In Section VII, the narrator (Bob) describes the seracs and chasms poetically, expressing the beauty and grandeur of nature. The chasms are a "gurgling world of crystal and cold blue," sparkling with frozen beauty. The chasms are like "frozen saltgreen waves." This is pleasant, even peaceful in its colorful description and the reference to the sea.
In Section IX, the narrator clearly has a new perspective of the chasms and seracs. Now, they are not described with his affections for the beauty of nature; now, they are associated with death and violence. The seracs are "fanged" and "blinding," two terms associated with violent potential. The "gaping greenthroated crevasses" are the mouths of those "fanged" seracs, like a beast's mouth waiting to devour its victim (David). The narrator continues to personify the mountain/glacier, giving it a snout, thus making it more like a predator; as opposed to the peaceful scene he describes in Section VII.
The narrator uses assonance and consonance in the second and third lines of Section IV.
The long ascent of the lonely valley, the live
Pine spirally scarred by lightning, the slicing pipe
Repeating the L-sound, the narrator uses "long," "lonely," "valley," and "live" to emphasize the length and depth of the valley and the depth of the feeling of loneliness, a foreshadowing element perhaps. The use of assonance is the repeating I-sounds of "live," "pine," "spirally," "by lightning," and "slicing pipe / Of invisible pika." The narrator draws attention to these words by connecting them with the repeating vowel sound. The reader is drawn to past signs of life in this lonely valley. Again, this emphasizes the beauty of nature but with a lonely mood and this is because only the remnants of life are there: the scarred pine and the invisible pika (and the prints of the grizzly). All I-sounds connect these visible echoes of life and events. These are signs of life that were there; this is also an element of foreshadowing - that signs of David's life (blood on the glacier) will be all that is left to see.