministry's running tally by Monday was 2,300 flights cancelled or delayed and more than 270,000 passengers hit.

The volcano sits in the Sunda Strait between Java and Sumatra. It began this sequence late on Friday. BMKG, the meteorology agency, recorded the latest burst at 8.23 p.m. on Sunday. Ash was detected to 20,000 feet east of the cone and to 50,000 feet to the west, over parts of Banten. The volcano monitoring office said the chance of further eruptions remained high. Purwagandhi's public line was that no one could say when the closures would end because the wind kept changing.

Sunday's first count had been 1,558 delayed flights and 170,000 stranded passengers, with more than 900 of those flights tied to Soekarno-Hatta alone. The Monday numbers show how fast a plume over Java's air lanes multiplies. Halim Perdanakusuma, Bandung's Husein Sastranegara, Radin Inten II near Bandar Lampung, Budiarto, Pondok Cabe, Taufik Kiemas and Atung Bungsu were on the closed list at various points in the weekend. Semarang, Surabaya, Yogyakarta and Kertajati were told to run around the clock as diversions. Singapore Airlines cancelled more than 19 flights out of Changi that would have used Jakarta.

Jakarta's schools went online on Monday. The city did not say for how long. Shipping in the strait has been disrupted. Airlines that do get a slot will have to inspect engines before they fly again. Volcanic ash is glass. It sandblasts compressor blades and can shut a turbine down in minutes. That is why a plume at 50,000 feet, well above cruise altitude on some tracks, is treated as a hard stop rather than a nuisance.

Anak Krakatau is the cone that grew from the caldera of the 1883 Krakatoa eruption. In December 2018 a flank collapse on this same island sent a tsunami that killed more than 400 people on the Java and Sumatra coasts. The present event is an ash crisis, not a tsunami bulletin, but the 2018 memory is why coastal offices watch the seismographs as closely as the airports watch the satellite plume.

Copernicus Sentinel-2 had already photographed an ash column from this volcano as recently as July, when authorities raised the alert to Level III. The weekend eruptions pushed that column over the busiest air corridor in the country. Soekarno-Hatta handled the better part of Indonesia's international traffic. Closing it for a second full day strands not only Jakarta passengers but every connection that used the city as a hub for Australia, the Gulf and the rest of ASEAN.

Purwagandhi's alternative-airport plan is a patch. Juanda in Surabaya and Yogyakarta International can take overflow. They cannot replace the slot capacity of Soekarno-Hatta. Cargo that sat on the ground on Sunday is still on the ground on Monday. Perishable export chains will feel that before the passenger queues clear.

The monitoring agency's warning that further eruptions are likely is the sentence that matters for Tuesday's roster. If the westbound plume holds at 50,000 feet, the 6 p.m. target for Soekarno-Hatta will slip. If the wind turns and drops the ash south of the field, inspections can start. Either way the 270,000 people already counted are the floor, not the ceiling, of this disruption.

Anak Krakatau does not need a new island-wide evacuation order to stop a capital. It needs only to keep putting glass in the airway that feeds it. That is the condition Jakarta woke up to on 7 September.