Eruption from Krakatau yesterday (image: PVMBG)
An eruption occurred from the active crater yesterday. The event was likely a phreatic explosion, i.e. steam driven only, caused by overheated water flashing to steam. It generated an ash- and steam column that rose to 1,500 m and rifted east.
The volcano observatory reported a seismic signal with a maximum amplitude of 45 mm and a duration of 45 seconds. During the past weeks, there have been no particular signs of unusual activity and relatively few quakes at the volcano (only about 6 daily quakes on average), which is why the explosion came as a surprise.