The Earth's structure is responsible for tectonic hazards Flashcards
What is the core?
Made up of dense rock containing iron and nickel alloys and is divided into a solid inner core and a molten outer one
How hot is the core?
Over 5000 degrees
How is the heat produced in the core?
Primordial heat left over from the earth’s formation
Radiogenic heat produced by the radioactive decay of isotopes
What is the mantle?
Made up of molten and semi-molten rocks containing lighter elements such a silicon and oxygen
What is the crust?
Even lighter than the mantle
Made of silicon, oxygen, aluminium, potassium and sodium
How thick is the crust under the ocean?
6-10km thick
How thick is the crust under the continents?
30-40km thick
How thick is the crust under the highest mountain ranges?
70km thick
What has new research suggested about the upper mantle and the crust?
It should be divided into the lithosphere and asthenosphere
What is the lithosphere?
Consists of the crust and the rigid upper section of the mantle
How thick is the lithosphere?
80-90km thick
Why is the lithosphere important?
It is divided into seven very large plates and a number of smaller ones
What are the seven plates in the lithosphere divided into?
Two categories - oceanic and continental
What is the asthenosphere?
Lies beneath the lithosphere and it semi-molten on which the plates float and move
What theory did Alfred Wegener publish in 1912?
The theory that a single continent existed about 300 million years ago called Pangea
What did Wegener theory state?
That the super continent (Pangea) had split into the two continents, where the two continents split again to form today’s continents
What were the two original continents after Pangea split in two?
Laurasia in the north and Godwanaland in the south
What Geological evident support Wegener’s theory?
Rock sequences in northern Scotland closely agreed with those found in Canada - must have been joined
Evidence of late-Carboniferous glaciation deposists found in South America, Antartica and India - must have been joined
What Biological evidence supports Wegener’s theory?
Fossil brachiopods found in Indian limestone are comparable with similar fossils in Australia
Fossil remains of the Mesosauras are found in South America and Southern Africa
What is ridge push?
Heating of rock - The hot molten magma that rises at a mid-ocean ridge heats the rocks around it.
Heated and expansion - As the asthenosphere and lithosphere at the ridge are heated, they expand and become elevated above the surrounding sea floor. This elevation produces a slope down and away from the ridge.
Rock cools and gravity causes the rock to slide away from ridge - However, as the newly formed rock ages and cools, it becomes more dense. Gravity then causes this older, denser lithosphere to slide away from the ridge, down the sloping asthenosphere.
Process happens again - As the older, denser lithosphere slides away, new molten magma wells up at the mid-ocean ridge, eventually becoming new lithosphere.
What is gravitational sliding?
The same thing as ridge push
What is convection?
Circulation of material caused by differences in density - less dense rises, more dense sinks
How do convection currents work?
Hot mantle rises upwards and comes into contact with Earth’s crust
As that material grows further apart from its heat source, it cools and therefore becomes more dense
It then sinks, forming a convection current
What drives convection?
The source of heat for convection currents are radioactive materials found in the Earth’s core
How does convection cause plate tectonics?
The motion of convection inside the earth, we see the same motion on the surface of the earth. This motion is connected to two processes
What is a divergent plate margin?
A tectonic boundary where two plates are moving away from each other and new crust is forming from magma that rises to the Earth’s surface between the two plates
What do oceanic divergent plate margins commonly form?
mid-ocean ridge, volcanic islands (which form as the plates move apart and a gap is produced, which molten lava rises to fill)
What happens at a continental divergent plate margin?
Continental plate is arched upwards from the convection current’s lift, pulled thin by extensional forces, and fractured into a rift-shaped structure. As the two plates pull apart, normal faults develop on both sides of the rift, and the central blocks slide downwards.
What do continental divergent plate margins commonly form?
Rift valleys, and Earthquakes occur as a result of this fracturing and movement
What is slab pull?
At a subduction boundary, one plate is denser and heavier than the other plate. The denser, heavier plate begins to subduct beneath the plate that is less dense. The edge of the subducting plate is much colder and heavier than the mantle, so it continues to sink, pulling the rest of the plate along with it. The force that the sinking edge of the plate exerts on the rest of the plate is called slab pull.
