Unit 1: Landforms
September 2014
What is Geography?
• Geography is the study of how the earth
works and how people interact with it.
• It is about the world we live in
Questions
• 1. Explain how compressional forces create fold
mountains.
• 2. What is the difference between anticline and
syncline.
• 3. How do tensional forces create a normal fault?
• 4. How do compressional forces create a reverse and
overthrust fault?
• 5. What causes a volcano to erupt?
• 6. Describe the characteristics of an ash-cinder, shield
cone and composite cone volcano
Canada’s Places
• What does landscape mean?
• Landscape refers to the natural features
(mountains, rivers) and human features
(farmers fields, buildings) that you can see in
an area
• How would you describe Canada’s landscape?
Earth’s Structure
•
•
•
•
•
Inner Core
Outer Core
Mantle
Mohorovicic Discontinuity
Lithosphere
The Earth’s Structure
• Any questions
• Read pp 2-9
• Describe in detail the five layers of the earth’s
structure
• What is the athenosphere?
Earth’s Structure (cont’d)
• Review video:
• http://www.youtube.com/watch?v=3MFr2cC3
erk
Landforms: Structures and Processes
• Topography: The natural and human
features of the earth’s surface
• Elevation:
The height of a particular point
of land from sea level
• Relief: The change in elevation over a given
distance
• Hill:
An area of high relief with elevations
no higher than 300-600 metres. Isolated
features
Landforms (cont’d)
• Mountain:
Areas of high relief with
elevations higher than 300-600 metres. Most
occur in long linear chains called ranges. Located
along the edges of continents
• Plains: A level tract of land. Found along
coastal areas or lower elevations. Very gentle
slope and no relief of 30 m or more
• Plateau: An extensive, flat upland area, often
found on the top of mountains. Raised upwards
Landforms
• Plateau (cont’d): by movements of the
earth’s crust. Often found in the interior of
continents. Deeply eroded by stream valleys
and often have more rugged appearances
Examples of Landforms
Plateau: Tablelands of Gros Morne
Examples of Landforms
Mountains: Rockies
Examples of Landforms
Plains: Plains of India
Landforms
• Plates: The earth’s crust is made up of
different plates
Landforms
• Plate Tectonics:
Movement of the earth’s
plates. Both compressional and stretching
forces
•
Compression
Stretching
Landform Processes
• Compressional Force:
Pushing part of the
earth’s crust, causing it to buckle. Plates move
toward one another, squeezing together.
Subduction zones sometimes form along
these areas
• Subduction zone: Place where two tectonic
plates collide. The more dense plate goes
under, or subducts, to the other
A Subduction Zone
Landforms
• Tensional Force:
A stretching force in the
earth’s surface which may cause faulting.
Plates break apart and move away, or past,
each other. This will often cause a trench as
one plate moves downward. Ridges
sometimes form a the magma rises between
the plates
Landforms
• Wegener’s Theory: All continents were once
joined together called “Panagaea”. Broke into
two sections about 200 million years ago.
These two sections broke into the pieces.
They drifted to their present locations. Based
upon fossils and rock formations we now
know today
Panagaea
Wegener’s Critics
• Argued how did the plates move?
• Wegener could not prove it
Wilson to the Rescue!
• In the 1960’s Canadian Tuzo Wilson revisited
Wegener’s work
• “Sea floor spreading” moved continents.
• Volcanoes beneath the ocean erupted lava.
New material pushed the continents further
away from each other
Landforms
• Read pp. 6-10
Landforms: Mountain Building
Three ways mountains are made:
1. Fold Mountains: Upland area formed by the
earth’s crust. Folds are caused by the
destructive collisions of the tectonic plates.
Different forces and pressures create simple
or complex forms
Landforms: Mountain Building
• Three ways mountains are made:
• 1. Folding
• 2. Faulting
• 3. Volcano
1. Fold Mountains
1. Fold Mountains (cont’d)
• Anti-Cline:
It is the peak. An arch-like
upfold in buckled, bent, or contorted rock.
Top of the letter A
• Syncline: It is the bottom or the trough. A
downfold of rock layers. Bottom of the S
1. Fold Mountains (cont’d)
• 1. Fold Mountains:
Landforms: Mountain Building
• Three ways mountains are made:
• 2. Faulting: Caused when rocks are
compressed together under intense pressure
and they break or fracture. Break maybe
shallow or deep into the earth’s crust. Result
of earth’s crust being pushed up or dropped
down as plates on either side move away, or
past each other
2. Faulting
2. Faulting
• Normal Fault: If a plate drops down lower
than the plate on the other side.
