Explosive activity at Mt. Semeru escalated on 4 December with an explosion at 14:50 WIB (UTC+7) producing an ash plume up to 15.2 km. As of 08:30 UTC on 5 December, the national disaster management agency, BNPB, is reporting 13 fatalities, with seven people missing and dozens injured. Hundreds took refuge in evacuation halls. Rockfalls and pyroclastic density currents have been reported by the seismic network and visual observations, while seasonal rain and thunderstorms that are forecast for the coming days present an increased risk of rain-triggered lahars. A number of villages have been covered in up to 4 metres of volcanic ash and sand, while housing, roads and bridges have been damaged. The BNPB is supporting in the immediate aftermath with helicopters, heavy machinery, food, shelter and PPE such as face masks. (ECHO, 5 Dec 2021)

According to the Indonesian National Board for Disaster Management (BNPB), the number of fatalities has increased to 15 and 27 people are missing, and 169 have been injured. More than 1,700 people have been displaced in 19 refugee posts, 5,205 people have been affected as well as 2,970 houses across Lumajang Regency and Malang Regency in Java Province. (ECHO, 6 Dec 2021)