Anak Krakatau eruption grounds more than 1,500 flights, strands 170,000 at Jakarta's main airport

Indonesia's Anak Krakatau volcano erupted almost continuously for roughly 25 hours over the weekend, sending ash plumes as high as 15 kilometers into the sky and forcing the closure of Jakarta's Soekarno-Hatta International Airport, the country's busiest, along with seven other airports across Java and Sumatra. Officials estimate more than 1,500 flights were delayed or canceled and roughly 170,000 passengers stranded.

The eruption began at 11:07 p.m. local time Friday and continued until just after midnight Sunday, according to Indonesia's Geological Agency, known as PVMBG, part of the country's Ministry of Energy and Mineral Resources. A further 30-second Strombolian eruption followed at 3:53 a.m. Sunday, and another eruption was recorded that evening. Ash drifted over Jakarta, Banten, West Java and Lampung provinces and out over the Indian Ocean, carried by seasonal wind patterns that shifted repeatedly through the weekend and complicated forecasting for aviation authorities.

A volcano born of history's most infamous eruption

Anak Krakatau — "Child of Krakatoa" — emerged from the caldera left by the 1883 eruption of Krakatoa, one of the deadliest volcanic events ever recorded, which killed more than 36,000 people, mostly in tsunamis triggered by the collapsing volcano, and altered global climate for years afterward. The younger volcano has built itself up from the seafloor over the past century and has erupted intermittently ever since, most notably in December 2018, when a partial flank collapse triggered a tsunami that killed more than 400 people along the coasts of Java and Sumatra without warning. That history is part of why authorities treat every escalation at the volcano with particular caution.

Anak Krakatau has been held at Level III, or "Siaga" (Alert) status, by Indonesia's Ministry of Energy and Mineral Resources since July 2, meaning this weekend's activity is an escalation of a volcano already under close watch rather than a sudden surprise. PVMBG said the alert level remains unchanged after the 25-hour eruption and maintained a 3-kilometer exclusion zone around the crater, barring boat traffic and fishing within that radius.

The Sunda Strait, which separates Java and Sumatra and is home to Anak Krakatau, is also one of Indonesia's busiest shipping lanes, carrying ferry traffic between the two islands as well as cargo bound for the country's western ports. Maritime authorities imposed the 3-kilometer no-sail zone around the volcano as a precaution against sudden explosive activity, a category of eruption that can generate little advance warning even when overall alert status has not changed, and ferry operators said they were rerouting around the exclusion zone without suspending service entirely.

Soekarno-Hatta repeatedly shut as ash conditions shifted

Jakarta's Soekarno-Hatta International Airport, roughly 150 kilometers from the volcano, bore the brunt of the disruption. Volcanic ash poses a well-documented hazard to jet aircraft, capable of melting inside turbine engines and re-solidifying on internal components, which is why aviation authorities worldwide close airspace at the first sign of an ash plume rather than waiting to assess its density. Indonesia's airspace falls under the Darwin Volcanic Ash Advisory Center, one of nine regional centers worldwide that track ash clouds and issue advisories to airlines; Darwin's forecasts guided much of the corridor-by-corridor reopening AirNav carried out over the weekend rather than a single nationwide order. AirNav Indonesia, the state air-navigation authority, said it repeatedly extended flight restriction notices as ash plumes shifted with the wind, closing and reopening airspace corridors over several hours rather than issuing a single blanket shutdown. Of the roughly 1,558 flights affected nationwide, more than 900 were at Soekarno-Hatta alone. Indonesia's state news agency Antara reported that AirNav tightened aerial monitoring of the ash cloud in coordination with PVMBG throughout the weekend to decide when corridors could reopen.

International carriers including Emirates canceled Jakarta-bound flights, and Al Jazeera reported that domestic carriers Garuda Indonesia and Lion Air were among the hardest hit by cascading delays as aircraft and crews became out of position across the archipelago. Because Indonesia's air network relies heavily on a small number of hub airports to connect its more than seventeen thousand islands, a shutdown at Soekarno-Hatta tends to disrupt domestic connections nationwide far out of proportion to the airport's own traffic.

The U.S. Embassy in Jakarta issued a travel alert to American citizens flagging the eruption and the resulting airport closures, a standard precaution embassies in the region take during significant ash events even when, as in this case, there is no indication of danger to people on the ground away from the immediate vicinity of the volcano.

170,000 stranded, no injuries reported

Indonesia's national disaster agency, BNPB, said no injuries or evacuations had resulted from the eruption itself, with the impact felt almost entirely through ash fall and the resulting air-travel chaos. BNPB chief Suharyanto said heavy rain over the region would help wash ash out of the air, easing disruption to what he called Indonesians' "daily lives." ABC News Australia reported that authorities were also considering cloud-seeding operations to accelerate the clearing of ash from affected airspace, a technique previously used elsewhere to induce rainfall that scrubs ash particles from the atmosphere.

"Aktivitas Gunung Anak Krakatau terus dipantau," PVMBG said in its official update — activity at Anak Krakatau continues to be monitored, with the Alert status remaining in force even after the 25-hour eruptive episode ended.

For the estimated 170,000 travelers affected, the disruption compounded an already busy travel period. NBC News reported that airport authorities set up additional rebooking counters and that some travelers waited more than a day for alternate flights as backlogs built through the weekend. Hotels near Soekarno-Hatta reported near-full occupancy as stranded passengers sought overnight accommodation, and airlines said they were working through insurance and rebooking claims that typically follow a multi-day airspace closure of this scale. Airline industry analysts said the financial impact of a multi-day closure at Indonesia's busiest airport, while difficult to tally immediately, typically runs into the tens of millions of dollars once rebooking costs, crew scheduling disruptions and lost cargo capacity are included, on top of the inconvenience to individual travelers.

What happens next

PVMBG said it would continue monitoring Anak Krakatau around the clock for further eruptive activity and has not ruled out additional ash-producing events in the coming days. AirNav said it will keep updating flight-restriction notices airport by airport as conditions change rather than lifting them all at once, meaning further short-notice closures at Soekarno-Hatta and other Java and Sumatra airports remain possible while the volcano stays at Alert status. Given the 2018 precedent, authorities said they are also watching for any signs of structural instability on the volcano's flanks, though officials stressed there is no current indication of the kind of collapse that triggered the earlier tsunami. Indonesia sits on the Pacific "Ring of Fire" and is home to more active volcanoes than almost any other country, meaning its aviation and disaster-management agencies have developed extensive protocols for ash events over decades of practice, even as each eruption still forces difficult judgment calls about when it is safe to reopen specific corridors. That expertise was on display over the weekend, as AirNav and PVMBG coordinated closely enough to avoid a single prolonged nationwide shutdown, instead threading a series of shorter closures that let some flights operate even as the volcano remained active.