IGCSE Plate Tectonics and Weathering- made for students.

1. Plate tectonics
Earthquakes
and
Volcanoes

2. Changing face of the world

3. Theory of Continental Drift
• Given by Alfred Wegner in 1912
• Believed that world was once only one piece of land
called the Pangaea which broke up into Gondwanaland
and Laurasia and the Tethys sea
• Evidence of Pangaea
▫ Biology: Remains of Mesosauras have been found in South Africa
and Brazil
▫ Geology: Similar rock type of Appalachians and mountains of
north-west Europe
▫ Climatology: Coal, sandstone and limestone could not been
formed in Britain with its present climate

4. What is Plate tectonics?
• It is the science which studies the movement of
plates
• These plates are either continental or oceanic
• There are 7 large and several smaller plates
• They are constantly in motion- move at a speed
of the growth of our nails.
• These plates move like a conveyor belt due to the
convection currents.

5. Distribution of various plates

7. Interior structure of Earth

8. LAYERS OF EARTH
• CRUST
▫ Oceanic crust is about 6-10km thick and is mainly formed of basalt
▫ Continental crust is up to 70 km thick
• MANTLE
▫ Mainly composed of silicate rocks rich in iron and magnesium. The
upper mantle is rigid whereas the lower mantle is semi-liquid known as
asthenosphere.
▫ Crust and upper mantle together are known as Lithosphere.
• CORE
▫ About 6371 Km deep
▫ Made up of mainly iron and Nickel
▫ Is the size of Mars
▫ Outer core is semi-molten and inner core is solid
▫ Hotter than surface of the sun (about 6200 C)

9. Types of Lithospheric Plates
• There are two types
▫ Continental Plate
 35-40km thick; about 60 km thick under the
mountains
 The rocks are about 1500 million years old
 Rocks are mainly composed of silica and aluminum,
granite is the most common
 Also known as SIAL

10. Contd:
• Oceanic Plate
▫ 6-10 km thick
▫ The rocks are about 200 million years old
▫ Higher density than continental crust
▫ Generally contains Silica and Magnesium; mainly
basalt
▫ Also known as SIMA

11. Different types of plate boundaries

12. Types of Plate Boundaries
• Constructive or Divergent
▫ Two plates moving away from each other
▫ New oceanic crust appears
▫ Forms mid ocean ridges and volcanoes
▫ E.g. Mid Atlantic Ridge
• Destructive or Convergent
▫ Two plates moving towards each other- one oceanic
and one continental
▫ Oceanic being heavier sinks
▫ Forms deep sea trenches and island arcs
▫ Andes; Rockies Island arcs of West Indies

13. CONTD:
• Collision zones
▫ Two continental plates collide
▫ As neither can sink, forms Fold mountains
▫ E.g. Himalayas and Alps
• Conservative or passive
▫ Along the transform Faults
▫ Plates brush past each other
▫ No land is formed or destroyed
▫ E.g. San Andreas Fault in California

14. Exceptions
• Generally the center of the
plates is rigid which forms
▫ Shield lands (cratons)-
Canadian or Laurentian
shield
▫ Depressions on the edges
of the shield from large
basins like Mississippi-
Missouri, Amazon
There is an exception to this
in the form of
Hotspots(shield
volcanoes)and African
rift valley.

15. Structure of a Volcano

17. Types of Volcanoes

18. Volcanic Explosivity Index (VEI)

19. Types of Faults
• Strike-slip faults indicate rocks are sliding past each other
horizontally, with little to no vertical movement. Both the San
Andreas and Anatolian Faults are strike-slip.
• Normal faults create space. Two blocks of crust pull apart,
stretching the crust into a valley. The Basin and Range Province in
North America and the East African Rift Zone are two well-known
regions where normal faults are spreading apart Earth's crust.
• Reverse faults, also called thrust faults, slide one block of crust on
top of another. These faults are commonly found in collisions zones,
where tectonic plates push up mountain ranges such as the
Himalayas and the Rocky Mountains.

21. Volcanic Hazards
• PRIMARY
▫ Lava Flows
▫ Pyroclastic flows
▫ Ash and Tephra
fall
▫ Volcanic gases
• SECONDARY
▫ Lahars
▫ Volcanic landslides
▫ Tsunamis

22. Source:http://pubs.usgs.gov/fs/2000/fs060-00/images/volcano-hazards.jpg

23. Source: http://science.kqed.org/quest/files/2012/02/INFOGRAPHIC-
WITH-TEXT-v5.jpg

24. Types of Seismic Waves
• Body Waves
P Waves
The first kind of body wave is the P wave or primary wave This is the
fastest kind of seismic wave. The P wave can move through solid rock and
fluids, like water or the liquid layers of the earth. It pushes and pulls the
rock it moves through just like sound waves push and pull the air. Have you
ever heard a big clap of thunder and heard the windows rattle at the same
time? The windows rattle because the sound waves were pushing and
pulling on the window glass much like P waves push and pull on rock.
Sometimes animals can hear the P waves of an earthquake. Usually we only
feel the bump and rattle of these waves.

