soil erosion vs wearing away

soil erosion and wearing away both are nouns.

Word	Noun	Adjective	Verb	Adverb
soil erosion	Yes	No	No	No
wearing away	Yes	No	No	No

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

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

Other hypernyms of soil erosion include eating away, eroding, erosion, wearing.

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