Downgraded: Anak Krakatau moves from Level III (Siaga) to Level II (Waspada) after over two weeks without a new eruption

Safety & SecurityUpdatedUpdated: September 25, 2026

Our other articles on this crisis track airport closures and reopenings, the missing-journalists search, and earlier health/ashfall guidance — this entry is a standing, dedicated log of the volcano's own activity, with every discrete eruption Badan Geologi/PVMBG has recorded since the continuous eruption began on 4 September. The picture has now changed materially. After eight confirmed discrete eruptions between 6 and 9 September, PVMBG recorded no further eruption through 20 September, and on the evening of 21 September (18:30 WIB) Badan Geologi head Lana Saria announced Anak Krakatau's alert level had been downgraded from Level III (Siaga) to Level II (Waspada) — its first change since 2 July. The exclusion radius was cut from 3 km to 2 km, on the basis of declining seismicity: 20 September's data showed only one low-frequency earthquake and continuous tremor averaging 2 mm. PVMBG stresses this is a downgrade, not an all-clear — the public, visitors and climbers are still barred from the 2 km zone, and periodic evaluation continues. The Merak–Bakauheni ferry crossing and Anyer-area tourism were reported unaffected even before the downgrade. PVMBG also reported on 22 September, from Sentinel satellite imagery, that the volcano's land area grew by 32.8 hectares in the 4–6 September eruption and that two small island-like mounds appeared to its northwest and southeast. We will keep updating this log independently of the other articles, since the volcano itself is what determines whether the underlying hazard has actually passed.

