Katla lies beneath the Mýrdalsjökull ice cap and has height of approximately 1512 m. Katla has been showing increasing signs of unrest for many months now with periods of harmonic tremor prompting news reports of an impending eruption. Also, historically, an eruption of the Eyjafjallajökull volcano is often followed by one at Katla.
However some of these news reports are citing the global impact an eruption may have. As a result I have a couple of comments about a recent BBC article titled New Icelandic Eruption Could Have Global Impact. First of all due to the high latitude of the volcano,a 'global impact' is unlikely, the majority of eruptions which transport ash globally and affect global temperatures are closer to the equator and if you look at past eruptions of Katla, the largest they reach is VEI 4/5 which is large, but not on the scale which Tambora or Pinatubo were. It is possible that ash will be transported through Europe again, although there are a number of factors which affect the transportation of ash other than wind direction, including ash particle size and strength of the eruption so even this isn't certain!
One of my main gripes, it is very unscientific and bad practice to say a volcano is overdue! Its seen with Yellowstone all the time, its not acceptable there so it isnt for Katla either!
Steam rising over the Mýrdalsjökull ice cap.
One of the major hazards from volcanoes such as Katla which lies beneath the Mýrdalsjökull ice cap is the jökulhlaup. These occur when an ice cap/glacier is heated from below, these events are usually triggered by a sub-glacial volcanic event. Such an event occurred on the 9th July from the Mýrdalsjökull ice cap and was likely trigger by an increase of heat flux from the caldera or a small sub-glacial eruption, this is a further indication of activity beneath the surface of Katla. There was also an episode of this kind in 1999.
I confess that I am not the first one to write about this, but I felt the point needed to be made that caution should be taken when reading articles making claims such as the BBC article.
So to summarise, Katla is showing signs of an eruption, with periods of harmonic tremor indicating the possible movement of magma beneath the caldera, however Katla will go when she wants to go!