To dive deep or to dive deeply?

Adverbs form one of the motliest groups of all our parts of speech. Their name ‘adverb’ suggests something quite straightforward – adverbs are those words we use to modify verbs. In something like he drove slowly, slowly modifies the verb drive. But adverbs can also be used to modify other modifiers. In he drove unbelievably slowly, unbelievably modifies the adverb slowly. In an unbelievably slow driver, unbelievably modifies the adjective slow. Then there are those adverbs that don't seem to modify anything at all. In an example such as Frankly, he's a twit, the adverb frankly provides more a comment on what's contained in the rest of the sentence.