Hazards Flashcards
define hazard
something thats a potential threat to human life or property
What are the types of natural hazard and give examples
Geophysical hazards - land processes such as earthquakes
Atmospheric hazards such as cyclones
Hydrological hazards such as floods and avalanches
Define disaster
when a hazard actually seriously affects humans
Define risk
likelihood of being affected by a hazard
Define vulnerability
how susceptible a population is to the damage caused by a hazard
What 5 circumstances affect perception of hazards
wealtj
religion
education
past experience
personality
Define hazard incidence
How often a hazard occurs
What are the different phases in the park model
Pre-disaster
Disruption
Relief
Rehabilitation
Reconstruction
What does the park model show
Shows how responses grow during a disaster and help planners predict what resources will be needed at each stage.
For example it also shows that the reconstruction stage is able to improve original conditions
What are the 4 phases of the hazard management cycle
Mitigation - minimise impacts of future disasters
Preparedness - planning how to respond to a hazard
Response - how people react when a disaster occurs e.g. evacuation
Recovery - getting the affected area back to normal
Name the layers of the Earth
Inner core
Outer core
Mantle
Asthenosphere
Lithosphere
Crust
Describe the inner core
solid ball containing iron and nickel 6000C heat from radioactive decay
Describe the outer core
Semi-molten and contains lots of iron and nickel
Describe the mantle
mostly made of silicate rocks and is quite rigid nearest the core
1000-3500C
Describe the asthenosphere
Semi- molten and can flow
made of silicate rocks
Describe the lithosphere
silicate rocks and quite rigid 80-90km
Describe the crust
There are two types of crust
continental is thicker (30-70km) and less dense
oceanic crust is thinner (6-10km) and more dense
Describe the convection current theory of tectonic movement
Circular movement of semi-molten rocks create drag on the base of the tectonic plates causing them to move
Describe the slab pull theory of tectonic movement
At destructive plate margins denser crust is forced under less dense crust and the sinking of the plate edge pulls the rest of the plate towards the boundary
Describe the ridge push theory of tectonic movement
At constructive plate boundarys magma rises to the surface and forms new crust which is very hot and heats surrounding rocks which expand and rise forming a slope
The new crust cools and becomes denser causing the denser rock to move downslope away from the plate margin puts pressure on the tectonic plates causing them to move apart
What are three theories of tectonic movement
Convection currents
slab pull
ridge push
Describe constructive/divergent plate margins
occur where two plates move apart
What events can occur at constructive plate margins
Volcano
earthquake
Ocean ridge
Rift valley
Describe how a volcano occurs at a constructive plate margin
pressure is released at the margin causing the mantle to melt producing magma which rises as it is less dense and can reupt to form a volcano
Describe how an earthquake occurs at a constructive plate margin
Plates dont move apart uniformly, some parts move faster tha others causing pressure to build up and when the pressure become too much the plate cracks making a fault line and causing an earthquake
Describe the formation of an ocean ridge
Diverging plates underwater cause underwater volcanoes to erupt along mid-ocean ridges and they can build up to be above sea level for example Iceland
Describe the formation of a rift valley
Where plates diverge beneath land rising magma causes the continental crust to bulge and fracture forming fault lines
As the plates keep moving apart the crust between parallel faults drops down to form a rift valley for example the East African rift system
Describe destructive/convergent plate margins
Where two plates are moving towards each other
What events/landforms can occur at destructive plate boundaries
deep sea trench
fold mountains
volcanoes
earthquakes
Island arcs
Describe what occurs at an oceanic - continental destructive plate margin
oceanic crust is forced under the less dense continental crust which forms a deep sea trench
Fold mountains also occur where the plates meet as the accumulated sediment on the continental crust is folded upwards along with the edge of the continental crust
oceanic crust is heated and turns into magma and will rise to the surface to form volcanoes
Plates can get stuck when they subduct and when the pressure gets too much they jerk past each other and cause an earthquake
Describe what occurs at an oceanic-oceanic destructive plate margin
The denser plate of the to will be subducted forming a deep sea trench and triggering earthquakes and volcanic eruptions
Volcanic eruptions that take place underwater can form island arcs
Describe what occurs at a continental-continental destructive plate margin
when two continental plates move towards each other neither is subducted so there aren’t any volcanoes but the pressure build up between them can cause earthquakes
Fold mountains form here
Describe what occurs at a conservative plate margin
Two plates are moving past each other
Describe the events that occur at a constructive plate margin
