Tectonic Plates Content

Question 1

What is a hazard?

Answer 1

A potential threat to human life and property
-Natural hazards can be either hydrometereological or geophysical

Question 2

What is a geophysical hazard?

Answer 2

These are hazards driven by geological processes in particular plate tectonics
-earthquakes
-landslides
-tsunamis
-volcanic activity

Question 3

What is the distribution of earthquakes?

Answer 3

-major earthquakes zones are clustered along plate boundaries
-highest magnitude are found at convergent and conservative boundaries
-Pacific Coast of the Americas, Japan and SE Asian islands are at particular risk
-Intraplate earthquakes can also occur e.g East Africa

Question 4

What is the distribution of volcanos?

Answer 4

-clustered in narrow bands in a pattern similar to earthquakes
-many active volcanoes are located around the ‘Pacific Ring of Fire’ where convergent plate boundaries dominate e.g Mt Pinatubo
-or along divergent boundaries such as Mid Atlantic Ridge
-some can be found in hotspots e.g Island chains in Hawaii

Question 5

What is the distribution of tsunamis?

Answer 5

-coastal zones are more prone
-areas at risk are near convergent boundaries- specifically SE Asia
-some occur away from plate boundaries due to coastal landslides like in Greenland

Question 6

What are the tectonic trends since 1960? Why?

Answer 6

Increased:
-total number of disasters- though there has been a recent fall= number of hydro-meteorological has increased more significantly than geo-physical
-Total number of tectonic hazards=due to improved technologies to detect them + increased connection with switched off locations so few disasters now go unreported.
-Total number of people being affected= population growth has led to increased population density
-Economic losses/costs= increased investment into expensive infrastructure because of economic development + increased number of insurance policies. (earthquakes are the most costly)

Decreased:
-Total number of fatalities= increased monitoring, prediction and mitigation strategies, vast mobile phone usage so can warn people
-deaths from volcanic eruptions have decreased over time and now are very rare

Question 7

Why is there difficulty reporting disaster impacts?

Answer 7

depends on whether lokking at direct deaths only or oth secondary and primary death- e.g. death caused by disease
location is importnat as rural and isolated locatiosn are hard to reach to collect data from
different methods may be used by diffrent organiations
numer of deaths quoted y givernment are subject to bias

Question 8

Name the four sections of Earths structure?

Answer 8

Crust (lithosphere)
Mantle (asthenosphere)
Outer core
Inner core

Question 9

What is the crust?

Answer 9

The uppermost layer of the Earth
thinnest
least dense and lightest
oceanic crust (7km thick) and continental crust (up to 70km)

Question 10

What are the characteristics of the mantle?

Answer 10

semi molten
generates convection currents
at a depth of 700-2890km below the crust

Question 11

What are the characteristics of the outer core?

Answer 11

dense
semi molten
containing iron and nickel alloys
at a depth of 2890-5150km

Question 12

What are the characteristics of the inner core?

Answer 12

similar to outer core
solid
high temperature as a result of premodial heat left over from earth’s formation and from radioactive decay.
at a depth of over 5150km

Question 13

What are the three types of plate boundaries?

Answer 13

Convergent/Destructive-towards each other
Divergent/Constructive- away from each other
Transform/Conservative- parallel to each other

Question 14

What happens in continental-oceanic convergent boundaries?

Answer 14

-convergent destructive boundary is formed
-Oceanic crust subducts as denser
-Leaves behind a deep ocean trench
-oceanic stick to continental plate as it sinks= pressure builds up until plates snap= large earthquakes
-can trigger tsunami
-As the plate subducts into the asthenosphere it melts (forms andesitic magma) so more magma which increases pressure and erupts explosively= composite/strato volcanoes.
-these volcanoes produce ash falls, volcanic bombs and pyroclastic flows rather than lava
-Fold mountains also form during subduction as sediment is pushed up

Question 15

What happens in oceanic-oceanic convergent plate boundaries?

Answer 15

Denser plate subducts
Ocean trench is formed
Sub marine volcanoes form

Question 16

What happens in continental-continental convergent plate boundaries?

Answer 16

-convergent collision boundary is formed
-neither plate subducts
- low density crust is crumpled upwards into fold mountains
-large earthquakes caused along faults

Question 17

What happens in oceanic-oceanic divergent plate boundaries?

Answer 17

convection currents in the asthenosphere drag two oceanic plates apart
magma rises between the gap left by the separation
this forms less explosive underwater volcanoes= shield volcanoes which have hot, runny basaltic lava
new land forms on ocean floor by lava= sea floor spreading occurs

Question 18

What happens in continental-continental divergent plate boundaries?

