Oct. 4th 1996; 08:05 GMT
Eruption continues at a similar rate. Observations yesterday showed that the erupting crater is still covered with a column of water, possibly as deep as 50 meters. Intermittent explosions threw black ash 200-300 meters in the air and a steam column rose to an altitude of 10000 meters. The depression in the ice at the eruption location has widened and there appears to be an elongated rift through the ice, but close inspection is not advisable. As of this morning the harmonic tremor continues, pulsating probably in tune with the ash explosions. A TV photographer flying over the eruption yesterday was lucky enough to get a video picture of two lightning in the ash cloud, but electric phenomena are a common features of such phreatic eruptions.
The water flowing into the Grimsvötn caldera appears to be close to filling the caldera lake and the glaciologists are predicting an imminent glacier burst (jökulhlaup) onto the sandur plain in south of the Vatnajökull. By 07:00 GMT no increase in discharge had been recorded in the river Skeidara.
A Coast Guard helicopter landed NORDVULK scientists on the glacier surface close to the erupting vent yesterday enabling them to collect a sample of the ash. Back in the lab the content of water soluble fluorine (adsorbed on the grain surfaces) was determined. It is 130 ppm F (parts per million; grams per ton), which is about one tenth of adsorbed fluorine on ash from Hekla eruptions. This means that there is no immediate danger for grazing animals due to tephra fall. However, since the ash is erupting through water it is likely that a substantial amount of soluble fluorine is caught in the water phase. If and when the orifice rises above the water level the amount of adsorbed fluorine is likely to rise substantially.
By midnight last night several tens of full chemical analysis on the volcanic glass and its mineral content had been made on the electron microprobe. The data are presently being evaluated and compared to earlier products from the respective volcanic centres.