STOCKHOLM (Reuters) - Iceland raised its aviation alert by a notch on Friday after several earthquakes hit one of the country's biggest volcanoes, the strongest tremors since a string of quakes last month raised concerns over a possible eruption.
The alert only moved to the second lowest level of the four colour scale, but in 2010, ash from an eruption of the nearby Eyjafjallajokull volcano resulted in a major part of Europe's airspace having to close for several days.
The Icelandic Met Office said two quakes, the largest with a magnitude of 3.7, had shaken the Katla volcano in southern Iceland and that "an intense seismic swarm" had been experienced since Thursday morning.
"Due to the unusually high level of unrest at the Katla volcano, we raise the aviation colour code from green to yellow," it said.
The warning levels for aviation run from green, through yellow and orange, to red. Yellow implies that a "volcano is experiencing signs of elevated unrest".
The Katla volcano has not had a major eruption since the beginning of the last century. However, scientists thinks a large eruption is overdue, although it still might be decades before it happens.
Last month, the volcano was rocked by two quakes measuring 4.5 and 4.6 in magnitude respectively, a level not recorded since 2011.