beach erosion vs eating away

beach erosion and eating away both are nouns.

Word	Noun	Adjective	Verb	Adverb
beach erosion	Yes	No	No	No
eating away	Yes	No	No	No

As nouns, eating away is a hypernym of beach erosion; that is, eating away is a word with a broader meaning than beach erosion:

beach erosion: the erosion of beaches
eating away: (geology) the mechanical process of wearing or grinding something down (as by particles washing over it), also figuratively

Other hypernyms of beach erosion include eroding, erosion, wearing, wearing away.

beach erosion (noun)	eating away (noun)
the erosion of beaches	(geology) the mechanical process of wearing or grinding something down (as by particles washing over it), also figuratively