Based on satellite observations and information from PVMBG, the Darwin VAAC reported that on 31 October an ash plume from Rinjani rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted W before it detached. During 1-3 November ash plumes rose to altitudes of 2.7-4.3 km (9,000-14,000 ft) a.s.l. and drifted as far as 350 km NW, W, WSW, and SW. BNPB reported that on 3 November ash plumes rose as high as 1 km above Barujari Crater and drifted W; ashfall was reported in seven villages in North Lombok. According to a November news article, ash plumes that drifted W and SW caused three airports to close during 3-4 November: Ngurah Rai (150 km WSW) in Bali, Selaparang Airport (40 km WSW) in Lombok, and Blimbingsari Airport (230 km W) in Banyuwangi, East Java. On 4 November BNPB reported that ash plumes rose to an altitude of 4.3 km (14,000 ft) a.s.l. and drifted W and SW.

Geological Summary. Rinjani volcano on the island of Lombok rises to 3726 m, second in height among Indonesian volcanoes only to Sumatra's Kerinci volcano. Rinjani has a steep-sided conical profile when viewed from the east, but the west side of the compound volcano is truncated by the 6 x 8.5 km, oval-shaped Segara Anak (Samalas) caldera. The caldera formed during one of the largest Holocene eruptions globally in 1257 CE, which truncated Samalas stratovolcano. The western half of the caldera contains a 230-m-deep lake whose crescentic form results from growth of the post-caldera cone Barujari at the east end of the caldera. Historical eruptions dating back to 1847 have been restricted to Barujari cone and consist of moderate explosive activity and occasional lava flows that have entered Segara Anak lake.

Sources: Darwin Volcanic Ash Advisory Centre (VAAC), Badan Nacional Penanggulangan Bencana (BNPB), The Jakarta Post