Anak Krakatau erupts (September 6) — ash to 15km, and Jakarta's airport stopped
Anak Krakatau, the volcanic island sitting in the Sunda Strait between Java and Sumatra, produced the strongest eruption of its current unrest between the night of September 5 and September 6, 2026. Ash reached a reported 15,000 metres toward Sumatra and parts of Banten province and about 6,000 metres over Java, with the detonation reported audible up to 700 kilometres away. Indonesian authorities closed Soekarno-Hatta International Airport outside Jakarta along with several others, though the number is given as six in Korean reporting and eight in international reporting. The scale of disruption is also unsettled: 1,558 flights delayed or cancelled and about 170,000 passengers stranded according to Al Jazeera and the disaster agency, against 467 flights and more than 150,000 passengers in MoneyToday. A three-kilometre exclusion zone is in place and this eruption has caused no reported casualties, in contrast with the 2018 flank collapse that killed more than 400 and the 1883 eruption of the parent volcano that killed more than 36,000
The three lines
- Eruption — began the night of September 5, two more on September 6. Ash to 15,000m, 3km exclusion zone
- Aviation — Soekarno-Hatta and others closed. 1,558 flights and 170,000 passengers (Al Jazeera) vs 467 and 150,000 (MoneyToday)
- Casualties — none reported from this eruption; the 2018 flank collapse killed more than 400
Key questions
- What happened with the Anak Krakatau eruption
- **The strongest eruption of the current unrest occurred between the night of September 5 and September 6, 2026, and it shut down much of Indonesia's air traffic for more than a day.** The volcano had been **intensifying since July.** Eruptive activity began around September 4 to 5 depending on the source, and wire reporting describes a roughly **30-second eruption at 3:53 am local time on Sunday.** Two further eruptions were recorded on September 6. **Ash height depended on direction:** up to **15,000 metres** (about 50,000 feet) toward Sumatra and parts of Banten province, and about **6,000 metres** (20,000 feet) over Java. The detonation was reported audible as far as **700 kilometres** away. A **three-kilometre exclusion zone** is in force around the volcano, and **no casualties have been reported from this eruption.** The head of Indonesia's disaster agency, BNPB, noted that sufficiently heavy rain would wash the ash away quickly.
- How many airports closed and how many flights were affected
- **This is where the reporting diverges, and both tallies should be read together.** International coverage — Al Jazeera citing Indonesia's disaster agency — gives **eight airports closed, 1,558 flights delayed or cancelled, and about 170,000 passengers stranded**, with more than 900 of those flights at Soekarno-Hatta alone. Korean coverage, including MoneyToday, gives **six international airports, 467 flights (58 international and 409 domestic), and more than 150,000 passengers.** **The two have not been reconciled.** Two explanations fit: the closures expanded over time and the counts were taken at different moments, or the larger figure includes delays while the smaller counts only flights that did not operate. The wording supports the second — 1,558 is described as delayed **or** cancelled, 467 as unable to operate. **Four airports appear in both accounts:** Soekarno-Hatta in Tangerang, Halim Perdanakusuma in Jakarta, Radin Inten II in Lampung, and Husein Sastranegara in Bandung. Soekarno-Hatta's closure was extended to 8:59 am local time on Monday. Services at Bali's I Gusti Ngurah Rai and at Medan were also disrupted.
- Should I change travel plans to Indonesia or Bali
- **Check your carrier's notice rather than the volcano's location — the two do not track each other.** Most flights from Korea and elsewhere in East Asia enter Indonesia through **Soekarno-Hatta in Jakarta** or **Ngurah Rai in Bali.** Soekarno-Hatta was closed; Bali was disrupted but not closed. **Ash moves with wind, so distance from the volcano predicts very little.** Bandung and Lampung, near the volcano, closed first; Jakarta closed later, once ash had climbed to 6,000 metres on the Java side. A workable order of checks: **① your airline's operational notice** (cancellation, delay, diversion); **② the arrival airport's resumption time**; **③ if connecting, whether the transit airport is on the closure list**; **④ the natural-disaster clause in your travel insurance.** That last one matters because **an ash cancellation is not the airline's fault**, so the compensation rules differ from an ordinary cancellation — rebooking and refunds are generally provided, while delay compensation and hotel accommodation depend on the carrier's conditions of carriage. Government travel advisories are worth reading alongside the airline notice.
