PVMBG reported that during 1-18 January white plumes rose 250-400 m above Ijen?s water lake surface and no change in the color of the water was noted.
An increase in the number of shallow volcanic earthquakes was detected; continuous tremor emerged on 11 January, peaked on 15 January, and then decreased during 17-18 January.
The temperature of the lake water fluctuated, though overall it decreased from 38 degrees Celsius in June 2019 to 20 degrees Celsius on 14 January; the lake water was 46 degrees Celsius during a period of increased activity from February to March 2018.
The Alert Level remained at 1 (on a scale of 1-4), and residents and visitors were advised to not approach the crater rim or descend to the crater floor.
Source: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM)