PVMBG reported that during 25 October-24 November 2015 white and gray plumes rose as high as 2.6 km above Rinjani's Barujari Crater. Incandescent material was sometimes ejected 30-150 m high. Gray plumes observed during 25 November-24 December rose as high as 2.5 km. During 25 December 2015-18 January 2016 white plumes rose 50 m above the crater. Seismicity had also decreased to background levels. On 20 January the Alert Level was lowered to 1 (on a scale of 1-4), and the public was reminded not to approach the crater.

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.

Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)