Pyroclastic flow

A pyroclastic flow is a rapidly moving, ground-hugging current of hot volcanic gas, ash, and rock fragments. It can travel down volcanic slopes at high speed and destroy or bury what lies in its path.

Pyroclastic density current: A gravity-driven mixture of volcanic particles and gas that moves away from an eruption. Pyroclastic flows are dense, ground-hugging examples of this broader class of currents.
Mount Pelée: A volcano on the Caribbean island of Martinique, known for its destructive 1902 eruption. Its 1902 eruption devastated Saint-Pierre with a fast-moving pyroclastic flow.
Volcanic hazard map: A map showing areas exposed to volcanic hazards, often with zones of differing likelihood or severity. Maps identify valleys and slopes that could be reached by pyroclastic flows.
Lahar: A destructive flow of water mixed with volcanic sediment and debris. Lahars are water-rich flows, unlike the hot gas-and-particle mixture of a pyroclastic flow.
Plinian eruption: A sustained explosive eruption that sends a high column of gas and volcanic debris into the atmosphere. When an eruption column collapses, it can generate a pyroclastic flow.
Saint-Pierre, Martinique: A coastal city in Martinique that was devastated by Mount Pelée’s 1902 eruption. The city’s destruction is a defining historical example of pyroclastic-flow impact.
Volcano observatory: An organization that monitors volcanic activity and communicates assessments of volcanic hazards. Observatories track eruption changes that can signal a risk of flow generation.
Lava flow: A stream of molten rock moving across the ground during or after an eruption. Lava is molten rock; pyroclastic flows are mixtures of hot gas and fragmented material.
Column collapse: The gravitational failure of an eruption column, sending its hot mixture back toward the ground. This process is one direct way a pyroclastic flow begins.
Mount Vesuvius: A volcano near Naples, Italy, whose AD 79 eruption buried settlements including Pompeii and Herculaneum. Pyroclastic currents during the AD 79 eruption overwhelmed settlements near the volcano.

Linked from 35 pages