Theme D: The Restless Earth Flashcards
Describe the density of continental crust
Less dense and light
Describe the thickness of continental crust
30-70km
Is continental crust young or old?
Old
List some characteristics of continental crust
Doesn’t sink into mantle easily
Hard to destroy
Describe the density of oceanic crust
Very dense and heavy
Describe the thickness of oceanic crust
5-10km
Is oceanic crust young or old?
Young
List some characteristics of oceanic crust
Sinks into mantle easily
Easily destroyed
What is the average speed of tectonic plates?
70mm per year
What is the place where tectonic plates meet?
Plate Margins
How do plates move?
Mantle heated by radioactive decay in core, setting up conversation currents due to hot magma rising towards the surface.
Here the magma cools and sinks down towards the core.
When magma rises near crust, if spreads out and drags tectonic plates apart.
When the magma sinks back down towards core it will drag tectonic plates closer together.
Name the 4 types of plate margin
Constructive plate margin
Destructive plate margin
Collision margin
Conservative margin
What is a constructive plage margin?
Where 2 plates are pulled apart and move away from each other. Magma wells up from the mantle to plug the gap causing new crust to be made. This rising magma pushes up the crust slightly at either side of plate margin forming a mid -oceanic ridge.
Describe earthquakes and volcanic activity at constructive plate margins
Weak earthquakes and gentle volcanic activity
What plate margin forms an oceanic ridge
Constructive plate margin
What is a destructive plate margin?
Where oceanic crust collided with another plate, causing crust to be destroyed.
It can happen when oceanic crust collides with continental crust or when oceanic crust collided with oceanic crust
Explain how crust is destroyed at an oceanic crust- continental crust margin
The two plates move towards each-other and collide. The heavy oceanic crust gets pushed down into the mantle, this is called subduction.
What is the area called where oceanic crust is being pushed into the mantle?
A subduction zone
What does subduction create?
An ocean trench
How do volcanoes happen at the oceanic crust continental margin?
Oceanic plate melts when subduction occurs due to intense heat.
The oceanic crust is full of water which means when it melts it will have a different chemical composition go the rest of the magma in the mantle. This creates a magma filled with gas bubbles from the evaporating water.
This makes the magma lighter and explode. It rises up and breaks through the surface which creates a volcano.
How do earthquakes happen at oceanic crust continental crust margins?
Plate movement isn’t smooth due to friction between rough surfaces. The plates may be stuck for years and pressure builds up. There is then a release of pressure between the plates suddenly which caused the plates to move, creating an earthquake on the surface.
How do fold mountains form at oceanic crust continental crust margins?
The continental plage is lighter than the ocean plate and can’t be subducted. The forces cause it to fold and buckle upwards which creates fold mountains
Explain how a volcanic island is formed at an oceanic crust continental crust margin
As the oceanic crust sinks into the mantle it melts, creating a less dense magma than the surrounding molten rock. This rises upwards and erupts on the crust. This creates a volcanic island. A chain of volcanic islands can be formed on the plate margin called a volcanic island arc
What is a collision zone?
A collision zone happens at a plate margin where continental crust meets continental crust.
The crust can’t be destroyed so both plates buckle and fold upwards, creating two sets of fold mountains which will overthrust one another.
This creates a very high and large range of mountains. There is little melting of plate material. Any magma that is created can’t make it through the high mountains to make volcanoes.
The magma that tries to rise through the mountains make a large intrusion into the mountain range called a batholith.
The magma cools down very slowly and fork a rock called granite.
This means the fold mountains have granite cores.
What is a conservative margin?
Where 2 plates try to slide pass eachother and friction causes them to get stuck. The pressure builds up and then there is a sudden movement between the 2 played which is felt as an earthquake on the surface.
What are the 3 types of rock?
Igneous
Sedimentary
Metamorphic
What is an igneous rock?
Magma that has cooled and solidified
How is granite formed?
The magma cools inside the earths crust, causing it to take a long time to solidify. This means there’s plenty of time for crystals to form, causing the crystals to be large. This makes a hard, crystalline rock called Granite
Is Granite intrusive or extrusive?
Intrusive
How is basalt formed?
If magma erupts on the surface the lava will solidify quickly. This causes there to be little time for crystals to form, causing the crystals to be form. Once the magma solidifies it creates a rock called basalt.
Is basalt intrusive or extrusive?
Extrusive
What type of rock are basalt and granite?
Igneous
Explain the formation of sedimentary rocks
Rocks worn away by weather and erosion produce tiny pieces of rock called sediments which are carried by rivers to the sea. These sediments are deposited on the sea bed which happens because the sediments loose energy as they enter the sea due to the sea moving at a slower speed than rivers.
These sediments accumulate on the sea bed and as more layers of rock fragments are deposited the more pressure put on the bottom layers of sediment. This causes air and moisture to be squeezed out from the sediments as they are compressed to form layers of rock called sedimentary rocks
What is sandstone made from?
Sand
What is shale made from?
Clay
How else can sedimentary rocks form?
From plant and animal remains
Chemicals left behind when water evaporates
How are fossils formed?
When plant and animal remains get trapped in the rocks but aren’t crushed by pressure of rock layers
What is limestone made from?
Layers of shells and skeletons of sea creatures
What type of rocks have bedding planes?
Sedimentary rocks
What are metamorphic rocks?
Rocks that have been changed by heat or pressure to a point where it is hard to see what rock they were originally.
How is marble made?
It was originally limestone however the limestone was subjected to heat and pressure causing the particles of the shell to crystallise by the heat and form marble.
Describe granite
Rough texture
Speckled colour
Describe basalt
Hard
Dark grey
Rough and heavy
Small glittery specks may be visible
Describe limestone
Grey , white or yellow
Contains fossils
Porous
Describe sandstone
Formed from grains of sand
No crystals
Rough
Hard
Describe slate
Dark grey
Smooth flat surface causing it to be impermeable
Describe marble
Pure white or swirls of colour through it.
Rough and grainy if not polished
What is an earthquake?
The shaking of the ground surface caused by a sudden movement of the earths crust
Where 3 main belts are earthquakes mostly found?
Around edges of pacific ocean
In an east - west line through Mediterranean sea, Himalayan mountains and SE Asia
Through middle of Atlantic ocean in a north - south line
Where do earthquakes mainly happen?
Plate boundaries
What type of pattern do earthquakes form?
A linear pattern
What is the place where the earthquake starts?
The focus
What are seismic waves?
Waves of energy released by a sudden movement in the crust
How do seismic waves move?
Outwards from the focus
What is the epicentre?
The point on the surface directly above the focus. It is where most deaths and description normally happen.
What happens as you get further away from the epi centre?
The damage gets less
Where do the strongest earthquakes happen?
Conservative margins & destructive margins
What measures an earthquake?
A seismograph
What is a seismogram?
A paper tracking of the seismic waves during an earthquake
What does the Richter scale do?
Measures the size of seismic waves during an earthquake
What are the main 2 physical impacts of an earthquake?
Liquefaction
Tsunamis
What is liquefaction?
The process that causes solid ground to turn into liquid mud. This happens because during an earthquake it brings water to the surface which mixes with the soul and changes into liquid mud.
What is a tsunami?
A large wave of sea water triggered by an underwater earthquake
Why do tsunamis happen?
The underwater earthquake sends seismic waves into the water which caused a surge of water to build up which travels towards the coastline
What speeds can a tsunami go?
500mph
What happens when a tsunami reachers shallow water near the coast?
It slows down and the top of the wave moves faster than the bottom which causes the sea to rise into a massive wave
