Activity at Bromo cone peaked on 20-21 June when 480 explosions were recorded during a 24-hour period. Ash-laden steam columns rose 1.2 km and bombs fell 1.5 km away, setting vegetation afire. Activity declined in late June and remained weak until mid-July. Frequent explosions resumed 15 July, when about 1,000 were recorded in 24 hours. Explosions remained frequent for more than a week, then declined steadily after 24 July to about one every 48 hours in August. Kompas newspaper reported a minor eruption on 9 September at 0825 and added that tourists were not being allowed to descend to the crater. However, by the end of September, activity had weakened sufficiently to allow tourists into the crater area.

Further Reference. Siswoyo, S., 1978, Report on seismic activity at Bromo and Lamongan (1977-78): Geological Survey of Indonesia, Bandung.

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.

Information Contacts: A. Sudradjat and L. Pardyanto, VSI; M. Krafft, Cernay; Kompas, Bandung.