Gush, as a volcano (4)
I believe the answer is:
spew
'gush as a volcano' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for spew that I've seen before include "Fetch up" , "Erupt, eject" , "Be sick" , "Gush forth, vomit" , "Be expelled rapidly in large quantities" .)