Volcanic Eruptions

MEDC Case Study - Mount St.Helens, USA

Mount St. Helens, USA – MEDC Case Study

• Is part of the ring of fire.

• Well known for ash explosions and pyroclastic flows.

• Most famous eruption – 18th May 1980.

• 57 people were killed, 250 homes destroyed.

• The 1980 eruption was the first time that it was possible to use modern technology to carefully monitor a volcano as it built up towards a violent eruption.

• Trees were pushed flat pointing away from the source of the blast. Such was the speed of the moving air and debris that it overtook cars as people tried to escape.

• Its last eruption was 10th July 2008!

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

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

This has created the Cascade Range of volcanoes.

Mt St Helens – causes of the eruption

Juan de Fuca plate North American Plate

The Volcano at Mt St Helens was formed because the _________ plate is ________ under the _________ plate. When this happens _________ occurs and _______is formed under ____________ . The magma rises and when the pressure is _________ a volcanic eruption occurs.

Juan de Fuca pressure North American Melting subducted magma released

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 northwards

May 18th rest of the day

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

http://www.youtube.com/watch?v=xP2dreOI8gI&feature=related

PRIMARY EFFECTS

Material from a massive landslide sped down the mountain, filling Spirit Lake and, mixed with lake water, racing down the Toutle and Kalama rivers as a mudflow (or lahar). Explosions of gas and steam flatened everything in its path

Snow melt mixed with ash and mud carried huge amounts of debris, trees, cars etc

Ash clouds circulated the earth for 7 days.

The volcano was reduced in height by 400 meters.

57 DEAD.

Pyroclastic Clouds

The pyroclastic cloud caused

hundreds of trees to be completely

destroyed beneath the volcano.

Pyroclastic Flows – Mt. St.Helens May 1980

Large bulldozer wrecked by the pyroclastic flow of May 18th 1980

The pyroclastic flow contained large boulders up to 1 metre in diameter

Pyroclastic Flows – Mt. St.Helens May 1980

Before After

The same marker pole

Ash Clouds

SECONDARY EFFECTSRoad accidents

Plane crash

Plant and animal life wiped out

Rivers polluted

$860 million costs to the economy

$450 in the timber trade

$150 Tourism

Rivers polluted, bridges wiped out.

(1) On your diagram from earlier, add some of the labels/numbers from diagram B.

(2) Copy and complete the table below using diagram C

(3) Complete the Mount St. Helens worksheet

Social Impacts Economic Impacts Environmental Impacts

Today’s Tasks