VOLCANISM Mount St. Helens, 1980 eruption. Where are volcanoes located?
The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.
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Transcript of The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.
![Page 1: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/1.jpg)
The Cause of the Mt. St. Helens Eruption.
It is a Destructive Plate Boundary
or subduction zone.
![Page 2: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/2.jpg)
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.
![Page 3: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/3.jpg)
![Page 4: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/4.jpg)
![Page 5: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/5.jpg)
The nature of the eruption
![Page 6: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/6.jpg)
April May 1980
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 northwardsMay 18th rest of the day
More and more ash shoots up high into the atmosphere. It gradually blows around the world.
![Page 7: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/7.jpg)
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.
![Page 8: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/8.jpg)
Peak
Blast zone to north
The blast zone stretching north
![Page 9: The Cause of the Mt. St. Helens Eruption. It is a Destructive Plate Boundary or subduction zone.](https://reader036.fdocuments.us/reader036/viewer/2022082805/5515c10255034693758b4643/html5/thumbnails/9.jpg)
The drift zone of ash blowing gradually westwards
And falling like rain to a depth of several centimetres.