Geography Paper 3 - Hazardous Earth

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What are the three primary layers of earth?

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1

What are the three primary layers of earth?

  • Core

  • Mantle

  • Crust

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2

Characteristics of the core?

  • Inner core is solid and is 5000km down

  • Outer core is liquid and is 2800km

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3

Characteristics of the mantle?

  • Asthenosphere 300km down and semi molten

  • Lithosphere 100km down rigid layer

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4

Characteristics of the crust?

  • Continental crust, 35km thick and granitic

  • Oceanic crust, 10km thick and basaltic

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5

What is continental drift and who came up with it?

  • Alfred Wagner 1912

  • He proposed Pangea which is a single large plate

  • This then split into north and south and then split again until continents formed

  • People were sceptical because he failed to provide an explanation

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6

Geological evidence for continental drift

  • Continents fit together

  • Effects of glaciation on continents suggests they were joined

  • Mountain chains and rock types that would have joined

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7

Biological evidence for continental drift

  • Similar marine and reptile fossils found in adjacent continents

  • Fossils from thousands of years ago show few similarities which suggests evolution

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8

What is palaeomagnetism?

Ancient record of changes in rocks

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9

How can technology measure variations in earths magnetic field?

  • Lava erupts and cools

  • Magnetic iron particles lock into rock

  • Magnetic field showed stripes across ocean floor

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10

What is sea floor spreading?

  • Lateral movement of new oceanic crust away from the mid ocean ridge

  • Moves material across the ocean floor

  • Sea floor reaches ocean trench and material subducts

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11

How can age of sea floor be found?

  • Ocean drilling investigated ocean sediment on ocean floor

  • Revealed spatial pattern of sediment due to sea floor spreading

  • Thickest and oldest sediment was nearest to the continents

  • But no sediment older than 200 million yrs so ocean crust constantly recycled

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12

How were tectonic plates discovered?

  • 1960’s nuclear tests were conducted underground

  • They released vast amounts of energy that were picked up by seismometers

  • Most earthquakes were shown to be in narrow bands

  • This suggested a tectonic plate boundary

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13

What happens at a divergent/constructive plate boundary?

  • Plates move apart

  • Magmas rises through the asthenosphere and forces its way to surface

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14

What forms at divergent plate boundaries?

  • Mid ocean ridges with a combined length of 60,000km

  • Mid ocean ridges are broken by transform faults

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15

What are transform faults?

  • Large faults in the crust that form at right angles to the mid ocean ridge

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16

Are there volcanoes/earthquakes at divergent boundaries?

  • Earthquakes when vast amounts of energy is released

  • Volcanoes from seafloor spreading

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17

3 types of spreading ridges and their characteristics?

  • Fast spreading form broad and smooth mountains and have no central rift valleys

  • Medium spreading form smooth mountain chains and poorly defined valleys

  • Slow spreading form steep slopes and clearly defined central rift valleys

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18

What happens when magma eruption is mostly uderwater?

  • Cools rapidly forming pillow lavas

  • As magma then rises to surface overlying rocks are forced upwards

  • Lithosphere is under stress and eventually fractures

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19

What happens at a convergent/destructive plate boundary?

Plates move towards each other

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20

What are the three ways plates can combine?

  • Oceanic-Continental

  • Continental-Continental

  • Oceanic-Oceanic

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21

What happens at the oceanic-continental boundary?

  • Denser oceanic plate submerges under the continental

  • It causes subduction

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22

What does subduction do?

  • Deepens the ocean causing an ocean trench

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23

What is an ocean trench?

An ocean trench is a long narrow depression and the steepest side lies towards the continent

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24

How do mountain chains form at oceanic-continental plate boundaries?

  • Layers of rock develop on oceanic plates

  • As they converge rock crumples and is lifted along the continental plate

  • Magma is also uplifted

  • And a mountain chain forms

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25

How do earthquakes form at o-c plate boundaries?

  • As oceanic plate descends it comes under immense pressure

  • Faulting and fracturing occur in the Benioff zone

  • And energy is released resulting in an earthquake

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26

How do volcanoes form at o-c plate boundaries?

  • The oceanic plate melts when it subducts

  • Because it is less dense than the surroundings it rises towards the surface as magma plutons

  • This can cause volcanoes

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27

What happens at oceanic-oceanic plate boundaries?

  • The slightly denser one submerges under the other

  • As it descends the plate melts and magma rises forming island arcs

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28

What are island arcs?

  • Volcanic islands

  • E.g. The Antilles formed by North America Plate subducting under the Caribbean plate

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29

What happens at a continental-continental plate?

  • Little to no subduction takes place

  • Due to similar densities

  • Collision of the two plates can they force them upwards resulting in mountain chains

  • E.g. African and Eurasian plates have created the Alps

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30

What happens at conservative plate boundaries?

  • They slide past each other in a shearing motion

  • Friction causes pressure and rocks sometimes fracture causing earthquakes

  • E.g. San Andreas fault system

  • No volcanoes though

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31

Features of explosive volcanic eruptions?