Answer 18

any land in the middle is forced apart= rift valley forms
volcanoes form where the magma rises= shield volcanoes
eventually gap is likely to fill with water

Question 19

What happens at conservative plate boundaries?

Answer 19

parallel plates move in different directions or at different speeds
no plates are destroyed so no landforms are created
plates are not smooth so stick together and pressure builds up and eventually crust fractures along faults triggering an earthquake= can be very large and destructive as shallow focus

Question 20

What is sea floor spreading?

Answer 20

when magma is forced up from the asthenosphere lithosphere is forced to split and new oceanic crust forms pushing plates apart
palaeomagnetism
as new rock is formed and cooled magnetic grains within the rock align with magnetic poles
geologist observed that there are a symmetrical bands of rock with alternating bands of polarity on the ocean floor either side of constructive plate boundaries

Question 21

What is ridge push?

Answer 21

force influencing how convergent boundaries form
the slope created when plates move apart has gravity acting upon it since at a higher elevation.
gravity pushes the plates further apart

Question 22

What is slab pull?

Answer 22

when a plate subducts the plate sinking into the mantle pulls the rest of the plate with it causing further subduction.
-thought to be the most significant process behind plate movement

Question 23

What is subduction?

Answer 23

Subductions drags oceanic crust into the mantle causing the movement of plates along the subduction zone

Question 24

What is mantle convection?

Answer 24

decay of radioactive elements in core produce thermal energy
lower mantle heats up and rises
as magma rises it cools condenses becomes dense and sinks back to core
these are convection currents which cause plates to move

Question 25

What is the Benioff zone?

Answer 25

zone where a descending oceanic plate is in contact with a continental plate as it is subducted
zone of earthquake activity due to friction between plates

Question 26

What is the focus of an earthquake?

Answer 26

-point of fracture underground where the earthquake originates from here there is a release of energy in the form of seismic waves

Question 27

What is the epicentre of an earthquake?

Answer 27

-area above ground directly above the focus
-seismic waves shake the ground most violently at this point

Question 28

What are the types of seismic waves?

Answer 28

Body waves: travel through Earth’s body
-primary
-secondary

Surface waves: travel through the surface of the crust only
-rayleigh
-love

Question 29

What are characteristics of primary waves?

Answer 29

travels through solids and liquids
first to reach surface
fastest= 4-8m/s
push through the crust (expansion ad compression)
vibrates in direction of travel

Question 30

What are characteristics of secondary waves?

Answer 30

travels only through solids
move crust up and down
vibrate at right angles to direction of travel
slower= 2.5-4km/s

Question 31

What are the characteristics of love waves?

Answer 31

-fastest surface wave
-largest amplitude= cause most damage
-near to ground surface
-move crust side to side
-travels at 2-6km/hr

Question 32

What are the characteristics of rayleigh waves?

Answer 32

-largest wave to arrive
-travels through surface of the crust with a rolling motion= move crust up and down
-vertical and horizontal displacement
-travels at 1-5km/hr
-compressional

Question 33

Which seismic waves are the most destructive?

Answer 33

secondary and love
as have a large amplitude
will hit location at different speeds=aftershocks
(intensity of waves will decrease further from epicentre)

Question 34

What are the secondary hazards of earthquakes?

Answer 34

Soil liquefaction
Landslides
Tsunamis

Question 35

What is soil liquefaction?

Answer 35

secondary hazard of earthquakes
-affects poorly compacted sand and silt
water moisture separates from soil particles and rises to the surface
-causes soil to behave like a liquid
-can cause building subsidence and landslides

Question 36

What are landslides?

Answer 36

-shaking caused by earthquake weakens cliff, hills and snow material
-unconsolidated material/loose rocks collapse
-can travel several miles accumulating material
-risk varies due to:
topography
rainfall
soil type
land use

Question 37

What is magnitude?

Answer 37

amount of energy released at the epicentre
measured using seismometer
Moment Magnitude Scale (1-10)

Question 38

What is intensity?

Answer 38

earthquakes effect on people, structures and the natural environment
measured using observations
Mercalli Intensity Scale (I-XII)

Question 39

What is the Modified Mercali Scale?

Answer 39

-measures destructiveness of an earthquake
-relative scale
-subjective
-scale from I (generally not felt or detected by seismographs) to XII (nearly total destruction)
-doesn’t consider economic, social and environmental impacts

Question 40

What is the Moment Magnitude Scale?

Answer 40

amount of enrgy relased in earthqauke
scale from 0-9
simple measure- environemntal or social impacts have to be inferred

Question 41

What is the Richter scale?