2 Plates get locked together and in places pressure build up causing the plates to jerk past each other releasing the energy as an earthquake e.g. the Pacific and N.American plates
What is a fold mountain and how do they form
made of sediments that have accumulated on the continental crust which are folded upwards along with the edge of the continental crust e.g. Himalayas
Describe how an island arc is formed
A magma plume rises up from the mantle and remains stationary but the crust moves above it and new volcanoes form in the part of the crust now above the magma plume e.g. hawaii
Describe the types of volcanoes that form at constructive margins
fissure and shield
Basaltic lava is formed here
Describe basaltic lava
it is very hot and has a low viscosity so it flows easily
Eruptions are frequent but effusive
Describe how a volcano forms on a constructive boundary
If the boundary is underwater magma rises to fill the space left by plates moving part forming ocean ridges
if the boundary is on land as plates pull apart forming rift valleys they become thinner and magma is able to break through the surface
What type of volcanoes form at destructive boundaries
Composite and caldera
rhyolitic and andesitic lava is formed here
Describe rhyolitic and andesitic lava
Cooler and more viscous so they flow less easily and they have a higher silica content
the eruptions are less frequent but more explosive
Describe how volcanoes form at destructive margins
At subduction zones where one plate is pulled under the other the melting of the plate forms magma which rises to the surface as volcanoes, because the lava is so viscous it forms blockages in volcanic vents causing pressure to build
What are some primary volcanic hazards?
Nuee ardente
lava flows
volcanic gases
pyroclastic and ash fallout
Describe nuees ardentes
A mixture of super-heated gas ash and volcanic rock that flows down the side of a volcano at a high speed and long distance (80km/h) (10-15km)
Describe lava flows
The speed of the lava flow and distance travelled depend on the temperature and viscosity of the lava as well as the steepness of the slope
Low viscosity lava can flow at up to 10km/h on a steep slope and may travel 10s of kilometres
Describe volcanic gases
Lava contains gases such as carbon dioxide and sulfur dioxide which are released into the atmosphere after a volcano explodes which can be harmful to o organisms if breathed in
Describe pyroclastic and ash fallout
Pyroclastic fallout is material that has been ejected from a volcano during an eruption and falls back to the ground and ash fallout consists of mostly gas
Fallout consists of material of a range of sizes from large rock weighing several tonnes to ash particles
Large pieces of falling tephra can damage infrastructure
What are the secondary hazards of a volcano
Lahars
acid rain
Describe lahars
they occur when volcanic material mixes with large amounts of water e.g. ice melt and flows very quickly (over 80km/h) and can travel for 10s of kilometres
Describe acid rain
Volcanic gases can react with water vapour in the atmosphere which then falls as acid rain and can damage buildings and ecosystems
Describe how the magnitude of a volcano can be measured
Volcanic events can be measured using the volcanic explosivity index which grades volcanoes on a scale of 0-8 based on the amount of material ejected
Describe how earthquakes are formed
Caused by tension that builds up at all three plate boundaries, when the plates jerk past each other it sends out shockwaves
Define focus
Near the focus the shockwaves are stronger
Origin
Define epicentre
point on Earths surface where the earthquake is felt first
directly above focus
What scales are used to measure earthquakes
The richter scale
moment magnitude scale
Mercalli scale
Describe the Richter scale
Measures the magnitude of an earthquake and is logarithmic
Describe the moment magnitude scale
based on the total amount of energy released from an earthquake and is also logarithmic and more accurate than the richter scale
Describe the Mercalli scale
Measures the impacts of an earthquake using observations of the event with a scale between 1-12
What are some seismic hazards
Earthquakes
Landslides and avalanches
Tsunamis
Soil liquefaction
Describe how tsunami is formed
Large waves cause by the displacement of large volumes of water which can be triggered by underwater earthquakes
A tsunami will usually be more powerful closer to the coast
Describe landslides and avalanches
shaking of the ground can often dislodge rock or snow and cause them to move downslope quickly
Shaking can also loosen ground making it easier for water to infiltrate which may trigger a landslide even when shaking has stopped due to the extra weight
Describe soil liquefaction
When soil is saturated with water the vibrations of the earthquake can cause it to act like water making it weaker and easier to deform so its more likely to subside
Describe how margin type affect the nature of an earthquake
The biggest earthquakes occur at destructive plate margins and those at constructive tend to be of a lower magnitude
Describe how rate of movement can affect the nature of an earthquake
No clear relationship
Describe how the depth of focus affects the nature of an earthquake
