This poem evokes the solitude and charged suspense of a high mountain pass or a rocky cliff. Its six lines are full of echoes, like standing in a canyon and shouting: "HELLO! Hello! hello! Hello!"
In the first line, listen to the sound of loose rocks falling down a slope, like when you kick a stone off a ledge to see how long you'll be able to hear it tumble. The alliteration of words that begin with "cl" and "cr" sound like rocks cl-icking and cr-ashing into one another. The falling rock and gravel echo through an enormous open space. There's a reason that so many related English words – words that can describe the sounds of large rocks – tend to begin with this hard "c" sound: crumble! crack! collide! Alliteration is built into the English language; Tennyson just takes advantage of tools that already exist.
The alliteration continues throughout the poem, from "lonely lands" in line 2 to the placement of "wrinkled" and "watches" in lines 4 and 5. It produces the same effect as an echo. Moreover, the unusual rhyming triplets produce another kind of echo at the end of each line. In stanza one: "ands...ands...ands." In stanza two: "awls...alls...alls." Rhyming couplets would have been more typical, but Tennyson wanted the poem to be saturated with similar sounds.
Finally, the syntax or sentence structure of the second stanza is an echo of the first stanza. Both stanzas have two instances of the repeated subject-verb structure, "He…(blanks)." In particular, lines 3 and 6 both place this structure at the end of a sentence. Both stanzas build toward a kind of climax, but the first stanza has a false climax that only increases our suspense. Surely we know that the eagle will do more than just stand around.
Despite its short length, by pairing sounds and images in the poem, Tennyson makes the reader feel like a speck in an immense landscape. The eagle rules here – not us.