EDEXCEL A GSCE Geography revision Unit 2 - Tectonics

1. Tectonics
Thursday 22nd May

2. The earth as a scotch egg
The crust of
our earth is
very shallow
like the
breadcrumb
layer of the
scotch egg. It
is what we live
on.
The mantle is like the
meaty bit of our scotch
egg. It is the largest section
and is made of liquid rock
called magma. It is
underneath the crust and
behaves a bit like jam
The outer core is what lies
beneath the mantle. This is
the white of our egg. This is
also liquid rock but moves
very slowly because it is
under so much pressure.
The inner core
of the earth is
solid because
of the
pressure. It is
also hotter
than the
surface of the
sun

3. Cross Section of the Earth Crust – very thin like the
breadcrumbs of our scotch egg.
6-70km thick
Mantle – very high
temps. Looks
like jam!
Between 5000
and 1300oC
Outer Core –
Liquid made
mostly of iron
Inner Core –
Solid made
of iron. Up to
5500oC

4. Distribution of Earthquakes and Volcanoes
Distributed on the plate boundaries
Mostly on the coasts or in the ocean
Around the edge of the pacific and through the
middle of the Atlantic
With the exception of Hawaii which is on a
hotspot

5. Convection
Currents
Mantle
Crust
Why the plates move
• Magma from the earths core is super heated and rises towards the crust
• As it rises and travels away from the core it begins to cool
• When it reaches the crust it is forced sideways and because it is not colder, sinks back
down again towards the core.
• Where is spreads out you will find divergent boundaries and where is sinks
downwards it full down crust from a convergent boundary.

6. Oceanic and Continental Crust
Continental Crust:
• 25 -100km thick
• Less dense
• Bigger crystals
• More easily eroded
• Youngest
Oceanic Crust:
• 5 -10km thick
• More dense
• Tiny crystals
• Very hard rock
• Very old rock

7. Divergent Plate Boundaries

8. The plates moving apart in this way is
known as sea floor spreading.
It is the reason for Iceland's existence and
the reason why volcanoes are present
there.
The island of Sursey, off the coast of
iceland erupted in 1963. Before then there
had been no land in that place.

9. Convergent Plate Boundary – two
continental crusts

10. Convergent Plate Boundaries – one
oceanic, one continental crust

11. It is on convergent plate boundaries that you find the deepest ocean
trenches and some of the most active volcanoes in the world.
The Cascade Mountain range is off the west coast of America and is a
line of volcanic mountains caused by the convergent plate margin.
Because a lot of earthquakes occur under the ocean it is only
destructive plate margins that cause tsunamis.

12. Conservative Plate Boundaries

13. The San Andreas Fault in California is
the best known example of a
constructive plate margin.
The can also be found near Fiji, Israel,
South Island in New Zealand and
Sumatra in Indonesia.

14. Type of plate
boundary
Diagram Description of
changes
EQ/Volcano
activity
Examples
Convergent
•Oceanic plate forced
downwards into the
mantle forming a
subduction zone.
•Deep trench formed
•Continental plate
forced up into mountain
range
Constructive
Conservative
Pacific and North
American Plates along
the San Andreas Fault
•Two plates move away
from each other
•New oceanic crust is
created forming mid-
oceanic ridges with
volcanoes
Two plates move
sideways past each
other – land is neither
formed nor destroyed.
•Heat from the mantle and
friction from contact between
the two plates causes violent
earthquakes to be triggered.
•These can also cause
tsunamis
•The melting plate creates
magma which rises to the
surface to form volcanoes
•Where magma builds
up above the surface,
volcanoes form.
•In the ocean these
quite often show as
islands
Plates do not tend to
move past each other
smoothly. Friction is
created and they tend
to get stuck. Pressure
builds until the plate
flips forward creating
violent EQ’s
Pacific ring of Fire
Japanese Island Arc
New Zealand
Iceland
Great Rift Valley Africa

15. Measuring Earthquakes
Richter Scale
Measures strength using numbers
No upper limit
Mercalli Scale
Measures effects using roman
numerals. Limited because there
is only so much damage that can
be done

16. How do earthquakes happen?
1) Pressure builds up at plate boundaries.
2) The plates cannot move though due to
friction, and pressure continues to build.
3) Suddenly the crust breaks along a fault.
4) The plates spring apart.
5) Stored energy is released in a few seconds
from the focus, and travels out from the
epicentre as seismic waves on the surface.

20. Silicon Valley, home of IBM and Apple. 23,000 jobs and
700,000 people. On the San Andreas Fault. There has not
been a large earthquake here for over 30 years.

21. The Soufriere Hills on the island of Montserrat erupted in 1995 in one of the most devastating
eruptions ever seen. It entirely covered the capital city of Plymouth in ash and closed the airport. It
was known that the island was highly volcanic but no-one wanted to leave the island even after the
eruption. Their families and their livelihoods were there and they had nowhere else to go.

22. Sorrento and the Island of Capri in Italy.
Massive tourist destination and people are attracted because
of the beautiful beaches and amazing weather. It also has a
historic interest with many people coming to visit Pompeii; the
ancient roman port that got destroyed by the volcano in 79AD.
Across the bay from Mt Vesuvius
It has not erupted violently for over 50 years.

