The term comes from the Greek pyro (fire) and klastos (broken). When a volcano erupts, it doesn’t just produce liquid lava; it pulverizes magma into tiny shards of glass (ash) and throws out larger chunks of rock. These materials can fall back to earth as “airfall” or race down the slopes as a “pyroclastic flow.” These flows are gravity-driven clouds of hot gas and pyroclastic debris that can reach speeds of over 100 km/h and temperatures of 1,000 degree C, making them the deadliest aspect of volcanic eruptions.