The Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) reported that eruptive activity continued at Semeru during 20-25 November. Eruptive events were recorded during 20-21 and 24 November, but weather conditions prevented visual confirmation. White-and-gray ash plumes rose 500-700 m above the summit and drifted SW on 23 November and rose 500-1,000 m and drifted N on 25 November. Incandescence at the summit on the upper SE flank was visible in several nighttime webcam images.

Around 300 residents were evacuated on 19 November after a series of pyroclastic density currents (PDCs) traveled as far as 13 km down the S and SE flanks. Authorities also evacuated 137 climbers who were camping within 8 km of the summit in the Ranu Kumbolo area. By the evening of 20 November there were 1,116 people in evacuation shelters. There were no fatalities, though three people were significantly burned. Rain continued in the area during 19-21 November. On the evening of 21 November lahars interacted with hot material that had been deposited along the Regoyo River, causing a burst of ash and steam that deposited material on the Piket Zero road, which connects Lumajang (32 km ESE) and Malang (35 km NW). Authorities temporarily closed access to the Besuk Kobokan Bridge (13 km SE) or Gladak Perak Bridge due to low visibility. The Badan Nacional Penanggulangan Bencana (BNPB) reported that drone surveys were carried out on 23 November to assess the areas impacted by ashfall, focusing on Sumbermujur (9 km ESE) and the Besuk Kobokan Bridge. They found that ashfall impacted Supiturang (8 km SE) and Oro-Oro Ombo (8 km SE) in the Pronojiwo District, and Penanggal Village (14 km ESE) in the Candipuro District. There were 21 severely damaged houses, damage to an education facility, and damage to a health facility. Additionally, about 204 hectares of agricultural land were impacted. The Alert level remained at 4 (the highest level on a scale of 1-4) and the public was warned to stay at least 8 km away from the summit in all directions and 500 m from the banks of the Kobokan drainage as far as 20 km from the summit.

Geological Summary. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Sources: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM), Badan Nacional Penanggulangan Bencana (BNPB), Antara News, Antara News, Antara News, Antara News