tephra

volcanism

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Last updated

July 17, 2026

Quick Summary

Tephra refers to solid material ejected into the air during a volcanic eruption, most commonly ash. This material originates from explosive volcanic eruptions where expanding gases shred magma into fragments. These pyroclastic materials are classified by size, ranging from dust and ash to larger fragments like cinders, blocks, and bombs.12

While tephra is material that falls through the air, pyroclastic flows are different. Pyroclastic flows are fast-moving, ground-hugging clouds of hot gas and rock fragments that can reach extreme temperatures and speeds, making them incredibly dangerous.2

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pyroclastic flow
The term tephra (ash) as originally defined was a synonym for pyroclastic materials, but it is now used in the more-restricted sense of pyroclastic materials deposited by falling through the air rather than those settling out of pyroclastic flows. For example, ash particles that fall from a…
Read More
The term tephra (ash) as originally defined was a synonym for pyroclastic materials, but it is now used in the more-restricted sense of pyroclastic materials deposited by falling through the air rather than those settling out of pyroclastic flows. For example, ash particles that fall from a…
Read More