Chapter 6: Natural Hazards

Question 1

What is a supervolcano?

Answer 1

Is when an eruption measures magnitude 8 or more on the Volcano Explosivity Index

Question 2

What is a natural hazard?

Answer 2

• a naturally occuring event that will have a negative impact on people
• is a physical event that has the potential to cause loss of life or injury and damage property and infrastructure
• can be short term or long term events
• can be geological hazards - earthquakes, volcanic eruptions
• climatic hazards - droughts, tropical cyclones, floods

Question 3

What are he factors that can classify natural hazards
(other than geological/climate)

Answer 3

• magnitude or intensity of event
• speed at which event takes place
• duration of event
• frequency of event

Question 4

What conditions need to be met for the UNISDR to qualify an event as a natural disaster?

united nations international strategy for disaster reduction

Answer 4

• a report of ten or more people killed
• a report of 100 or more people affected
• a state of emergency declared by the government of the affected country
• a request by the relevant govt for international assistance

Question 5

What factors affect the impact of a natural disaster on a community

Answer 5

• length of time people are exposed to the natural hazard
• vulnerability of the people affected
• people’s ability to cope with the effects

Question 6

What is vulnerability?

Answer 6

the characteristics and circumstances of people in a community that make thm susceptible to the impacts of a natural hazard

Question 7

Compare the inner core, outer core and mantle (in terms of temperature and structure)

Answer 7

Inner core - temp 5000-6000 - solid because of intense pressure from overlying rocks - made of iron and nickel
Outer Core - tems 4000-5000 - liquid - iron and nickel
Mantle - more than 80% of volume of earth - silicate minerals - lower mantle aka asthenoshere - temp 1000 - 1200 - behaves like plastic - flows slowly due to convection currents - upper mantle - more brittle - joines with top layer of crust - called lithosphere

Question 8

What are the main differences between a Oceanic Crust and a Continental Crust?

Answer 8

Oceanic (sima)
- mainly made of basalt
- thinner, avg depth is 6km
- denser, 3 g cm(-3)
- younger
- it can sink and is continually being renewed and destroyed
Continental (sial)
- mainly made of granite
- thicker - avg depth of 35 km - can be over 100kn under mountai nranges
- lighter, 2.6 g cm(-3)
- older
- cannot sink and neither detroyed or renewed

Question 9

Describe tectonic plates (using key words)

Answer 9

a piece of lithosphere that moves slowly on the asthenosphere, seven major, eight minor and numerous micro plates have been identified

Question 10

How do convection currents make tectonic plates move?

Answer 10

• transfer heat from place to place, denser colder fluid sinks into warmer areas, heat from the earth’s core causes convection currents in the mantle (what they are, not relevan to answer)
• heat from core creates CC in magma of mantle and these cause plates to move - when CC rise to the surface plates move away from each other - when CC sink plates move towards each other
• plates only move a few mm each year

Question 11

what are hot spots?

Answer 11

A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.

Question 12

Describe conctructive plate boundaries

Answer 12

• aka divergent
• two oceanic plates move away from each other
• a gap/weakness is formed and magma from mantles rises to surface due to CC
• magma solidifies when it comes into contact with cold ocean water
• magma turns to lava - forms new basaltic ocean
• process called sea - floor spreading/ridge push
• may create submarine volcanoes which are shield volcanoes
• for eg Mid Atlantic ridge

Question 13

Descrbie destructive plate boundaries

Answer 13

• aka converging
• found b/w oceanic and continental plate OR tw oceanic OR tw ocontinental
• more towards each other because of CC
• denser, oceanic plate is subducted under lighter continental plate
• process called slab pull and takes place in subduction zone
• ocean trench is formed
• as oceanic plate moves downwards - pressure and friction can cause severe earthquakes in benioff zone
• descending plate disintegrates
• magma starts to rise can create a composite or acidic volcano
• fold mountains are formed
• magma rising can also create chain of volcanic islands called island arc

Question 14

Describe Conservative plate boundaries

Answer 14

• no palte is beign destroyed or created
• plates sliding past each other
• can create earthquake

Question 15

What is the subduction zone?

