More pleasant to avoid most of volcanic eruption (5)
I believe the answer is:
nicer
'more pleasant' is the definition.
('nice' can be similar in meaning to 'pleasant')
'to avoid most of volcanic eruption' is the wordplay.
'to avoid most of' indicates the answer is hidden within the clue (only some letters from the clue).
'NICER' can be found hidden inside 'volcanic eruption'.
(Other definitions for nicer that I've seen before include "improved" , "More pleasant or fine" , "Even more 7 down!" , "Pleasanter" , "More pleasing" .)