The Demon Of Scattery.
How Halldor disposes of the monster is neat. He must keep its attention from everyone else so that they can escape from the island so he lets it chase him to the round tower, then he enters the building. The beast can neither destroy the tower nor get more than the end of its muzzle through the door and he can hit the muzzle with his hammer.
Storm and monster had come together so, when the monster is dead, the storm ends:
"The wind had shifted; rain blew straight in. But it was a softer wind, a milder and hail-free rain. The day was brightening. The storm was almost over." (p. 181)
Not quite the pathetic fallacy because the same curse had brought both monster and storm.
Mildred Downey Broxon writes in her Historical Notes that the large serpent of the novel bears no resemblance to the tenth-century description of the monster but asks:
"At a distance of four centuries, however, who is to say whether the medieval chronicler was correct?" (p. 200)
Is it a distance of four centuries? The novel is set in 835 AD. (p. 196) But, in any case, I agree that two twentieth century novelists have a better knowledge of sea monsters than a medieval chronicler.