Restless Earth Flashcards
What is the density and rock type of the oceanic crust?
Density of 3.3 g/cm3
Solid basalt
What is the asthenosphere?
It is the upper mantle, below the lithosphere.
It has a density of 3.4-4.4(g/cm 2)
It is partially molten
What is the density and rock type of the continental crust?
2.7 g/cm3 solid granite
What is the lithosphere?
The uppermost layer of the earth. It is cool and brittle. It includes the mantle, and, above this the crust.
What is the order of the earths layers?
Ocean/land↘️ Crust➡️ Lithosphere Uppermost mantle↗️ Upper mantle ➡️ asthenosphere Lower mantle Outer Core Inner core
How fast do tectonic plates move?
Very slowly at 2-5 cm per year, on top of the asthenosphere.
What are the differences between oceanic and continental crust?
The continental crust is made of granite whereas oceanic crust is predominantly basalt.
Continental crust is thicker and oceanic crust is denser.
Most continental crust is 3-4 billion years old whereas oceanic crust is 180 million.
What is radioactive decay?
Some elements are naturally unstable and radioactive, atoms of these elements release particles from their nuclei and give of heat. This is called radioactive decay.
What are the parts of convection cells where heat moves towards the surface?
Plumes -these are concentrated zones of heat.
How does magma rise to form constructive plate boundaries?
Some plumes rise like long sheets of heat, forming the constructive boundary.
What does a plume shaped like a column of heat form? - give an example.
Theses form hotspots that can be in the middle of a plate, like Hawaii.
What movement do plumes cause?
Convection cells and currents that are caused by the rising of magma as it heats up near the core and consequently cools down away from the core, therefore beginning to sink in a circular current that causes plates to move at a similar rate to the magma below.
Why is the earths core so hot and what is it’s temperature?
The centre of the earth is over 5000°c because heat is produced by radioactive decay of elements such as uranium in the core and mantle.
How did continents form before the formation of plates?
All the land masses were together; forming a super continent called Pangea. When the boundaries formed the plates moved at a rate of 5cm a year.
Name the major plates.
Nazca American Eurasian plate Indo-Australian plate Antarctic plate
Name the four major plate boundaries.
Conservative margin
Collision zone
Constructive margin
Destructive margin
Explain, using examples what a conservative margin is.
A conservative plate boundary is when two plates rub past each other.
As plates rub past friction causes earthquakes, these are rare but destructive because the epicentre is shallow.
An example is the San Andreas fault line.
Explain, using examples what a collision zone is.
Collision zones are a type of destructive plate boundary.
It is when two continental granite plates collide; pushing up to form mountains.
Earthquakes happen on faults ( huge crams within the crust)
This forms mountain ranges like the Himalayas.
Explain, using examples what a constructive margin is.
When two plates move apart, magma rises through the gap.
It forms lava flows and shallow sided sheild volcanoes.
Earthquakes are caused by friction as the plates move, these are small and don’t cause much damage.
Iceland on the mid-Atlantic ridge
Explain, using examples what a destructive plate margin.
As a continental and oceanic plate are pushed together, the oceanic plate is subducted.
Sea water is dragged down with the volcano which erupts as steam making the volcanoes very explosive, also it makes the magma less dense so it rises through the continental crust.
Sinking oceanic crusts stick to the continental crust, when they snap a lot of energy is released.
As the oceanic crust sinks it melt forming magma called andesite.
An example is the Andes Mountains.-
Give an example of a conservative plate boundary and explain the threats from earthquakes and volcanoes.
The San Andreas fault
Up to a magnitude of 8.5 earthquakes
No volcanoes
Give an example of a constructive plate boundary and explain the threats from earthquakes and volcanoes.
Iceland on the mid-Atlantic ridge
Small 5.0 to 6.0 on the richer scale
Non explosive sheild volcanoes.
Give an example of a destructive plate boundary and explain the threats from earthquakes and volcanoes.
Andes mountains
Up to 9.5 on the richer scale
Very explosive, steep sided volcanoes.
These are composite volcanoes.
Give an example of a collision zone and explain the threats from earthquakes and volcanoes.
Himalayas
Up to 9 on the richer scale
Volcanoes are very rare
Give an example of conservative plate boundary and earthquake.
1994 San Francisco earthquake 6.9 on the richer scale Killing 67 1906 8.5 From San Andreas fault 2 miles offshore from San Francisco 700 killed 11 refugee camps
Give an example of destructive plate boundary and earthquake.
Kamchatka earthquake magnitude 9
Caused by Pacific plate sub ducting beneath the okhotsk plate
1737
Depth of 50km
Give an example of constuctive plate boundary and earthquake.
The mid Atlantic ridge
Discovered 1872
Epicentre for many earthquakes
Give an example of collision zoneand earthquake.
Brandi Arc Australian collision zone.
January 1987
The Brandi Arc is a double island formed by a collision zone.
