Sure. The ocean is full of waves. If one wave crashes on a cliff, there's a whole ocean of other waves lining up right behind it. So how does a crashing wave represent impermanence? Glad you asked.
Waves are kind of like snowflakes in that no two are identical. So, when that wave you're watching crashes on the cliffs, that's it. That wave is gone forever. Hope you didn't miss it.
Teasdale also makes a point of telling us that the waves are "blue" even though we all probably would have pictured them that way even if she hadn't. The result is a heightened sense of contrast when she describes the waves as "whitened" on the cliff.
Teasdale wants us to realize that things change from moment to moment—blue one second, white the next. If you don't take the time to appreciate things in the moment, you'll miss out. Thanks for the heads-up, Sara.
Soaring fire that sways and sings. (4)
We go from water to fire—another nice contrast. Even though fire and water are about as opposite as you can get, the fire and water imagery function in a pretty similar way in this poem. Teasdale gives us a nice, clear image of the movement and sound of a fire, swaying and singing. Even though Teasdale doesn't follow the fire image through to its conclusion, the first image of the waves crashing on the cliffs puts us in a state of mind to picture these images as progressions: the waves rolling across the sea and then crashing on the cliffs. We see the firing dancing and then, prompted by the previous image, we are likely to see the fire getting lower until it burns out and all we are left with is a pile of black ash. Once again, things change over time.
(Note: The fire image also reminds us of life's progression: young, full of life and color, old and gray, and then ashes to ashes and the end. Keep that in mind as we move to the next image.)
And children's faces looking up Holding wonder like a cup. (5-6)
Remember that life thing we said to remember? Here it is again.
Just like with the fire imagery, Teasdale only gives us the first half. But our minds fill in the blank. The same way we get to ash from the fire image, we end up at old age with the image of children. Kids don't stay kids forever. Over time, those little, innocent faces grow up into worldly adults.
Again, we only get the front side of these images. But Teasdale chose images with direct, clear, universal opposites that pop into our heads as soon as one half is introduced: big and small, hot and cold, young and old. Get it?