Structure Of The Earth GCSE Flashcards
Features of the earth
The core is the centre and its temperatures vary from 4400-6000 degrees
The mantle is made from silicon rock and the temperature range from 1000-3700 degrees
Outer layer is the crust
Continental crust is thicker but less dense
Oceanic crust is thinner but more dense
How do tectonic plates move?
Radioactive decay of elements in the mantle generates heat
The lower piece of the mantle becomes less dense and rises
As it moves up it begins to cool and begin to sink
The movements caused by the molten rock are convection currents
The movements causes drag on the bottom of the plates moving them
What are convergent plate boundaries?
When an oceanic plate meets a continental plate , the oceanic plate is forced under the mantle and destroyed .
Can often create volcanoes
When 2 continental plates collide they fold the ground up forming mountain ranges .
What are divergent boundaries?
Where 2 plates move away from each other , magma rises to fill the gap and will cool creating new crust
What are conservative plate boundaries?
Where 2 plates move sideways in the same direction at different speeds or the opposition direction. Crust is nor created nor destroyed .
How do volcanoes form?
In convergent plate boundaries the oceanic plate is melted and destroyed , magma rises through the cracks. These cracks are called vents .
At divergent boundaries the magma rises up to fill the gap created by the plates moving plates
What is a composite volcano?
Composite e,g mount Fiji
Occur at convergent plate boundaries
The subducted oceanic crust contains water . The water reacts with the magma creating gas causing the sub ducted crust to erupt.
The erupted andesitic lava contains a high silica content which makes it thick . The lava cannot flow very far so it forms a steep sided cone
What is a shield volcano ?
Shield volcanoes occur at divergent plate boundaries
They are not very explosive
The basaltic lava that it erupts is low in silica content so it flows fast and wide causing the volcano to have low sided wide volcanoes .
How do earthquakes occur?
Tension in the plates build
Eventually the plates jerk past each other
The movement sends out vibrations which causes earthquakes
What are shallow focus earthquakes?
Caused by tectonic plates moving near the surface of the earth between 0-70 km deep
What are deep focus earthquakes
Earthquakes that occur when subducted crust moves towards the centre of the earth . This occurs between 70-700km below the earths surface
How to predict the occurence of an earthquake
Lasers can monitor the movement of the plates
Vibrations can be monitored using a seismometer
Scientists can measure gas that has escaped the surface
How to detect the occurence of a volcanic eruption
Thermal imaging cameras detect temp changes around a volcano
Scientists analyse gases released from the volcano. If it is sulfurous gas then an eruption is likely to occur
Preparing for tectonic hazards
Emergency services are trained to to complete tasks in unsafe areas
Buildings can be specially designed to withstand earthquakes
Civilians are regularly drilled so evacuation is efficient
Goverments plan evacuation routes
Short term relief after disaster
Well prepared countries are able to:
Provide supplies for the people
Treat the sick
Recover dead bodies reducing the spread of disease
Provide the people with power and communications
