Pyroclastic Flows and Surges

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Questions and Answers

What are 'cold' pyroclastic surges and under what conditions do they occur?

'Cold' pyroclastic surges are flows containing steam, water, and rock at temperatures less than 250 °C, which occur during eruptions from vents under shallow lakes or seas.

How can pyroclastic density currents interact with topography?

Pyroclastic density currents can flow over higher topographic features like ridges and hills due to their lower density.

What catastrophic event arose from the eruption of Mount Pelée in 1902?

The eruption of Mount Pelée in 1902 produced a fully dilute pyroclastic current that overwhelmed the city of Saint-Pierre, killing nearly 30,000 people.

What is the scientific abbreviation commonly used for pyroclastic density currents?

Pyroclastic density currents are often abbreviated as PDC in scientific literature. Signup and view all the answers

Why are pyroclastic flows classified as gravity currents?

Pyroclastic flows are classified as gravity currents because they move due to the force of gravity, flowing down slopes or along the ground. Signup and view all the answers

What is a pyroclastic flow and how can it be produced by a Plinian eruption?

A pyroclastic flow is a fast-moving current of hot gas and volcanic matter. It can be produced when an eruption column collapses due to insufficient heating of the surrounding air, causing the material to fall and flow down the volcano's flanks. Signup and view all the answers

In the context of a Vulcanian eruption, what causes the formation of a pyroclastic flow?

In a Vulcanian eruption, the fountain collapse of a dense gas and projectile cloud creates a pyroclastic flow because it is denser than the surrounding air. Signup and view all the answers

Describe how frothing at the vent can contribute to the formation of ignimbrite.

Frothing at the mouth of the vent occurs during the degassing of erupted lava, which can lead to the production of ignimbrite, a type of volcanic rock. Signup and view all the answers

What role does convection play in the production of pyroclastic flows?

Convection generates upward movement of the erupted material and surrounding air, but if it is insufficient, the material can collapse and flow down the volcano as a pyroclastic flow. Signup and view all the answers

How does the density of a pyroclastic flow compare to surrounding air?

A pyroclastic flow is denser than the surrounding air, which allows it to flow rapidly down the slopes of the volcano. Signup and view all the answers

Flashcards

Pyroclastic Flow

A type of gravity current, sometimes abbreviated to PDC, involving a high-density flow of hot gas and volcanic fragments.

Pyroclastic Density Current (PDC)

A high-density flow of hot gas and volcanic matter, a type of gravity current, often associated with volcanic eruptions

Cold Pyroclastic Surge

A pyroclastic density current with lower temperatures (still lethal) than other pyroclastic flows, possibly occurring from underwater eruptions.