Indonesia’s Semeru volcano erupts, dozens of homes buried by rain lahar, hundreds flee to hills

LUMAJANG - Indonesia’s Mount Semeru - located in Lumajang regency, East Java - erupted again on the evening of Dec 8, sending an ash column 1,000m above its summit and producing molten lava flows.

Officials at the Semeru Volcano Observation Post reported the eruption occurred at 9.24pm local time (10.24pm, Singapore time).

“An eruption of Mount Semeru took place on Dec 8, 2025, at 9.24pm,” said Mr Mukdas Sofian in a written statement received in Lumajang.

Mr Mukdas added that the ash column appeared white to gray, with thick intensity, drifting southwest.

The activity was recorded on a seismograph with a maximum amplitude of 22mm and a duration of 182 seconds.

In addition to the ash plume, the 3,676m high volcano, the tallest peak on Java, also discharged incandescent lava clearly visible streaming down from the summit.

Mount Semeru has been very active lately, having previously erupted on Dec 5 and

Nov 19

.

Throughout Dec 8, Semeru registered 171 eruptions.

From morning until early dawn, the volcano experienced dozens of eruption quakes lasting between 62 and 180 seconds, accompanied by rockfall tremors, gas emissions and deep volcanic quakes.

The volcano’s alert status remains at Level III, or “standby”.

The Volcanology and Geological Hazard Mitigation Center (PVMBG) has advised residents to avoid activities in the southeastern sector along the Besuk Kobokan river up to 13km from the summit.

“Beyond that distance, residents are urged not to conduct activities within 500m of the riverbanks along Besuk Kobokan, as hot clouds and lahar flows could extend up to 17km from the summit,” Mr Mukdas said.

PVMBG also prohibits activities within a 5km radius of the crater due to the risk of incandescent rock ejections.

The agency further warned residents to remain vigilant for potential pyroclastic flows and lava along rivers originating from Mount Semeru’s summit, particularly Besuk Kobokan, Besuk Bang, Besuk Kembar and Besuk Sat.

These rivers serve as natural channels for lava and lahar during eruptions, making them highly vulnerable disaster zones.

Lahar flood

Meanwhile, dozens of houses in Lumajang were buried after a rain lahar from Mount Semeru swept through residential areas on Dec 6.

Lumajang Disaster Mitigation Agency (BPBD) head Isnugroho said on Dec 7 that at least 13 houses, one food stall and a mosque were heavily damaged by the cold lahar in the Sumberlangsep hamlet of Jugosari village, Candipuro district.

Volcanic material from Mount Semeru and mud piled up to 4m high, leaving only rooftops visible. Three motorcycles were also submerged.

Emergency aid has been distributed since Dec 6, but logistics delivery remains ongoing as some residents are still isolated.

“Today [Sunday], we also sent aid to residents in Sumberlangsep, who are cut off, to ensure food and other needs are met,” Mr Isnugroho said.

The hamlet has 138 households, or 512 residents. Most were forced to flee to the hills as lahar floods continued to inundate homes.

Residents took shelter at three hillside evacuation posts, the first housed 107 people, the second 173 people and the third 115 people.

Jugosari village official Ali Murtopo confirmed that many residents remain in the hills, fearing further lahar surges.

“There are 137 households from Sumberlangsep still staying in the hills. They fled because the lahar flood from Semeru, accompanied by secondary eruptions, was quite hot,” he said.

Logistics distribution to evacuees has been challenging.

Lumajang regency secretary Agus Triyono said aid had to be delivered by crossing the Regoyo River, which was filled with lahar, for 300m.

The regency has also opened public kitchens and distributed 500 meal packs to isolated evacuees.

“Based on monitoring, today (Dec 7) we have met the needs, dropped off by BPBD officers,” he said.

Lumajang Regent Indah Amperawati urged residents to reconsider relocating to a permanent housing site in Sumbermujur village, which is safer from lahar threats.

“The Lumajang administration had previously offered relocation to Sumberlangsep residents during Semeru’s eruption a few years ago, but they rejected the offer,” she said.

She said residents opposed relocation because their livelihoods depend on farming, as the hamlet’s land is fertile.

Ms Indah stressed the government would again propose relocation for safety.

“We will again offer relocation to Sumberlangsep residents to move to a safer place. But if they still reject it, then the risk is theirs, and they must sign an official statement because it is the government’s responsibility,” she said.

The Lumajang administration is coordinating with the National Disaster Mitigation Agency (BNPB) to build a 270m suspension bridge to improve access.

“The emergency steps now are rescuing residents. We will ensure no one remains in low-lying areas because they are unsafe. Then we will repair lahar channels to prevent further spread and restore flows,” Ms Indah said. THE JAKARTA POST/ASIA NEWS NETWORK