Iceland's huge volcano Katla is stirring into life after tell-tale signs of the potential for an eruption were monitored by observers.
A harmonic tremor has been recorded for two days and small earthquakes have been confirmed at the volcano by the Icelandic Met Office this morning.
It is highly unusual for an eruption in Iceland to occur in the middle of winter but the early indications show Katla is building up power. Experts are unclear as to whether it is water or magma that is causing this week's sudden increase in activity and the seismic recordings are currently lower than when the volcano first showed signs of a minor eruption last July.
In September, Katla again stirred into life with a harmonic tremor and earthquakes in the volcano's caldera - its magma chamber. Katla, which has not experienced a significant eruption for 93 years, is the second largest volcano on Iceland and the consequences of a major eruption will be felt across Europe.
In 2010, the country's president Ólafur Grímsson warned "the time for Katla to erupt is coming close, Iceland has prepared and it is high time for European governments and airline authorities all over Europe and the world to start planning for the eventual Katla eruption". It is believed Katla, named after a vindictive troll of Viking folklore, has the potential to be much stronger and disruptive than the last two Icelandic volcanic eruptions that caused chaos across Europe's air space, grounding flights and closing airports.
Katla is much larger than its neighboring Eyjafjallajokull – which erupted in 2010 - with a magma chamber about 10 times the size. Volcanologists warn that if Katla does erupt, the combination of the magma and the large ice sheet covering the volcano could lead to explosive activity and an ash plume for weeks, if not months.