  • Form at convergent plate boundaries

  • Lava is acidic

  • High viscosity

  • Lower temperature

  • Violent bursts of gas bubbles

  • Gas, dust, ash and lava bombs occur

  • Strato volcanoes

  • Don’t erupt frequently

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32

Features of effusive eruptions?

  • Occur at Divergent plate boundaries

  • Lava is basaltic

  • Low viscosity

  • Higher temperature

  • Limited explosive force

  • Gas and lava flows

  • Happen more frequently

  • Shield volcanoes

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33

What is a product of an explosive eruption?

  • A caldera

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34

How does a caldera form?

  • The acidic magma doesn’t flow easily so vents are often filled with solidified magma

  • Enormous pressure builds up resulting in an explosive eruption

  • This destroys the cone of the volcano and empties magma chamber

  • Without support of the magma the sides collapse resulting in a depression known as a caldera

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35

Example of a cladera?

  • Krakatoa eruption of 1883 left a 7km wide caldera

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36

2 products of effusive eruptions

  • Lava Plateux

  • Shield volcanoes

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37

What is a lava plateux?

  • Flat elevated platform

  • Basic magma erupts and areas are covered by free flowing lava

  • This is called flood basalts

  • Weathering of the earths surface creates varied relief

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38

What is another word for weathering of the earths surface?

Deundation

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39

How do effusive eruptions cause shield volcanoes?

  • Basaltic lava results in gentle sloping sides which can extend for tens of kilometres

  • Most occur unseen on ocean floor in mid ocean ridges

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40

What is a hot spot?

  • A fixed area of intense volcanic activity where magma from a rising plume reaches the earths surface

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41

What is a super volcano and give an example?

  • A volcano that erupts more than 1000km³ of material

  • Yellowstone in Wyoming is 75km in diameter

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42

Facts about Yellowstone super volcano?

  • Volcanic activity began 2 million years ago

  • Since then 2 major eruptions

  • It decreased global temperatures due to ash cover over the sun

  • There is a hot spot underneath but the probability of eruption is very low

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43

Misconceptions about Yellowstone?

  • People say its due an eruption but it has no particular pattern

  • People say it will have global implications but it will have little impacts outside of the Yellowstone area

  • People say its growing larger but there is no evidence of this

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44

How is volcanic activity measured?

  • Volcanic Explosivity Index (VEI)

  • Measures magnitude (amount of material erupted)

  • Measures intensity (speed at which material erupts)

  • 0 (least) to 8 (most)

  • Also includes, height material reaches, the duration, volume of erupted material and many qualitative descriptions

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45

What are the 7 hazards of a volcano?

  • Lava flows

  • Pyroclastic flows

  • Tephra

  • Eruptions

  • Lahars

  • Floods

  • Tsunamis

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46

How are lava flows a hazard?

  • Everything in the lavas path is burned, buried or bulldozed

  • Destroys infrastructure, crop, residents

  • But rarely lead to fatality and injury

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47

How are pyroclastic flows a hazard?

  • 500 degrees + of hot gases and ash

  • Rock travels at 100km/hour

  • Destroy everything in their path

  • Inhalation of gas causes instant death

  • e.g. Pompeii AD79

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48

Why is tephra a hazard?

  • Material ejected from the air

  • Buries farmland

  • Disrupts transport

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49

Why are eruptions a hazard?

  • Emit a wide range of toxic gases like CO2, CO and SO2

  • Can pose deadly threat to humans if inhaled

  • When rain and SO2 combine acid rain

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50

Why are lahars a hazard?

  • Mud flows of about 50km/hour

  • Snow, ice, ash, soil all mix to create a large flow

  • Destroy everything in their path

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51

Why are floods a hazard?

  • Volcanic eruptions below glaciers can cause rapid melting and floods

  • Water accumulates until it finds an exit

  • This is known as a jokulhlaup in Iceland

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52

Why are tsunamis a hazard?

  • Can cause massive displacement of water resulting in 600km/hour waves

  • Can cause drowning

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53

What is an earthquake?

  • A release of stress that has built up in the earths crust caused by tension, compression and rock shearing

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54

Where is an earthquakes epicentre?

  • A series of seismic waves originates from the focus

  • The epicentre is directly above the focus

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55

Where do earthquakes tend to happen although they can anywhere?

  • Mid ocean ridges

  • Ocean trenches

  • Collision zones

  • Conservative plate margins

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56

What are the 3 types of seismic waves?

  • Primary (P) waves

  • Secondary (S) waves

  • Surface (L) waves

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57

Characteristics of primary waves?

  • Low frequency

  • Fast travelling

  • Happen everywhere

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58

Characteristics of secondary waves?

  • Half the speed of primary

  • High frequency

  • Cant pass through the outer core as its liquid

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59

Characteristics of surface waves?

  • Slowest waves

  • Low frequency

  • Occur in outer crust

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60

What are characteristics of an earthquake with a shallow depth focus?

