Plate Movement

Question 1

Describe the structure of the earth

Answer 1

At the centre of the earth is the core which is split into the inner and outer core. the inner core is a solid ball containing lots of iron and nickel whereas the outer core is semi-molten but also contains a lot of iron and nickel
Around the core is the mantle which is mostly made of silicate rocks. The part nearest the core is quite rigid, the layer above this is called the asthenosphere which is semi-molten and the very top bit of the mantle is rigid.
The outer layer of the earth is called the crust and together with the top part of the mantle make the lithosphere. Continental crust is thick and less dense and oceanic is a thinner crust which is denser.

Question 2

What is the plate tectonics theory?

Answer 2

The lithosphere is divided into lots of slabs called tectonic plates which are moving due to convection currents in the asthenosphere. convention currents are caused by heat in the core an mantle from radioactive decay, friction and heat from the big bang.
when lower parts of the asthenosphere is heated it becomes less dense and starts to rise, as they move towards the top they cool down becoming denser and start to sink.
The convection currents create a drag on the base of tectonic plates causing them to move. Ridge push is the process of the plates being pulled apart and slap pull is the movement of plates being dragged towards each other.

Question 3

Describe the process of sea floor spreading

Answer 3

Convection currents drag plates causing them to diverge, magma rises up to fill the created gap and the cools to form new crust. Over time the new crust is dragged apart and even more new crust forms between it. if this is happening at a plate margin under the sea the sea floor gets wider and structures called mid-ocean ridges are created on either side of the margin.

Question 4

What is the evidence for continental drift? (4)

Answer 4

Geology
- areas of South America and Africa have rocks the same age and composition
- age and rock type distribution matches up in same mountain ranges - Scotland, Norway, Sweden and Finland are similar to North America
- so they must have formed under the same conditions in the same place in order to be so alike.
Fossil records
- By fitting land masses together fossil distributions can be matches - fossil of Lystrosaurus is found in Africa, India, Antarctic and Australia - it is very unlikely that these species migrated across thousands of miles of water of that they evolved in different places
Living species
- earth worms in the family of Magascolecidae are found in New Zealand, parts of Asia and North America suggesting that the continents were once joined
Climatology
- there is evidence that the past climates of some continents were similar even though they are thousands of miles apart today
- there are similar glacial deposits in Antarctica, Africa, South America, India and Australia fitting then together suggest they were once joined close to the south pole
- large coal deposits have been found in tropical conditions in North America and parts of Europe suggesting they were once closer to the equator

Question 5

What is a destructive plate boundary?

Answer 5

Where two plates are moving towards each other

Question 6

Explain what happens at a destructive boundary with a oceanic and a continental plate

Answer 6

Subduction
The denser oceanic crust gets subducted under the continental crust forming a deep sea trench to mark the point where the plate is forced under.
Fold mountains form where the plates meet as the sediment accumulated on the continental crust is folded upwards along the edge of the continental crust.
Friction between the two plates heat the oceanic plate causing it to melt into magma. The magma is less dense and will rise back to the surface to create volcanoes.
Along the line where the plates slide past each other pressure builds up and creates an earthquakes when the energy is released.

Question 7

Explain what happens at a destructive plate boundary with two oceanic plates

Answer 7

Subduction
the denser of the two oceanic crust will be subducted forming a deep sea trench and triggering earthquakes and volcanic eruptions. The volcanic eruptions that are underwater will create a cluster of islands that sit in a curved line called island arcs.

Question 8

Explain what happens at a destructive boundary with two continental plates

Answer 8

Collision
Neither plate is subducted so no volcanoes are formed , the two plates push against each other to create fold mountains from accumulated sediment. the pressure between the two plates can build up to cause earthquakes

Question 9

Explain what happens at a constructive plate margin

Answer 9

Constructive margins occur when two plates are moving apart. the mantle is under pressure from the plates above which release pressure when they move apart causing the mantle to melt and create magma. The magma is less dense so it rises and can erupt to form a volcano.
Some parts of the plate move faster than others which causes pressure to build up, which may cause fault lines and earthquakes.
Mid-ocean ridge are formed when there is two oceanic plates and rift valleys form where there is two continental plates

Question 10

Explain what happens at a conservative plate boundary

Answer 10

Conservative plate margins occur when two plates are moving past each other. They often get locked in places and pressure builds up. This causes them to jerk past each other releasing energy as an earthquake.

