pile up vs stow away

pile up

verb
  • To collect or accumulate, as a backlog. 

  • To form a pile, stack, or heap. 

stow away

verb
  • to stow or secure aloof in a safe place 

  • to obtain passage (on a ship or similar vehicle) by secreting oneself inside before departure 

How often have the words pile up and stow away occurred in a corpus of books? (source: Google Ngram Viewer )