Sinabung volcano (Sumatra, Indonesia): new activity and very strong explosion during the night

Just few days after the official alert level had been decreased, a massive explosion occurred during the last night at 02:53 local time, generating an ash plume that rose to possibly up to 15 km altitude (50,000ft).
The height of the plume was estimated by VAAC Tokio using satellite imagery. It quickly drifted and dissipated in southerly directions. Even if the plume was (which is likely) a bit smaller than the estimate, it illustrates that the volcano is unpredictable. and capable of producing strong eruptions. According to seismic data, the event lasted more than 7 minutes and produced a very strong signal (120 mm amplitude).
Following a prolonged phase with little to no activity during 2018 until early May 2019, the alert status, which had been at the highest level 4 ("Awas") almost uninterruptedly for almost 6 years, was decreased to level 3 ("Siaga"). However, at the same time, activity seems now on the rise again as last night's explosion illustrates.

New activity since early May
The volcano had been almost completely calm for almost a year with no activity observed since 26 June 2018. However, this changed: strong ash venting was observed again on 7 May and lasted nearly 50 minutes. It produced significant ash falls in some areas. Seismic activity also increased.