Earlier this summer, Iceland’s Katla caused a bit of a buzz when it had a moderate earthquake swarm. At the time, the Icelandic Meteorological Office chalked it up to typical summer seismicity at the ice-capped volcano and added that no tremor (a sure sign of magma moving under a volcano) was noticed. The volcano settled back down with a little bit of increased outflow from the rivers that drain the caldera–likely caused by some release of hydrothermal fluids or gases–and things went back to normal.

Yesterday, Katla decided to up the ante. An ongoing earthquake swarm has been rattling the volcano (see below), some reaching as large as M3, but all at fairly shallow depths within a few kilometers of the surface. The IMO continues to say that there are no particular signs of an eruption happening in the near term (i.e., hours to days) but with the intensity of the seismicity, they have raised the aviation alert status at Katla to Yellow from Green. What this means is the volcano is showing signs of unrest above the background of earthquakes, so it bears close watching while the earthquake swarm continues.

No other signs such as deformation of the caldera or increases in hydrothermal gas release have been noticed so far. Even so, Icelandic officials are sending police out to watch the popular tourist destinations around Katla, so if an evacuation is needed, people can be moved quickly.