While the eruption of Eyjafjallajokull left millions of travelers stranded across Europe and cost airlines an estimated $200 million a day for six days, signs of high activity beneath the much larger, neighboring Katla caldera are a possible sign of an impending eruption that could be more dangerous, Andy Hooper at the Delft University of Technology in the Netherlands said.
Historically, Katla has erupted on average of every 60 years but has not had a significant eruption since 1918, Hooper told Britain's The Daily Telegraph.
Also, he said, eruptions of Eyjafjallajokull in 1821-23 and 1612 were followed within months by eruptions of Katla, and Katla's 1918 eruption produced five times as much ash as the 2010 Eyjafjallajokull one.
Erratic movements of the surface of the volcano, measured by precise GPS instruments, and bursts of high earthquake activity have been recorded beneath Katla's caldera, researchers said.
Both are possible signs that magma has risen to shallower depths beneath the caldera, they said.