• Rift Valley:
When two faults move away
from each other, and the plate in between
drops down
2. Faulting
2. Faults
• Reverse Fault: When the two layers around a
fault push against each other. There are
compressional forces pushing one block up
over the other
2. Faults
• Overthrust Fault: When the plate has
already undergone folding and, its folded
layers are pushed up and thrust over layers on
the fault’s other side
3. Volcanoes
• 3. Volcanoes: Trigger is heat. Magma is
produced when crusts meet. Magma is
melted rock. Magma flows into underground
pockets and in many cases cools
Volcanoes
• Usually found along plate boundaries
• Heat is generated because of friction, pressure
and decay of materials
• Magma is produced when heat melts rock and
materials beneath the crust
• Magma reaches the surface through fractures,
vents or craters
• Lava is liquid rock. It is magma that reaches
the earth’s surface
Volcanoes
• Ash:
Small dust like fragments of rock,
minerals and glass emitted from volcanoes
• Vent:
Small opening where magma erupts
• Crater: Large opening where magma erupts
• Cinder: Low density igneous rock, charcaterized
by bubbles, emitted from volcanoes. Larger than
ash.
• Explosive volcanic eruptions take place when
thick magma hardens. Pressure builds and it
must be exploded out
Volcanoes
• Volcanic Ash
Volcanoes
• Cinder
Volcanoes
•
•
•
•
Three kinds:
1. Ash and Cinder Cones:
Eruptions consist of mainly ash and cinder
Thick, slow flowing, rapidly solidifying lava
which creates violent eruptions
• Shape is symmetrical
• Steep sides
• Large crater
3 kinds of Volcanoes –Ash and Cinder
Volcanoes
•
•
•
•
•
•
3 Kinds of Volcanoes:
2. Shield Cone:
Usually milder eruption
Little or no ash or cinders
Very thin, liquid lava
Broad, flat cones
Volcanoes
• 3 Kinds:
• Composite Cones:
• Undergoes periods of explosive and quiet
activity
• Ash and cinder mixed with lava
• Weak spots may develop on sides with smaller
lava flows forming smaller craters
Composite Volcanoes
Shield Volcanoes
What is Plate Tectonics?
• A scientific theory which describes the large
scale motions of Earth's lithosphere (crust).
The theory builds on the older concepts of
Continental Drift.
• The lithosphere is broken up into what are
called tectonic plates.
• The lithospheric plates ride on the
asthenosphere.
Earth’s Structure
Earth’s Plates
Plate Tectonics
• Compressional Forces (process/cause)
– The magma in the asthenosphere flows in such a
way as it carries two floating tectonic plates
towards each other.
– When this happens the two plates collide and
compress against one another. This pressure is
referred to as compressional forces.
– These forces are so strong that one plate is forced
beneath the other. These zones are referred to as
subduction zones.
A Subduction Zone
Plate Tectonics
• Tensional Forces (process/cause)
– The magma in the asthenosphere flows in such a way
as it forces itself upwards between two floating
tectonic plates forcing them apart. These tectonic
forces which move plates apart are referred to as
tensional forces.
– These forces are so strong that an opening is created
allowing the magma to force its way through.
– Ridge Zones occur when magma rises between
tectonic plates, cools and forms a ridge.
Plate Tectonics
a) Convection Currents: Created by heating and cooling of
magma in the asthenosphere. Magma rises and falls due
to different temperatures and viscosity (thickness) in the
magma.
b) As these currents move through the asthenosphere, they
drag with them the rigid parts of the crust immediately
above them.
c) Two plates moving towards each other compact or
squeeze together the area between the plates, causing
compressional forces.
• http://www.youtube.com/watch?v=Kpoko_l34ZE
• http://www.youtube.com/watch?v=ryrXAGY1dmE&feature
=related
Plate Tectonics (Boundaries)
• Three types of plate boundaries:
• 1. Convergent, or collisional boundaries
(compressional forces)
• 2. Divergent
boundaries,
also
called
spreading centers (tensional forces)
• 3. Conservative transform boundaries.
3 Kinds of Plate Boundaries
1. Convergent
or
collisional
boundaries
(Destructive): Occur where two plates slide towards
each other. Commonly forming either a subduction
zone (if one plate moves underneath the other) or a
continental collision (if the two plates contain
continental crust). An example of this are the Andes
mountain range in South America.
Convergent or Collisional Boundaries
3 Kinds of Plate Boundaries
2. Divergent boundaries (Constructive): Occur where
two plates slide apart from each other. Mid-ocean
ridges (e.g., Mid-Atlantic Ridge) and active zones of
rifting (such as Africa's Great Rift Valley) are both
examples of divergent boundaries.
Divergent Boundaries
3 Kinds of Plate Boundaries
3. Transform boundaries (Conservative):
Occur where plates slide or, perhaps more
accurately, grind past each other along
transform faults. The San Andreas Fault in
California is an example of a transform
boundary.
