Two Irish scientists have been dispatched to Iceland to analyse the Bardarbunga volcano after an eruption sparked a red alert aviation warning.
Just after midnight last night a small fissure, estimated to be about 1km long, was recorded on the northern end of where seismic activity has been occurring since August 16.
Bardarbunga is covered by glacier several hundred metres thick and has been experiencing dozens of earthquakes - some more than four on the Richter scale - for days.
It has sparked concerns that a large eruption under the ice could throw a giant ash cloud into the atmosphere, shutting down air space in the same way the Eyjafjallajokull volcano shut much of Europe's air space for six days in 2010.
Chris Bean, Professor of Geophysics at University College Dublin (UCD), was setting special seismic recording devices to measure sound waves created by earthquakes 20km from the eruption.
"If it completely blows its lid I certainly would not want to be any closer than 30km, but if it is effusive it would certainly keep you warm on a cold night," he said.
Icelandic authorities called in experts, including Prof Bean and Dr Aoife Braiden from UCD and the European Union-funded FutureVolc research group, to closer monitor how the volcano is interacting with a glacier it is threatening to melt.
The only significant eruption occurred about 40km from the main Bardarbunga site, Iceland's largest volcano system, but 20km from another volcano Askja.
The Geological Survey of Ireland, which is advising the Irish Government's Office of Emergency Planning on potential hazard from the volcano, said the eruption site is ice-free and north of Dyngjujokull glacier.
Prof Bean said: "If it breaks the surface of the earth under the glacier it will melt the water and that will interact with the magma at depth, and the system will become explosive.
"It will pulverise the glacier and rock into fine particles, and that is where the danger of the ash cloud comes. That is the scare story."
The Irish Aviation Authority said an exclusion zone of 120 nautical miles up to 5,000ft was put in place around the volcano.
All Irish and European airspace are operating as normal, the IAA said, and it added that it was closely monitoring the situation.
The UCD geophysicists have a niche specialism in using equipment to record seismic activity in a defined area.
The team hope to analyse earthquakes occurring at about 5km deep and lava on the surface below the glacier which may not be visible for up to 10 hours.
"There's activity in Bardarbunga - it's quite active. There's stuff going on at depth, big earthquakes for this volcano," Prof Bean said.
"The idea is to give a heads-up that an eruption has happened under the glacier.
"We are looking for fingerprint signals for eruptions under the surface and identify where it has broken ground under the glacier."
The GSI said information from authorities in Iceland showed last night's eruptions involved magma coming to the surface in a small fire fountain, producing small lava flows and scoria or cinder cones - the steep sided hill around a volcanic vent.
It said eruption intensity decreased by 2.30am but the aviation warning code remained.
The red alert indicates that an eruption is imminent or under way, with a risk of ash.
The Icelandic Met Office has been publishing up-to-date reports of the continuing seismic activity around the Bardarbunga and Askja volcanoes on its website, http://en.vedur.is/.