Mount Semeru, the highest and one of the most volatile volcanoes on Java island, erupted violently on Wednesday, triggering mass evacuations and forcing authorities to raise the alert status to its maximum level. The eruption sent towering columns of ash into the sky and released fast-moving pyroclastic flows that swept several kilometres down its slopes.
Throughout the afternoon and evening, Semeru discharged clouds of scorching ash mixed with lava fragments, rock, and toxic gases, travelling as far as 7 kilometres from the crater. The Geology Agency reported that thick grey plumes rose nearly 2 kilometres into the air, repeatedly darkening nearby districts and coating villages in volcanic dust.
As volcanic activity intensified, officials elevated the alert level twice in a matter of hours, moving it from Level 3 to Level 4 — the highest threat designation. Although no casualties have been reported so far, the situation remains dangerous and unpredictable.
More than 300 residents from three high-risk villages in Lumajang district were immediately evacuated to government shelters, according to disaster agency spokesperson Abdul Muhari. Authorities expanded the exclusion zone to 8 kilometres around the crater, urging residents and evacuees to avoid the Besuk Kobokan River channel, the primary route for Semeru’s pyroclastic flows.
Footage circulating online showed dense ash clouds roaring through forested ravines and sweeping across rivers beneath mountain bridges. Villagers, many covered in volcanic grime, rushed to safe zones as emergency teams fanned out across affected areas.
Local media also reported that 178 people remain stranded at the Ranu Kumbolo monitoring post on the mountain. The stranded group includes 137 climbers along with guides, porters, and tourism officials. According to national park spokesperson Endrip Wahyutama, they are safe at the moment, as the post lies on the northern slope of Semeru, away from the direction of the pyroclastic flows. However, heavy rain and dangerous visibility have prevented rescue teams from bringing them down.
Semeru — also called Mahameru — has a long history of eruptions stretching back two centuries. Despite its volatility, tens of thousands of people live on its fertile flanks, which are prized for agriculture. The mountain’s last major eruption in December 2021 killed 51 people, injured hundreds, and displaced more than 10,000 residents, prompting authorities to relocate nearly 3,000 homes out of the hazard zone.
Indonesia, located on the Pacific “Ring of Fire,” remains one of the world’s most active volcanic regions, with 129 active volcanoes spread across the archipelago. Semeru’s latest eruption underscores the ongoing risks faced by communities living in these geologically dynamic zones.
