Hazards 🌋 Flashcards
What is a hazard?
A natural event with potential to cause harm to life or property
becomes disaster when buses significant impacts to people
3 types of hazard
Geophysical (caused by land processes) earthquakes, volcanoes, tsunami
Atmospheric (caused by climate) tropics, storms, droughts
Hydrological (caused by water) floods
Risk definition
Likelihood humans will be affected by hazard
Vulnerability definition
How susceptible the population is to damage caused by hazard
what is hazard perception?
the way people view and processes hazards
determines how they respond
Factors that affect people’s perception of hazards
Wealth (richer perceive as smaller, can move away or prepare)
Religion (act of god)
Education (better understanding)
Past experience
Personality (fear)
responses to hazards (based on perception)
Fatalism - accept they are part of life, may be religious reasons, loses are inevitable
fear - people move away
active:
mitigation - actions aimed at reducing severity of event and therefore impacts
Through:
Adaptation - changing behaviour accordingly to reduce impacts
prediction - advancements in technology, can give warnings and evacuate
risk sharing - sharing the costs of reducing the hazard and the benefits of preventing it
eg insurance (richer) all buy but only some use
Management - governments may coordinate responses to manage them effectively
Outline the park model
Pre disaster - before event, QoL normal
Disaster - during and directly after, destruction, deaths, reduced QoL
Relief - short term aftermath, focus on saving people and preventing further damage
Rehabilitation- temporary shelter and aid for people
Reconstruction - rebuilding houses and infrastructure
(QoL either returns to same standard or can improve)
Identifies stages of recovery
Assists in planning for future hazards and therefore improve outcomes by reducing impacts
Steeper drop shows larger magnitude of event
Steepness of upwards curve depends on - planning, development and aid
Use of park model
Identifies stages of recovery
Assists in planning for future hazards and therefore improve outcomes by reducing impacts
Steeper drop shows larger magnitude of event
Steepness of upwards curve depends on - planning, development and aid
+ shows rate of recovery
+ shows how QoL affected after hazard
- doesn’t show preparedness before
- doesn’t show quantitative data
Outline hazard management cycle
Continuous loop explains an approach to managing hazards
Preparedness- using evidence and data from previous events to plan, key to minimising impacts
Response - deploying services and resources to rescue people eg emergency services
Recovery - post disaster reconstruction
Mitigation - action taken to reduce impacts of future hazards eg life safe buildings
Comparison of park model and HMC
Both show response of community based on a natural disaster
PM shows impacts of event
- steepness depends of magnitude and response (aid, development and preparation)
HMC more concerned with management before and after - show little of its impact
HMC is a cycle, shows that hazards are ongoing
Unlike future
PM tracks stages of community after (QoL) - help to plan future responses
HMC doesn’t
Structure of the earth
Centre - core - iron and nickel
- inner core, solid ball
- outer core, semi molten
Mantle -
lower mantle - hotter and denser then upper
upper mantle
- rigid upper layer (+ crust is lithosphere)
- asthenosphere - plastic, carries lithosphere
Crust
- continental - thicker, less dense, mainly granite
- oceanic - thinner, more dense, mainly basalt
Why is the core hot?
Radiogenic heat - due to radioactive decay of elements
Primordial heat - heat left over from earths formation
Heat drives tectonic activity
Ways techtonic plates move (theories of movement)
Convection currents
Slab pull
Ridge push
What are convection currents?
Heat from core heats magma in mantle
Magma becomes less dense and rises
Spreads in asthenosphere
Cools
Become more dense and sinks
Creates circular movements which create drag underneath the plates
What is slab pull?
At destructive subduction plate margins
Denser crust forced under less dense
Plate edge sinks and gravity pulls rest of plate with it towards boundary
landforms associated: volcanoes, island arcs
What is ridge push?
Constructive plate margins (mid ocean ridges)
Magma rises to surface, creates new crust
new rocks solidifies and cools, becomes denser and thicker
Causes lithosphere to slope away from ridge
gravity pulls lithosphere down slope
known as gravitational sliding - contributes to movement of plates apart
landforms associated: mid ocean ridges, rift valleys (c)
sea floor spreading
What is sea floor spreading?
Happens when plates move apart (constructive)
Magma rises to form new crust
Pulled apart and new crust rises
Causes sea floor to get wider
Cause formation of mid ocean ridges (higher area either side of margin)
evidence from paleomagnetism
- when earths polarity reverses
- magnetite lines up with magnetic field, reverses
= alternating bands as crust forms overtime
What is plate tectonic theory?
