Pyroclastic Flows

Watching pyroclastic flows traveling down the side of a volcano at hurricane speeds are awe inspiring sights. They occur during large volcanic eruptions. At the beginning stages of a large eruption a column forms over the vent of the volcano. The eruption column blasts superheated ash and rocks high into the atmosphere.

Pyroclastic flow, USGS

Flows of superheated ash, rock and other debris flow
down the side of a volcano at hurricane speeds

Formation of a flow
A ground-hugging avalanche of hot ash, pumice, and rock fragments forms when part of the eruption column collapses and begins flowing down the side of the mountain. The flow travels down the slope of the volcano at speeds up to 150 miles per hour.

Temperatures in the flows
The temperature inside the flow of hot gases and rock can reach 1500 degrees Fahrenheit. These "stone winds" traveling at hurricane speeds kill or destroy everything in their path.

Following the curvature of the land
The flows usually follow the curvature of the land to the valleys below the mountain. Sometimes a pyroclastic surge will jump ridges and flow down nearby valleys spreading the destruction into new areas.

Pyroclastic flows traveling across water
Island volcanoes sometimes create these flows that travel across the surface of the ocean to nearby islands. During the eruption of Krakatoa in 1883 it is estimated that at least 10% of the deaths were due to falling tephra and ash flows. The superheated material traveled over 25 miles across the Sunda Straits to the island of Sumatra in Indonesia

More Volcano Links

Volcano Rocks Find out about the four major groups of volcano rocks and the volcanic eruptions that produce them.

Hawaiian Volcanoes Find out more about the Hawaiian volcanoes which are the largest volcanoes on Earth.

Dome Volcano Find out more about these small crumbly volcanoes that form on the sides of larger volcanoes and in their craters.

Alaskan Volcanoes Find out more about the Alaskan volcanoes that frequently erupt all along the coast of Alaska.

Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.

Pyroclastic Flows Find out more about these stone winds that travel down the sides of volcanoes at hurricane speed destroying every thing in their path.

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