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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.