25. • S Waves
▫ The second type of body wave is the S wave or
secondary wave , which is the second wave you
feel in an earthquake. An S wave is slower than a P
wave and can only move through solid rock. This
wave moves rock up and down, or side-to-side.

26. • Surface Waves
▫ Love Waves
• The first kind of surface wave is called a Love wave ,
named after A.E.H. Love, a British mathematician who
worked out the mathematical model for this kind of wave
in 1911. It's the fastest surface wave and moves the
ground from side-to-side.

27. • Rayleigh Waves
The other kind of surface wave is wave is the Rayleigh wave ,
named for John William Strutt, Lord Rayleigh, who mathematically
predicted the existence of this kind of wave in 1885. A Rayleigh
wave rolls along the ground just like a wave rolls across a lake or an
ocean. Because it rolls, it moves the ground up and down, and side-
to-side in the same direction that the wave is moving. Most of the
shaking felt from an earthquake is due to the Rayleigh wave, which
can be much larger than the other waves.

28. Earthquakes can be:
• Shallow: If the focus is near the surface—
between 0 and 70 km (0 and 40 mi) deep—
shallow-focus earthquakes are produced.
• Deep: If it is deep below the crust—between 70
and 700 km (40 and 400 mi) deep—a deep-focus
earthquake will be produced.
Benioff Zone: Line along the subduction zone
Either TECTONIC or MAGMATIC

29. Hazards caused by Earthquakes
• PRIMARY
▫ Ground movement/shaking
• SECONDARY
▫ Soil Liquefaction
▫ Landslides/Avalanches
▫ Tsunamis
▫ Fires
▫ Aftershocks

30. Mercalli Vs Richter
Source: http://i.imgur.com/i17siUM.png

31. Managing earthquake hazards
• Impact of this hazard depends on:
▫ PHYSICAL FACTORS
 Location of Epicenter
 Depth of focus
 Duration of shaking
 Time of the day
 Structure/material of the rocks
▫ HUMAN FACTORS
 Building style and land use
 People’s reactions
 Preparedness of the community
 Emergency services and relief
 Economic and social structure for preparedness; education
about the hazard and ability to recover

32. Predicting earthquakes and
Volcanoes
Not easy and accurate but :
• Use laser beams to detect plate movements
• Monitor release of Radon gas
• Seismometers
• Monitoring the changing shape of a
volcano/ground
• Increased frequency of earthquakes indicates an
oncoming eruption

33. Preparedness
• Important to-
• Have regular evacuation drills, including schools
• Building which are quake resistant
• Pre conceived, Emergency plans

34. Why do people continue to live in
areas prone to hazards?
• Fertile soil
• Tourism opportunities
• Emotional attachment
• Cannot move due to financial reasons- no where
else to go- No choice
• Government is equipped to cope with the
hazard- people have faith in the administration
• Leaving would mean evacuating the entire
country.

35. Weathering
• The disintegration and decomposition of rocks
in situ i.e in its original position due to
▫ Exposure to air and water
▫ Release of pressure
▫ Fluctuation in temperature
As it does not involve movement, it is cannot be
equated with erosion!!!

36. Types of Weathering
• Physical Weathering
▫ Frost Shattering
 Caused due to alternating
freeze-thaw action
 Forms Block fields
(felsenmeers )
 Talus or Scree is formed
at the bottom of slopes

37. • Salt Crystallization
 Occurs in deserts and
near coasts
 Water evaporates leaving
salt crystals behind which
lead to the disintegration
of rocks

38. • Pressure release
▫ When intrusive igneous rocks are exposed to surface,
the pressure release develops cracks
▫ If these are parallel to the surface, sheeting occurs
▫ This process is responsible for exfoliation domes

39. • Thermal Expansion or Insolation weathering
▫ High Diurnal range of temperature
▫ Generally happens in deserts
▫ Outer layers gets heated quicker than inner one- peels off
▫ Sometimes the minerals present in rocks can also lead to the rock
peeling

40. • Biological Weathering
▫ Trees growing along the bedding plans or extending
into joints
▫ Can also be caused by burrowing

41. Bibliography
IMAGES
• www.amonline.net.au/.../earth/volcanism.htm
• www.georesources.co.uk/volgen.htm
• mediatheek.thinkquest.nl/.../en/fullvolcano.htm
• http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/map_plate_tectonics_wo
rld.gif
• http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/tectonics/earth_struct
ure.jpg
• http://www.geo.brown.edu/People/Grads/abt/Tools/Seismology/SeismoIntro.htm
• http://justquikr.com/wp-content/uploads/2013/06/Rift-valley.jpg
• http://www.seismolab.caltech.edu/images/gallery/anatomy/image-6.jpg
• http://pubs.usgs.gov/fs/fs002-97/images/volcBMeyers.png
• http://climateswag.files.wordpress.com/2014/04/6ac18-veitable.jpg?w=500
Information
1. Codrington, S. (2005) Planet Geography, 3rd
edition, Solid Star Press
2. Waugh, D. (2002) Geography An Integrated Approach, Nelson Thornes
3. Waugh, D. (2003) The New Wider World, 2nd
Edition, Nelson Thornes
4. Microsoft ® Encarta ® Encyclopedia © 1993-2004 Microsoft Corporation