Comparisons have been made between a potential new volcanic eruption in Iceland and a previous that occured there in 2010.

Volcanic activity has been recorded near the town of Grindavik, with a number of earthquakes leading to the evacuation of the area. Even though earthquake activity has died down a little, an eruption of the Fagradalsfjall volcano in the next few days is still "highly likely", according to Bill McGuire, professor emeritus of geophysical and climate hazards at University College London.

Modelling suggests that magma is rising along the fracture and is now as close to the surface as 800m or even less. What is also uncertain is where exactly along the fracture the eruption will start. "If magma breaks the surface at the southern end of the fracture, however, it could erupt beneath the sea. This would be a more explosive event that would build a cone of fragmental material." He also said there was no reason, currently, to think that the eruption will be as large as the Eyjafjallajökull, April 2010 eruption, but added that it is notoriously difficult to forecast how big eruptions will be.

Situation on the Ground

Iceland is still open to tourists, despite the threat of a volcanic eruption not far from the international airport. Grindavik, which was evacuated in the early hours of Saturday after an earthquake swarm, is around 12 miles from the runway. But the current risk assessment by the authorities is that flights can take off and land as normal.

Sudden Developments

The head of the Geoscience Research Department at the Icelandic Met Office, Kristin Jonsdottir said: "What has happened extremely quickly is we have a magma-filled crack - a very long one," she says. "It's extends over about 15km, it's a vertical crack and it's a really bad scenario since at the southern end, the crack goes through the town where about 3,000 people live," she says, referring to Grindavik.

How unusual is this?

On average, there is an eruption in Iceland every four or five years, but in more recent years there has been more activity in the southwestern peninsula called Reykjanes.

Sky News Science correspondent, Thomas Moore said: "Now, Fagradalsfjallthe has been dormant for 800 years, but it's just started up again and it's possible that we are into a new volcanic era in this part of the island."

Many people will remember the 2010 ash cloud that saw air travel severely disrupted. Could it happen again?  "[Scientists] can't exclude the possibility that this will be a huge eruption," he says.

Conversely; Dr Dave McGarvie, a volcanologist with the University of Lancaster, says a potential eruption will not lead to disruption like that of Eyjafjallajokull. He added: "The volcanoes on the Reykjanes Peninsula do not have the ability to produce the disruptive ash clouds that characterised the Eyjafjallajokull 2010 eruption."

What's more, he says, lessons have been learned since the 2010 incident and even if a future event produced a similar ash cloud there would only be about one-third of the flight cancellations compared to what occurred in 2010.

Wider consequences

Dr Phil Collins, deputy dean and reader in geology and geotechnical engineering at Brunel University London suggested we might also look back further to the deadly Laki eruption in 1783 for comparison.

Back then, toxic gases were dispersed from Iceland across Britain and Europe though as things stand, a repeat of an eruption on the scale of Laki "doesn't seem likely". But Dr Collins says... "There may be a substantial release of volcanic gases such as sulphur dioxide which reacts with water in the ground and atmosphere to create tiny droplets of sulphuric acid, and fluorine.  "This may cause a significant health hazard to people in the region. 

"A large Icelandic eruption at Laki in 1783 released enough toxic gas to kill large numbers of livestock in Iceland, leading to a famine.  "The gas spread across northern Europe, including the British Isles, leading to changes in weather patterns and a significant number of deaths from lung problems. There were knock-on effects elsewhere in the northern hemisphere.  "At present, it doesn't look like a Laki-scale disaster is likely, but there will be local and regional effects." As for a smoke cloud? Well, in 2010 there was a glacier on top of the eruption - hence the rising cloud. That isn't the case at Fagradalsfjall eruption, whose peak stands at 385m compared with Eyjafjallajokull at over 1600m, rising into substantially colder air.

Svartsengi Geothermal Power Plant

Icelandic authorities are taking the opportunity to try and protect a power plant within the high-risk zone by building a two-mile long gravel wall several metres high. The hope is that it would divert a lava flow away from the Svartsengi facility, which provides heat and electricity to 35,000 homes. The wall was approved by the Icelandic government on Monday evening and dozens of lorries began moving gravel onto the site overnight. However, according to local media, the planning assumption had been that the lava would flow from a rupture west of the plant placing it away from the favoured path. 

How unusual were the impacts of Eyjafjallajokull?

The eruption ranked only three on the volcanic explosivity index (VEI) which theoretically rises to nine, albeit nothing above a seven has been recorded since the most recent ice age circa 10,000 years ago. Around 15 eruptions on this scale usually happen each year in Iceland. However, in this case, a combination of a settled weather pattern with winds blowing towards Europe, very fine ash and a persistent eruption lasting 39 days magnified the impact of a relatively ordinary event.

On 14th April 2010, Violent eruptions belched huge quantities of ash into the atmosphere.

Airspace around the British Isles was shut down for several days, resulting in 108,000 cancelled flights. However, the Icelandic Grímsvötn volcanic eruption only 13 months later (in May 2011) had only limited impacts. Despite the Grímsvötn eruption being the most powerful Icelandic eruption in almost 100 years, just 900 flights were cancelled.

While both eruptions produced ash clouds which impacted on aviation, the stark differences in impacts between the two eruptions can be predominantly attributed to differences in atmospheric circulation. In April 2010, Atlantic high pressure drove the flow (and therefore volcanic ash) from Iceland towards the British Isles. Whereas in May 2011, a low-pressure system in the North Atlantic drove the ash cloud away from the British Isles and towards northern Scandinavia, therefore limiting the impact of the volcanic ash on trans-Atlantic and European aviation.

What can we expect if a large eruption occurs in the coming days?

Currently a continuation of low pressure (unsettled) systems seems destined for the UK and NW Europe for the coming week, not too dissimilar to conditions in May 2011, so potentially good news should the worst happen in the coming days. However there are signs that High pressure may start to assert itself (dry, settled weather) into next week across the Atlantic and if it pushes North towards Greenland, could result in a reversal of fortunes and winds could – for a time – start to move into the North West (of the UK) and transport any potential debris towards Europe. This is however a long way off – meteorologically speaking, and lots could change – especially this time of year as we transition from Autumn into Winter.