Symbolism, Imagery, Allegory
Sula is a book that turns symbolic meaning on its head. Here, flames are purifying (check out our Symbols analysis of "Fire" for more) and water...is destructive.
For Sula (and Nel, to a lesser degree), water directly represents Chicken's horrible death-by-drowning. Fire might be a cleansing force, but water engulfs and consumes the young boy. Water doesn't comfort Sula but rather agitates and upsets her because of her responsibility for Chicken's death.
To compound matters, at the end of the novel one of the townspeople who dies in the tunnel slides and hits the ice below.