Question: why is eyjafjallajokull called e15?
Answer: The word fjalla is the genitive plural of fjöll, and so Eyjafjalla is the genitive form of Eyjafjöll and means: "of the Eyjafjöll". A literal part-by-part translation of Eyjafjallajökull would thus be "Islands' Mountains' ice cap". Eyjafjallajökull is sometimes referred to by the numeronym "E15".