One of Iceland’s largest volcanoes is in the habit of erupting every 50 years or so, but has been quiet since 1918. Now she is rumbling in her slumber

Will she or won’t she? Recent media reports have suggested that the Icelandic volcano Katla may be poised to blow, following two large earthquakes near to the volcano this summer. Katla’s last eruption, in 1918, produced five times more ash than its neighbouring volcano – Eyjafjallajökull – did in 2010, and Katla’s 98-year period of dormancy is unsettling for a volcano that averages an eruption approximately every 50 years. Adding to the jitters is the knowledge that two of Katla’s previous eruptions have followed eruptions of Eyjafjallajökull.

Everyone agrees that Katla is due an eruption, but volcanologists are refusing to become excited just yet. They point out that similar quakes have happened in previous decades and that increased earthquake activity is common in late summer, as glacial melt-water increases the pore pressure in underlying rocks. Furthermore, there is no sign of volcanic swelling or rhythmic earthquakes, that often accompany magma movement.

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Nonetheless Katla is a concern. Like Eyjafjallajökull, Katla is capable of producing a large long-lived ash-cloud and, if the wind blows the right way, she too could cause widespread disruption to air travel. Studies of Katla’s previous ash deposits show that prevailing winds usually carry ash northwards, but southerly plumes travelling towards Europe are not uncommon. Essentially if the eruption carries on for long enough then the winds will swing towards Europe at some point.

However, eruptions large and long-lived enough to cause this kind of disruption are not so common from Katla, and more likely we can expect a small explosive eruption in the coming years, bringing a couple of weeks of upheaval to Iceland.