Mount Semeru Erupts Three Times as Heavy Rains Trigger Dangerous Lahar Threats in East Java

Mount Semeru, the highest volcano on Indonesia's densely populated island of Java, erupted three times on Monday morning, September 14, 2026, projecting a dense column of grey ash 1,000 meters above its summit.[1][2][5]

The eruptions, recorded by the Center for Volcanology and Geological Hazard Mitigation (PVMBG) starting at 5:30 a.m. local time, mark a sharp escalation in seismic activity following a week of smaller tremors and localized forest fires that forced the closure of all hiking trails on September 6.[4]

While the immediate ash fall has blanketed several villages in the Lumajang Regency, local authorities are primarily focused on a secondary, more lethal threat: lahars.[3]

Heavy seasonal rains are currently sweeping across East Java, mixing with the fresh volcanic deposits resting on the mountain's steep slopes to create cold lava mudflows that can travel at speeds exceeding 60 kilometers per hour.[3]

"The combination of fresh volcanic material and intense rainfall creates a highly volatile situation for communities along the Besuk Kobokan river basin," a PVMBG monitoring official said in a statement released to Beritasatu. "Residents must remain vigilant and avoid the riverbanks entirely."[3]

The Lumajang Regional Disaster Management Agency (BPBD) has dispatched rapid response teams to monitor the river levels and has prepared evacuation centers in the Pronojiwo and Candipuro districts, which house over 15,000 residents combined.[1][3]

Semeru's current alert status remains at Level III (Siaga), prohibiting any civilian activity within a five-kilometer radius of the crater and extending to 13 kilometers along the southeastern sector where the Besuk Kobokan river flows.[1][2]

The 3,676-meter volcano has a history of devastating rain-triggered lahars; a sudden eruption and subsequent mudflows in December 2021 killed more than 50 people and displaced thousands when early warning systems were overwhelmed by the speed of the debris.[2]

Aviation authorities have issued a Volcano Observatory Notice for Aviation (VONA) with an orange color code, though the nearby Abdul Rachman Saleh Airport in Malang continues normal operations as prevailing winds push the ash plume toward the southwest.[5]

As the rain continues into Monday afternoon, emergency crews are using heavy machinery to clear critical bridges and drainage channels, attempting to maintain escape routes before the rivers breach their banks.[3]