hazards Flashcards
define natural hazard
a perceived event that threatens people, the built environment and the natural environment. natural disaster only become hazards when a vulnerable population becomes exposed to it (deggs model)
how can you categorise hazards and examples
geophysical (land processes)- earthquakes, volcanic eruptions, landslides, tsunamis
atmospheric (climatic processes)- tropical storms, droughts extreme hot or cold weather, wildfires
hydrological (water processes)- floods, avalanches, storm surges
define disaster
hazardous event that caused unacceptably large numbers of fatalities and/or overwhelming property damage, UN defines as 10+ people being killed and 100+ people being affected
define risk
likelihood that humans will be affected by the hazard
define vulnerability
how susceptible a population is to the damage caused by a hazard
define hazard perception
how we view and process information about a hazard
factors affecting hazard perception
- wealth - richer people can have better provisions in place to not being badly affected
- religion- some people see hazards as being in God’s will
- education- more education means they have better understanding of the risks or hazards, and how to mitigate against
- past experience- people in hazard prone areas will know how to act
- personality- some fear hazards others may find them exciting and interesting
human responses to hazards
fatalism- view where people cannot influence the outcome and nothing can be done to mitigate against it
adaptation- attempts to live with the hazard and reduce their levels of vulnerability, like earthquake proof buildings
prediction- use last research to know the warnings of a hazard and help prevent major damage
prevention- ways of weakening the system as it approaches the land like seeding clouds
mitigation- strategies to lessen the severity of the hazard
risk sharing- pre arranged measured and public awareness to reduce the impacts on property and life, like through evacuation responses
what is parks model of human response to hazards and how can it vary
-describes a sequence of three phases following a hazard event
- model works as a control line and varying the steepness can show more catastrophic hazards with a slower response time
different stages of parks model
relief stage- immediate local response like food and medical services, immediate appeal for foreign aid
rehabilitation stage- services restore, temporary shelters food and water distributed
reconstruction stage- restore the area back to normal, rebuild new infrastructure
evaluation of parks model
+ useful to pinpoint the different kinds of response needed at different times
+ deepen understanding of responses
- does not take into account inequalities of development
- does not take into account varying capacity to response
- too general and not specific enough with the different magnitudes of hazards
- differences with climate change
stages of hazard management cycle
mitigation- minimise the impact of future disasters like building flood defences
preparedness- planning how to respond to a hazard like putting in warning systems
response- how people react when a disaster occurs like emergency services
recovery- getting the affected area back to normal
characterises of a hazard
- frequency- distribution of a hazard through time
- distribution- spatial coverage of a hazard
- magnitude- size of a hazard
- intensity- power of a hazard
features of inner core
- solid ball of iron and nickel
- very hot due to pressure and radioactive decay
- 6000C
features of outer core
- iron nickel
- less pressure so the metal can melt and it is semi molten
features of mantle
- thickest layer (2900 km)
- mainly solid rock
- very top layer is semi molten magma known as asthenosphere
- lithosphere is between mantle and crust and is where tectonic plates lie
features of continental crust
- 30-70km thick
- light so doesn’t sink
- known as SIAL due to larger amounts of silica and aluminium
- not created or destroyed
features of oceanic crust
- 5-10 km thick
- made of basalt
- constantly being destroyed and replaced
- heavy and dense so sinks below continental crust
- known as SIMA as it made of silica and magnesium
what did wegener suggest about how the continents once were
used to he one giant continent called pangea, which split into the continents we have today
geological evidence for plate tectonic theory
- continents vaguely fit together
- evidence of similar ancient glacial deposits in south america, antarctic and india
- similar rock type and structures along northern scotland and eastern canada
biological evidence for plate tectonic theory
- fossils found in india are comparable to those in australia
- fossil remains of mesosaurus found in southern africa and eastern south america
- identical plant fossils found in coal deposits in india and antarctica
what is palaeomagnetism
- discovery that earths polarity reverses on either side of the mid-atlantic ridge at regular intervals
- oceanic crust got older with distance from the middle of the ridge, and was mirrored on both sides
what is sea floor spreading and explain the process
