Anak Krakatau ash closes four airports and strands 22,800 passengers at Soekarno-Hatta

Indonesia's main airport stayed shut through Sunday morning after ash from Anak Krakatau reached Jakarta. Soekarno-Hatta International Airport first halted operations at 5:30 a.m. local time, then pushed the closure to 9:30 a.m. and later to 1:30 p.m. after a paper test between 12:35 a.m. and 1:05 a.m. confirmed ash on the ground.

The Directorate General of Civil Aviation said the 9:30 a.m. window alone hit 209 flight movements and 22,798 passengers. Sixteen international flights were cancelled. Seven were delayed and five were retimed. Singapore took the largest share of the international disruption. Doha, Sydney, Seoul, Hong Kong, Amsterdam and Kuala Lumpur were also on the list. One hundred and seventy aircraft that had parked overnight stayed on the aprons.

BMKG deputy for meteorology Andri Ramdhani said satellite images at 7:00 a.m. Western Indonesia Time showed two ash clusters. The lower cluster, from the surface to 20,000 feet, moved northeast to south and covered parts of Jakarta, Banten, West Java and nearby waters. The higher cluster, up to 50,000 feet on the Sumatra side and over parts of Banten, drifted with winds at different layers. Ramdhani said the Sunday spread was wider than the 2018 eruption and that four airports were directly affected for the first time in that comparison.

Those four were Soekarno-Hatta, Halim Perdanakusuma in Jakarta (closed until 10:00 a.m.), Radin Inten II in Lampung (closed until 10:00 a.m. in the BMKG note) and Budiarto in Curug (closed until 9:30 a.m.). State operator InJourney said schedule changes also reached Yogyakarta International, Minangkabau in West Sumatra and Supadio in West Kalimantan.

Singapore Airlines cancelled two Jakarta flights on Saturday and, by late Sunday morning, listed 19 cancelled services including two that had already been retimed. Director General of Civil Aviation Lukman F. Laisa said the extra halt followed the paper test and that safety would govern later reopenings. Airlines, air navigation services and BMKG were to keep watching the plume together.

The volcano sits in the Sunda Strait, more than 150 kilometres from the airport. Eruptions began late on 4 September, with lava fountains and booming sounds around the strait. Two further bursts came early Sunday. The volcanology centre and the Darwin Volcanic Ash Advisory Centre both mapped the clouds. Indonesia's disaster agency said there was no tsunami warning.

Health Minister Budi Gunadi Sadikin told people in the ash belt to stay indoors and wear masks against eye, skin and breathing irritation. Schools in parts of Banten and Lampung cancelled Saturday activities after students reported stinging eyes. Fishermen in the strait stayed ashore.

Anak Krakatau, Child of Krakatoa, grew from the caldera left by the 1883 eruption that destroyed most of Krakatau. It has been active off and on since it broke the sea surface in the 1920s. A flank collapse in December 2018 sent a tsunami that killed hundreds on the Java and Sumatra coasts. The present burst is milder than that collapse, but ash at jet altitudes is enough to ground an airport that handles the country's busiest domestic trunk, including the Jakarta-Makassar run, and the main Singapore shuttle.

Jet engines ingest volcanic glass and turn it to melt that coats turbines. That is why even a thin, confirmed layer on an apron is treated as a stop, not a delay. The paper test is a simple field check: a sheet left in the open picks up grit the eye can miss. Once it came back dirty, the airport had little room to reopen on the first timetable.

Passengers who overnighted at Terminals 2 and 3 were told to wait for airline notices rather than queue at empty counters. Domestic carriers with spare aircraft at other Javan fields began looking at reroutes through Surabaya and Yogyakarta once those fields stayed clear. The transport ministry said it would publish a new slot plan only after BMKG signed off on the next satellite pass.

For a Sunday in early September, the cost sits first with short-haul travellers and with freight that cannot sit on a hot apron. The longer question is whether the plume stays in the lower 20,000 feet or keeps pulsing to 50,000. If the high cluster holds over Banten into Monday, Soekarno-Hatta will lose another morning bank and Singapore will keep cancelling the shuttle.