23. Mount Etna in Italy, Europe's most active volcano but ‘safe’ enough for tourists to go and watch.
Many farmers also grow olives, grapes and citrus fruits because the volcanic ash produces
extremely fertile soil here. Siciliy is quite a poor area of Italy too with a very close knit community.

24. Iceland straddles the Mid Atlantic ridge; a divergent plate boundary. The magma near the surface
heats water in the rock causing warm pools of water to rise up. People visit Iceland to bathe in
these pools. The hot water can also be harnessed for geothermal energy. This is extremely
environmentally friendly and renewable.

25. Haiti - LIC Earthquake Case Study
Effects Responses
• The main port was closed after severe damage to
the docks and a crane.
• Some roads are impassable - either because of
earthquake damage, or because they are blocked
by rubble or smashed vehicles.
• Between 500,000 and 700,000 people are
believed to have been left homeless
• Even before the earthquake only half of Haitians
had access to clean water. Now most of the
remaining water supply been cut off.
• Eight hospitals or health centres in the capital
collapsed or suffered severe damage.
• US engineers and dive teams fixed piers, cranes,
and buildings.
• Around 3,000 UN troops and police worked to
clear some of the major roads.
• More than 500 makeshift camps have been
identified by the Haitian government, which has
requested large tents be set up as reception
centres for the homeless.
• On 20 January, 755,000 litres of water were
provided to 151,000 people.
• Field hospitals have been set up by teams from
Russia, Israel, Colombia, Jordan and Brazil.
Causes
• Haiti is located on a conservative plate margin between the Caribbean and
North America plate which are slowly moving past each other.
• 7.0 magnitude which stuck on Tuesday 12th January at 16:53 (Haiti Time)

26. Iceland – HIC Volcano Case Study
Causes
•Iceland lies on a divergent plate boundary between the North American and Eurasian plates which are
moving apart at a rate of 2cm per year.
•As they move apart, lava wells up in the gap in between towards the surface.
•As this process continues and consecutive lava eruptions cool and build up, volcanoes are created.
Effects
•The cloud of ash went 20,000ft into the atmosphere and blew on westerly winds cross Europe.
•95,000 flights had to be cancelled in the UK as the ash was at the height that plans normally fly at.
•The flight ban was imposed because in the high temperatures of an engine turbine, ash can turn to molten
glass and cripple the engine.
•The airline industry said its losses soared to over £650 million
•Other transport companies benefitted as passengers looked for alternatives to flying.
•Eurostar in particular saw a huge demand from and said it carried 50,000 extra passengers just on one day
alone.
•Kenyan farmers were forced to dump stocks of fresh food and flowers destined for European consumers
which cost the Kenyan economy $3.8m a day as a result of flight cancellations to Europe.
•Locally 700 farmers around the volcano were evacuated due to the melting ice cap on top of the mountain
which caused flooding and property to be washed away.
Responses
•Some 60 volunteers and staff of the Icelandic Red Cross provided food for the farming population living in
the vicinity of the glacier.
•Some 700 people were evacuated from the disaster zone three times in the past month.
•A 24-hour emergency information hotline was also activated. Red Cross volunteers are also providing meals
twice a day in Heimaland, as most people have not been able to stock up on food.

27. Prediction - Volcanoes
Volcanoes can be monitored to predict eruptions with:
• GPS - to see if the ground is rising up as magma approaches the surface
• Gas sampling – changes to gases coming out of the volcano might mean
an eruption is coming
• Geothermal monitoring – the ground gets hotter as magma rises to the
surface
• Seismic monitoring – to ‘listen’ to the rising blobs of magma as they force
their way upwards and cause small earthquakes
• Looking at historical records to see if
there is a past pattern of eruptions that
might be repeated.

28. Prevention - Volcanoes
Once an eruption has happened it is possible to prevent it from having major
effects on the local people by;
• Spraying the lava with water to cool it down and stop it flowing
• Putting concrete barriers in the path of lava forcing it away from villages
• Setting off explosive to divert the lava flow
• Digging ditches to funnel it away from homes

29. Prediction - Earthquakes
Earthquakes are much harder to predict because they happen underground
so are not visible. Methods used to predict earthquakes include;
• Noting strange animal behaviour – cats, dogs, birds and snakes are known
to behave differently before an earthquake
• Monitoring electrical discharges – there is some evidence that these
increase before an earthquake. Some scientists believe that they appear in
the sky as a rainbow glow, known as earthquake lights.
• Recording minor tremors as these could be small foreshocks

30. Planning for Earthquakes
Because so little warning can be given it is
better to plan for the worse to limit the effects
such as;
• Providing education for local residence who
are taught how to react
• Have an emergency kit ready including a
torch, bottled water, first aid kit and tinned
food.
• Design buildings that can withstand
earthquakes by having flexible steel frames;
shutters can be used to cover windows that
might shatter; rubberised foundations can
be used to absorb the energy of a quake
• Planning regulations so buildings are not
built too high.