Transcript Year 3 Plate Tectonics

The main physical features of the Earth.
North America
Rocky
Mountains
Europe
Alps
Asia
Himalayas
Atlantic
Ocean
Pacific
Ocean
South America
Africa
Indian
Ocean
Andes
Oceania
Southern Ocean Antarctica
1
Definition of ‘Plate tectonics’
A plate is a large, rigid slab of solid rock. The word
tectonics comes from the Greek root "to build."
Putting these two words together, we get the term
plate tectonics, which refers to how the Earth's
surface is built of plates.
The theory of plate tectonics states that the Earth's
crust is broken into a number of large and small
slabs of rock called plates.
The formation of mountains and volcanoes, and the
occurrence of earthquakes have been explained
using this theory.
2
CROSS-SECTION OF THE EARTH
CRUST:
SOLID THIN LAYER.
MADE OF TWO MAIN TYPES:
-CONTINENTAL (60 KM THICK)
-OCEANIC (8 TO 10 KM THICK)
(MUCH HEAVIER THAN CONTINENTAL)
DIVIDED
INTO PLATES
WHICH
FLOAT ON
THE MANTLE
MANTLE:MOLTEN
ROCK WHICH MOVES
IN CIRCLES DUE TO
CONVECTION
CURRENTS
THE CORE GIVES OFF
INCREDIBLE HEAT
WHICH CAUSES THE
MANTLE TO FLOW.
3
How plates move
Huge convection currents occur in
the mantle. The cause of these
currents is radioactive decay in the
core. Motion is driven by friction
between the solid top layer of the
earth [crust] and the semi-liquid
layer below [mantle].
4
The importance of crust
There are two types of crust which have different
characteristics.
Older, lighter, cannot
sink and is permanent.
Younger, heavier,
can sink and is
constantly being
destroyed and
replaced.
5
World map of plate boundaries
6
Label the map with the name of the plates in Figure 4
7
Plate boundaries
The boundaries between plates can be
classified into three main types according to
the direction of movement of the plates on
either side of the boundary. Plates may
either move away from each other
(divergence), towards each other
(convergence), or past each other.
8
MANTLE
MANTLE
MANTLE
9
Destructive/convergent
boundaries
• Plates collide. The oceanic crust which is denser is
forced beneath the lighter continental crust. This
process is called subduction.
• The descending plate creates friction and a build-up
of pressure which causes partial melting of the crust
and earthquakes.
• Magma from below the crust can rise to form
volcanoes.
10
B- Ocean-to-continent boundary
6-The collision causes
folding and uplift of
rocks which form fold
mountains.
5-The Peru-Chile
trench
forms where the
oceanic plate is
being
subducted.
4-The melting plate
creates lighter
magma that rises
towards the surface
to form volcanoes.
Andes fold mountains
Pacific
Ocean
Trench
Volcano
South American
Plate (Continental)
Nazca Plate
(Oceanic)
Mantle
1-The Nazca Plate
is being subducted
below the South
American Plate.
Earthquakes
Subduction
zone
2-Friction and pressure
cause earthquakes to
occur along the subduction
zone
3-The heat from
the mantle causes
the oceanic plate
to be destroyed.
11
Draw, label and annotate
12
Fold Mountains along destructive margins: The Andes
The Andes are located where the Nazca Plate, made of
dense oceanic crust, is subducted beneath the South
American Plate, made of lighter continental crust.
More than 100 million years ago, the Andes began to form
by the uplifting and folding of sedimentary rocks
accumulated along the edge of the continental plate.
Massive layers of rock got folded by compressional forces
as a result and formed a narrow belt along the western
edge of the continent.
During the last 20 million years, parts of the Andes have
been lifted over 1500 m.
Massive layers of rock got
folded by compressional forces
13
2- Constructive/divergent boundary
As plates move apart, magma comes to the
surface, forming new crust on the ocean floor
at the mid-ocean ridges and forcing plates
apart.
When the magma builds up above the surface
of the ocean, volcanic islands form, e.g.
Iceland
Next slide shows the mid-Atlantic Ridge which
marks the divergent boundary in the Atlantic
Ocean.
14
4-Submarine
volcanoes appear
along the ridge. Some
may grow to form
islands, e.g. Iceland.
Oceanic crust
1-Convection
currents pull
plates apart.
3-A mid-ocean ridge is
formed by the new crust.
Oceanic crust
2-As the plates move apart,
magma from the mantle rises to
fill the gaps and forms new
oceanic crust.
15
Draw, label and annotate
16
Mid-Atlantic
ridge
17
Surtsey [volcanic island near Iceland] 1963
18
Describe and explain the characteristic features of a
constructive boundary. (4)
What are features? Mid-ocean ridges and volcanic islands
are the features of a constructive boundary.
The question asks for an explanation , i.e. the reasons for
these features.
You may answer this question using the ‘case study’, i.e.
located example, of the Mid-Atlantic constructive
boundary.
19
20
Why do some volcanoes not occur on
plate boundaries?... Hot spots
21
Understanding hotspots
Some volcanoes do not occur on plate
boundaries. These volcanoes are formed over
hotspots.
These are fixed points in the mantle that
generate intense heat. Small, long lasting,
exceptionally hot areas of magma exist under
the Earth's surface which in turn sustains longlasting volcanic activity.
22
At areas where the pressure is greater in the
mantle, magma erupts through the crust as
when the plume reaches the crust it causes the
crust to dome (and crack).
Volcanoes are created if the magma rises above
the ocean surface.
As the crustal plate moves over the stationary
hotspot, new volcanoes are formed.
Hotspots are associated with chains of islands
such as Hawaii.
23
24
As the plate moves over the stationary hotspot,
new volcanoes are formed.
25
26
Case study: The Hawaiian Islands, which are
entirely of volcanic origin, have formed in the
middle of the Pacific Ocean more than 3,200
km from the nearest plate boundary. The
Hawaiian Islands are located over a hotspot.
The magma rises through the Pacific Plate to
supply the active volcanoes.
27