Timeline

2 Jul 2026
Badan Geologi / PVMBG raises Anak Krakatau to Level III (Siaga) and sets a 3 km exclusion radius around the crater for residents, visitors, fishermen and climbers. More than 240 eruptions are recorded between then and 5 September.
Fri 4 Sep, 23:07 WIB
A continuous eruption begins, with booms and rumbling audible from the Pasauran observation post in Serang and reported across Banten, Lampung and West Java. The seismograph records a single eruption tremor of 70 mm amplitude lasting 21,600 seconds (six hours) — the strongest activity since the alert was raised. PVMBG interprets it as a lava fountain producing lava flows.
Sat 5 Sep, 00:50 WIB (02:50 JST)
The Japan Meteorological Agency reports a large eruption; Himawari-9 satellite imagery puts the plume at roughly 15 km (48,000–50,000 ft) above sea level.
Sun 6 Sep, 00:04 WIB
The continuous eruption ends, roughly 25 hours after it began. Badan Geologi confirms activity has "decreased again" but keeps the alert at Level III, saying monitoring continues given the potential for further eruptions.
Sun 6 Sep, 03:53 WIB
The first discrete eruption after the continuous episode: maximum amplitude 46 mm, duration 30 seconds. The ash column is not observed.
Sun 6 Sep, 07:10 WIB
A second discrete eruption: maximum amplitude 50 mm, duration 16 seconds. Again the ash column is not observed.
Sun 6 Sep, 20:23 WIB
A third discrete eruption: maximum amplitude 58 mm, duration roughly 44 seconds. Badan Geologi's own recap the next morning describes these three as strombolian eruptions producing black ash columns of unrecorded height.
Mon 7 Sep, 06:00 WIB recap
Badan Geologi's instrumental summary for 6–7 September logs 3 eruption earthquakes, 9 explosion earthquakes, 93 low-frequency earthquakes, 98 hybrid/multi-phase earthquakes, 4 continuous tremors and 1 shallow volcanic earthquake — a busy seismic day even without a further discrete eruption being separately announced. Visual observation is variable (clear to overcast, weak-to-moderate winds from the north/northwest), and the alert stays at Level III.
Tue 8 Sep, 05:08 WIB
The first eruption of the day: maximum amplitude 47 mm, duration 15 seconds. The column is not visually observed — fog is covering the volcano at the time, per the Anak Krakatau monitoring post in South Lampung.
Tue 8 Sep, 05:34 WIB
A second eruption follows about 26 minutes later: maximum amplitude 44 mm, duration 10 seconds.
Tue 8 Sep, 07:49 WIB
A third eruption of the morning: maximum amplitude 48 mm, duration 19 seconds — this time with an observed ash column reaching roughly 7,000 ft (2.1 km), moving south-southwest toward northwestern Banten and the northwestern Indian Ocean. BPBD Lampung issues an eruption-detection alert. This brings the confirmed discrete-eruption count since 6 September to six.
Tue 8 Sep, 11:34 WIB
A fourth eruption of the day: maximum amplitude 50 mm, duration 17 seconds, ash column not visually observed. This is the seventh discrete eruption confirmed since 6 September.
Tue 8 Sep, ~12:00 WIB
The latest forecast has the news turning more favourable: BMKG's ash-dispersal forecast now has the plume moving away from Indonesian territory rather than over it, a reversal from the westward-expansion forecasts earlier in the week. Badan Geologi's hazard assessment still flags an elevated probability of further eruptions in coming days, with the main threats being ejected incandescent rock and heavy ashfall near the crater, and renewed lava flow if a continuous eruption resumes.
Wed 9 Sep, 00:47 WIB
An eighth discrete eruption since 6 September: maximum amplitude 51 mm, duration 28 seconds — at the time, the strongest single reading since the 58 mm eruption on 6 September evening. The ash column height was not observed. PVMBG's instrumental log for the event also records one eruption earthquake, one low-frequency earthquake, one hybrid earthquake and continuous tremor. Alert level remains Level III (Siaga); the 3 km exclusion radius is unchanged.
Thu 10 Sep
Eruptions continue at a lower frequency — Badan Geologi's later reporting confirms this is the last day any were recorded before activity paused — but we did not find individual amplitude/duration figures for this specific day's event(s) from a source we could verify, so none are itemized here.
Fri 11 Sep – Sun 13 Sep
No further eruptions are recorded for three consecutive days — the longest quiet stretch since the crisis began on 4 September. Seismicity is trending down overall, but Suwarno, head of the Anak Krakatau monitoring post in South Lampung, says a status downgrade "is not that simple" and requires more sustained data: "even though the earthquake frequency is declining, the tremor is still fairly large, and that has to be taken into account." On Sunday, low-frequency earthquakes and continuous tremor of 1–10 mm amplitude were still being logged. Badan Geologi separately notes that deeper volcano-tectonic earthquakes — an indicator of magma supply from depth — have shown an increasing trend, which is why Level III (Siaga) stays in force despite the pause in surface eruptions.
Mon 14 Sep
Anak Krakatau logs four more earthquakes today; the summit itself is obscured by thick fog, so no visual confirmation of activity is possible. Alert level remains Level III (Siaga), unchanged since 2 July.
Tue 15 – Thu 17 Sep
PVMBG confirms no eruptions were recorded on 14 or 15 September. On 17 September PVMBG head Rita Susilawati says activity "has returned to a normal Strombolian eruption pattern of short duration," and describes the volcano's rapid regrowth as normal behaviour for a young cone: it now stands about 150 m high with relatively gentle slopes, so "if a collapse happens now, it will not cause a tsunami." Monitoring continues around the clock. No change to Level III (Siaga) or to the 3 km exclusion radius has been announced, and we found no report of an eruption on 16 or 17 September.
Fri 18 – Mon 21 Sep, morning
We found no report of a new eruption over these days. Badan Geologi's MAGMA observation report for 00:00–06:00 WIB on Monday 21 September still shows Anak Krakatau at Level III (Siaga): the volcano is covered by fog and no crater smoke is observed, under cloudy skies with weak winds toward the northwest.
Mon 21 Sep, 18:30 WIB
Badan Geologi head Lana Saria announces Anak Krakatau's alert level is downgraded from Level III (Siaga) to Level II (Waspada), effective immediately: "The activity level of Anak Krakatau volcano is downgraded from Level III (Siaga) to Level II (Waspada)." The exclusion radius is cut from 3 km to 2 km around the crater. The stated basis is declining seismicity — 20 September's data logged just one low-frequency earthquake and continuous tremor averaging 2 mm amplitude — continuing the trend since the last confirmed eruption on 9 September. Residents, visitors, tourists and climbers remain barred from the new 2 km zone, and Badan Geologi says it will keep evaluating and adjust the status again if activity changes significantly.
Tue 22 Sep
PVMBG head Rita Susilawati reports, via the Badan Geologi's official account, that Sentinel satellite imagery shows the volcano's land area has grown by 32.8 hectares — new material on its northwest, west and southwest sides from the pyroclastic deposits and lava flows of the 4–6 September continuous eruption — and that two small island-like mounds have appeared to its northwest and southeast. PVMBG's preliminary reading is that thin magma reached the surface through a fracture opening from the west; it will compare before-and-after imagery and verify in the field, so treat the mounds' origin as unconfirmed for now. The 2 km exclusion radius stays in force.
Thu 24 Sep
No new eruption has been reported since the downgrade. Separate reporting says the Merak–Bakauheni ferry crossing and Anyer-area tourism remain unaffected. Hazards Badan Geologi still flags within the 2 km zone: ejected rock, heavy ashfall and potential lava flow; the agency repeats that any viral tsunami warning not sourced to BMKG or Badan Geologi itself should be treated as unconfirmed.

