Indonesia’s Mount Semeru, the highest peak on Java island, erupted on Wednesday, unleashing fast-moving pyroclastic flows and prompting authorities to raise the volcano’s alert level to the maximum, or Level IV (Warning). The eruption began in the afternoon, generating massive ash clouds that rose as tall as 5.6km (3.48 miles) into the sky.
The accompanying pyroclastic flows, searing clouds of hot ash, rock, and gas, traveled up to 7 kilometers (4.3 miles) down the volcano’s slopes, with some reports indicating a runout distance of up to 13 kilometers. Consequently, authorities widened the danger zone, strongly advising residents to stay at least 8 kilometers (5 miles) away from the crater.
Mount Semeru in East Java, Indonesia, erupted violently on Nov 19, sending pyroclastic flows 7-8.5 km and ash clouds 2 km high.
Over 300 residents evacuated from Lumajang Regency; several injured.
Around 178 hikers safe at Ranu Kumbolo. Alert level highest; damage from… https://t.co/ejO6VlWG3I pic.twitter.com/mSa2lffXun
— GeoTechWar (@geotechwar) November 20, 2025
Over 300 residents from the most at-risk villages in Lumajang District were successfully evacuated to temporary government shelters, and the East Java Regional Disaster Mitigation Agency (BPBD) deployed personnel and essential logistics like respirator masks and safety goggles. Additionally, a group of approximately 178 climbers and guides who were stranded on the mountain were confirmed to be safe and are currently being evacuated.
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The active volcano, which sits on the Pacific “Ring of Fire,” requires continuous monitoring due to the high risks it poses to the densely populated region, having caused a deadly episode in 2021 that killed 62 people.
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