In this presentation you will:

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In this presentation you will
Plate Tectonics

• explore the movements of the plates that make up
  the Earths surface

• explore geological events caused by plate motion

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Introduction
The outer layer of the Earth is broken up into a
number of different tectonic plates, which are
constantly moving at a very slow speed.
The movements of the plates can dramatically
change the Earths surface. Volcanic eruptions,
earthquakes and mountain building all occur as a
result of plate motion.
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Basic Structure of Earth
The Earth is made up of several layers. The
layers are called

• Inner core

• Outer core

• Lower mantle

• Upper mantle

• Crust

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Tectonic Plates
The lithosphere is made up of the crust and a
part of the upper mantle.
The lithosphere is divided into tectonic plates
that fit together like a giant puzzle wrapped
around the Earth.
The map shows major plates, and some minor ones.
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Tectonic Plates
The plates float on the semi-liquid asthenosphere
(part of Earths mantle), which enables them to
move.
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What Causes Plate Motion?
Imagine that you are cooking an egg in a pot of
water.
As the water temperature increases, the egg
floating at the surface begins to move.
This is because the hot water rises to the
surface, where it then cools and sinks back down
in a cycle called a convection current.
The movement in the water causes the egg to move.
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What Causes Plate Motion?
In a similar way, convection currents within the
Earths mantle cause the plates floating above to
move.
However, while convection in the pot takes a
matter of seconds, convection within the mantle
takes millions of years.
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Question 1
Tectonic plates include approximately how much of
the Earth surface?
A) 20
B) 40
C) 60
D) 80
E) 100
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Question 1
Tectonic plates include approximately how much of
the Earth surface?
A) 20
B) 40
C) 60
D) 80
E) 100
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Plate Boundaries
There are many convection currents within the
mantle.
The speed and direction of the currents vary.
This means that plates are all moving with
different speeds and directions.
Plates
Mantle
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Plate Boundaries
The plates collide or pull apart depending on
their relative directions and speeds.
The interactions of the plates at their
boundaries cause geological events such as
volcanic eruptions, earthquakes and the formation
of mountains.
Although such events can occur in other parts of
the Earths surface, the majority occur at plate
boundaries.
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Plate Boundaries
There are three types of boundaries between
plates

• Convergent The boundary between two plates that
  are moving towards each other.

• Divergent The boundary between two plates that
  are pulling apart.

• Sliding The boundary between two plates that
  are sliding past each other horizontally.

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Convergent Boundaries
When two plates collide, one plate is forced
below the other.
At convergent plate boundaries on the ocean
floor, a trench is formed. Trenches are narrow,
deep cuts.
Convergent boundaries also lead to the formation
of volcanoes at the ocean floor.
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Convergent Boundaries
The edge of the lower plate is pushed into the
mantle where it melts and turns into magma.
This extra magma creates more pressure, and the
magma is forced out in a volcanic eruption.
Volcano
Extra magma forced out
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Convergent Boundaries
Volcanoes are also formed on land when both
plates are mainly made of continental crust
rather than oceanic crust.
The higher plate crumples at the boundary,
forming mountains and volcanoes.
The formation of mountains is very slow,
occurring as plates converge over millions of
years.
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Convergent Boundaries
The Himalayas were formed when the Eurasian and
Indian plates collided about 50 million years
ago.
This convergence continued for some time. Most of
the mountains only reached their full height in
the last 10 million years.
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Convergent Boundaries
Earthquakes can occur at convergent boundaries as
one plate grinds over the other, causing rock to
deform and become brittle.
Earthquakes occurring at convergent boundaries
can be very large and devastating.
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Convergent Boundaries
Earthquakes at underwater convergent boundaries
can create a tsunami a potentially devastating
wave that dumps an enormous amount of water onto
coastal land when it comes ashore.
Damage caused by a tsunami
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Divergent Boundaries
When a convergent boundary forces one plate to
sink into the mantle, the edge melts and
disappears.
However, the Earths surface remains the same
size because roughly the same amount of crust
that is lost at a convergent boundary, is created
when plates pull apart at a divergent boundary.
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Divergent Boundaries
As plates pull apart, they cause cracks to appear
in the surface.
Magma escapes through the cracks onto the surface
from the mantle.
Magma hardens to form rock
Magma escapes
The magma then hardens to form new rock.
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Divergent Boundaries
Volcanic activity refers to magma escaping onto
the surface.
Magma hardens to form rock
When magma escapes quickly, mountains (including
volcanoes) are formed.
Magma escapes
However, when the magma pushes onto the surface
slowly, the new rock that is formed is relatively
flat.
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Divergent Boundaries
Divergent boundaries that occur on the ocean
floor can also lead to the formation of mountains
and volcanoes.
The Mid-Atlantic Ridge is a mostly underwater
mountain range created by the divergent boundary
between the North American and Eurasian plates.
Mid-Atlantic Ridge
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Divergent Boundaries
Some of the underwater mountains in the Ridge are
taller than Mount Everest, the tallest mountain
on land.
The highest peaks extend above the surface of the
ocean, forming islands.
As two plates pull apart, cracks can develop and
one part may slip down in relation to the other.
Earthquakes occur as a result of this movement.
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Question 2
Volcanoes can be formed at diverging boundaries
as magma flows up between the plates." Is this
statement true or false?
Answer True or False.
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Question 2
Volcanoes can be formed at diverging boundaries
as magma flows up between the plates." Is this
statement true or false?
Answer True or False.
True
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Sliding Boundaries
At sliding boundaries, also called transform
boundaries, two plates slide past each other
horizontally.
San Andreas Fault,California
When this happens, enormous stress is put on the
rocks at the surface, causing them to deform.
Eventually, the stress becomes so great that the
rocks break apart, leaving a crack in the Earths
surface.
Such a crack is called a fault.
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Sliding Boundaries
When a fault appears, an enormous amount of
energy is released in the form of an earthquake.
San Francisco earthquake 1906
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Sliding Boundaries
Sliding boundaries do not destroy part of the
crust, or create new crust.
However, because sliding boundaries cause rock to
deform, the edge of the plates may become jagged.
Sliding boundaries and the resulting faults are
more common at boundaries under the ocean than on
land.
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Question 3
What is a convergent boundary?
A) The boundary between two plates moving towards
each other
B) The boundary between two plates moving apart
C) The boundary between two plates sliding past
each other
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Question 3
What is a convergent boundary?
A) The boundary between two plates moving towards
each other
B) The boundary between two plates moving apart
C) The boundary between two plates sliding past
each other
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Question 4
"A fault can appear in the Earth's surface at a
sliding boundary." Is this statement true or
false?
Answer True or False.
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Question 4
"A fault can appear in the Earth's surface at a
sliding boundary." Is this statement true or
false?
Answer True or False.
True
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Ocean Basins
The surface of the Earth is covered in lots of
peaks and troughs (basins).
The peaks are clearly obvious as mountains.
Height and depth of Earth surface
The basins are not so obvious, but are filled
with water, and are what we know as oceans.
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Ocean Basins
The basin is formed where a tectonic plate has
been stretched and made thinner.
This thinner part of the Earth crust is known as
oceanic crust.
The thicker part is known as continental crust.
Ocean floor
Oceanic crust
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Summary
In this presentation you have seen

• where the major tectonic plates are and what they
  are called

• how plate movement causes major geological events

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