Transform Boundary –San Andreas
Fault
Plate Boundaries
• Earthquakes, volcanic activity, mountainbuilding, and oceanic trench formation occur
along these plate boundaries.
Plate Boundaries…and Volcanoes
Plate Boundaries…and Volcanoes.
How Volcanoes are Formed
• Why?
• Because that’s where plates collide or
converge
• Denser plate melts at the subduction zone
• Rocks melt to form magma
• Pressure increases, magma rises and erupts
• Volcanoes form
Volcanoes…not near Plate Boundaries
Intra-Plate Volcanoes
Intra-Plate Volcanoes
• Why?
• Plates move over magma hot spots in the
lithosphere
• Magma bursts through the crust
• Forms linear chain of volcanic mountains
• i.e. Hawaiian Islands
Continental Drift
• According to Alfred Wegener the super
continent of Pangaea broke up 225 million
years ago.
• The continent initially broke into Laurasia and
Gondwanaland
and
then
eventually
continents we know today.
• Evidence suggest that continents are still
drifting on the tectonic plates that form the
earth’s surface.
Continental Drift
• Continental Drift
– It refers to the movement of the more than 20
plates (9 major) due to convergent, divergent, and
transform boundaries.
– The continents drift at a rate of 2 inches a year, or,
as fast as a fingernail grows.
Questions
•
•
•
•
•
•
1.
2.
3.
4.
5.
6.
• 7.
• 8.
• 9.
Explain how compressional forces are caused.
Explain how tensional forces are caused.
Explain how compressional forces create fold mountains.
What is the difference between anticline and syncline.
How do tensional forces create a normal fault?
Explain how compressional forces create reverse and
overthrust faults?
What causes a volcano to erupt?
Describe the characteristics of an ash-cinder cone, shield and
composite cone.
Describe how the location of a volcano is related to the places
where plates meet. Describe situations when there is an
exception.
Introduction
• Unit 1 introduces you to the concept that the
earth’s surface is shaped by building-up and
wearing away forces.
• The unit helped examine the constituent parts
of the physical environment and the forces
that created them.
• Today we are going to look at patterns in their
distribution, and how they influence selected
human activities.
What is a Landform?
• Landform are natural elements of
topography. It includes land such as hills,
mountains, plateaus, canyons, valleys. It also
includes the oceans. It includes interface
areas, such as bays, deltas and peninsulas.
• It also includes sub-aqueous terrain features
such as mid-ocean ridges, volcanoes, and the
great ocean basins.
Patterns in the Location of Landforms
1. What landform
distribution patterns
can be seen from the
diagram of landforms
illustrated here?
Relief Map of North America
Q#1 How would you describe
the distribution of landforms
illustrated in this map?
Q#2 What type of landforms
can you identify on this map?
Q#3 Where in the Americas
are you most likely to
encounter mountains
Large Lakes
Plains and Plateaus
Large Rivers
River Deltas
How did this Land Distribution Come
About?
• The earth’s landforms are never static: That is
to say, they are constantly in a state of change
due to forces at work that both wear down
the land, as well as build up and shape the
land.
In Conclusion
• First, we looked at forces that build up and
shape landforms….next we will look at forces
which wear down the land
Questions-Checking for
Understanding
• 1. Explain how compressional forces are caused.
• The magma in the asthenosphere flows in such a way as it carries two
floating tectonic plates towards each other.
• These are called convection currents
• 2. Explain how tensional forces are created.
• The magma in the asthenosphere creates convection currents in such
a way that lava forces itself upwards between two floating tectonic
plates forcing them apart. These tectonic forces which move plates
apart are referred to as tensional forces.
• 3. Explain how compressional forces create fold mountains.
• Folds are caused by the destructive collisions of the tectonic plates.
Different forces and pressures create simple or complex forms
Review Questions
• 4.
What is the difference between anticline and syncline.
• Anticline is the top part of a fold mountain, while the syncline is the bottom
part of the fold
• 5. How do tensional forces create a normal fault?
• When rocks fracture or break apart after compression. Rocks maybe
pushed up or dropped down as plates move over or away from each other.
Read pp.14-15
• 6. Explain how compressional forces create reverse and overthrust
faults?
• Reverse: When the two layers around a fault push against each other.
There are compressional forces pushing one block up over the other
• Overthrust: When the plate has already undergone folding and, its folded
layers are pushed up and thrust over layers on the fault’s other side
• 7. What causes a volcano to erupt?
