While the ash cloud from the Eyjafjallajökull volcano eruption has already caused mass inconvenience in Europe, historically its eruptions have always been followed by those of Iceland’s other, much larger, volcano, Katla. Known as one of the “Angry Sisters,” Katla has erupted 16 times since 930 AD. Data do not suggest that an eruption from Katla is imminent, but scientists suggest that it is of great concern.