The clause contains a direct address, an imperative verb, and an object. Earth denotes the actual earth and water denotes real water; yet swallow ordinarily belongs to a living being taking something into its mouth.
A derivative-metaphor reading regards the verb as transferred to the earth’s absorption of water. An implicit-metaphor reading compares the earth covertly to a creature that swallows, while the imperative marks that image.
Identifying the verb's ordinary sense, its new use, and the nature of its addressee is more instructive than memorizing the figure's label alone.