Answer 15

a zone where the oceanic plate is deflected (subducted) down into the mantle, at the surface the subductino zone coincides with ocean trenches

Question 16

What is the benioff zone?

Answer 16

an inclined zone in which many deep earthquakes occur, situated beneath a destructive plate boundary where oceanic crust is being subducted.

Question 17

What is the focus and epicenter of an earthquake?

Answer 17

• the focus is where the earthquake begins underground
• the point directly aboce the focus on the earth’s surface is the epicentre from where the seismic waves erupt

Question 19

what is liqufaction?

Answer 19

the process by which loose sediments with a high water content behave like a liquid when shaken by an earthquake

Question 20

What are the factors that affect the impact of earthquakes

Answer 20

• the location of the epicentre - the closer to the epicentre the greater the damage
• the time of the earthquake - more deaths at night/winter
• geology of the area
• relief of the area - mountains landslides - coastal tsunami
• severity of aftershocks
• level of development of human settlement - affect ability to cope
• population density
• building density
• building strength

Question 21

What is a volcano? (characteristics)

Answer 21

• volcano is a hole or crack (fissure) through which magma/gases/pyroclastic material erupts onto the surface
• volcanoes are mixture of solidified magma and ash which build up over time
• when magma erupts it can form different types of volcanoes depending on viscosity
• intrusive volcanoes - when magma cools underground to form igneous rocks
• extrusive - when magma flows out onto the Earth’s surface as lava

pg 140

Question 22

What are shield/basic volcanoes? (characteristics)

Answer 22

• found on constructive plate boundaries and hotspots
• cover a wide area with gentle slopes (2 to 10 degrees)
• upto 900m in height
• magma has low viscosity
• eruptions are usually non explosive and consist mainly of basalt lava flows from a vent

Question 23

What are composite volcanoes? (characteristics)

Answer 23

• aka strata volcanoes
• found on destructive plate boundaries
• conical in shape with steep slopes (10 to 30 degrees) and narrow bases
• 100-3500m in height
• formed by alternating layers of ash and lava
• magma is viscous
• eruptions are explosive but infrequent and consist of ash, shattered lava, volcanic bombs and gases - lava flows are limited in extent - because of the high viscosity of the magma

Question 24

Facts about tropical cyclones

Answer 24

• cyclones, hurricanes, and typhoons
• cyclones - Indian Ocean + Australia
• hurricanes - atlantic ocean + eastern pacific ocean
• typhoons - western pacific ocean
• are large areas of very low pressure with wind speeds of over 119km h(-1)
• saffir-simpson hurricane scale
• category 1-5
• super typhoon - more than category 5

Question 25

What conditions are needed for tropical cyclones to form?

Answer 25

• ocean surface temperature must be atleast 27(degree C) as warm water provides the energy for increased evaporation of water which rises, condenses and releases huge amounts of energy
• warm ocean water must be atleast 60m deep
• conditions must occur b/w latitudes 5 and 20 north and south - any closer to the equator and there is insufficient coriolis force (rotation of earth) to make the air spin - at higher latitudes the oceans are too cold
• should be very little wind shear (change in wind speed+direction) - strong wind shear can stop the vertical development of a storm
• these conditions b/w may and november in northern hemisphere and b/w novemeber and may in southern hemisphere

Question 26

How are tropical cyclones created?

Answer 26

• start as clusters of thunderstorms that grow in size and start to spin
• air rises as it is heated from below - it cools, condenses and releases latent heat - causes air to rise faster
• low pressure area is intensified and more air is tucked towards center of storm
• cumulonimbus clouds are formed
• aur cools at Hugh altitudes and Sinks firming the eye of the storm
• cyclones derived energy by evaporating moisture from a warm ocean - when it passes over land or a cold ocean Current it loses the source of energy and speed decreases

Question 27

What are some characteristics of tropical cyclones?

