alluvion vs calamity

alluvion

noun
  • The increase in the area of land due to the deposition of sediment (alluvium) by a river. 

calamity

noun
  • The distress that results from some disaster. 

  • An event resulting in great loss. 

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