cumulate vs pile up

cumulate

verb
  • To be accumulated. 

  • To accumulate; to amass. 

noun
  • An igneous rock formed by the accumulation of crystals from a magma either by settling or floating. 

adj
  • accumulated, agglomerated, amassed 

pile up

verb
  • To collect or accumulate, as a backlog. 

  • To form a pile, stack, or heap. 

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