Lumajang, Indonesia – November 20, 2025 – Mount Semeru, Java island’s tallest and most active volcano, erupted explosively on Wednesday, November 19, sending towering columns of hot ash and searing pyroclastic flows racing down its southern slopes. The sudden outburst forced the evacuation of nearly 1,000 residents from surrounding villages in East Java’s Lumajang Regency and left 178 climbers stranded high on the mountain. All climbers were safely rescued by Thursday evening, and no fatalities have been reported.
The series of eruptions began in the early afternoon and intensified rapidly, with at least ten major explosive events recorded between midday and nightfall. Ash plumes rose as high as 2 kilometers above the 3,676-meter summit, while glowing avalanches of superheated rock and gas surged up to 13 kilometers down the Besuk Kobokan River valley. Dense ash clouds plunged nearby villages into near-darkness, coating homes, roads, and farmland in thick gray layers. Residents fled on motorbikes and on foot, many covering their faces with cloths to breathe through the choking dust.
Indonesia’s Center for Volcanology and Geological Hazard Mitigation (PVMBG) immediately raised Mount Semeru’s alert status to the highest level, Level IV (Awas), and expanded the exclusion zone to 8 kilometers from the crater. Authorities warned of the continuing danger of pyroclastic surges and urged the public to stay clear of river valleys prone to deadly volcanic mudflows. Aviation authorities also issued alerts due to ash drifting toward flight paths, including routes to nearby Bali.
By Wednesday evening, approximately 956 people from the villages of Supiturang, Sumbermujur, and Pronojiwo had been moved to temporary shelters in schools, mosques, and village halls. Evacuees arrived covered in ash, some carrying children and pets. Early damage reports indicate at least a dozen homes were affected, along with a local school and large areas of rice fields and coffee plantations buried under ash. Three people suffered minor burns, but no serious injuries were recorded. Relief teams distributed masks, drinking water, food, and blankets, while the government began preparing financial aid for affected families.
Meanwhile, 178 climbers (137 hikers, 15 porters, seven guides, and six national park staff) were trapped at Ranu Kumbolo, a scenic crater lake about six hours below the summit on the popular northern ascent route. Although they were on the opposite side of the mountain from the main pyroclastic flows, heavy ashfall made descent dangerous. The group spent the night in emergency shelters as the ground shook beneath them.
Rescue teams from the National Search and Rescue Agency (Basarnas) reached the climbers early Thursday and guided them down ash-covered trails to the Ranu Pani climbing post. By late afternoon, park authorities confirmed that every person had reached safety, though some reported eye and throat irritation from inhaling fine volcanic particles. Mount Semeru’s hiking routes have been closed indefinitely, and new climbing permits suspended.
Known locally as Mahameru (“Great Mountain”), Semeru has been almost continuously active since 1967 and is one of Indonesia’s most frequently erupting volcanoes. Its history includes deadly events: the December 2021 eruption killed 51 people and displaced more than 10,000 when a lava dome collapsed and unleashed devastating pyroclastic flows and lahars. Earlier major eruptions in 1909, 1946, 1979, and 1981 also claimed lives or caused widespread destruction.
Indonesia sits on the Pacific Ring of Fire, where colliding tectonic plates fuel intense volcanic and seismic activity. The country is home to more than 120 active volcanoes and experiences thousands of earthquakes each year. Fertile volcanic soil draws dense populations to live near dangerous peaks, making rapid evacuations and early-warning systems critical to saving lives.
As of Thursday evening, seismic activity at Semeru remained high, with continuous tremors suggesting magma movement beneath the crater. Officials expect the Level IV alert to stay in place for weeks. Cleanup efforts have begun in affected villages, but many residents face an uncertain future as they wait to learn when, or whether, they can safely return home. For now, the mountain continues to rumble, a stark reminder of the unpredictable power that shapes life across the Indonesian archipelago.
