The April 2010 eruption of Eyjafjallajokull volcano (Figure 1), located on Iceland's southern coast, created unprecedented disruptions to European air traffic during 15–20 April, costing the aviation industry an estimated $250 million per day (see the related news item in this issue). This cost brings into focus how volcanoes can affect communities thousands of miles away.
Eyjafjallajokull rises to 1666 meters above sea level and hosts agricultural land on its southern slopes, with farms located as close as 7 kilometers from the summit caldera. In the past 1500 years, Eyjafjallajokull has produced four comparatively small eruptions. The eruption previous to 2010 began in December 1821 and lasted for over a year, with intermittent explosive activity spreading a thin layer of tephra (ash and larger ejected clasts) over the surrounding region. In contrast, the explosive 2010 eruption, sourced within the ice-capped summit of the volcano, so far is larger and characterized by magma of a slightly different composition. This may suggest that deep within the volcano, the 1821 magma source is mixing with new melt, or that residual melt from past intrusive events is being pushed out by new magma.