A volcanic island between Java and Sumatra woke up over the weekend, and Southeast Asia's second-busiest airport stopped.
1. What is confirmed
Anak Krakatau had been intensifying since July. This weekend produced the strongest eruption inside that period.
| Item | Confirmed |
|---|---|
| Location | Sunda Strait, Indonesia (between Java and Sumatra) |
| Timing | Began night of September 5; two further eruptions September 6 (Korean reporting says late September 4) |
| Ash height | 15,000m toward Sumatra and Banten / 6,000m over Java |
| Exclusion zone | 3km radius |
| Casualties | None from this eruption |
Anak means child in Indonesian. The island grew inside the caldera left by the 1883 Krakatau eruption, which killed more than 36,000 people. In 2018, a flank collapse of Anak Krakatau itself generated a tsunami that killed more than 400.
This time the damage is concentrated in aviation.
2. The counts do not agree
This is the part of the story that needs care.
| Tally | Airports | Flights | Passengers |
|---|---|---|---|
| Al Jazeera / Indonesian disaster agency | 8 | 1,558 (delayed or cancelled) | ~170,000 |
| MoneyToday and other Korean outlets | 6 (international) | 467 (58 international + 409 domestic) | 150,000+ |
Do not add these together. The wording differs in a way that matters: 1,558 is "delayed or cancelled", 467 is "unable to operate". Including delays plausibly triples the figure — the most likely explanation, though not one we could confirm against source data.
The airport count divides the same way. Korean reporting counts six international airports; international reporting reaches eight by including smaller fields such as Pondok Cabe and Taufik Kiemas.
Four airports appear in both: Soekarno-Hatta (Tangerang), Halim Perdanakusuma (Jakarta), Radin Inten II (Lampung), Husein Sastranegara (Bandung). Soekarno-Hatta's closure ran to 8:59 am local time on Monday.
3. Why ash closes airports
The intuitive answer — visibility — is wrong.
Volcanic ash is pulverised rock and glass. Drawn into a jet engine, the silicate melts in the combustion section and resolidifies further back, on cooler turbine surfaces. It coats blades and plugs the small cooling passages that keep the hot section alive. In the worst case every engine flames out at once, because every engine breathes the same air.
Two accidents established this, and in both the crew never saw the cloud: ash does not return a signal on weather radar. The regulatory response built afterwards is not measurement but avoidance — forecast ash areas are simply not entered.
That is why closures do not follow distance. Wind decides. Bandung and Lampung closed first; Jakarta closed once ash climbed on the Java side. The mechanism is set out in「Why volcanic ash stops aircraft」.
4. What remains unresolved
- The tallies are unreconciled across airports, flights and passengers. Indonesia's transport ministry figures will need checking against both.
- The start date is disputed — September 4, the night of September 5, and 3:53 am Sunday all appear. Since the unrest is continuous, this may be a question of where an eruption is deemed to begin.
- The alert level is not clearly reported. Indonesia runs a four-level scale; which one applies here was not stated in the coverage reviewed.
- Route-level cancellations must be checked with carriers. This article did not check them.
- Weather decides the next phase. Rain clears ash from the air, as the disaster agency noted, but ash mixed with water produces lahars, a separate hazard. And the unrest has been running since July.
Sources
- Al Jazeera — Thousands stranded as Anak Krakatau eruption shutters Indonesian airports
- MoneyToday — Ash to 15km: airport closures across Indonesia strand 150,000
- The Watchers — Strong eruption at Anak Krakatau closes 8 airports, disrupts 1 558 flights in Indonesia
- The Washington Post — Indonesia cancels flights at Jakarta airport and others as Anak Krakatau volcano erupts
- CNBC — Flights canceled at Jakarta airport as Anak Krakatau eruption disrupts regional travel
- Financial News — Ash to 15km, blast heard 700km away, six airports temporarily closed