Iceland volcano erupts on Reykjanes peninsula
A volcano has erupted on the Reykjanes peninsula of south-west Iceland after weeks of intense earthquake activity.
About 4,000 people were earlier evacuated from the fishing town of Grindavik and the nearby Blue Lagoon geothermal spa was closed. The eruption started north of the town at 22:17 local time (22:17 GMT), the Icelandic Met Office said.
The region around the capital Reykjavik has been experiencing an increase in earthquake activity since late October. The Met Office said that the eruption was located about 4km (2.5 miles) north-east of Grindavik and the seismic activity was moving towards the town.
Images and videos posted on social media showed lava bursting from the volcano just an hour after an earthquake swarm, or seismic events, were detected. The eruption can be seen from Reykjavik, which is about 42km (26 miles) north-east of Grindavik.
One eyewitness there told the BBC that half of the sky in the direction of the town was "lit up in red" from the eruption, and smoke could be seen billowing into the air.
Police have warned people to stay away from the area. The length of the crack in the volcano is about 3.5km, with the lava flowing at a rate of around 100 to 200 cubic metres per second, the Met Office said. It added that this was many times more than in previous eruptions on the Reykjanes peninsula in recent years.
A senior police officer at the Civil Defence told national broadcaster RUV that the eruption had happened quickly and appeared to be "quite a large event".
"The jets [of lava] are quite high, so it appears to be a powerful eruption at the beginning," he said. Iceland has been on high alert for a potential volcano eruption for several weeks, and last month authorities ordered people to leave Grindavík as a precaution. There were no reports of injuries as of 07:00 GMT
Iceland's Prime Minister Katrin Jakobsdottir said defences recently constructed would have a positive effect. She said her thoughts were with the local community and she was hoping for the best despite the "significant event".
President Gudni Johannesson said safeguarding lives was the main priority but that every effort would be made to protect structures too. In April 2010, the Eyjafjallajokull volcanic eruption caused the largest closure of European airspace since World War Two, as a result of an extensive ash cloud. Losses were estimated at between 1.5bn and 2.5bn euros (£1.3-2.2bn; $1.6-2.7bn)
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.
Listen now: The volcano that stopped Europe
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.
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.