Yup...I think I read that the last three times this one erupted, Katla followed.
If Katla blows, well.....
There is also a chance that a horizontal sheet of magma under Eyjafjallajokull could shoot out and enter a magma chamber beneath Katla. Hitting the roots of its neighbor would almost certainly trigger an eruption.
The three eruptions of Eyjafjallajokull on record were each associated with a subsequent eruption of Katla. There are no signs of turbulence beneath Katla but, since it last erupted in 1918, a new blast is overdue. Katla tends to erupt every 40 to 80 years.
“So far there have been no signs of the reawakening of the Katla volcano, but a lot of things can still happen, so we are monitoring it quite closely,” said Pall Einarsson, a geophysicist at the University of Iceland.