Final answer:
Volcanic ash consists of fragments of rock, minerals, and volcanic glass. An avalanche of hot ash flowing down the flanks of a volcano is known as a pyroclastic flow.
Step-by-step explanation:
Volcanic ash consists of fragments of rock, minerals, and volcanic glass. It is created during volcanic eruptions and measures less than 2 mm in diameter. An avalanche of hot ash flowing down the flanks of a volcano is known as a(n) pyroclastic flow.