PHYSICAL - The Restless Earth Flashcards
What is the crust fractured into?
Tectonic Plates
The Mantle
A zone of molten Silicates and other minerals. Molten so it moves, the source of this is the Earths intence inner heat which sets up convection currents.
How thick is the mantle?
2,900km thick
What are the 2 types of crust?
Oceanic and Continental
What are the characteristics of Oceanic crust
- Denser
- Newer
- Thinner
What are the characteristics of Continental crust?
- Older
- Thicker
- Less dense
What are convection currents?
Heat currents in the molten magma that move the crust above very slowly
Why is the inner core solid?
The inner core is solid (despite temperatures of 3700°C_ because of the intense pressure there
Plate Margin
The edges of plates where 2 plates are either moving apart, colliding together or sliding past one another
What drives plate movement?
Convection currents
Why do convection currents determine the direction of plate movement?
Because slabs of crust fload like rafts on top of the mantle. Heat from within the earth causes the molten rock in the mantle to rise and fall in convecton cells.
These cause the plates to move either together, apart or along side eachother.
Name 3 plate boundries and their type
- San Adreas Fault - Conservative↑↑
- Mid-Atlantc Ridge - Constructive ← →
- Andes Mountains - Destructive → ←
Explain a Constructive plate boundry
Two plates move apart
↓
A ‘gap’ apears
↓
Lava escapes, usually as a gentle erruption
↓
Creates a mid-ocean ridge
Eg Mid-Atlantic Ridge (North American plate/Eurasian Plate)
Explain what happens at a Destructive plate boundry
An ocean crust moves towards a continental crust
↓Denser Oceanic crust is forced down or ‘subducted’
↓
Friction between the plates can cause earthquakes
↓
Friction also causes heat, which melts the ocean plate
↓
Hot magma rises to the surface in violent erruptions
Eg Andes (Nazca Plate and South America plate)
Explain what happens at a Constructive plate boundry
Two plates move apart
↓
A ‘gap’ apears
↓
Lava escapes, usually as a gentle eruption
↓
Creates a mid-ocean ridge
Eg **Mid-Atlanic Ridge **(North American Plate/Eurasian Plate)
Explain what happens at a Conservative plate boundry
Two continental plates move together
↓
They are equally dense, so neither can sink
↓
Sedimentary rocks between the plates are pushed up
↓
Earthquakes occur and fold mountains are formed
Eg **Himilayas **(Indo-Austrailian Plate/Eurasian Plate)
Explain what happens at a Collision plate boundry
Two plates try to move side by side
↓
Friction makes them stick, so movement is very difficult
↓
Pressure builds up steadily
↓
The pressure gets great, so a catastophic slip occurs
Eg **San Andreas Fault **(Pacific plate/North American Plate)
What is the earth divided into (plates?)
- 38 minor plates
- 14 major plates
- 52 segments in total
What are Fold Mountains?
Fold mountains are large mountain ranges where the layers of rock within them ave been crimled as they have been forced together.
How are fold mountains formed?
- Sediments accumulate in shallow seas or epressions known as geosynclines as rivers enter those areas
- This creates a sea or lake bed of layered sedimentary tocks as compression takes place
- Two plates move together because of convetion currents in the mantle
- This starts to crumple the rocks together
- Therocks start to form fold which have anticlines and synclines, which are pushed upwards to form fold mountains
- These mountains are then subject to erosion, weathering and mass movement
Anticlines (fold mountains)
The upward folds of sediment
Synclines (fold mountains)
Downward folds of sediment
Overfolds
When the fold are pushed over to one side forming an overhang
Human settlement in fold mountain areas?
- Valley floor - soils are fertile, deeper and more silty
- High population densitie are found in high regions of Colombia, Ecuador and Peru - rich, fertile, volcanic soils
- The highest settlements found in the Andes where rich mineral resources are present - Copper, Tin, Silver and Gold. They are well above the height of civilisation and owe existence entire to minerals.
Physical Problems of living in fold mountain areas
- Relief - high, steep, rocky outcrops, narrow valleys, little flat land for farming and setlements
- Climate - altitude increases the climate gets wetter and colder, percipitation falls as snow, short growing season and cultivation impossible at high levels
- Soils - stony, thin and infertile
- Accessability - infastructure exoensive to install, travel frequenty disrupted by avalanches and rock falls, high inland areas are accessible only by foot
Name the 4 landforms found at plate boundries
- Fold mountains
- Mid-ocean ridges
- Ocean tenches
- Types of volcano
What is an ocean trench?
Ocean trenches are deep water areas that run along a costline which had a destructive plate margin created by subduction, and mark the point where oceanic crust is being pushed under continental crust.
There is often quite a large section fo continental crust between this margin and the oceans edge, and sometimes a volcanic island arc, such as Japan and the Aleutian islands which can be found in between the trench and the continental shelf
What are mid-ocean ridges?
**Long ridges of mountains created by 2 plates moving apart at a contructive plate margin. **
Where these mountains rise above sea level islands like Iceland are formed.
What is a volcano?
Anywhere on te earths crust where magma escapes from the surface, over time magma is ejected and builds up to form a mountain