Seismic activity has been increasing under and around Katla, an Icelandic volcano near Eyjafjallajokull, the volcano that caused a massive disruption in air travel in 2010. Katla is estimated to be at least 10 times larger than Eyjafjallajokull, indicating a greater potential for a large eruption should one take place. Both Eyjafjallajokull and Katla lie underneath glaciers, and the rapid cooling that occurs when lava encounters ice often produces fine, light-weight ash, which can be carried a considerable distance by the jet stream if the eruption pushes it high enough into the air. The direction of the prevailing winds at the time of an eruption is also important; when ash from Icelandic volcanoes is carried into the jet stream, it can shut down European air travel. During the April 2010 eruption, Iceland was experiencing a negative North Atlantic Oscillation (NAO), which shifted the jet stream around Iceland and then toward continental Europe. (A positive NAO levels out the jet stream and pushes it north toward Scandinavia.) If Katla erupts, it will be important to monitor the direction of the jet stream, in addition to the size of eruption, when estimating the possible economic costs.