Key points

Volcano status: downgraded on 21 September (18:30 WIB) from Level III (Siaga) to Level II (Waspada) — its first change since 2 July 2026. The exclusion radius was cut from 3 km to 2 km around the crater, still binding on residents, visitors, fishermen and climbers.
This is a dedicated eruption-activity log, separate from our articles on airport closures/reopening, Jakarta-city ashfall, and the health-ministry response — check those for operational and health guidance rather than this page.
Basis for the downgrade: seismicity kept declining after the last confirmed discrete eruption on 9 September. Badan Geologi's 20 September data logged only one low-frequency earthquake and continuous tremor averaging 2 mm amplitude. Badan Geologi head Lana Saria made the announcement; the agency says it will keep evaluating and can adjust the status again if activity changes.
Not an all-clear: PVMBG still flags ejected rock, heavy ashfall and potential lava flow as live hazards inside the new 2 km zone, and repeats that any viral tsunami warning not sourced to BMKG or Badan Geologi itself should be treated as unconfirmed. The rebuilt cone remains, PVMBG has said, too small for a collapse to trigger a tsunami-scale wave.
Running tally: eight discrete eruptions confirmed between 6 and 9 September, none with a reported ash column above 7,000 ft — well below the 4–5 September continuous-eruption phase's estimated 15 km plume. None have been recorded since 9 September, the longest quiet stretch of the crisis and the basis for the downgrade.
Knock-on effects reported as unaffected even before the downgrade: the Merak–Bakauheni ferry crossing and Anyer-area tourism.
Land growth: on 22 September PVMBG reported from satellite imagery that the volcano's land area has grown by 32.8 hectares since the 4–6 September eruption, and that two small island-like mounds have appeared to its northwest and southeast. PVMBG's preliminary reading is a fracture opening from the west; field verification is pending, and the exclusion radius remains 2 km.
For the human cost connected to this eruption, see our separate article on the search for eight people, including five journalists, missing near the volcano since 7 September — one of whom, crew member Surakman, has since been identified and buried.

What this means for your Indonesian entity

This log is a standing reference for one question: is the volcano still active? Keep it bookmarked separately from operational updates. The alert level has now dropped for the first time since the crisis began — from Level III (Siaga) to Level II (Waspada) — and the exclusion radius has narrowed from 3 km to 2 km, but this is a downgrade, not a declaration that the hazard has passed. If your staff or operations are in Banten, Lampung, or coastal West Java, the practical trigger for action remains the same as before: watch for fresh ashfall or mask advisories from BPBD, not the alert level alone, and keep any exclusion-zone planning to the new 2 km figure rather than the old 3 km one. We will add new eruptions to this timeline as Badan Geologi confirms them, and will note here if the status changes again in either direction.

Sources

This page summarises publicly available information for orientation. It is not tax, legal, or accounting advice, and regulations change. Verify against the linked primary sources and contact us before acting on anything here.

この記事の日本語版を読む

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