Answer 27

• can be upto 800km in diameter and upto 20km in height
• usually last for a week, moving 17-32km h(-1)
• rotate anticlockwise around the eye of storm in the NH
• Clockwise in SH

Question 28

Typical weather conditions associated with tropical cyclones

Answer 28

• sky becomes cloudy
• wind speed increases
• rain with sunny intervals
• air pressure falls, wind speed continues to rise to 119km h, large cumulonimbus clouds form and very heavy rain falls - this is vortex
• in eye of storm, sky is clear, winds are light, there is little rain , temperatures are warm
• After eye has passed, again heavy clouds and strong winds for.
• wind speed and rainfall decreases - sunny intervals

Question 29

Hazards of tropical cyclones

Answer 29

• structural damage to buildings - heavy stones
• River flooding and landslides - heavy rainfall
• flooding in low lying coastal areas- intense low pressure can raise sea levels and strong winds can push waves upto 5m inland

Question 30

Describe the physical causes of flooding

Answer 30

Weather - heavy/intense rainfall may exceed infiltration capacity of soil - lead to increase in overland flow - can saturate soil and water table can rise - reducing infiltration capacity - if ground below is frozen and snowmelt is rapid - overland flow increases
Previous Weather - antecedent soil moisture - the more saturated the soil the less infiltration - more overland flow
soil/rock type - impermeable=>low infiltration capacity + low perlocation rate = more overland flow
natural disasters - can produce tsunamis and storm surges that flood low lying coastal areas

Question 31

What are human causes of flooding?

Answer 31

deforestation - reduces interception and infiltration
urbanisation -concrete+tarmac=impermeable surfaces=more overland flow - storm draisn speed up movement of water into rivers
Agriculture - overgrazing+leavnig soil exposed reduces interception - heavy machinery compacts soil/impermeable - ploughing down rather than across slopes quickly channles water downward
climate change - rise in sea level - more rainfall and storms - more snowmelt

Question 32

Give examples of how natural weather patterns change and how they cause droughts

Answer 32

• most droughts occur when natural weather patterns are interrupted -> evaporation exceeds precipitation
• changes in atmospheric circulation patterns - altering storm tracks and wind patterns for e.g. patterns that prevent northwatrd movement of ITCZ into sahel region of africa
• In high pressure systems air sinks and rain clouds do not form
• EL Nino Oscillation - can alter storm patterns - droughts in australia
• climate change

Question 33

Intertropical convergence zone? (ITCZ)

Answer 33

• A low pressure belt that lies around the equator, where the north east and south east trade winds meet, it recieves high precipitation because fo intense heating from the sun

Question 34

How can human practices influence drought in an area?

Answer 34

• Agricultural - make land vulnerable to drought - irrigation techniques increased farmers dependance on water - overcultivation+overgrazing = soil compaction - soi is less able ot hold water - vulnerable to erosion -> desertification
• deforestation - decreases soil infilatration
• building dam on river can create drought downstream by reducing flow of water

Question 35

What are some of the impacts of a drought?

Answer 35

• people + animals have to travel long distances to get water
• loss of crops, farm animals, plants + wildlife
• decrease in land prices
• unemployment - production declines and farmers loose money
• poor nutrition - health problems
• famine + dehydration - elderly+youngsters prone to heat stroke
• plant diseases + insect infestation
• soil erosion + desertification
• risk of wildfires
• poor air quality
• conflict over water

Question 36

What are the imapcts of flooding?

Answer 36

• dispossession and migration
• contamination of water supplies -> disease
• loos of crops + famr animals = food shortages
• deposition of silt
• recharge of groundwater stores
• rivers can change course

Question 37

What are the impacts of tropical cyclones?

