cave in vs go under

cave in

verb
  • To collapse inward or downward. 

  • To relent; to grant approval against one's initial will. 

noun
  • The act of relenting. 

  • The location where something has caved in. 

  • The act of something collapsing or caving in. 

go under

verb
  • To collapse or fail, e.g. by going bankrupt. 

  • To enter a trance, state of hypnosis, etc. 

  • To be named; to call oneself. 

  • To descend into a body of water; to founder. 

How often have the words cave in and go under occurred in a corpus of books? (source: Google Ngram Viewer )