• Usually found along plate boundaries
• Heat is the trigger. Heat is generated because of
friction, pressure and decay of materials
• Plates collide
• Magma is produced when heat melts rock and
materials beneath the crust in the subduction
zone
• Magma reaches the surface in the crust or
lithosphere through fractures, vents or craters
• 8. Describe the characteristics of an ashcinder cone, shield and composite cone.
• Ash-Cinder: Eruptions consist of mainly ash
and cinder. Thick, slow flowing, rapidly
solidifying lava which creates violent
eruptions. Shape is symmetrical. Steep sides
and large crater
• Shield: Usually milder eruptions. Little or no
ash or cinders. Very thin, liquid lava. Broad,
flat cones
• Composite: Undergoes periods of explosive
and quiet activity. Ash and cinder mixed with
lava. Weak spots may develop on sides with
smaller lava flows forming smaller craters.
More than one crater
• 9. Describe how the location of a volcano is related to
the places where plates meet. Describe situations
when there is an exception.
• Where plates meet: Denser plate melts at the
subduction zone. Rocks melt to form magma.
Pressure increases, magma rises and erupts
• Exception: Plates move over magma hot spots in the
lithosphere. Magma bursts through the crust. Forms
linear chain of volcanic mountains i.e. Hawaiian Islands
Check for Understanding
– Read pp. 10-11
– Do Questions: 9 a), b), & c) and 10 a), & b)
– Worksheet 1.6 (Reproducible worksheet)
Answers -Question 9 (Text)
a) Convection currents are created by unequal
heat distribution in the asthenosphere. As
these
currents
move
through
the
asthenosphere, they drag with them the rigid
parts of the crust immediately above them.
b) Two plates moving towards each other
compact or squeeze together the area
between the plates, causing compressional
forces.
c)
Two plates moving apart pull the area
between the plates apart, causing tensional
forces.
Question 10
a) The South American Plate and the Nazca
Plate are colliding along the Peru-Chile Trench.
This collision is causing the edge of the South
American Plate to bend and buckle upward
forming the Andes Mountains. The Nazca Plate
is being forced under the South American Plate
to create the trench. Similar processes are
underway in Central America (Chocos Plate),
along the B.C. Coast and in India along the line
of the Himalaya’s.
Question 10
b) Iceland is located along the Mid-Atlantic
Ridge, where plates are being pushed apart.
(We can tell by looking at the legend in the
map on page 12). As the plates move apart ,
volcanic activity brings molten rock up and
out of the rift, to flow out on both sides,
thereby creating the ridge. These lava flows
have created the island of Iceland on top of
the Mid-Atlantic Ridge.
Worksheet 1.6
1. Use the key/legend on page 12 to indicate the
location of the subduction zones (arrows where
plates meet)
2. Self explanatory
3. Red triangle=Volcano and Yellow bolt for
earthquake OR V for Volcano and E for
Earthquake
4. Do question 11 d). 1 is the highest; 5 is lowest
5. Does not need to be done! Should know
number 5!
Check for Understanding
– Read pp. 13-16
– Questions: 14 b), c), 16 and 17
Answers -Question 14
b) Volcanic eruptions vary in violence,
depending upon viscosity (thickness) of the
magma, chemical composition and the amount
of trapped gas in the lava.
Thick lava tends to solidify and plug. When
gases build up behind the plug, an explosion
may result.
c) Violent eruptions result in thick lava flows
and steep-sided volcanic cones normally
composed of ash and cinders.
Milder, more frequent eruptions usually result in
thin, liquid lava flows and broad, flat cones
composed almost entirely of lava. (Shield cones)
Question 16
a)
Shade. Use a photocopy of a world map and
an atlas to identify mountain ranges
b)
Most of these mountain ranges almost are
found on the edges, or margins of continents. Most
mountain ranges are formed through a combination
of volcanic activity, faulting, and folding, all of which
occur on the edges of continental plates when they
collide or subduct under one another.
Question 17
a)
Use a photocopy of a world map and an
atlas to identify location of volcanic eruptions
b) Most of these active volcanoes are located
in the mountain ranges on the margins of
continents. Most mountain chains are formed
on the edges of tectonic plates, where plates
collide, slide past each other, or are pulled apart,
or where one plate is subducted below another.
Case Study -Question 18
Physical evidence of the eruption of Mount
Pinatubo
– Steam explosions
– Ash eruptions
– Massive lateral explosions of ash, cinders, & steam
– Ash and cinder flows
– Extensive ash and cinder eruptions over a period
of several days
Question 19
The Mount Pinatubo disaster affected human
activity in the following ways
– Forcing the evacuation of nearly 200,000 people
– Causing over 300 deaths
– Producing ash and cinder falls & flows that damage
crops, destroyed buildings & homes, and blocked
transportation routes
– Burying important crops and cropland
– Affecting weather patterns around the world
– Contributing to the acid rain problem