The literary device the writer Dante uses in this excerpt for allowing the readers a better understanding of the scene is Imagery:
The ideas of a <em>"blasting sound"</em> or of a roar that causes <em>"both sides of the shore to tremble" </em>appeal to a person's sense of hearing. In sum, this can be identified as an imagery device since the words or phrases used allow the reader, appealing to human senses, to make a <u>visual or mental representation</u> of the story scenario.
Most of the time, the writer will give you key clues to his/her piece. Usually, in order to know his/her motivation, it is best to look at reoccurring clues. <span />