There is a massive shift suddenly in the poem as there is a 'huge peak, black and huge, As if with voluntary power instinct, Upreared its head'. The poet is now in a state of shock. There is a repetition of 'huge' is notable. The repetition means it's clunky and doesn't read or flow well like the previous parts of the poem did. The mountain has drained him of sense of power. He's realised that humans are not powerful: nature is powerful