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Singapore Sec 4 Geography Notes
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Notes taken in Singapore Secondary 4 level on Weather and Climate
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Chapter 1 : Living with Tectonic HazardsInternal structure of the earth
Crust :
↳ 5 - 70km thick
↳ solid, made up of basalt and granite rocks
Mantle ( upper + lower ) :
↳ 2900km thick
↳ solid, 800°C - 3000°C, made up of solid rock that flows under ↑ temp and pressure
Core ( outer + inner )
O : 2100km thick, liquid
I : 1400km thick, solid
↳ 3000°C - 5000°C, made up of mostly iron and nickel
Asthenosphere : Upper mantle
Lithosphere : Crust + upper mantle
Tectonic Plates :
Oceanic :
↳ beneath deep ocean
,↳ 35 - 70km thick
↳ light rock ( eg : granite )
Continental :
↳ beneath land masses
↳ 5- 8km thick
↳ heavy & dense rock
Plate Tectonic Theory
Convection currents :
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.
2. This causes the plates to be dragged along and move away from each other.
3. The hot mantle material cools slightly and sinks, pulling the plates away from each other. This
causes the plates to diverge.
4. As it gets near the core, the sinking mantle material is reheated by the ↑ temp and the cycle
repeats, setting up a convection current.
Slab pull force :
1. Slab pull force occurs when a dense, sinking oceanic plate is pulled under a less dense
continental / oceanic plate. This process is called subduction.
2. As the plate subducts, it pulls the rest of the plate along. The subducting plate drives the
downward moving portion of convection currents.
3. The mantle material which is found away from where the plates subduct drives the rising
portion of convection currents.
Different plate boundaries :
, Plate boundary type Landforms Examples of plates involved Keywords
Divergent : - Mid oceanic ridge North American & Eurasian - Diverge
O-O - Volcanoes plates - Fractures
- Sea floor spreading
Eg : Mid-Atlantic ridge - Magma rising from the
mantle
Divergent : - Block mountains Australian & Pacific plates - Diverge
C-C - Rift valley - Tensional forces
Eg : Hutt Valley, New Zealand - Faults
- Middle section sinks
Convergent : - Oceanic trench Pacific & Philippine plates - Converge
O-O - Volcanoes & volcanic - Compressional forces
island arcs Eg : Mariana Trench - Denser oceanic plate
- Earthquakes subducts = oceanic trench
- Less dense oceanic plate
fractures
- Magma escapes from the
fault = underwater volcano
Convergent : - Fold mountains Indian & Eurasian plates - Converge
C-C - Compressional forces
Eg : Himalayas - Both plates too buoyant to
subduct = fractures
Convergent : - Oceanic trench Australian & Eurasian plates - Converge
O-C - Fold mountains - Denser oceanic plate
- Volcanoes Eg : The Sunda Trench subducts = oceanic trench
- Less dense continental
plate folds = fold mountains
Transform - Earthquakes Anatolian & Eurasian plates - Slide past each other
= vibrations in the crust
Eg : North Anatolian Fault - Stress is built up
Sketches of landforms :
Landforms :
Landform Characteristics / Shape Formation process
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