Answer 41

-measures amplitude of seismic waves in earthquake
-most widely used- as its absolute
-must infer social or environmental impacts
-highest Richter readings may not be worst disasters
-scale is logarithmic

Question 42

What are the tsunamis?

Answer 42

-a series of larger than average waves which are usually caused by submarine earthquakes or volcanic eruptions therefore tend to occur along plate boundaries
-less frequently submarine landslides and asteroid strikes can displace water and cause tsunamis

1.oceanic crust jolted during an earthquake
2. water column above plate is displaced upwards
3. this water is pulled down due to gravity
4. energy transferred to water so travels through it like a wave as an oscillation
5. water travels fast but with with a low amplitude in all directions
6. as the waves get closer to the coast the sea level decreases= friction occurs between the sea bed and waves
7. waves slow down and gain height reaching up to 100 feet
8. 4-5 waves arrive over several hours (40% energy scattered back to sea 60% used at coast)

Question 43

What factors affect tsunami impact?

Answer 43

-plate boundary type (generally occur at convergent subduction zones)
-population density
-coastal defences (e.g Tsunami wall)
-duration
-wave amplitude + distance travelled
-gradient of continental shelf
-shape of land (bays will funnel and concentrate tsunami waves)
-warning and evacuation systems
-level of economic and human development

Question 44

What are volcanoes?

Answer 44

-formed by the extrusion of lava onto the Earth’s surface
Two main types:
-Shield volcano
-Strato/composite volcano

Question 45

What are primary impacts of volcanoes?

Answer 45

-Lava flows= stream of lava that erupt into Earths surface (can be fast flowing and dangerous which depends on silicon dioxide content/viscosity)
-Ash flows and tephra= pieces of volcanic rock and ash are blasted into the air. (can cause damage to buildings)
-pyroclastic flows= mixture of hot dense lava, ash and gases which move very quickly along the surface of the Earth (can cause asphyxiation)
-Volcanic gases= e.g sulphur dioxide and carbon monoxide released into atmosphere during eruption (can travel long distances)

Question 46

What are secondary impacts of volcanoes?

Answer 46

-Lahars= combination of rock, mud and water which travel quickly down the sides of volcanoes
-Jokulhlaup= snow and ice in glaciers melt after an eruption which can cause floods
-Acid rain= caused when gases such as sulfur dioxide are released into atmosphere

Question 47

What are the different types of magma and what are their properties?

Answer 47

Basaltic
-low silica
-forms at: oceanic hotspots, mid-ocean ridges (shield volcanoes) e.g Mauna Loa, Hawaii

Andesitic
-intermediate silica
-forms at: subduction zones (stratovolcanoes) e.g Montserrat

Rhyolitic
-high silica
-formed at: super volcanoes e.g Yellowstone

Temperature:
basaltic is hottest followed by andesitic then rhyolitic

Gas content:
rhyolitic has the highest gas content followed by andesitic followed by basaltic which has very low

Eruption energy:
rhyolitic is the most violent/cataclysmic followed by andesitic which is moderatively explosive and then andesitic which is gentle

Viscocity:
rhyolitic lava is thick and stiff so high visocity trapping gases, andesitic is intermediate still trapping gases and finally andesitic is thin and runny so low viscocity

Question 48

What are the differences between the two types of volcanoes?

Answer 48

Strato volcanoes:
-found at convergent plate boundaries
-steep slopes above 10degrees
-alternating layers of lava and ash/pyroclastic materials
-viscuous andesitic or rhyoliyic magma which prevents the release of volcanic gases and causes pressure to build up within the volcanic vent
-eruptions therefore explosive
-produce pyroclastic flows which can travel great distances

Shield volcanoes:
-found at divergent plate boundaries
-gently sloping sides
-layers of solidified lava
-wider
-erupt low viscosity basaltic magma which flows as lava
-volcanic gases diffuse away easily

Question 49

What are hot spot volcanoes?

Answer 49

Volcanoes that occur away from plate boundaries
-mantle plume is the heat source of hot spot volcanoes it is a column of very hot rock that rises through the mantle to the base of the lithosphere where it partially melts and produces magma that seeps through the lithosphere= volcanoes
-mantle plumes are fixed relative to the moving plate
- chain of extinct volcanoes/hot spot track forms as the overlying plate moves over a fixed plume so that it becomes extinct and a new volcanoes grows over the plume
Example: Hawaiian chain= oldest is Kauia

Question 50

What is the VEI?

