The crater at Grímsvötn
Small vents surrounded by a thin circle of tephra
The volcanic tremor recorded from Grímsvötn has dropped significantly since yesterday (as shown on tremor plot below). The largest pulse of increased explosive activity was observed at around 02:00 AM last night.
The eruption site was observed during a flight yesterday evening. The eruption plume was rather low (approx. 3 km high) and white when the flight arrived at Grímsvötn but at 20:55 GMT explosive activity increased again and the plume rose to about 7.5 km height. The increased activity was observed for about 20 minutes, then the activity dropped down at 21:15 GMT and increased again at 21:45 GMT. This pulsating activity is also clearly seen on tremor plots (click to enlarge) from near seismic stations, i.e. at Grímsfjall, located 5 km east of the eruption site, and at Skrokkalda located 50 west of the eruption.
Water is clearly seen in the fissure (photo below). The eruptive activity is now concentrated at two small vents surrounded by a thin circle of tephra. The eruption plume drifted slowly southwards but ash fell down from the plume into a brownish layer of ash which spread out over southern Iceland beneath a steady layer of air, located at 2-3 km height a.s.l.
Tremor graph from Grímsfjall in Vatnajökull and from Skrokkalda at Sprengisandur (enlarge):