Download File - Leaving Certificate Geography

•
•
•
•
•
4 Layers of the earth
7 main plates of the earth
3 main plate boundaries
2 types of crust
3 main features of plate tectonics
(F.E.E.D)
• 3 main theorists and theories
• Human interaction
 The
Earth is
made up of 3
main layers:
Mantle
Outer core
• Core
Inner core
• Mantle
• Crust
(Lithosphere and
the Athenosphere)
Crust
 “Plates” of
lithosphere are moved around by
the underlying hot mantle convection cells


This is where we live!
The Earth’s crust is made
of:
Continental Crust
Oceanic Crust
- thick (10-70km)
- buoyant (less dense
than oceanic crust)
- mostly old
- thin (~7 km)
- dense (sinks under
continental crust)
- young
 Plates
are
made of rigid
lithosphere.
The lithosphere is
made up of the
crust and the upper
part of the mantle.
 Below
the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
Three types of plate boundary



Constructive (known
as Divergent)
Destructive (known
as Convergent)
Transform/Passive/
Neutral/Conservative
Constructive Boundaries
 Spreading
ridges
• As plates move apart new material is erupted to
fill the gap
Age of Oceanic Crust
Can you find ICELAND?
ICELAND
Iceland: An example of continental rifting
 Iceland
has a divergent
plate boundary running
through its middle
Destructive Boundaries
 There
are three styles of
destructive/convergent plate
boundaries
• Continent-continent collision
• Continent-oceanic crust collision
• Ocean-ocean collision
Continent-Continent Collision
 Forms
mountains, e.g. European Alps, Himalayas
Himalayas
Continent-Oceanic Crust Collision
 Called
SUBDUCTION
Subduction




Oceanic lithosphere
subducts underneath the
continental lithosphere
Oceanic lithosphere heats
and dehydrates as it
subsides
The melt rises forming
volcanism
E.g. The Andes
Ocean-Ocean Plate Collision
 When
two oceanic plates collide, one runs over
the other which causes it to sink into the mantle
forming a subduction zone.
 The subducting plate is bent downward to form
a very deep depression in the ocean floor
called a trench.
 The worlds deepest parts of the ocean are
found along trenches.
• E.g. The Mariana Trench is 11 km deep!
Neutral / Transform Boundaries
 Where
plates slide past each other
Above: View of the San Andreas
transform fault

If you look at a map of the world, you may notice that some of the
continents could fit together like pieces of a puzzle.
The study of plate tectonics has been furthered by the work
of three main theorists.
Alfred Wegener – a German Meteorologist
Maurice Ewing – an American oceanographer/geophysicist
Harold H. Hess – Professor of Geology, Princeton, USA
In his published work “The origins of continents and
Oceans” (1912) Wegener proposed that millions of years
ago all the continents of the earth were once joined
together in one large land mass called….Pangea
Slowly, due to magma convection currents deep within the
mantle, Pangea broke into two large continents called
Laurasia and Gonwanaland.
Over millions of years these two broke and moved into the
main continents we know today.
 Same
fossils and
rocks found in
different parts of the
world
 Africa
and South
America look like
pieces of a jigsaw




Some people thought the Earth
was shrinking and cracking
Wegener thought whole
sections of the crust moved
(plate tectonics)
Some people did not
understand and thought the
continents floated around in
the oceans (continental drift)
He died before people
accepted his ideas
Ewing studied and photographed much of the
earths ocean floors. Once, during a transAtlantic flight, he looked down and noticed a
dark shadow running along the Atlantic
Ocean. Research showed that the American
and Eurasian plates were separating and new
crust was forming. Layers and ages of each
new magma flow showed the widening of the
sea floor over millions of years.
Hess was an American professor who furthered the study
of plate tectonics with his theory of Sea Floor Spreading
and the creation of new crust and volcanic ridges.
• Alfred Wegener (1912) – Continental Drift
• Maurice Ewing (1947) – Mid Atlantic Ridge
• Harry Hess (1960s) – Sea Floor Spreading
All combined, plus the study of countless others, creates
the Theory of Plate Tectonics
• Volcanoes
• Earthquakes
• Fold Mountains
 Plates
moving in any
direction causes
earthquakes
 The worst are caused
by plates rubbing
past each other as in
C
 This happens along
the Californian coast
 Large
continents
begin to crack and
split apart
 The gaps fill with
water
 Small seas become
oceans
 The mid ocean ridge
continues to produce
new crust

Why is the Atlantic still getting
wider

The plates are pulled apart by
convection currents in the
mantle below

Caused by heat released from
natural radioactive processes

At the mid Atlantic ridge molten
rock from below rises up to fill
the gap with new basaltic rock
 More
evidence has been
found for Wegener's theory
 The
Earths North and South
pole have flipped many
times
 These
leaves magnetic
‘stripes’ in rock containing
iron minerals

Dense heavy oceanic crust
can be subducted below less
denser continental crust.

The friction melts rock

This magma rises through the
crust to form new volcanoes

This is happening in South
America (The Andes)

Eventually when plates move
together the continental crust
collides

The heat and pressure make
metamorphic rock

It also pushes and folds the
rocks into high mountains

The Himalayas rise to 8848m
and are still growing today
Volcanoes and Plate
Tectonics…
…what’s the connection?
Pacific Ring of Fire
Volcanism is
mostly
focused at
plate
margins
Volcanoes are formed by:
- Subduction - Rifting - Hotspots
Pacific Ring of Fire
Hotspot
volcanoes
What are Hotspot Volcanoes?
 Hot
mantle plumes breaching the
surface in the middle of a tectonic
plate
The Hawaiian island chain are
examples of hotspot volcanoes.
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The tectonic plate moves over a fixed hotspot forming a
chain of volcanoes.
The volcanoes get younger from one end to the other.
Earthquakes and Plate
Tectonics…
…what’s the connection?
 As
with volcanoes, earthquakes are not
randomly distributed over the globe
Figure showing
the distribution of
earthquakes
around the globe
 At
the boundaries between plates, friction
causes them to stick together. When built up
energy causes them to break, earthquakes
occur.
Figure showing the tectonic setting of earthquakes
 The
Earth is made up of 3 main layers (core,
mantle, crust)
 On the surface of the Earth are tectonic
plates that slowly move around the globe
 Plates are made of crust and upper mantle
(lithosphere)
 There are 2 types of plate
 There are 3 types of plate boundaries
 Volcanoes and Earthquakes are closely
linked to the margins of the tectonic plates