Lithosphere broken up into plates
Move due to convection currents in asthenosphere
Caused by less dense magma rising, cooling and sinking
move by:
convection currents, slab pull, ridge push, sea floor spreading
can help with knowing which areas are at risk along margins
- but not all hazards occur here
Evidence for plate tectonic theory
Continental fit
- continents fit together
Geological evidence
- rocks of same type and age found across
continents (used to connect)
Climatological evidence
- some continents contain coal deposits
formed in tropical conditions, must have
drifted (eg UK)
Biological evidence
- similar fossils found across continents (eg mesosaurus)
palaeomagnetism
- earths polarity reverses every 40,000 years
- magnetite (magnetised rock) is created as plates move
- polarity of magnetite changes with poles, showing bands of reversed
destructive subduction
plates move together - of different densities
- denser plate (oceanic) subjects below less dense plate (continental)
- subducted plate melts, due to heat and friction
molten material rises = volcanoes
C-O
composite volcanoes
earthquakes
fold mountains
trenches
O-O
oceanic trenches
island arc
destructive collision
plates move together - 2 continental
plates equal densities so neither subducts, force each other up
C-C
fold mountains
earthquakes
no volcanoes as no subduction
constructive
plates moving apart
new crust continuously created - lava rises to fill gap
mantle under pressure from plates, release when move apart
melts mantle so magma rises = volcano
pressure builds up when plates don’t move at same speed - earthquake when released
O-O
ocean ridges
underwater shield volcanoes
C-C
composite volcanoes
rift valleys
earthquakes at all
- transform faults at right angles to margin - create shallow focus
conservative
plates move past each other in different directions or same direction at different speeds
no volcanic activity - no subduction
friction causes plates to lock together causing build up of pressure
earthquakes when released
magma plumes
forms volcanoes away from plate margins
- vertical column of extra hot magma
- creates volcano when magma breaks through surface
- crust moves but magma stays still, creates chain of volcanoes
constructive margin landforms
earthquakes (all)
ocean ridge (O-O)
rift valley (C-C)
volcanoes (all)
destructive margins landforms
subduction
(O-C)
volcanoes
earthquakes
fold mountains
trenches
(O-O)
oceanic trenches
island arcs
collision (C-C)
earthquakes
fold mountains
what is adaptation?
accepting natural hazards are inevitable and changing behaviour accordingly
what is mitigation?
actions taken to reduce the severity of the event and therefore impacts
can be before or after the event
what is preparedness?
how ready an area is to deal with the hazard, aims to reduce the impacts
what is prevention?
actions aimed at preventing large scale events occurring
Why are poorer areas more vulnerable to hazards?
Fewer warning systems - lack technology
Fewer defences
Weaker infrastructure
Fewer emergency services
Slower responses
formation of an island arc
plates move together (destructive)
O-O
denser plate subducts beneath less dense
rising magma from melting crust creating volcanoes
form along plate boundary = cresent of submarine volcanoes
rise above sea level = islands
eg Japan
formation of a rift valley
plates move apart (constructive) under land
lithosphere stretches, fractures into parallel faults
land between faults collapses into deep valleys - separated by blocks of land
formation of fold mountains
plates moving together (destructive)
O-C or C-C
created by deformation of the lithosphere
C-C pushed together, no subduction so ride up into each other
O-C subduction but plate still folds
eg The Andes
formation of mid ocean ridges
plates move apart (constructive) under water (O-O)
creates mountains
- magma rises up, accumulates over time
creates underwater volcanoes
- magma rises through gap
causes earthquakes
- at transform faults (due to plates spreading at different speeds)
eg Mid Atlantic Ridge
formation of deep sea trench
plates move towards (destructive)
O-O or O-C
denser oceanic plate subducts under less dense
= trench
outer slope shallower as oceanic plate bends into trench
inner slope steeper
eg Peru-Chile trench
formation of island chains
occur at magma plumes
hot spot remains the same, but plate moves due to convection currents
= volcanoes in lines along plate
overtime eroded below sea level
new ones created next to extinct one (old volcano moved away from hot spot, not active)
formation of a volcano
where magma escapes to the surface
constructive - moving apart
- magma allowed to rise
destructive subduction - moving together
- denser plate subducts, friction and heat cause it to melt
- rises to crust
nature of volcanoes at constructive margins (and plumes)
- basaltic lava
- low viscosity, lower levels of silica
creates gentle sloping, wide base volcanoes
- as lava can flow further
- shield
- high frequency eruptions
- low magnitude
hazards: lava flow, mud flows
eg Eyjafjallajokull
nature of volcanoes at destructive margins
- andesitic lava
- high viscosity, higher levels of silica
creates steep sides, tall
- as lava can’t flow far, solidifies fast, builds up
- low frequency eruptions
- higher magnitude, explosive (vicious lava can block vents, more pressure)
hazards: pyroclastic flow, tephra
eg Mount Pinatubo
Factors that create landforms at margins
Plate tectonic theory:
convection currents
Gravitational sliding
- Slab pull
- ridge push
Magma plumes (not at margins)
Compare volcanic impacts with seismic
Seismic generally more destructive
- unpredictable
- violent shaking and infrastructure collapse, especially if epicentre in urban area (9000 deaths in Nepal)
- tsunamis
Volcanic generally more widespread
- ash clouds disrupt travel and agriculture (Iceland)
- Lahars, widespread (Nevada del Ruiz)
- more predictable than earthquakes, can prepare and evacuate (Iceland, 30mins)
factors affecting impacts of hazards
physical
- magnitude
- duration or frequency
human
- population density
- level of development
- proximity
