head for the hills vs run away

head for the hills

verb
  • To go to a safe place; to seek refuge; to flee. 

  • To travel to a higher elevation, especially to a rural region on vacation. 

run away

verb
  • To flee by running. 

  • To leave home, or other place of residence, usually unannounced, or to make good on a threat, with such action usually performed by a child or juvenile. 

  • To become a runaway. 

How often have the words head for the hills and run away occurred in a corpus of books? (source: Google Ngram Viewer )