pyroclastic material
Technical term in volcanology for fragmented material ejected during a volcanic eruption, including ash, lapilli, and volcanic bombs.
The scale of past eruptions can be estimated from deposits of pyroclastic material.
火砕流 is a pyroclastic flow, a fast-moving current of hot gas and volcanic matter, whereas 火砕物 refers to the solid material itself.
Compound of 火 (ka, 'fire') + 砕 (sai, 'break into pieces') + 物 (butsu, 'thing'), literally 'fire-broken material'. The term is a modern technical coinage for pyroclastic material.