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

Seven Indonesian airports, including the two that serve Jakarta, were still closed on Monday morning because of ash from Anak Krakatau. Transport Minister Dudy Purwagandhi said Soekarno-Hatta would stay shut until 6 p.m. local time. The other fields, including Husein Sastranegara in Bandung and Radin Inten II near Bandar Lampung, had earlier windows that ran to at least 8.59 a.m. One South Sumatra airport had reopened. The ministry's running count moved from 1,558 delayed flights and 170,000 stranded passengers on Sunday to 2,300 flights cancelled or delayed and more than 270,000 people affected by Monday.

Anak Krakatau sits in the Sunda Strait, between Java and Sumatra. It began a new eruptive phase late on Friday. Saturday produced a lava fountain and a boom that the geology agency said could be heard a few hundred kilometres away, and in one later note as far as 700 kilometres. Two further bursts were logged on Sunday. The last of those came at 8.23 p.m. The Geological Agency said a continuous 25-hour eruption ended on Sunday and that Monday's activity was moderate and intermittent: dark ash, small local quakes, weather hiding the crater. It also said the chance of further eruptions remained high.

BMKG, the meteorology office, measured ash to 20,000 feet east of the volcano on the Java side and to 50,000 feet west of it, over Sumatra and parts of Banten. AirNav Indonesia found ash in the airspace around Jakarta and several other cities. That is why the capital's international and Halim Perdanakusuma fields closed together. InJourney Airports, the state operator of four of the closed fields, put the passenger hit at those four alone at 268,539. More than 900 of Sunday's disrupted flights were to or from Soekarno-Hatta. A handful of Bali flights were also caught. Semarang and Surabaya were named as alternate landing fields.

Purwagandhi said no one could yet say when the closures would end because the weather over the strait keeps shifting. Airlines must inspect engines before they fly again. Volcanic ash melts in a turbine and can stop it. That rule, not the spectacle of the plume, is why a capital of 30 million people lost its main airport on a work-week morning. Schools in affected zones moved to remote classes. Health offices issued mask advice.

The 2018 collapse of Anak Krakatau's flank sent a tsunami that killed more than 400 people. Monday's problem is aviation and air quality, not a wall of water. The memory of 2018 is why coastal offices watch the seismographs as closely as the airport managers watch the ash forecasts. The island is young. It grew from the caldera of the 1883 Krakatau eruption and has a habit of building and shedding itself. A 25-hour lava fountain is a large event even by that standard. A 50,000-foot ash column is a problem for any jet that has to cross the strait.

Passengers slept on the floors at Soekarno-Hatta on Sunday night. The photographs from Tangerang show the usual airport furniture and none of the usual departures. Jakarta is a hub for the archipelago and for the region. A one-day closure ripples into Bali connections, Sumatra hops and long-haul banks that use the field as a night stop. The 6 p.m. Monday target is a hope tied to a forecast, not a promise. If the next burst sends another high plume west, the clock resets.

For now the operational facts are short. The volcano is still active. Ash is still in the Jakarta airspace. Seven airports are still on the closed list. The geology office is still using the word high for the odds of another eruption. Travellers who need a number should watch Purwagandhi's next window, not the colour of the plume on social media.