ICELAND remained on full alert yesterday as a volcanic eruption under Europe's largest glacier threatened to burst through the ice cap and cause widespread flooding along the south coast.
Icelanders continued to reinforce barriers along river banks and prepared to dig channels through roads in the threatened region to give the expected torrent of water a free path, limiting damage to bridges, power stations and phone lines.
"As soon as we know that the water has begun to flow, we'll start to dig through the road to try and save the bridges on the central plain in front of the glacier," Mr Pall Imsland, a geologist at the University of Iceland said.
The glacier lies 200 km east of Reykjavik and about the same distance south of the Arctic Circle. It is separated from the coast by a fringe of farmland.
Farmers in the area have been warned to bring their livestock into shelter to reduce the danger from toxic gases in the week old eruption.
But fears that sheep and cattle would be threatened by flourosis - a disease affecting bones, joints and teeth - caused by an overdose of flourine had abated, Mr Imsland said.
"The flourine content is very low in this eruption. The bulk of material in the column is steam, and there are very few magmatic gases. The effect on the atmosphere will be limited."
Scientists monitoring the eruption at the Vatnajokul ice sheet said about two cubic km of water and debris (enough to cover a square mile 850 yards deep) had collected under the glacier, bringing the water level in the underglacial lake to its highest level this century.
"The reservoir is filling very fast. We're just waiting for the starting mechanism of the flood, which is a process we don't really understand," Mr Imsland said.
"Our seismic instruments are monitoring a steady pattern of tremors indicating that the eruption is continuing at a stable pace."
The eruption at the Grimsvotn crater burst through 500 to 600 metres of ice on Wednesday spewing up a column of steam and ash up to 10 km high.
The column has since subsided to between one and three km in height. Vatnajokul stretches over 8,300 square km and reaches in parts a depth of a thousand metres (3,280 feet).
The name which means "water glacier", originates from the large lakes and rivers under the ice sheet which are created from the ice melted by the heat of the underlying volcano.
The last major eruption was in 1983, when the ice sheet was pierced for a short time.
There was no flooding on that occasion, but an eruption in 1938 at exactly the same site as the present activity, caused massive flooding.
Hydrothermal activity in the area tends to result in flooding every five years or so.