Indonesia’s Mount Semeru erupts repeatedly, ash plumes up to 1,200 metres as safety zones enforced

Indonesia’s Mount Semeru erupted repeatedly on Thursday morning, 16 April 2026, with authorities maintaining the volcano at Level III (Alert) and urging residents to observe strict safety measures.

According to reports from the Semeru Observation Post, located in Lumajang Regency, a series of eruptions occurred between 05:00 and 08:54 Western Indonesian Time. Officials recorded between five and seven eruptions during this period, with ash columns reaching heights of up to 1,200 metres above the summit.

The first eruption was recorded at 05:11, producing an ash column approximately 800 metres high. A second eruption followed at 06:21, sending volcanic ash to around 1,200 metres above the peak. Subsequent activity continued throughout the morning, with eruptions at 06:57 reaching about 1,100 metres, at 07:08 reaching approximately 500 metres, and at 07:32 reaching around 700 metres.

Further eruptions were observed at 08:06, with an ash column of approximately 900 metres, while the final eruption at 08:54 was ongoing at the time of reporting, although the plume was not visually observed.

The ash columns were generally described as white to grey in colour, with moderate intensity. Most plumes drifted towards the north-east and north, although the initial eruption produced thicker ash moving towards the north and north-west.

One of the eruptions was also detected instrumentally, with a recorded maximum amplitude of 22 millimetres and a duration of 159 seconds, according to observation post officer Liswanto.

Mount Semeru, which lies on the border between Lumajang and Malang Regency, is the highest mountain on the island of Java and remains one of Indonesia’s most active volcanoes.

Authorities from the Centre for Volcanology and Geological Hazard Mitigation have issued a series of restrictions in response to the continued activity. Members of the public have been instructed not to carry out any activities within a 13-kilometre radius of the summit, particularly in the south-eastern sector along the Besuk Kobokan river channel, which originates from the volcano’s crater.

In addition, residents have been warned to avoid areas within 500 metres of riverbanks along Besuk Kobokan, where pyroclastic flows and lahar currents could travel as far as 17 kilometres from the summit. A separate exclusion zone of five kilometres has also been established around the crater due to the risk of incandescent rock ejections.

Officials have further advised communities to remain vigilant for secondary hazards, including pyroclastic flows, lava avalanches, and lahars, particularly along river systems such as Besuk Kobokan, Besuk Bang, Besuk Kembar, and Besuk Sat, as well as smaller tributaries connected to these waterways.

The alert status of Mount Semeru remains unchanged as monitoring continues.