1A2 Geography24 February, 2015

Objectives:•To introduce students to a case study on a volcanic eruption in North America – Mount St. Helens.

Homework

• Textbook, page 79, question 2.

Homework for today’s class

• Textbook, page 79, question 1 (i) & (ii).

Advantages of volcanic activity

• During yesterday’s class, we listed some of the ways in which a region can benefit from volcanic activity.

• Can you remember some of the benefits discussed?

1. Land creation.2. Fertile soil.3. Geysers/geothermal energy.4. Tourist attractions.

Disadvantages of volcanic activity

• We also listed some of the disadvantages associated with volcanic activity in a region.

• Can you remember these?1. Loss of life.2. Destruction of property.3. Emission of toxic gases – sulphur dioxide.4. Creation of lahars – rivers of boiling mud

formed from the combination of lava and snow.

Mount St. Helens

• You are about to view two videos illustrating the effects of a volcanic eruption that occurred at Mount St. Helens, in North America, more than 30 years ago.

• Watch the recordings carefully.• Has the volcanic eruption produced positive or

negative effects. Make points to support your answer.

Mount St. Helens

• https://www.youtube.com/watch?v=-H_HZVY1tT4

• https://www.youtube.com/watch?v=njV9ski1gB4

Mount St. Helens

• Based on what you have seen, do you think that the volcanic eruption at Mount St. Helens has produced positive or negative effects on the surrounding region?

• Give reasons for your answer.

Mount St. Helens

• An eruption at Mount St. Helens on the 18th May 1980 had a devastating effect on the surrounding region. (Worst volcanic eruption in US history.)

• There was loss of life. Between 50-60 people were killed. 7000 large animals and hundreds of smaller creatures also died.

• There was massive destruction within a 300km² area of the mountain. Forests were destroyed. 200 homes were also ruined by a lahar.

Mount St. Helens

• March 1980: Earthquake under mountain.• April 1980: Bulge formed on the mountain’s

side and grew daily.• May 18th 1980: Eruption.• Avalanche of rock and hot ash down

mountain.• Ash cloud reached a height of 10 miles.• The eruption lasted 9 hours approx.

1A2 Geography24th February, 2015

Objective:• To introduce students to fold mountains,

and discuss their formation.• To introduce students to periods of folding.

Tectonic Plates

• Earth’s crust is not one whole piece, it is divided into sections called plates.

• There are two types of tectonic plate, continental and oceanic.

• Continental plates are located under land masses (e.g. Eurasian plate, African plate).

• Oceanic plates are located beneath the seas (e.g. Pacific plate).

Fold Mountains

• Fold mountains are formed when land buckles at destructive plate boundaries (i.e. where plates collide).

Formation of Fold Mountains

• If an oceanic plate meets a continental plate at a destructive plate boundary, part of the oceanic plate will sink below the continental plate and descend into the mantle.

• The oceanic plate will sink because it is heavier.

• See Fig. 4.18 page 74.

Formation of Fold Mountains

• As the oceanic plate sinks, the continental plate buckles upwards, causing fold mountains to form.

• The part of the oceanic plate that descends into the mantle melts to form new magma. This can move to the surface, forming volcanoes.

The Andes

• The Andes, a mountain range stretching through several South American countries, are an example of fold mountains.

• The Andes formed when the Nazca (oceanic) plate collided with South American (continental) plate.

The Andes

Snow-capped mountains Nevado del Ruiz

Formation of Fold Mountains

• If two continental plates meet at a destructive plate boundary, both will buckle upwards.

• For example, the Himalayas have formed where the Indo-Australian plate is colliding with the Eurasian plate.

• Mt. Everest, which is part of the Himalayan mountain range, was formed in this way, and continues to grow higher as these plates continue to buckle upwards.

Anticlines & Synclines

• Anticline: This is an up-fold.

• Syncline: This is a down- fold.

Himalayas Video

• https://www.youtube.com/watch?v=PDrMH7RwupQ

• https://www.youtube.com/watch?v=HuSHOQ6gv5Y

Fold Mountains: Periods of Folding

• Fold mountains are categorised according to the time period in which they formed.

• Categories of fold mountains include Alpine and Armorican.

Fold Mountains: Alpine

• Alpine Fold Mountains formed 30-35 million years ago.

• Examples can be found on four continents.• Alps, Europe; Himalayas, Asia; Rockies, North

America; Andes, South America.

Fold Mountains: Armorican

• Armorican Fold Mountains formed approximately 250 million years ago, when the Eurasian plate was colliding with the African plate.

• Fold mountains in Ireland formed during the Armorican period include the Macgillicuddy’s Reeks, the Galtees, the Comeraghs, and the Knockmealdowns.