Topic 1 Our Restless Planet Flashcards
Layers of the Earth from inner to outer
Inner core, outer core, mantle, crust
Characteristics of the inner core
1260 km thick
Made out of solid iron and nickel
6000°C
Densest layer because of immense pressure
Characteristics of the outer core
2200km thick
Made of molten iron and nickel
Denser than the mantle + crust
Characteristics of the mantle
2900km thick
Denser than the crust
Upper mantle is rigid
Lower mantle is semi-molten and zone of convection currents
Characteristics of the crust
Thinnest and lowest density layer of the Earth
What is the crust and rigid upper mantle called?
Lithosphere
Characteristics of continental crust
Thicker than OC (30-50km)
Less dense than OC
Made of granite
Characteristics of oceanic crust
Thinner than CC (7km)
Denser than CC
Made of granite
What are the four plate margins?
Constructive, destructive, conservative, collision
When does a collision margin occur?
Both plates (made of continental crust) are pushing upwards (converge), because neither plate is denser.
They create a range of fold mountains.
Very powerfu earthquakes can occur.
When do constructive margins occur?
Two plates diverging (moving away from each other) because of the upward plume of a convection cell.
Magma rose through the gap resulting in volcanoes.
Eruptions and earthquakes tend to be gentle.
When do conservative margins occur?
Two plates moving alongside one another in opposite directions or the same direction but one is moving faster than the other
Friction can cause the two plate plates to stick and pressure builds up , when the plate slip, the pressure is released in powerful earthquakes
When do destructive margins occur?
Two plate one of continental crust and one made of oceanic are converging. When the two plates meet, the oceanic plate subducts under the continental plate because it is denser.
This can cause fold mountains when the plates slip, it result in a powerful earthquake
The friction causes heat, causing the descending crust to melt, creating extra magma resulting in violent volcanic eruptions
What is a primary hazard?
A direct consequence
What is a secondary hazard?
An indirect consequence (primary hazard interacts with environment)
What is the Richter scale?
It assesses the amount of energy released by the earthquake and the intensity of shaking.
It is a logarithmic scale, which means that every point you go up on the scale sees a 30-fold (30x) increase in energy released.
What is the Mercalli scale?
It assesses at the impact of an earthquake by looking at things like the structural damage to burdings.
This is correlated with the earthquake’s energy, but is influenced by other factors too (e.g. building quality).
(May be more useful for aid workers)
What is a stratovolcano?
Tend to be found on destructive margins (e.g. Pacific Ring of Fire)
The lava is called acidic lava
Erupts less often because lava gets stuck in volcanic vents.
The result a volcano with narrow base and steep slopes. It is also sometimes called a composite cone, because the volcano is made up of layers of compressed ash and solidified lava.
What is a shield volcano?
Tend to be found on constructive margins ( e.g. Mid-Atlantic Ridge or the Hawaiian hotspot)
The lava is called basic lava
Eruptions are effusive (gentle) and more frequent.
The volcano that is created has a very wide base, but very gentle slopes.
What is acidic lava?
It has a high viscosity (sticky) and is 800°C
What is basic lava?
I has a low viscosity (very runny) and 1200°C.
What is the focus in an earthquake?
The point underground where the plates slip, and from where the seismic waves radiate outwards
What is the epicentre in an earthquake?
The point on the Earth’s surface directly above the focus; in theory, shaking here will be strongest
What is the fault line in an earthquake?
A fracture in the rock at a plate margin where pressure builds up if the moving plates stick
