Authorities raised the risk level around Semeru, the Java southeast volcano, to the highest alert Sunday after a morning explosion that prompted evacuations of about 100 residents. Officials cited increased volcanic activity, including explosive activity and the threat of hot clouds, as a key reason for the shift to a more cautious stance.
The National Disaster Management Agency, BNPB, said heavy rains on Semeru intensified the risk of gas clouds, steam, or lava flows. This combination of factors led the center for volcanology and geological risk mitigation, PVMBG, to upgrade Semeru’s status from Warning to Alert, effectively moving from Tier III to Tier IV in their risk framework.
BNPB reported a gray ash column rising from the crater and reaching up to 1.5 kilometers at 2:46 am local time. Earlier in the day, seismic readings showed ash-containing gases and water vapor accompanying several explosions, described as eight explosive events and one hot cloud eruption of medium to thick intensity.
The morning deterioration came with heavy rainfall in the area, causing ashes to fall across multiple districts in Lumajang. About 93 residents were evacuated to designated safe zones as authorities worked to minimize exposure to the ash and potential lava flows.
Video footage released by BNPB depicted a dense plume of smoke and ash sweeping through towns connected to the mountain. Some areas reported damaged structures and residents seeking help from local responders as the eruption continued to unfold.
As of now, authorities have not released a detailed assessment of property damage or casualties. Ground monitoring remains continuous, and officials urged residents southeast of Besuk Kobokan, roughly 13 kilometers from the summit and central eruption zone, to avoid activity in the area.
Residents were advised to stay away from riverbanks and to keep clear of zones that could be affected by advancing hot clouds or lava flows, which authorities warned could extend up to 17 kilometers from the summit. A cautionary radius of five kilometers around the crater was emphasized due to the danger of incandescent ejecta.
Indonesian officials noted that the Japan Meteorological Agency was monitoring the potential for a tsunami following the eruption, with NHK reporting no definitive assessment of giant waves at that time. The Semeru eruption, standing at 3,676 meters, is among the country’s most active volcanoes and has already triggered mass departures in Lumajang as communities fled in alarm, a situation captured in numerous social media videos.
Historically, Semeru has shown sudden, intense outbreaks. Roughly a year earlier, a sudden eruption led to more than 40 deaths and displaced about 5,000 people, with many others injured by burns. Indonesia sits on the Pacific Ring of Fire, a vast belt of seismic activity featuring around 120 active volcanoes that experience thousands of tremors annually, most of them mild or moderate in strength.