Based on satellite images, wind data, and information from PVMBG, the Darwin VAAC reported that during 6-12 July ash plumes from Tengger Caldera's Bromo cone rose to altitudes of 2.7-3 km (9,000-10,000 ft) a.s.l. and drifted as far as 120 km S, SSW, SW, and W. BNPB reported that the Abdul Rachman Saleh Airport in Malang (26 km W) closed from 2300 on 11 July to 0900 on 12 July due to thin ash deposits around the airport. The Alert Level remained at 2 (on a scale of 1-4); residents and visitors were reminded not to approach the crater within a radius of 1 km.

Geological Summary. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

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