Since the publication of "Scandinavian Scotland" by Barbara E. Crawford in 1987, there has been a growing volume of work dedicated to the understanding of Norse influence in this period. However, from 849 on, when Columba's relics were removed from Iona in the face of Viking incursions, written evidence from local sources in the areas under Scandinavian influence all but vanishes for three hundred years. The sources for information about the Hebrides and indeed much of northern Scotland from the eighth to the eleventh century, are thus almost exclusively Irish, English or Norse. The main Norse texts were written in the early thirteenth century and should be treated with care. The English and Irish sources are more contemporary, but according to historian Alex Woolf, may have "led to a southern bias in the story", especially as much of the Hebridean archipelago became Norse-speaking during this period.