lava vs tephra

lava

noun
  • The molten rock ejected by a volcano from its crater or fissured sides. 

  • Magma. 

  • A shade of red, named after the volcanic lava. 

tephra

noun
  • The solid material thrown into the air by a volcanic eruption that settles on the surrounding areas. 

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