Merapi remains on Level III alert as authorities warn residents around hazard zones.
Volcanic monitoring across Java continues to show significant activity, with Mount Merapi producing repeated lava avalanches while both Merapi and Semeru recorded hundreds of earthquakes over a 90-day monitoring period.
Five Lava Avalanches Recorded Monday Morning
Mount Merapi recorded five lava avalanches between midnight and 6 a.m. on September 21, 2026, all moving toward the southwest sector. Four traveled toward the upper Kali Sat/Putih with a maximum distance of 2,000 meters, while another moved toward the upper Kali Krasak for up to 1,000 meters. Merapi remains at Level III, or Siaga, as volcanic activity continues.
Dozens of Volcanic Earthquakes Detected
During the same six-hour monitoring period, instruments recorded 16 avalanche earthquakes with amplitudes of 2 to 24 millimeters and durations ranging from 29.12 to 199.93 seconds. Authorities also recorded 18 hybrid or multiphase earthquakes, with amplitudes between 2 and 28 millimeters. Monitoring data indicated that magma supply to Merapi was continuing.
Merapi Records 300 Quakes Over 90 Days
Data from MAGMA Indonesia cited by Ngopibareng showed that Mount Merapi recorded 300 earthquakes between June 23 and September 18, while Mount Semeru recorded 225 earthquakes during the same 90-day monitoring period. Both volcanoes continued to show volcanic activity during the monitoring period.
Residents Warned to Stay Outside Hazard Zones
Authorities said potential hazards from Merapi include lava avalanches and pyroclastic flows in the south-southwest and southeast sectors. The danger zone extends up to 5 kilometers along the Boyong River, 7 kilometers along the Bedog, Krasak and Bebeng rivers, 3 kilometers along the Woro River and 5 kilometers along the Gendol River. Volcanic material from an explosive eruption could reach a radius of three kilometers from the summit, and residents are urged not to enter designated danger areas.
Semeru Also Remains Under Close Monitoring
Separately, monitoring data for Semeru recorded 27 eruption earthquakes, seven avalanche earthquakes, five emission earthquakes, five harmonic earthquakes and one distant tectonic earthquake. Authorities continue to prohibit activity along Besuk Kobokan for up to 13 kilometers from the summit and within five kilometers of the crater, while residents are also warned about pyroclastic flows, lava avalanches and lahars along rivers originating from Semeru.
The latest monitoring shows that both Merapi and Semeru continue to require close observation and compliance with official safety zones. For Indonesians living around the volcanoes, authorities continue to emphasize avoiding designated hazard areas and following official updates. The reports do not identify any direct impact on Singapore, but they provide an important update on volcanic conditions in Java.
Sources: Investor (2026) , Ngopi Bareng (2026) , Tribun News (2026)
Keywords: Mount Merapi 2026, Merapi Lava Avalanche, Merapi Earthquakes, Mount Semeru Activity, BPPTKG Merapi, Indonesia Volcano Alert
