hollowing out vs mining

hollowing out

mining

noun
  • Any activity that extracts or undermines. 

  • The activity of removing solid valuables from the earth. 

  • The activity of placing mines (the explosive devices). 

  • Creation of new units of cryptocurrency by validating transactions and demonstrating proof of work. 

How often have the words hollowing out and mining occurred in a corpus of books? (source: Google Ngram Viewer )