Plate tectonics Flashcards
Whats the crust made up of?
Oceanic crust:
- Thinner and denser.
- Found below oceans and bottom of continental crust.
Continental crust:
- Thicker, less dense
- Forms land masses.
Description of the mantle:
Upper mantle:
- Mostly solid.
- Some areas molten due to convection currents.
Lower mantle:
- Both semi-molten and solid depending on convection currents.
Description of the core and the internal energy source?
Outer core:
- Semi-molten and molten due to the heat.
Inner core:
- Solid.
- Highly radio-active due to the decay of uranium.
- Decay creates a hot internal energy source and subsequent convection currents throughout.
Whats the plate tectonic theory?
- Radio active decay = high temperatures
- Convection currents heat and melt outer core and mantle which creates magma.
- Magma through convection currents melts the upper mantle and crust.
- Crust heats and expands = ridge push and magma pushed out.
- Magma cools becomes denser/ heavier than existing rock pulls down slope= gravitational sliding
- Continues, new rock now heavier than mantle so sinks and pulls plate with it, subduct below lighter plate = slab pull.
What are the two previous plate tectonic theories?
Pangea and continental drift:
- Wegener believed continents had moved and that they were once joined together.
Sea floor spreading:
- Hess found oldest rocks of the ocean where nearer to land while newest were in the middle, believed it was spreading from the middle.
- Confirmed by paleomagnetism, when the earths magnetic field changes magnetite aligns itself with the magnetic north at time.
What are the 3 main plate boundaries (See diagram)?
- Destructive plate boundaries (Plates move together)
- Convergent plate boundaries (Move next to each other)
- Constructive plate boundaries (Move apart)
What are earthquakes?
Most commonly where plate movement is trying to happen but cannot so friction builds up along the boundary. Eventually boundary moves and earthquake occurs at the focus.
Also formed due to magma plutons rising through the rock.
Whats the epicentre and focus of the earthquake?
- Begins at the focus and the shock waves produced radiate from this point.
- Epicentre is where the seismic waves first hit earths surface and are felt the most due to highest energy.
- Waves lose power as move from the epicentre.
Types of seismic waves?
P-Waves:
- Arrive first and are the weakest.
- Travel through solids and liquids by moving horizontally.
S-Waves:
- Only travel through solids but are much stronger.
- Move in a vertical direction.
Rayleigh waves:
- Through both solids and liquids.
- Have a rolling motion and are the most damaging.
What are the forms of seismic hazard?
- Earthquake (P)
- Shockwaves (P)
- Tsunami (S)
- Liquefaction (S)
- Landslides (S)
What is a triggered earthquake and whats an aftershock?
Triggered earthquake:
- Earthquake as a result of the effects of the original earthquake outside of the immediate aftershock zone.
Aftershocks:
- Smaller earthquake/ shaking that follows the main earthquake in the same area as the original shock.
How predictable are seismic events and warning signs?
Usually able to predict where they will occur through looking at where haven’t recently occurred but there is no way to exactly predict where or when it will occur.
Warning signs are:
- Higher water table levels
- Variations in temperature
- Behaviour of animals
- Seismo- electromagnetic precursor
How are earthquakes measured?
- Seismographs record the ground motion from seismic waves.
Why does a tsunami form?
- Earthquake which causes the lighter plate to rebound.
- Debris from a volcano displaces water.
- Volcano debris builds up to eventually create a landslide which displaces water.
Characteristics of a tsunami?
- In open ocean wave hardly detectable- 30 to 50cm.
- 100 to 150km wavelength in open ocean and they travel much quicker.
- At impact travelling at around 30-50km/h and reach up to 15m.
- Water recedes before tsunami arrives to fill vid created on sea floor.
