The following was received by the Smithsonian's Global Volcanism Network. This report is preliminary and subject to change as the event is studied in more detail. We will forward additional significant information as it becomes available.
Thursday 3rd October 15:00
According to measurements the waterlevel in Grimsvotn caldera has reached the same level as was highest before the surge (jokulhlaup) last summer. As the glacier is fractured and uneven after the great inflow of water to the caldera several m uncertainity exists on when the surge will start, but it is not long time left to wait. It is expected it takes 2-3 days to reach maximum. The water has to lift the Skeidararjokull glacier to make an outlet for the meltwater. Seismometer on Grimsfjall mt. and it is hoped it will show the beginning of the flood.
Direct observation from the air (Magnus Tumi) indicates that the northern end of the eruption fissure is more N-striking than the first subsidences and eruptions in the beginning. It is believed to be related to the last day's earthquakes in Bardarbunga further west. There is still possibility that the eruption moves over the watershed and meltwater could flow north, still water goest to Grimsvotn.
There is not much ash coming from the eruption but has been falling on the glacier and to north. Usually not much ash has come from eruptions in Vatnajokull. Now the ash is distributed to W and SW. There is good and clear weather over the eruption today, the observations are mostly from the air.
Friday 4th October 1996 10:00
The eruption continues. The eruption fracture is now about 8 km long, not much ash is ejected, but flight is not encouraged over Iceland. The Grimsvotn caldera is now full of meltwater but the water has not started to flow under Skeidararjokull to the sandur plain to the south.
The waterlevel in Grimsvotn intra-glacier lake, is higher than before in the century, or since measurements started. As some volcanic material has been gathering in the Grimsvotn caldera since the flood/surge in 1938 it is not expected that the surge will be as great as then. It has been estimated that the flow in 1938 was around 50.000 m3/sec but now it is hoped it will not be more than 10-20.000 m3/sec - these are speculations of course. The bridges S of the glacier are built to withstand 9000 m3/sec. The surge last summer was 3000 m3/sek.
The site of the volcanic fissure is according to the Weather bureau at N 64 30-32' W 17 22'. The Tomso sattellite station has been thinking of putting images on the net http://www.tss.no, I have not seen this myself.
In morning: N strong wind in Vatnajokull and surroundings At 8:45 some changes in the eruption fissure, large columns rose many km up in a short time, no changes in Skeidara. It is common that the eruption site changes along the fissure, lastly finding a nice spot to be concentrated on.
Helgi Torfason
National Energy Authority
Grensasvegur 9
108 Reykjavik