Most people know that the Icelandic volcano Eyjafjallajokull (try to pronounce that) has been erupting for a month now, and that its ash cloud has caused major flight disruptions in Europe. It is not so widely known that, historically, a nearby volcano called Katla has also consistently erupted on a ten times larger scale following its neighbor. The 3 eruptions at Eyjafjallajokull in the past 1,000 years have all been followed by eruptions of Katla.
Small earthquakes have recently been detected at Katla, which can be the precursor to an eruption. If this volcano erupts as it has in the past, not only will European air travel and climatic conditions be severely impacted, the world could see another "year without a summer" as happened when a volcanic eruption in 1815 caused crops to fail around the world in 1816.
Katla is overdue for another eruption based on past cycles. A major eruption now could be very dangerous for more than just Iceland.