- tectonic plates diverge and magma rises up to fill the gap, and cools to form new crust
- over time the new crust is dragged apart so more crust can form, as the sea floor gets wider
- however, crust is being destroyed elsewhere accommodate for new crust forming, and acts in a constant cycle
how can plates move
- convection currents
- ridge push or gravitational sliding
- slab pull
explain convection currents
- heat from earths inner and outer core heats the mantle, which rises upwards
- this cools and as it falls it drags the lithospheric plate with it
explain ridge push or gravitational sliding
- magma wells up and forms an ocean ridge above the ocean floor, which gets older and cools and condenses
- gravity pushes down the older lithosphere as new crust forms on top causing it to slide away from the ridge
explain slab pull
- older, colder plates sink at subduction zones and pulse the rest of the warmer plate along with it via gravity
- major driving force for most plate movement
how do constructive plate margins move apart
- pressure is released and causes the mantle to melt with produces magma
- when the pressure builds up too much, the plate cracks and makes a fault line
- transform faults are perpendicular to the ridge and divide the plate into sections to which they move
ocean ridge features
- in oceanic plates
- mid- atlantic ridge- where eurasian plate and north american plate are moving apart
- magma rises in between the gap left by plates separating and forms new land as it cools
- new land forming is also called sea floor spreading
rift valley features
- on continental plates
- plates diverge beneath land, where rising magma causes continental crust too bulge and dome
- as the plate is pulled apart, the crust between the faults sink
- east african rift valley
oceanic and continental plates destructive margin
- more dense oceanic crust is subducted under the continental crust, forming a sea trench
- fold mountains form when continental crust is deformed by folding and then forced upwards
- oceanic crust is heated and me,ted by friction into the subduction/ benioff zone
- magma can then be pushed up to create volcanoes
- as one plate moves, the friction causes pressure to build up and cause an earthquake
oceanic and oceanic plates destructive margin
- more dense oceanic crust subducts
- island arc (cluster of islands in a curved line) can appear when volcanic eruptions take place underwater, as the subducted plate melts and rises to the surface as magma
continental and continental plate destructive margin (collision boundary)
- neither is subducted so there aren’t any volcanoes but pressure can build for earthquakes
- fold mountains form like Himalayas
what are conservative plate margins
- parallel plates moving in different directions or at different speeds
- pressure can build up from the friction and cause earthquakes
what are magma plumes or hotspots
- hot magma plumes from the mantle rise and burn through weaker parts of the crust
- can create volcanoes and islands
- when plates move, it can take volcanoes with it and over millions of years a chain of islands can form
- oldest volcanoes move further away from hotspot
- hawaiian hot spot has been active for around 70 million years and created 6000 km chain of volcanic islands
features of volcanoes at constructive plate margins
- magma reaches surface quickly
- runny basaltic lava with low silica content
- can flow a long way before it hardens
- gentle sloping volcanoes- shield
- gentle but frequent eruptions
- low VEI
- icelandic/hawaiian eruptions
features of volcanoes at destructive plate margins
- rocky andesite lava with high silica content
- steep sided- stratovolcano or composite
- violent eruptions
- high VEI
- plinian/ pelean eruptions
features of volcanoes at hot spots
- low viscosity, basaltic lava
- low angled slopes
- lava flows great distance from volcanic vent
define active volcano
erupted in living memory
define dormant volcano
erupted within historic record
define extinct volcano
will not erupt again
features of fissure and shield volcanos
- low slopes and is associated with conservative plate margins with runny lava
- ash
- lava runs quickly downhill and over a large distance
- lava escaped through more than one vent
- gentle eruptions
features of ash cinder or composite volcano
- composed of tephra and happen at destructive plate margins with viscous lava
- pyroclastic flows, bombs
- violent eruptions
- narrow base due to slow moving lava
factors affecting the viscosity of lava
temperature- higher the temperature, runnier it is
silica content- higher silica content leads to thicker magma
volume of dissolved gases- higher the dissolved gases the more runny magma
primary volcanic hazards
tephra
pyroclastic flow/ nueés ardentes
volcanic gases
lava flow
ash
secondary volcanic hazards
lahars
flooding
volcanic landslides
tsunamis
acid rain
climate change
features of tephra
- solid material ejected from volcanoes
- endanger aviation and infrastructure
features of pyroclastic flow
- very hot mixture of gas and tephra moving at high speeds
- deadly
- destroys everything in its path
- can lead to secondary hazards like flooding and lahars