Tectonic hazards Flashcards
Describe the Earths structure.
The Earths internal structure is divided into layers: the core, mantle, and crust (continental and oceanic).
What is the crust?
The crust is broken into several major fragments called tectonic plates. Tectonic plates are rigid and can move very slowly, floating across the heavier semi-molten rock in the mantle. Continental plates are less dense but thicker than oceanic plates.
What is the inner core?
The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C.
What is the outer core?
The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel.
What is the mantle?
The mantle is the thickest section of the Earth at approximately 2,900 km. The mantle is made up of semi-molten rock called magma.
What causes tectonic plates to move?
One theory is called convection. Another theory is ridge push and slab pull.
Describe the process of ridge push.
Magma rises as the plates move apart at constructive plate margins.
The magma cools to form new plate material.
As it cools it becomes denser and denser and slides down away from the ridge.
This causes tectonic plates to move away from each other.
Describe the process of slab pull.
At destructive plate margins, the denser plate sinks back into the mantle under the influence of gravity.
It pulls the rest of the plate along behind it.
Describe convection currects.
The core is heated by radioactive decay, which causes magma to rise in the mantle and sink towards the core when it cools.
Convection builds pressure and carries plates with it.
There is only limited evidence of this so far.
What is the global distribution of earthquakes and volcanoes in relation to plate margins?
The distribution is not random.
They occur in narrow bands along plate margins.
Found on both land and in the sea.
Earthquakes are found at all 3 types of plate margins: constructive, destructive and conservative.
Volcanoes are found at constructive and destructive plate margins only.
There are anomalies as some occur in the middle of plates called ‘hot spots’.
What are the 3 types of plate margin?
Constructive, destructive and conservative.
What is the direction of plate movement at a constructive plate margin?
Diverging away from each other e.g. the Eurasian and North American plates.
how does a constructive plate margin work
What physical processes occur at a constructive plate margin?
Hot molten magma rises between the plates.
Tectonic plates move away from each other by ridge push and slab pull.
The magma cools to form a new plate.
On land rift valleys form, such as the East African rift valley.
Do earthquakes and volcanic eruptions occur at constructive plate margins?
Yes (usually small, not violent)
Volcanoes= shield volcanoes
What is the direction of plate movement at a destructive plate margin?
Converging towards each other e.g. the Pacific and Philippine plates
What physical processes occur at a destructive plate margin?
When tectonic plates converge, pressure builds between them. The rock eventually fractures, causing earthquakes.
When oceanic and continental plates collide, the denser oceanic plate is subducted under the continental plate into the mantle, where it melts.
Hot magma can rise through the lithosphere and erupts as lava through volcanoes.
Do earthquakes and volcanic eruptions occur at destructive plate margins?
Earthquakes (violent)
Volcanoes (composite)
What is the direction of plate movement at a conservative plate margin?
Sliding parallel past each other e.g. Pacific and North American plates
how does a conservative plate margin work
What physical processes occur at a conservative plate margin?
Pressure builds at the margin of the tectonic plates as they are pulled along behind a plate being subducted elsewhere (slab pull)
The rocks are not smooth and so they snag agaisnt eachother as they pass. this creates seismic waves.
As friction is overcome, the rock fractures in an earthquake.
Do earthquakes and volcanic eruptions occur at conservative plate margins?
Earthquakes
No volcanoes
Which plates experience a) earthquakes and b) volcanoes
a) Constructive, destructive, conservative
b) Constructive, destructive
