What are pyroclasts?
Pyroclasts (or "tephra') are any volcanic fragment that was hurled through the air by volcanic activity. A pyroclastic eruption is one in which the great majority of activity involves fountaining or explosions. A pyroclastic deposit is the resulting layer or pile of material that has fallen to the ground by one or many pyroclastic eruptions. A pyroclastic rock is the hardened, solidified, or compressed version of an originally loose pyroclastic deposit.
The word is a combination of “pyro” or fire, and “clastic” or made up of many pieces.