Tectonic plates and Earth structure (1) Flashcards
What type of structure does the Earth have?
Layered
Name and describe what it at the centre of the Earth
The Inner and Outer CORE
- Ball of solid and liquid iron and nickel
- Very dense at the centre, becomes less dense further out
- Temperature ranges from 4400-6000C
Name and describe what is found around the core
The MANTLE
- Made up of silicon based rocks
- The part of the mantle nearest to the core is quite rigid
- The layer above this is the ASTHENOSPHERE - it id semi-molten
- Temperature ranges from 1000-3700C, cooler towards the Earth’s surface
Name and describe the solid outer layer of the Earth
The CRUST
- Also made of silicon based rocks
- Two types of crust: continental and oceanic
Continental crust: thicker and less dense
Oceanic crust: thinner and more dense
- Divided into slabs called tectonic plates
Why do tectonic plates move?
Due to Convection Currents
(1) Tectonic plates float on the mantle
(2) Radioactive decay of elements in the mantle and core generates heat
(3) When lower parts of the asthenosphere heat, they become less dense and rise
(4) As the reach the top, they become cooler and more dense, slowly sinking
(5) Circular movements of semi-molten rock are Convection currents
(6) Convection currents in the asthenosphere create drag on the base of tectonic plates, causing them to move
Name the 3 types of plate boundaries
Convergent (destructive)
Divergent (constructive)
Conservative
Describe Convergent boundaries
- Where 2 tectonic plates move towards each other
- Oceanic plate meets a Continental plate, the denser Oceanic plate is forced downwards into the mantle and destroyed, creating COMPOSITE CONE volcanoes and ocean trenches
- 2 Continental plates collide, folding the ground upwards, creating mountain ranges
Describe Divergent boundaries
- Where 2 tectonic plates move away from each other
- Magma (molten rock) rises from the mantle to fill the gap, forming new crust and SHIELD volcanoes
Describe Conservative boundaries
- Where 2 tectonic plates move sideways past each other, or moving in the same direction at different speeds
Name the 2 types of volcanoes
Shield
Composite cone
Describe Shield Volcanoes
- Occur at hotspots or divergent boundaries
- Not very explosive
- Erupt BASALTIC lava which has a low viscosity. It flows quickly over a wide area, forming a low, gentle-sided volcano
Describe Composite cone volcanoes
- Occur at convergent boundaries
- Subducted oceanic crust contains lots of water, which reacts with magma, creating gases, causing the subducted crust to erupt
- Explosive eruptions that deposit a layer of ash
- Erupt ANDESITIC lava which has a high viscosity. The lava can’t flow far, forming a steep-sided cone
What is a Hotspot? + and how are they formed?
Places where magma rises through the crust
- They occur where a plume of hot magma from the mantle moves towards the surface, causing an unusually large flow of heat from the mantle to the crust
- Sometimes, the magma can’t break through the crust, so an eruption, forming a volcano
- Hotspots remain stationary over time, but the crust moves above them, which can create chains of volcanic islands eg. Hawaii
What happens at Convergent plate boundaries?
- Oceanic plate goes under Continental plate as it is more dense
- Oceanic plate moves into the mantle, where it is melted and destroyed
- A pool of magma forms, which rises through cracks in the crust called vents
- The magma erupts onto the surface, forming a volcano
What happens at Divergent plate boundaries?
- The magma rises up into the gap created by the plates moving apart, forming a volcano
What is a subduction?
When the Oceanic plate is forced beneath the Continental plate
Name some methods of predicting Earthquake hazards
- Lasers to detect the movement of tectonic plates
- Vibrations in the Earth’s crust can be monitored using seismometers
- Rocks will crack and expand due to high pressures before an earthquake
- Scientists can measure gases (eg radon) that escapes from cracks in the crust
Name some methods of predicting Volcanic hazards
- Thermal imaging can detect changes in temperatures before an eruption
- Tiny earthquakes and changes in shape of the volcano means eruption is more likely
- Scientists can analyse the gases escaping from a volcano - they emit sulfurous gases before an eruption
Name some ways in which (developed) countries can use Long-Term planning to prepare for a Tectonic hazard
- Emergency services can train for disasters and prepare to save people from collapsed rubble, set up shelters etc
- The government can educate people on what to do in the situation of a disaster
- Evacuation routes can be planned before - reducing the death toll as more people escape
- Emergency supplies can be given out on a large-scale to ensure people can survive after
- Use strong building materials designed to withstand earthquakes or special foundations that absorb seismic energy to ensure buildings don’t collapse
Name some ways to suggest why Short-Term Relief in needed after a disaster
- Recovering dead bodies prevents the spread of disease
- Rescuing people under collapsed rubble can save more lives
- Provide food, drink and shelter to evacuated people
- Treat people who have been injured to prevent more deaths
- Provide temporary supplies (eg gas, electricity) to affected areas
Why do Earthquakes happen?
They are caused by tension that builds up at all 3 plate boundaries
- Plates eventually jerk past each other, sending out shockwaves (vibrations)
- They are measured on the moment-magnitude scale - measures energy released
What are Shallow and Deep focus earthquakes caused by?
Shallow: Tectonic plates moving at or near the surface (0-70km below the surface)
Deep: Crust that has previously been subducted in the mantle moves towards the centre of the Earth, heating up/decomposing (70-700km below the surface)
- In general, deeper earthquakes do less damage at the surface than shallow ones as the waves from deeper ones have to travel through more rock, reducing their power
How can Earthquakes cause Tsunamis and which earthquakes cause more damage?
Tsunamis are a series of large waves caused when huge amounts of water gets displaced
- Underwater earthquakes cause the seabed to move, which displaces water
- Waves spread out from the epicentre of the surface (above the focus)
- Shallow-focus earthquakes displace more water, increasing the size of the tsunami
- Waves can travel very fast, so hit the shore without much warning - vulnerable
