Transcript 1A2 Geography 24 February, 2015

1A2 Geography
24 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=njV9ski1
gB4
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 Geography
24th 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 upfold.
• Syncline: This is a
down- fold.
Himalayas Video
• https://www.youtube.com/watch?v=PDrMH7
RwupQ
• https://www.youtube.com/watch?v=HuSHOQ
6gv5Y
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.