Answer 50

Volcanic Explosivity Index
-measures relative explosiveness of a volcanic eruption
-based on height of ejected material
-scale goes 0-8
logarithmic scale

Question 51

What is a disaster?

Answer 51

a serious disruption of a normal conditions to a point where which exceeds the ability for them to cope using their own resources and there is a significant loss of life/injuries/economic costs

EM-DAT definition:
>10 deaths
>100 affected
declared state of emergency/aid request

Question 52

What are mega disasters?

Answer 52

UN states a megadisaster is where there is:
-more than 2000 deaths
-over 2000000 homeless
-GDP reduced at least 5%
-dependency on international aid for more than a year after

However can still be considered mega disasters if they don’t meet criteria as long as they are considered globally significant

Question 53

What are multiple hazard zones?

Answer 53

areas with vulnerable populations at risk of two or more natural hazards
can be either geophysical or hydrometeorological
Example: Philippines

Question 54

What is the risk calculation equation?

Answer 54

risk= Hazard x Vulnerability/ Capacity to Cope

Question 55

What is Deggs model?

Answer 55

states that if the community is not vulnerable then the hazard will not become a disaster
-Venn diagram
-hazard one one circle
-vulnerability in the other
-disaster in the overlapping area

Question 56

What is the Park Model?

Answer 56

-geographical representation of human responses and recovery to hazards
-shows the steps carried out after a hazard- providing an idea of time frame
-steepness of a curve shows deterioration
-depth shows the scale of disaster
Stage 1 Relief= search and rescue, medical aid, appeal for
foreign aid (hours-days)
Stage 2 Rehabilitation= foreign aid, temporary
shelters/hospitals built, services start to be
restored (days-weeks)
Stage 3 Reconstruction= restoring to normalcy or better,
infrastructure rebuilt, mitigation investment for
future(weeks-years)

Question 57

What is the PAR model?

Answer 57

The Pressure and Release Model
-on one side (right) we have the natural hazard
-on the other side (eft) we have factors that increase a population vulnerability to the hazard:
1. Root Causes= (caused by economic, demographic and/or political processes e.g corruption or low GDP) leads to…
2. Dynamic Pressures= (local economic or political factors e.g rapid urbanisation) leads to…
3. Unsafe Living Conditions (physical conditions affecting an individual e.g lack of infrastructure or unsafe conditions
-both hazard and unsafe conditions lead to disaster

Question 58

What is the definition of vulnerability?

Answer 58

how susceptible an area or population is to damage from a particular hazard event

Question 59

What are the types of vulnerability to hazards?

Answer 59

-Physical vulnerability= hazard-prone location
-Economic vulnerability= risk of loosing employment, wealth and assets during a hazard (developing > developed at risk)
-Social vulnerability= communities unable to support their most vulnerable
-Knowledge vulnerability= individuals lack training education on what to do/evacuation
-Environmental vulnerability= population density

Question 60

What is a hazard profile?

Answer 60

Compares the physical characteristics which hazards share:
-Frequency
-Magnitude
-Duration
-Speed of onset
-Spatial Predictability

Question 61

What is the Hazard Management Cycle?

Answer 61

Outlines the stages of responding to an event:
1.Preparedness= being ready for an event to occur
- warning systems
-education, training, drill
- stockpiling medicines, food, water

2.Response= immediate action taken after event
- search and rescue efforts
-evacuating response
- restoring water and electricity

3. Recovery= long term responses
   -rebuilding infrastructure
   -restoring services

4.Mitigation=lessen effect of another hazard:
-land use zoning
-building codes and regulation
- protective defences (e.g. tsunami wall)

Question 62

What is prediction and forecasting?

Answer 62

Prediction= knowing where and when a natural hazard will strike so it can be meaningfully acted upon
Forecasting= provides a percentage chance of an event occurring (less accurate)

Earthquake:
-not possible to predict accurately when an earthquake will occur
-but can forecast based on statistical likelihood using historical records
-seismographs can detect tremors

Volcanoes:
-can sometimes predict with some level of accuracy
-can monitor changes to the top surface as it swells when magma builds
-changes to the tilt as slope angle changes when magma builds up

Question 63

What are the three management approaches?

Answer 63

-Modify the event
-Modify the vulnerability
-Modify the Loss

Question 64

What are modify the event strategies?

Answer 64

-resistant buildings
-tsunami walls
-lava diversion
-land use zoning

Question 65

What are modify the vulnerability strategies?

Answer 65

-education
-training of emergency personnel
-evacuation strategies
-warning systems
-hi tech scientific monitoring

Question 66

What are modify the loss strategies?

Answer 66

-Long and short term aid
-Insurance