The Restless Earth Flashcards
What is the structure of the Earth? Give a description of each part.
What are the differences between the continental and oceanic crust?
Why do plates move?
Convection currents from the core travel through the mantle and when it reaches the crust, it changes direction and travels beneath the plates dragging them with it. As they have been away from the core for so long, they cool and sink back.
What are the type of boundaries determined by?
The way they are moving
What are the differences between the constructive, destructive, conservative and collision plate boundaries?
Explain what happens at a constructive boundary with the aid of diagrams.
- Convection currents from the core travel through the mantle and they drag the Eurasian and North American plates away from each other.
- The two plates moving away from each other create the Mid Atlantic Ridge.
- This is due to a weak point forming when the oceanic plates are dragged causing the plates to be pushed above.
- The magma coming from the mantle oozes through the weak point and slowly reaches the Mid Atlantic Ridge and causes the lava to be released gently creating an underwater volcano.
- This builds up forming new material creating a shield volcano as a volcanic island which is gentle.
Explain what happens at a conservative plate boundary.
Convection currents from the core travel through the mantle and drags the plates past each other in opposite directions. However, the movement is not smooth due to friction and the plates locking each other. Pressure is built up and finally released as a jolt. for San Francisco, the North American plate and the Pacific plate moved in similar directions but at different rates and this caused the 1989 earthquake on the San Andreas Fault.
Explain what happens at a collision plate boundary.
Convection currents from the core travel through the mantle and drag two continental plates towards each other to collide. As the continental plates are less dense they can’t sink so crumple to form fold mountains. Earthquakes are common as the movement is not smooth but no volcanoes as magma cannot escape from mantle. For the Himalayas, the Indo-Australian and Eurasian plate move towards each other.
Describe an ocean trench.
It’s a long, narrow, V-shaped extra deep part of the sea. Found at the subduction zone of a destructive boundary. Some are around 6 miles deep.
What’s an ocean trench’s location?
At a destuctive boundary where oceanic plate subducts continental, particularly around ‘The Ring of Fire.’
What are the possible human uses of ocean trenches?
- Increased depth causes greater pressure, less light and colder temperatures so hard to explore
- Potential for different species of fish and sealife adapted to the ecosystem
- These may be potential for exploration for oil or gas drilling
Explain what happens at a destructive boundary with the aid of diagrams.
- Convection current from the core travel through the mantle therefore passing the heat from the core through the mantle.
- When the convection currents reach the oceanic and continental crust, they change direction and travel beneath the plates dragging them towards each other.
- The continental plate crumples to form fold mountains as it is pushed.
- A subduction zone is created due to the oceanic plate being denser than the continental plate and therefore sinking below it.
- In the subduction zone, an ocean trench is created since the oceanic plate has slid under the continental plate.
- Friction is created between the oceanic and continental plate as they rub against each other.
- The pressure created between the two plates builds up and is eventually released as a jolt.
- Due to the broken, melted pieces of the oceanic crust and the magma in the mantle having different densities, the pieces of crust have a lower density so try to find a weakness in the continental plate.
- After finding a weakness, the magma rises from the chamber out of the vent creating a volcano.
Describe fold mountains
Are a ridge of highland formed when continental crust buckles due to the pressure at the plate boundary.
What are the three theories stating how fold mountains are formed?
- At destructive boundary
- At collision boundary
- In a geosyncline
Explain how fold mountains are formed in a geosyncline.
A large depression in the continental crust creates a sea and when this happens, rivers deposit their load as sediments into depressions called geosynclines. Gradually, these sediments become compressed into layers as more sediments are deposited, this soon forms sedimentary rock such as sandstone and limestone. Due to the continued compression from the plate movement, the sedimentary rocks are forced upwards into a series of folds and crumple to create fold mountains. Sometimes the rocks are foled upwards as anticlies or downwards as synclines. Eg. the Alps
What is the case study for a fold mountain at a destructive boundary?
Andes
What is the location of the Andes?
West side of South America, at a destructive boundary and the plates are Nazca (oceanic) and South American (continental)
What are the uses of the Andes?
- Terracing
- Mining
- Hydroelectric power
- Tourism
What is done for terracing on the Andes?
- Terracing of steep slopes to create flat land for growing potatoes. Substistence farming (growing enough for the family) as markets are too remote to reach and difficult transport. Increases infiltration reduced soil erosion.
- Llamas used for transportation, meat, milk and wool. Thick coats to cope with the cold temperatures at high altitude.
What is done for mining on the Andes?
- Peru has the largest gold mine in the world. The jobs mean settlements grown abd more services are being provided. The open pit method with dynamite and cyanide is destroying the environment.
What is done for hydroelectric power on the Andes?
- Steep slopes and narrow valleys make it perfect for hydroelectric power schemes. The turbines are turned by fluctuating discharge. The melted snow causes high discharge in the upper course however this then decreases due to low precipitation in the summer.
What is done for tourism on the Andes?
- There are physical attractions such as mountain peaks, volcanoes, glaciers and lakes, forest and tropical jungle, orchids and species of birds. The human attraction is the 4 day trek, “The Inca Trail” and historic ruins.
How can we classify a volcano through its frequency?
- Active
- Dormant
- Extinct
What is meant by active?
Volcano that has erupted and it’s usually taken 20 years and can erupt again.
eg. Mount St Helens (after 1980), USA
What is meant by dormant?
Volcano that has erupted in the last 2000 years but not recently (in the last life time) - 80 years and can erupt again. Dangerous because you don’t know when.
eg. Mount St Helens (before 1980), USA
Give the differences of basic and acid lava.
What are the differences between a sheild and composite volcano?
How are supervolcanoes formed?
- Convection currents from the core travel through the mantle and cause magma to escape from its magma chamber. However this is unable to escape due to the main vent being blocked so the pressure builds up gradually causing the magma to rise up and cause a large bulge in the crust on the surface.
- The pressure then forms cracks on the crust and thi results in ash and gas erupting.
- As more and more cracks form into vents there’ll be nothing to support the magma chamber so it collapses, creating a caldera.
What are the differences between the characteristics? Give a comparison of the scale. Give the advantages and disadvantages of both.
