Major eruption at Semeru volcano produces large pyroclastic flow, ash to 16.5 km (54 000 feet) a.s.l., Indonesia

Satellite data from JMA’s Himawari-8 showed a rapidly intensifying ash column during the morning hours, with the Darwin Volcanic Ash Advisory Centre (VAAC) confirming ash reaching approximately 16.5 km (54 000 feet) above sea level (a.s.l.) at 09:20 UTC (16:20 WIB).

Although the plume was partially obscured by meteorological cloud, infrared analysis indicated continuous emissions from the summit crater and dispersal toward the north and northwest.

Ground observations confirmed the generation of a large pyroclastic density current (PDC) moving through the southeastern drainage network. The flow followed the Besuk Kobokan valley, which has historically acted as the primary channel during major eruptive episodes at Semeru.

Local CCTV recordings and community livestreams documented the propagation of low-lying, ash-rich pyroclastic density currents (PDCs) throughout the afternoon. According to early local observations, PDC activity initiated at approximately 14:30 WIB (07:30 UTC), with runout distances reaching at least 5 km (3.1 miles) by 15:00 WIB (08:00 UTC).

Subsequent field reports indicated that later PDC pulses may have extended to distances of up to 15 km (9.3 miles) along the southeastern drainage system.

PVMBG issued hazard advisories for areas surrounding the volcano, maintaining an 8 km (5 miles) exclusion zone along Besuk Kobokan and recommending that residents avoid activity within 500 m (1 640 feet) of riverbanks beyond that distance due to the risk of expanding PDCs and lahar flows.

A 2.5 km (1.5 miles) exclusion radius around the summit remained enforced because of ballistic ejecta hazards associated with ongoing eruptive activity. Additional warnings applied to valleys draining the upper cone, including Besuk Bang, Besuk Kembar, Besuk Sat, and tributaries of Besuk Kobokan.

Eruptive activity continued into the late afternoon, with persistent ash emissions and elevated hazard conditions across the southern and southeastern sectors of the volcano.

Teo Blašković

I'm a dedicated researcher, journalist, and editor at The Watchers. With over 20 years of experience in the media industry, I specialize in hard science news, focusing on extreme weather, seismic and volcanic activity, space weather, and astronomy, including near-Earth objects and planetary defense strategies. You can reach me at teo /at/ watchers.news.

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