Pyroclastic Flows and Surges

'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.

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

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.

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

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

<p>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.</p> Signup and view all the answers

<p>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.</p> Signup and view all the answers

<p>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.</p> Signup and view all the answers

<p>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.</p> Signup and view all the answers

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