The blank verse we discussed in "Form and Meter" does not, by any means, indicate that this poem is without any rhythm or cool sound effects. Quite the opposite, really. The iambic pentameter gives "Storm on the Island" a nice, smooth flow. Check out the smooth chuggity-chug of the very first line: "We are prepared: we build our houses squat." That regular rhythm is the just the tip of iceberg, though.
Though there is no formal rhyme scheme in this poem, Heaney employs some other subtle sound effects that make for a poem that sounds pretty sweet when read aloud. Consonance is the echo of repeated consonant sounds, and we get that quite a bit here. In the first line, for example, we encounter "squat," which has hard T sounds; in the next line, you get "sink" and "rock," which both have a hard K sound, as well as "slate," which echoes the hard T sound of "squat" in the first line. Consonance is kind of like rhyming in that it tries to tie things together through sound. You'll see more of it throughout the poem. For example, in lines 4 and 5 you'll see "stacks" and "stooks" both have hard K sounds. Then in lines 12 and 13 there's "company" and "cliffs," which share the hard C sound (that sounds exactly like the K sound).
Toward the end of the poem, Heaney switches gears and uses sibilance, which is a special kind of consonance where the slippery S sound repeats. If sibilance really gets going, it can sound like a snake hissing, or wind whirling at high speed. Heaney keeps it under control in this poem by spacing the words out far enough, but if you read lines 14–17 you'll hear it at its height:
[…] spray hits
The very windows, spits like a tame cat
Turned savage. We sit tight while wind dives
And strafes invisibly. Space is a salvo,
In addition, among all that sibilance is more regular consonance (with the T sounds) and even some good, old-fashioned internal rhyme ("hits" rhymes with "spits").
Most of the poem, though, is unrhymed. Still, Heaney can't help himself at the close of the poem. Lines 18 and 19 end on a half rhyme, or slant rhyme, meaning two words that almost rhyme, but not as perfectly as, say, the "hit" and "spit" from lines 14 and 15. The half rhyme of "air" and "fear" closes the poem gently, but with just enough flair.
Sound, then, is an important part of this poem. It mimics the sounds of the natural world, and in that way serves as a subtle reminder that, as humans, we're on a kind of island—surrounded by the natural world in every way. Even this poem is surrounded, and subject to, the sounds of Mother Nature. As well, that final slant rhyme is a reminder that we may not totally be safe in this position. After all, we can hardly expect things to rhyme, to match up exactly, in a world where even the very air we breathe might one day turn into a wind that destroys our house. Talk about unsettling.