Jakarta. Indonesia’s Meteorology, Climatology and Geophysics Agency (BMKG) has intensified 24-hour monitoring of the eruption of Mount Anak Krakatau and its impact on the atmosphere, aviation and sea conditions around the Sunda Strait.

Satellite imagery analyzed from 8 a.m. local time on Sunday showed two clusters of volcanic ash spreading across parts of Banten, Jakarta, West Java and as far as Bengkulu, BMKG said.

Andri Ramdhani, acting deputy for meteorology at BMKG, said the agency’s Soekarno-Hatta Meteorological Station quickly issued its first Significant Meteorological Information (SIGMET) following Anak Krakatau’s initial eruption at 11:23 p.m. on Friday.

By Sunday, BMKG had issued 50 SIGMET updates to support aviation safety.

“The latest SIGMET update shows ash spreading at altitudes of up to 20,000 feet toward the east and up to 50,000 feet toward the west,” Andri said.

Volcanic ash at altitudes of up to 20,000 feet was moving from the northeast toward the south, affecting parts of Jakarta, Banten and West Java as well as surrounding waters.

Meanwhile, ash reaching altitudes of up to 50,000 feet was moving southwest to northwest, covering parts of Banten, Lampung and Bengkulu, southern areas of the Sunda Strait and the Indian Ocean.

BMKG has also established dedicated satellite monitoring of Anak Krakatau’s volcanic ash plume, with updates based on the volcano’s activity and ash advisories for aviation meteorology.

Four airports temporarily closed
The eruption has disrupted aviation operations, with four airports temporarily closed at different times on Sunday under Notices to Airmen, or NOTAMs, issued by AirNav Indonesia, the country’s air navigation services provider.

The affected airports are Soekarno-Hatta International Airport and Halim Perdanakusuma Airport in Jakarta, Radin Inten II Airport in Lampung and Budiarto Airport in Tangerang.

Airport operating conditions may change depending on the movement of volcanic ash and aviation safety assessments, authorities said.

The temporary closures were coordinated by airport authorities with BMKG, AirNav Indonesia, airport operators, airport management units, InJourney, local authorities and the Indonesian military.

NOTAMs are used to alert airlines and aviation stakeholders to changes in operating conditions or potential hazards. They complement volcanic ash advisories and SIGMETs issued periodically, allowing airlines to adjust their operations accordingly.

No tsunami anomaly detected
BMKG is also monitoring the potential impact of the eruption on sea conditions around the Sunda Strait.

As of 7 a.m. Sunday, data from 20 tsunami gauges showed no abnormal sea-level changes, said Ardhasena Sopaheluwakan, acting deputy for geophysics at BMKG.

Analysis from high-frequency radar arrays in Carita and Tanjung Lesung also put the probability of a tsunami at a low level, below 40%, while wave heights were around 1 meter.

At Carita Port, sea conditions remained relatively calm, with forecasts for several periods on Sunday putting wave heights at between 0.4 and 0.8 meters.

BMKG also detected secondary phenomena associated with the eruption, including geomagnetic disturbances and volcanic lightning.

Sensors in South Lampung and Serang recorded geomagnetic disturbances coinciding with an increase in volcanic lightning strikes over the previous 12 hours. The disturbances, however, were less intense than those recorded during the initial eruption, Ardhasena said.

Authorities maintain 24-hour monitoring
BMKG said it was maintaining round-the-clock monitoring using multiple instruments and combining its data with analysis from the Center for Volcanology and Geological Hazard Mitigation (PVMBG) at the Geological Agency.

The integrated monitoring is intended to accelerate the availability of data and support government decision-making as the eruption develops.

BMKG said coordination among agencies was essential to maintain aviation safety and anticipate potential impacts on communities living and working along the Sunda Strait coast.

Residents and others in coastal areas around the Sunda Strait have been urged to remain alert without panicking and to rely on official sources for information.

The agency also warned the public against sharing unverified information about the Anak Krakatau eruption.

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