Question 11

What is Palaeomagnetism?

Answer 11

Palaeomagnetism - the study of the earths magnetic fields

• once ever 200,000 years the Earths magnetic fields reverses polarity causing the magnetic mineral in the crust to align with the new polarity
• this creates strips of aligned material with normal polarity and reverse polarity showing that older crust lies further away from the mid-ocean ridge suggesting the plates are moving apart.

Question 12

Explain the formation of YOUNG FOLD MOUNTAINS

Answer 12

Example - The Himalayas
Form from the accumulation of sediment on continental crust which is folded upwards to create a mountain.
Continental - Oceanic
Sediments on the sea floor settle into depressions to become sedimentary rock
Continental - continental
layers of sedimentary rock push up against each other the resistance causes the sediment to rise.
No volcanoes but deep focus earthquakes

Question 13

Explain the formation of RIFT VALLEYS

Answer 13

Example - East African Rift Valley
Where plates diverge beneath land rising magma causes continental crust to bulge and fracture into fault lines. As two continental plates move apart the crust between parallel faults drop down to form rifts

Question 14

Explain the formation of OCEAN RIDGES

Answer 14

Example - Mid-Atlantic ridge where the Eurasian and North American plate are moving apart
Where diverging plates are under water a mid-ocean ridge forms. The sea floor is uplifted as convection currents cause magma to rise at the weakness of the oceanic crust. As the plates move apart new crust is forced up by the cooling of the magma. Underwater volcanoes can erupt along mid-ocean ridges and they can build up to be above sea level

Question 15

Explain the formation of DEEP SEA TRENCHES

Answer 15

Example - Marianas trench or Peru-Chile trench
A very deep trench in the sea formed when a denser plate is subducted at a destructive boundary, marking the subduction zone. It can be between an oceanic and continental or two oceanic pates which is very rare. Hundreds of KM long and up to 11KM deep. Usually parallel to an island arc.

Question 16

Explain the formation of Island Arcs

Answer 16

Marianas islands
Found opposite deep sea trenches where volcanic eruptions occur under the ocean, cluster of island in an arc shape. Usually the result of the subduction of one oceanic plate under another.
The oceanic plate is saturated with water which lowers the boiling point of the mantle. The plate melts to form a magma chamber, the magma ascends to form an arc of volcanoes parallel to the subduction zone.

Question 17

What are hotspots?

Answer 17

Hotspots are places where a plume of magma, which can be up to 11km wide, rises from the mantle punching a hole through the lithosphere and crusts, and erupts on the surface. A plume is an upwelling of abnormally hot rock within the earth’s mantle which can partly melt when it reaches shallow dept. Hot spots form above the plume and magma generated by the hot spot rises and produces active volcanoes away from plate boundaries.
There is thought to be 125 hotspots that have been active in the last 10 million years all located away form any plate margins.

Question 18

Explain the formation of island chains

Answer 18

The magma plume remains stationary but the movement of the crust above it causes a chain of volcanoes to form. As the crust moves away form the hotspot the part becomes less volcanically active. They are usually associated with intense volcanic activity and eruptions of basaltic lava. The Hawaiian islands are an example of an island chain made form a hotspot. The Hawaiian hot spot has been active for at least 70 million years producing a volcano chain that extends 3.750 miles across the NW pacific ocean. The hot spot occurs in the middle of the Pacific plate.

Question 19

What is a volcano?

Answer 19

A volcano is an opening or rupture in a planet’s surface or crust which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface

Question 20

How does silica and the type of lava affect volcanoes and eruptions?

Answer 20

If silica content in lava is high, rhyolitic and andesitic, the lava is thick causing steep sided volcanoes and large eruptions. The silica content is determined by the distance that the magma has travelled through the lithosphere and crust. High levels of silica have greater gas pressure which lock gas bubbles in making explosions more violent.

Question 21

At constructive boundaries what type of volcanic activity and lava is found?

