According to news articles, ash plumes from Tengger Caldera's Bromo cone caused flights between Perth and Bali to be disrupted during 27-28 January. Based on analysis of satellite imagery, the Darwin VAAC reported that on 28 January an ash plume rose to an altitude of 5.5 km (18,000 ft) a.s.l. and drifted 370 km E and SE. On 29 January an ash plume rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 93 km E. The ash cloud from the previous day was again detected and slowly drifted N. Based on analysis of imagery from multiple satellites and information from CVGHM, the VAAC reported that during 29-31 January ash plumes rose to an altitude of 3.7 km (12,000 ft) a.s.l. and drifted 55 km NW.

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: The West Australian, The Sydney Morning Herald, Darwin Volcanic Ash Advisory Centre (VAAC)