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[O] Geography(Pure) Smart Guides

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  1. Topic I: Coasts(Physical)

    1. How and why are coastal environments different and dynamic?
    5 Topics
  2. 2. Why are coastal areas valuable?
    4 Topics
  3. 3. How can we manage coastal areas in a sustainable manner?
    2 Topics
  4. Topic II: Living with Tectonic Hazards(Physical)
    4. Why are some areas more prone to tectonic hazards?
    2 Topics
  5. 5. What landforms and associated tectonic phenomena are found at plate boundaries?
    3 Topics
  6. 6. How do people prepare for and respond to earthquakes?
    3 Topics
  7. Topic III: Variable Weather and Changing Climate(Physical)
    7. Why do different places experience different weather and climate?
    7 Topics
  8. 8. What is happening to the Earth’s climate?
    5 Topics
  9. 9. Is the weather becoming more extreme?
    4 Topics
  10. Topic IV: Global Tourism(Human)
    10. How does the nature of tourism vary from place to place?
    2 Topics
  11. 11. Why has tourism become a global phenomenon?
    3 Topics
  12. 12. Developing tourism at what cost?
    2 Topics
  13. Topic V: Food Resources(Human)
    13. How and why have food consumption patterns changed since the 1960s?
    6 Topics
  14. 14. What are the trends and challenges in the production of food crops?
    4 Topics
  15. 15. How can the problem of food shortage be addressed?
    1 Topic
  16. Topic VI: Health and Diseases(Human)
    16. What are the global patterns of health and diseases?
    3 Topics
  17. 17. What influences the spread and impact of infectious diseases?
    3 Topics
  18. 18. How can we manage the current and future spread of infectious diseases?
    4 Topics
  19. Topic VII: Geography Skills and Investigations
    19. Map Reading
    11 Topics
  20. 20. Tourism Fieldwork
    1 Topic
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Why do tectonic plates move?

  1. Convection currents are movements of heat within the mantle. Material in the mantle is heated by the core, causing the mantle material to expand, rise and spread out beneath the plates.
  2. This causes plates to be dragged along and to move away from each other.
  3. Then, the hot mantle material cools slightly and sinks, pulling the plates along.
  4. The sinking mantle material heats up again as it nears the core and the whole process repeats.
  5. ‘Slab-pull force’ occurs when a denser oceanic plate is forced beneath a less dense continental plate in a process called subduction.
  6. As the rest of the plate subducts, it pulls the rest of the plate along. The subducting plate drives the downward-moving portion of convection currents.
  7. The mantle material which is found away from where the plates subduct drives the rising portion of convection currents.

DIFFERENT TYPES OF PLATE BOUNDARIES

[Divergent plate boundaries]

1. OCEANIC-OCEANIC Plate divergence

Mid-Atlantic Ridge. In the North Atlantic it separates the Eurasian and North American Plates. It is seen in a spectacular way in Iceland, near Pingvellir. Is also known as the Reykjanes Ridge.
  • Convection currents in the mantle cause the magma to expand, rise, and spread out beneath the plates, thus dragging the plates away from each other.
  • When two oceanic plates diverge, fractures are formed at the plate boundary.
  • Magma rises from the mantle through the fractures, cools and solidifies to form new seafloor. This process is called seafloor spreading.
  • Magma rises at the zone of divergence to create a ridge of new oceanic floor known as the mid-oceanic ridge.
  • At various points along the mid-oceanic ridge, magma builds up and solidifies to form undersea volcanoes. When these volcanoes grow in size and emerge above sea level, they are known as volcanic islands. Eventually, an arc of volcanic islands called the volcanic arc is formed.
  • Example: Mid-Atlantic ridge

2. CONTINENTAL-CONTINENTAL Plate divergence

Great Rift Valley (East African Rift) panoramic scenic view, landscape of continuous geographic trench. Kenya, Africa
  • Convection currents in the mantle cause the magma to rise, thus dragging the plates away from each other.
  • When two continental plates diverge, they are stretched, causing fractures to form at the plate boundary.
  • The land in between the two continental plates sinks, forming a depression known as the Rift Valley.
  • Example: East African Rift Valley (Nubian section of African plate and Somalian section of African plate)

[Convergent plate boundaries]

1. OCEANIC-OCEANIC Plate convergence

  • Convection currents in the mantle cause the magma to rise, cool and sink, dragging the plates towards each other.
  • When two oceanic plates converge, one subducts under the other due to differences in density.
  • A subduction zone forms, creating a depression in the seafloor called the oceanic trench. At the same time, the sinking crust of the denser plate melts, forming magma.
  • The magma rises through the crust to form undersea volcanoes. When the undersea volcanoes grow in size and emerge above sea level, they are called volcanic islands.
  • Eventually, an arc of volcanic islands called the volcano arc is formed.
  • Earthquakes might occur at the boundary between two plates. This is due to friction created between the moving rock masses when a plate subducts under another.

2. CONTINENTAL-CONTINENTAL convergence

Evening colored view of Mount Everest from Gokyo valley
  • Convection currents in the mantle cause the magma to rise, cool and sink, thus dragging the plates towards each other.
  • When two continental plates converge and collide, the crusts are compressed and cause massive folding.
  • Folding of the crusts forms a range of fold mountains.

3. OCEANIC-CONTINENTAL convergence

Andes in the Nazca Plate. Peru.
  • Convection currents in the mantle cause the magma to rise, cool and sink, thus dragging the plates towards each other.
  • When an oceanic plate converges with a continental plate, the denser oceanic plate subducts under the less dense continental plate.
  • A depression called the oceanic trench is formed at the subduction zone while the continental plate buckles and folds, forming fold mountains.
  • At the subduction zone, the sinking plate causes the mantle material above it to melt, forming magma. The magma also rises through the crust, giving rise to volcanoes and volcanic eruptions

[Transform plate boundaries]

  • Plates slide past each other along transform plate boundaries. This movement results in the formation of a transform fault. In the process, tremendous stress builds up and is eventually released, often in the form of violent earthquakes
  • Eg. In the last 70 years, a major earthquake has occurred every 10 years on average along the Anatolian Fault, putting a population of more than 10 million people in considerable danger.