Ignimbrite is a type of rock born from one of the most violent events on Earth: explosive volcanic eruptions. It forms when a fast-moving flow of hot ash, gas, and volcanic glass shards spreads across the ground and solidifies.
The roots of the word ignimbrite include igni, meaning "fire," and imbr, meaning "rain" or "storm cloud." The -ite suffix is used in names of rocks and minerals. The geologist who named the rock in 1932 wanted to capture the terrifying nature of how these rocks form — raining down from a fiery cloud. The cloud is called a pyroclastic flow, and it rushes down a mountain as a scorchingly hot mixture of particles, dumping a thick layer of incredibly hot debris that fuses together into hard rock.