This icon depicts the events of St. Brendan's voyage, as described in the text. Which to me, reads like a somewhat garbled story of a voyage to America, so....I'm convinced, anyway. We have the volcano on the right, the green lands of the blessed on the left. In the center, of course, is the iceberg (described as an island of crystal) and the seabeast.
I tried to use Celtic iconographical tradition for this, as opposed to the Byzantine--since, of course Brendan was an Irish Saint. And yes, there's a sight nod to the Secret of Kells there in that monk on the far left.