Depressed after almost reaching the bottom of crater, as it's empty (6)
I believe the answer is:
hollow
'it's empty' is the definition.
(hollowing is a kind of emptying)
'depressed after almost reaching the bottom of crater' is the wordplay.
I cannot quite see how this works, but
'depressed' could be 'low' (similar in meaning) and 'low' is found within the answer.
'of' could be 'o' and 'o' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'as' acts as a link.
Can you help me to learn more?
(Other definitions for hollow that I've seen before include "Concave; empty inside" , "Empty; worthless" , "Empty - insincere" , "Dent; echoey" , "Not solid, having hole in the middle" .)