How Far Has Anak Krakatau's Ash Spread? BMKG Gives Latest Update

The answer to how far Anak Krakatau's volcanic ash has spread depends heavily on one detail: when the observation was made.

On September 6, Indonesia's Meteorology, Climatology and Geophysics Agency, or BMKG, detected ash extending across Banten, Jakarta, West Java and as far as Bengkulu.

By the morning of September 7, however, the atmospheric pattern had changed.

BMKG's latest satellite analysis showed the main ash plume moving predominantly westward rather than farther east across Java.

Where Is the Ash Now?

BMKG's latest SIGMET covering 6:30–9:30 a.m. local time on September 7 detected volcanic ash at altitudes up to approximately 15,000 feet, or 4.57 kilometers.

The plume was moving west at around 15 knots.

A Himawari-9 satellite analysis at 9 a.m. showed ash spreading southwest to northwest across parts of Banten, western and southern West Java, Lampung and Bengkulu, as well as surrounding waters.

At higher levels, ash was observed farther over the Indian Ocean west and southwest of Bengkulu, Lampung and Banten.

That upper-level plume was moving away from Indonesia.

Why Jakarta Appeared in Earlier Reports

Earlier reports were also accurate—they reflected an earlier atmospheric situation.

BMKG's September 6 satellite analysis identified two ash clusters extending over Banten, Jakarta, West Java and Bengkulu.

The shift between the two updates demonstrates how quickly volcanic ash dispersion can change.

Wind speed and direction vary over time and at different atmospheric heights.

An area affected one day may not remain beneath the main plume the following morning.

Could the Ash Reach Central Java?

It is possible in meteorological terms, but it is not what BMKG's latest observation currently shows.

BMKG Acting Deputy for Meteorology Andri Ramdhani said any movement toward Central Java would depend on changes in wind direction across different layers of the atmosphere.

If winds turn eastward at the relevant altitudes while Anak Krakatau continues releasing ash, the plume could travel farther along Java.

Without that combination, distance alone does not determine where ash goes.

What About East Java?

The same principle applies to East Java.

BMKG has not said East Java will definitely be affected.

Its position is conditional: ash can travel farther if atmospheric winds change in a favorable direction.

As of Monday midday, East Java provincial monitoring also indicated that Anak Krakatau ash had not reached the province.

That status could change, so it should be treated as a time-specific observation rather than a permanent all-clear.

Different Altitudes Mean Different Directions

Volcanic ash does not move as a single cloud at one height.

An eruption can inject particles into several atmospheric layers.

Near-surface winds may blow in one direction while winds several kilometers higher move another way.

This is why one part of an ash plume can travel west while another portion takes a different path.

It is also why aviation agencies monitor altitude as closely as horizontal position.

How Long Could Jakarta Remain Affected?

BMKG has not set a definite end time.

Two factors determine the duration.

The first is Anak Krakatau's eruptive activity and whether new ash continues to enter the atmosphere.

The second is atmospheric transport: wind speed and direction determine whether ash remains, disperses or moves into a different region.

For that reason, a forecast stating that ash will disappear from Jakarta at a specific hour would be unreliable without updated observations.

The Continuous Eruption Has Ended, but Activity Continues

Indonesia's Geological Agency reported that a continuous eruptive episode beginning at 11:07 p.m. on September 4 ended at 12:04 a.m. on September 6 after roughly 25 hours.

Three Strombolian eruptions were subsequently recorded.

The agency says the probability of further eruptions remains high.

Potential hazards include incandescent projectiles, heavy ashfall and lava flows if prolonged eruptive activity resumes.

Anak Krakatau remains at Alert Level III.

That means the end of one sustained eruption does not mean volcanic activity has ended.

Aviation Has Already Been Disrupted

The ash cloud has affected more than air quality.

BMKG said eight airports in Java and Sumatra were temporarily closed as of September 7 as a preventive aviation-safety measure.

Volcanic ash can damage aircraft engines and other critical systems.

Airspace decisions therefore depend on the location, altitude and concentration of ash rather than whether people can visibly see ash from the ground.

Health Risks Remain

Indonesia's Health Ministry has advised people in affected areas to limit unnecessary outdoor activity.

High volcanic-ash exposure can trigger acute respiratory problems, eye irritation and skin problems.

Children, older adults and people with chronic respiratory or cardiovascular conditions are considered particularly vulnerable.

When going outdoors is necessary, authorities recommend masks and protective eyewear.

Old Ash Maps Can Be Misleading

Volcanic-ash maps can become outdated quickly.

A map from September 6 showing Jakarta beneath an ash cluster does not contradict a September 7 map showing the plume moving mainly west.

They represent different moments in a changing atmosphere.

For readers and social-media users, the timestamp may therefore be as important as the map itself.

Sharing an ash image without its observation time can create unnecessary alarm or false reassurance.

Where to Check the Latest Map

BMKG maintains a dedicated satellite product for Anak Krakatau volcanic-ash dispersion.

The product incorporates volcanic-ash analysis associated with information from the Darwin Volcanic Ash Advisory Centre.

Residents should also follow Indonesia's Geological Agency and local authorities for updates on volcanic activity and safety recommendations.

Air travelers should check directly with airlines and airport authorities because operational conditions can change quickly.

Bottom Line

Anak Krakatau's ash has already affected a broad part of western Indonesia.

On September 6, BMKG observed ash across Banten, Jakarta, West Java and Bengkulu.

By 9 a.m. on September 7, the main plume was moving westward, covering parts of Banten, western and southern West Java, Lampung and Bengkulu, with higher-level ash extending into the Indian Ocean.

Central and East Java are not currently the main areas identified in the latest plume analysis.

They could be affected only if atmospheric winds shift in a direction that carries new ash farther east.

That is why there is no permanent answer to the question of how far the ash can travel.

The answer changes with the eruption, altitude, wind direction, wind speed and observation time.

Disclaimer: Readers should rely on the latest official BMKG, Geological Agency and local-authority updates for real-time safety decisions.