Answer 21

Shield and fissure volcanoes
Frequent eruptions and for long periods
Basaltic lava - low viscosity so flows easily, eruptions aren’t violent as gas can escape easily

Question 22

At destructive boundaries what type of volcanic activity and lava is found?

Answer 22

Explosive acid volcanoes but none at collision zones
Dome volcanoes and Caldera
Eruptions occur every once in a while and are short lived.
Andesitic and rhyolitic lava, high viscosity so flows less easily creating steep sided volcanoes. Gases cannot escape easily so pressure builds up because of the lava blockages until they are cleared causing violent eruptions

Question 23

At conservative boundaries what type of volcanic activity and lava is found?

Answer 23

No volcanoes

No lava

Question 24

At hot spots what type of volcanic activity and lava is found?

Answer 24

Shield volcanos

Basaltic lava

Question 25

What are intrusive features?

Answer 25

Intrusive igneous features are those created below the ground where magma is intruded into the rock structures where it solidifies before it reaches the surface. Intrusive features are made from igneous rock with large crystals as the magma cools slowly

Question 26

What are Batholiths?

Answer 26

large masses of intrusive rock, most commonly granite. They were formed from huge masses of magma that cooled slowly in the earths crust. Subsequent erosion of overlying rocks has exposed batholiths as large masses of resistant rock on the surface. An example is the Sierra Nevada batholith in California.

Question 27

What are Dykes and Sills?

Answer 27

Small-scale igneous intrusions. Dykes are think vertical intrusions which have formed as magma rising has slowly cooled after intruding into cracks. A large number of dykes occur in the Inner Hebrides on the island of Mull and Skye.
Sills are horizontal sheets of magma which often create cliffs as the igneous rock is harder than the surrounding rocks. The Great Whin Sill in northern England forms steeps cliffs at High Cup Nick in Cumbria and a section of Hadrian’s wall.
Sills and Dykes are found in Jersey at portlet bay

Question 28

Where does minor forms of eextrusive activity occur?

Answer 28

In places that are geothermal. They need key ingredients including a heat source, groundwater supply, porous rock and a rock structure that forms a plumbing system containing sufficient pressure

Question 29

Extrusive activity

Geysers

Answer 29

Examples - Strokkur, Iceland and Old Faithful, Yellowstone
Geysers are hot springs that periodically erupt when the pressure has built up enough to force water out of the ground. The source of heat is from rocks above magma which heats the water in surrounded porous rock. As the water is heated it rises and pressure builds up in the vents. The pressure increases the boiling point and eventually turns water in the chamber into steam and erupts through the hot spring above. A period of recharge is required after for the water to return to the chamber.

Question 30

Extrusive activity

Hot springs

Answer 30

Examples - Rio Hondo, Argentina and North Island, New Zealand
Hot springs are places where groundwater emerges to the surface. The temperature of he springs vary from around 20 degrees to 90 degrees. The geothermal heat makes the water rise within fractures in the rock until it pools on the surface.

Question 31

Extrusive activity

Boiling mud

Answer 31

Examples - Yellowstone and Iceland
Mud pools form where steam an gas rise up to the surface. The acidic gases attack the surface rock forming clay which mixes with the water t produce hot muddy pools.

Question 32

Type of volcano - Dome volcano

Answer 32

Examples - Puy de Dome in France
Rhyolitic and Andesitic lava
Found at destructive margins
Steep sides due to the silica content of the lava and the viscosity. This means that it cant flow very far before it cools and hardens.
Eruptions are violent because the silica locks gas bubbles in the magma which increases the pressure.

Question 33

Types of volcano - Caldera

Answer 33

Example - Aira Caldera in Japan
Rhyolitic and Andestic lava
Found at destructive margins
Steep sides due to more viscous lava, rhyolitic lava is acidic and has a very high silica content.
It has a large open creator because rhyolitic lava is so explosive that the summit can be blown off in the process.

Question 34

Types of volcano - Shield volcano

Answer 34

Example - Mauna Loa in Hawaii
Basaltic lava
Found at constructive margins or hotspots
Gently sloping sides due to the low viscosity of basaltic lava which can flow for longer before it cools and hardens.