Deep focuses tend to be of a higher magnitude than shallow focus earthquakes however deep focus earthquakes tend to do less damage
Describe how tropical storms form
A disturbance near the sea surface triggers the storm e.g. an area of low pressure
Sea water thats warm (above 27C at least 50m below the surface)
A convergence of air in the lower atmosphere ( boundary between warm and cold air this forces warm air to rise)
location at least 5 from the equator because the coriolis effect is stronger further away from the equator
what happens when tropical stoms reach land
they lose energy
describe the structure of a tropical storm
they are circular and hundreds of kilometres wide and usually last 7-14 days
The eye is very low pressure and rising air spirals in eyewall causing strong winds
Near the top of the storm there is an outflow of moisture laden air
how is storm strength measured
using the Saffir-Simpson scale
based on wind speed and estimating damage caused
How can a tropical storm be followed
cloud formation can be identified from satellite imagery and used to tell when a tropical storm is forming and be tracked
what are the 3 types of wildfire
ground fire
surface fire
crown fire
describe crown fire
where the ground itself burns
it is a slow smouldering fire with no flame and little smoke
describe surface fire
where leaf litter and low lying vegetation burn
fire can be low or high intensity
Describe crown fire
Where fire moves through the canopy
fires are likely to be intense and fast moving
what conditions affect intensity of wildfires
vegetation
fuel characteristics
climate and weather
fire behaviour
describe how vegetation type can cause intense wildfires
thick undergrowth
closely spaced trees
trees such as pine that contain a lot of oil
describe how fuel characteristics can cause intense wildfires
fine dry materials
large amount of fuel with continuos cover
describe how climate and weather can favour intense wildfires
rainfall must be sufficient for fuel growth
dry season
strong winds
Describe how fire behaviour can favour intense wildfires
a running fire is more rapid than a creeping fire
describe the natural causes of wildfires
lightning in absence of rain
volcanic eruptions
what are the human causes of wildfire
dropping cigarettes
arson
uncontrolled bbq and bonfire
sparks from fireworks
what are the types of perception of a hazard
fatalism
adaptation
fear
define fatalism
losses are accepted as inevitable and people remain where they are
define adaptation
belief that survival is viable due to prediction prevention and protection
define fear
people feel vulnerable to a hazard and move away
define community resilience
sustained ability of a community to utilise available resources to respond withstand and recover from effects of a natural hazard
what management system do many governments use
integrated management risk which incorporates identifying a hazard analysing the risk and establishing priorities
why might people put themselves at risk from a hazard
hazard unpredictability
lack of alternatives
changing risk level
cost/benefit
how are hazards mainly managed
prediction, prevention, protection
what does the risk management cycle illustrate
the ongoing process which governments plan and reduce the impact of disaster reacting during and immediately after an event
appropriate actions at all points can lead to greater preparedness
what is one of the main goals of the risk management cycle
promotion of sustainable livelihoods because people then have greater capacity to deal with disasters and recovery is rapid and long lasting - used by FEMA
what could the difference in recovery periods be due to
related to the types of hazard, degree of preparedness, speed of relief effort, nature of recovery and reliability
describe the theory of crustal evolution
states that the lithosphere is able to slide over the asthenosphere and this allows plate movement evidence supporting this main theory is that oceanic crust is slowly moving away from plate boundaries and it gets older with distance
define palaeomagnetism
magnetic signatures of the rocks on the ocean floor
how does palaeomagnetism support the theory of plate tectonics
patterns of opposite directions of magnetic fields were discovered this shows that magma rises from the ridges in the ocean floor and forms new rock recording a more recent alignment of magnetic fields pushing old rock with more outdated magnetic field further from the ridge
what is the theory of plate tectonics
Alfred Wegner suggested that continents have moved into their current positions from Pangea through the process of continental drift
what is the geological evidence that supports the theory of plate tectonics
continental fit coast of S.America and west coast of Africa
glacial deposits 290m years ago found in India, antarctica and south America
matching rock sequences in Scotland and Canada
What is the biological evidence for the the theory of plate tectonics
fossils found in india and Australia of similar species
Mesosaurus fossils found in south America and south Africa
plant fossils found in antarctica and india meaning they’re climates were similar at some points
describe sea floor spreading and its evidence
mid-atlantic ridge
alternating polarity of rock
age of rock
