The Cause of the Mt. St. Helens Eruption.
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The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone . The little Juan de Fuca ocean plate slides under the continent. As the ocean plate descends the rock melts and magma rises. This has created the Cascade Range of volcanoes.

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The Cause of the Mt. St. Helens Eruption.

It is a Destructive Plate Boundary

or subduction zone.


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The little Juan de Fuca ocean plate slides under the continent.

As the ocean plate descends the rock melts and magma rises.

This has created the Cascade Range of volcanoes.



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April May 1980 continent.

A bulge was growing on the north flank.

May 18th at 8.32 a.m.

An earthquake occurs under the volcano and triggers a huge landslide.

May 18th at 8.33 a.m.

With the pressure released a huge lateral blast heads northwards

May 18th rest of the day

More and more ash shoots up high into the atmosphere. It gradually blows around the world.


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The first minute of the eruption produced a 2.8 cubic kilometre debris avalanche,

a powerful laterally directed (to the north and northwest) blast,

and the start of a 9-hour-long plinian eruption.


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Blast zone to north kilometre

Peak

The blast zone stretching north


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The drift zone of ash blowing gradually westwards kilometre

And falling like rain to a depth of several centimetres.


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