Question 35

Types of volcano - Fissure volcano

Answer 35

Example - Laki fissure system in Iceland
Basaltic lava
Found at constructive margins
Elongated cracks in the surface of the crust, as the plates move apart the basaltic lava is able to rise through the crust, as the plates move apart the basaltic lava is able to rise through the cracks.

Question 36

Types of volcanic eruptions - Plinian

Answer 36

Example - AD 79 eruption that buried Pompeii and Herculaneum
Magma is highly viscous and contains a lot of silica, eruptions are very explosive. As the magma emerges it depressurizes and this allows the gas to expand, propelling pyroclastic material as high as 45km in the air, at hundred of feet per second, up and out of the troposphere. These eruptions can last for days and sustain a large eruption plume which can drop lots of Tephra

Question 37

Types of volcanic eruptions - Hawaiian

Answer 37

Example - 1969-74 Mauna Ulu eruption, Hawaii
Basaltic lava produced, with low gas pressure and low silica content.
These eruptions are generally not explosive or destructive and don’t throw a huge amount of tephra or pyroclastic material in the air. Lava flows over large areas producing gently sloping shield volcanoes and lava plateaus

Question 38

Types of volcanic eruptions - Strombolian eruptions

Answer 38

Example - Stromboli volcano, Italy
Small amounts of lava shot 15 to 90 metres in the air, in very short bursts. Regular explosions can produce impressive booming sounds, but the eruptions are relatively small. Don’t tend to have lava flow but there is a small amount of ash.

Question 39

Volcanic hazards - Lava flows

Answer 39

Most lava flows are unstoppable, although occasionally some have been halted by spraying them with cold water and diverted by controlled explosions. Lava flows can cause enormous damage to property but are rarely a threat to human life.

Question 40

Volcanic hazards - Pyroclastic flows

Answer 40

Pyroclastic flows are high-speed avalanches of hot ash, rock fragments and gas that destroy everything in their path. They can reach speeds of 200 KM/h and temperatures of more than 1000 degrees Celsius

Question 41

Volcanic hazards - Lahars

Answer 41

Lahars are mixtures of water, rock, sand and mud that flow valleys leading away from the volcano. They can be caused by an eruption melting snow and ice, the rapid release of water following the breakout of a summit creator lake or by heavy rain washing away loose volcanic ash. Lahars are fast moving and can travel long distances. They are particularly destructive because they follow valleys where settlements and population are often concentrated

Question 42

Volcanic hazards - Jokulhlaups

Answer 42

Volcanic eruptions that happen beneath the ice field or glacier causes rapid melting releasing enormous volumes of water leading to massive floods, which are known as Jokulhlaups in Iceland.

Question 43

How can volcanic hazards be mitigated?

Answer 43

Depends on the monitoring and warning people of impending eruptions.
Monitoring includes recording seismic shocks, measuring ground inflation and collecting gas and lava samples.
Hazard mapping can reveal areas most at risk from lava flows, lahars and pyroclastic flows
Lava can be diverted away from centres of population. MEDCs are most advanced in preparedness

Question 44

What are earthquakes?

Answer 44

Earthquakes are vibrations in the earth’s crust caused by the fracturing of rocks and sudden movements along fault lines. They are highly unpredictable and occur without warning, there are around 50,000 occurring every year around the globe. They result in violent shaking of the ground, landslides and tsunamis.

Question 45

Hoe are earthquakes caused?

Answer 45

Constructive boundary - caused when pressure pushes the plates upwards leading to fracturing and shifting of rocks. The release of pressure causes earthquakes that tend to be shallow.
Destructive boundaries - caused by the friction of two plates moving past each other as one is subducted. When the build-up of pressure overcomes friction the continental crust springs up, elastic rebound, to create shallow, intermediate and deep focus earthquakes.
Conservative - when the plates sliding past each other get locked and pressure builds up, when this is released it creates earthquakes

Question 46

What is the focus of an earthquake?

Answer 46

The precise location of an earthquake within the crust

Question 47

What is the epicentre of an earthquake?

Answer 47

The point on the surface immediately above the focus

Question 48

What are seismic waves?

Answer 48

Seismic waves are shock waves released during an earthquake, they radiate from the focus and travel through rocks.