Answer 37

• flooding from storm sturges
• heavy rainfall
• water borne diseases
• economic losses
• dramage to crops
• food shortages
• loss of export earnings
• loss of wildlife habitats
• loss of infrastructure

Question 38

List some of the impacts of Tectonic Hazards

Answer 38

• ground shaking, lava flows, pyroclastic flows, lahars, ash
• landslides cover buildings + roads
• tsunamis hit coastlines
• fires from rupture of gas pipes
• destruction of farmland and starvation
• aid cannot reach victims
• diseases
• trauma - poor mental health
• loss of wildlife habitats

Question 39

What are the three Ps of management strategies?

Answer 39

prediction, prevention, protection

Question 40

How can earthquakes be predicted?

Answer 40

• instruments such as seisometers can monitor tremors, groundwater gas, and radon levels
• epicentres and the frequency of past events an be mapped to see pattern
• measurement of local magnetic fields
• hazard zone map can be drawn based on geological information and ground stability
• unusual animal behaviour

Question 41

What are some preparation and prevention strategies for earthquakes?

Answer 41

• make earthquake proof or aseismic buidings - older buildings can be retrofitted
• smart emters that cna cut off gas suplies to prevent fires
• land use planning - imp services such as schools, hospitals built in low risk areas

Question 42

What are some features of an earthquake proof building?

Answer 42

• rubber shock absorbers at the base to absorb tremors
• foundations sunk deep in the bedrock
• cross bracing steel beams allowing buildings to move as a rigid structure
• computer controlled weights on he roof to reduce shaking
• construction using fire resistant materials
• no bricks or concrete blocks

Question 43

What are some prediction measures for volcanic eruptions?

Answer 43

• seisometers monitor tremors caused by rising magma
• heat seeking cameras in satellite can measure increasing global temperatures in certain areas
• tiltmeters and global poistioing sytems moniter changes in volcanic shape
• emissions of steam and gas can be monitered

Question 44

What are some preparation and protection measures that can be taken in the event of volcanic eruptions?

Answer 44

• volcano hazard map - study past volcanic eruptions/patterns
• lava diversion channels, lava barriers, spraying lava with water, halting lava by concrete slabs (plan)
• building reinforcements for example sloping roofs to protect agaisnt ashfall

Question 45

What are some preparation and protection measures for tropical cyclones?

Answer 45

• cyclone shelters
• buildings on stilts - so not flooded by storm surges
• embankments built along coast
• preserve mangrove swamps to absorb energy of storm surges

Question 46

How can floods be predicted?

Answer 46

• monitoring amount of rainfall and river discharge (hydrograph)
• knowledge about characteristics of drainage basin and type of storm can help determine severity of flooding

Question 47

What preparation and prevention measures can be taken for floods?

Answer 47

• hard engineering projects - levees, flood barriers, flood control channles, dams
• soft engineering projects - afforestation, controlled flooding of meadowland and storage basins
• straghtening, widening + deepening the river channel by dredging + clearing vegetation
• land use planning to use higher land for settlements - restrict development on floodplains - increase green space
• adapt houses
• use sandbags and pumps

Question 48

Describe some protection and prevention measures against droughts

Answer 48

• increase water supplies by dams + reservoirs, percolation ponds, wells, pums + aquifers, pipelines, desalination
• water conservation - storage tanks, spray irrigation
• drought tolerant crops
• reduce deforestation + increase water recycling
• planting shelter belts to reduce wind and evaporation
• building bunds to encourage infiltration and fencing ot control overgrazing
• govt stockpiling supplies

Question 49

Despite known risks why do people still live in areas prone to natural disasters?

Answer 49

• the risk may not be perceived high
• individuals may ahve lived there their whoel lfie
• employment oppurtunites - tourism - souvenier sellers - fishing
• in case of volcanoes soil is fertile - high crop yields - scenery spectacular - geothermal power - mining minerals such as sulphur, gold, and diamonds
• in case of flooding - rivers provide source of food + water - farming - easy to build on flat side of river bank