  • 70km down

  • Very common

  • Release low energy but sometimes can be high

  • Occur in cool brittle rock

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61

What are characteristics of an earthquake with a deep depth focus?

  • 70-700km down

  • Pressure high

  • Temperature high

  • not very well known as they can explore that far down

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62

How are earthquakes assessed?

  • Richter scale made in 1935

  • 1(least) to 9(highest recorded) but there is no limit

  • Anything under a 2 not usually felt

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63

What affect do earthquakes have on landforms?

  • Associate with the formation of mountain chains

  • Create large fold mountains

  • Rift valleys occur along mid ocean ridges

  • Fault scarps form where tension has been from an earthquake

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64

What are the 4 hazards of earthquakes?

  • Ground shaking an displacement

  • Liquefaction

  • Landslides/Avalanches

  • Tsunamis

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65

Why is ground shaking/displacement a hazard?

  • Its the vertical and horizontal movement of the ground

  • Rips apart pipes and railways

  • Buildings can better withstand vertical than horizontal displacement

  • Disrupts groundwater and can cause it to become contaminated

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66

Why is ground liquefaction a hazard?

  • When an earthquake strikes an area with high water content vibrations can cause solid materials to act like liquids

  • Materials lose their strength, slopes collapse and places shrink

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67

Why are ground landslides/avalanches a hazard?

  • Ground shaking and liquefaction can both cause landslides

  • Steeper slopes more vulnerable

  • Deforestation and heavy rain also increases vulnerability

  • Block transport and rivers

  • Can cause flooding

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68

Why are tsunamis a hazard?

  • underwater earthquakes displace water

  • Wave height increases as they approach the shore

  • Tsunamis can spread far inland if no precautions have been taken against them

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69

What is an active volcano?

  • One that has erupted in the last glacial period or within the last 10,000 years

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70

What is a dormant volcano?

  • One that has not erupted in the past 10,000 years but is expected to erupt again

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71

What is an extinct volcano?

  • One that is not expected to erupt again

  • There are exceptions though as Yellowstone hasn’t erupted in 70,000 years but is not considered extinct

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72

What are the 5 reasons people choose to live in tectonically active places?

  • Fertile soil

  • Tourism

  • Geothermal energy

  • Minerals

  • Poverty

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73

Why does fertile soil make people want to stay in an area?

  • Fertile soil is produced by weathered lava

  • Its possible to grow 2-3 crops on the same piece of land in a year

  • Places that rely on agriculture tis brings in more economy and food into the country

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74

Why does tourism make people want to stay in an area?

  • Places like Sakurajima is low magnitude eruptions so attracts tourists for sight seeing

  • Brings economy into the country

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75

Why does Geothermal energy make people want to stay in an area?

  • Japan has had power stations since 1960s

  • promotes renewable energy and helps countries progress

  • However much of the energy is in conservation sites so can’t be accessed

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76

Why do minerals make people want to stay in an area?

  • Minerals produced by earthquakes are used in manufacturing

  • Such as sulphur in chemicals

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77

Why does poverty make people want to stay in an area?

  • They can’t leave due to travel costs

  • Or they can’t pay for education to get a better job somewhere else

  • So they must rely on primary industry such as agriculture for a source of income

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78

What does WAPMERR stand for?

  • World Association of Planetary Monitoring and Earthquake Risk Reduction

  • Formed in 2001

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79

What does physical exposure to hazards depend on?

  • Frequency of earthquakes and volcanoes

  • Magnitude

  • Type of hazard in a particular area

  • Number of people that live there

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80

What is a recurrence interval?

  • Average time between 2 events of equal magnitude

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81

What is vulnerability?

  • Ability of a person or community to withstand a hazard

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82

What is resiliance?

  • Rate of recovery from a hazard or event

  • It links with effectiveness of measures designed to protect people

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83

What are the 5 stages of disaster response?

  1. Modify the cause of the event

  2. The even occurs

  3. Search and rescue

  4. Relief and rehabilitation

  5. Nature of recovery and reconstruction

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84

What does the graph for this look like?

knowt flashcard image
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85

How can you mitigate against the event for volcanoes?

  • Lava diversion channel

  • Spraying lava so it cools

  • Slowing the flows by putting obstacles

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86

How can you mitigate against the event for earthquakes?

  • nothing can be done

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87

How can you mitigate against vulnerability for volcanoes and earthquakes?

  • Education in recognising signs of eruption and what to do along with evacuation drills

  • Preparedness as in building shelters and strengthening buildings

  • Warning as in using technology to monitor

  • Hazard resistant buildings such as steep sloping rooves

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88

How can you mitigate against loses for volcanoes and earthquakes?

  • Emergency aid

  • Disaster response teams

  • Search and Rescue

  • Insurance

  • Resources for rebuilding

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89

What is aseismic design?

  • Buildings being built adjacent so they can sway and bump into each other

  • Stepped buildings with a larger bottom on them to offer support

  • Excavating weak material so you can build on flat land

  • Reinforcements below buildings

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