Question 49

What are p waves and s waves?

Answer 49

Primary and secondary waves, travel through the interior of the earth.
P-waves can travel through solids and liquids. They push and pull the earth in the same direction as the wave is travelling in, they travel faster than other waves.
S-waves can only travel through solids but not liquids, the waves move at a 90 degree to the direction of travel. These waves can cause a lot of damage because of their shearing effect

Question 50

What are surface waves?

Answer 50

Can only travel near the surface and travel more slowly than p and s waves.
Lowe waves can only travel through solids. They move the earth’s surface from side to side and can cause a lot of damage due to their shearing effect.
Rayleigh waves can travel through liquids and solids moving the surface in a rolling motion.

Question 51

How are earthquakes measured?

Answer 51

The Richter scale measures the magnitude of an earthquake which can vary from 2.5 to 9. Seismographs record the amplitude of earthquakes waves which give a measure of the amount of energy released.
The Mercalli scale measures the intensity of the earthquake for example the impact on people and structures. The scale runs from, instrumental to catastrophic.

Question 52

What are the impacts of earthquakes?

Answer 52

• damage buildings and infrastructure
• cause injury and death
  Large earthquakes can devastate an entire region and kill tens of thousands of people. Collapsed buildings and other structures are the main cause of death and injury. In the aftermath of an earthquake fire and disease may add to the death toll.
  The impacts of an earthquake are influenced by the time of day, population size and density and economic development. An earthquake that strikes at night will cause more death and injury. The larger and denser the population in an earthquake zone the ore people at risk. Earthquakes are more damaging in poor countries which lack resources to construct earthquake-proof buildings and to put in place effective emergency procedures

Question 53

How can earthquake hazards be mitigated?

Answer 53

Earthquakes are not possible to predict and therefore give warning. The main human response to earthquake hazards is to minimise their impact.
Building technology is controllable and has a significant influence on the impact of an earthquake. In poor countries buildings are often poorly built and collapse during earthquakes.
Although there is often strict building regulations in developing countries they are usually ignored shown by the large death toll in Kashmir and Sichuan, 2008.
Rich countries such as Japan may avoid building high-rise structures in areas at risk. In populated urban centres this may not be an option so instead strict building regulations are enforced to ensure that buildings and other structures survive the largest quakes.
Building designs include
- steel frames and braces that twist and sway with out collapsing
- foundations mounted on rubber shock absorbers
- deep foundations sunk into bedrock
- first-storey car parks allowing the upper floors to sink and cushion the impact
- Concrete counterweights on the top of buildings which move in the opposite direction to the force of the quake

Question 54

How does disaster planning and prevention work for earthquakes?

Answer 54

In Japanese cities, earthquake zones have disaster plans to manage major earthquakes. This involves upgrading millions of houses to make them fire proof: strengthening roads, expressways, bridges and public buildings; planning for an evacuation to safe locations and educating people in disaster awareness and how to cooperate with others to build a “strong society” against earthquakes.

Question 55

What is a Tsunami?

Answer 55

A Tsunami is a series of ocean or sea waves caused by a large displacement of water most often caused by earthquakes but also landslides and comet impacts in the ocean.

Question 56

What are the characteristics of Tsunamis?

Answer 56

• Movement of water comes all the way from the sea floor and as it approaches land the sizes of the wave increase, the front slows but the rear is going faster so it bunches up.
• Waves are fastest in deep water and slower in shallow water.
• They have along wavelength and a small amplitude of about 1m
• Just before the tsunami reaches he coast the water withdraws down the shore, then the wave hits with great force but only travels a short distance inland.

Question 57

What are the causes of Tsunamis?

Answer 57

Under the sea earthquakes result in a sudden rise of fall in a section of the crust creating rise or fall in the level of the ocean. Near the source of the earthquake the sea floor s uplifted pushing the water column up. The initial tsunami is split and travels out and into nearby coasts. As the wave travels over the continental slope the amplitude increases and the wave length decreases.
1. an earthquake rocks the ocean floor
2. displaces a large volume of water pushing it up
3. sets off an oscillation which develops underwater at great speed - sea water is sucked back from the shore
4 waves get bigger as the water gets shallower