Iceland volcano: What could the impact be?

The activity is concentrated around the Fagradalsfjall volcanic area in the southwest of the country

Iceland is bracing itself for a volcanic eruption in the coming days. Why is this happening, and what might be the impact?

If there is an eruption, there could be significant damage to local infrastructure and a release of toxic fumes, but initial concerns about much wider disruption are now receding.

Since late October the region surrounding the Icelandic capital, Reykjavik, in the south-west has been experiencing an increase in earthquake activity.

This is due to a underground river of magma - hot liquid or semi-liquid rock - about 15km (10 miles) in length moving upwards below the earth's surface.

This runs under Iceland and part of the Atlantic Ocean, and the impact of an eruption on the country - and further afield with regard to aviation - will depend on where exactly the magma breaches the surface.

One town, Grindavik, which lies directly above the magma, has already been evacuated, due to the risk of 'fire fountains' and noxious gasses.

Thousands of earthquakes precursor to eruption

Dr Bill McGuire, professor emeritus of Geophysical & Climate Hazards, UCL, said: "Grindavik is very close to the position of the new fracture, and its survival is far from assured. Everything depends upon where magma eventually reaches the surface, but the situation doesn't look good for the residents of the town."

If a volcano erupts offshore, or erupts on land and then flows into the sea, then there is the risk of an explosive ash cloud as the super hot rock comes into contact with the water.

In April 2010, the Eyjafjallajokull volcanic eruption, caused the largest closure of European airspace since World War II, as a result of an extensive ash cloud, with losses estimated at between 1.5bn and 2.5bn euros (£1.3-2.2bn).

The circumstances of this volcanic activity are very different and therefore such an extensive impact is not expected.

"The Eyjafjallajokull eruption of 2010 was quite different as it was associated with a shield volcano topped by a glacier. It was the interaction of the magma with ice and melt water that made that eruption so explosive and dangerous for aviation. This is not the case here," said Dr Michele Paulatto, volcanologist at Imperial College London.

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The Icelandic meteorological office estimates that currently the magma is less than 1000m from breaking ground, and as a result the likelihood of an eruption is "high" and could happen in the coming days.

The earthquakes continue to weaken but ground deformation remains, with rifts and cracks of a metre in depth reported in roads suggesting that the magma could be even closer to the surface - a sign that things may be coming to a head.

"In the last few years we have had a diminishing and pause in earthquakes before volcanic eruptions happen," Dr Evgenia Ilyinskaya, Icelandic geophysicist and co-director of the International Volcanic Health Hazard Network, told the BBC.

Dr Tom Winder installs a seismograph near the Grindavik area to monitor activity

Iceland is very used to volcanic activity - successfully building a tourist industry on it - because it sits over the Mid-Atlantic Ridge. The Earth's crust is fractured into different plates, and at the ridge the Eurasian and North American plates are moving apart at a few centimetres a year. This allows magma to rise up to the surface, which erupts as lava and/or ash.

The nature of volcanic eruptions varies depending upon the rock type and how the plates are moving. This magma is believed to have originated within the Reykjanes-Svartsengi volcanic system.

One of the most extensive eruptions in Iceland was back in 1783 when there was a flood of lava which lasted for eight months, and produced extensive sulphur clouds which hung over Northern Europe for more than five months and is estimated to have caused cooling of about 1.3C for the following two years.

Dr Ilyinskaya, who is in regular contact with geologists on the ground, told the BBC that: "It looked concerning back on Friday and Saturday that we could have something of that scale, in those rare but large events of course that would have huge implications for air quality in the Northern hemisphere.

"That is not the situation that is likely at the moment."

The latest evidence that emerged on Sunday and Monday she said suggests the eruption will be much smaller than previously thought.