PVMBG reported that during 16-21 May gray-to-white plumes from Sinabung rose as high as 700 m above the crater rim and drifted in multiple directions.
At 0900 on 20 May an event produced an ash plume that rose 700 m and drifted NW.
An ash plume from an event later that day at 2122 rose 2.5 km and drifted W and NW.
The Alert Level remained at 4 (on a scale of 1-4), with a general exclusion zone of 3 km and extensions of 7 km on the SSE sector, 6 km in the ESE sector, and 4 km in the NNE sector.
Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)