Tectonics Flashcards
Hazard risk equation
Risk = Event x Vulnerability
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Capacity to cope
Natural hazard vs disaster (events)
Hazard = potential threat to people / property
Disaster = losses experienced & harm caused (impact on community)
What’s important / needed for resilience
Vulnerability & community threshold (capacity to cope)
Types of vulnerability
- physical (hazard prone area, physical barriers)
- economic (losing jobs/incomes)
- social (DWAGES - disadvantaged / most vulnerable)
- knowledge (lack training & education /religion & beliefs may limit understanding)
- environment (high population density in risky areas)
Resilience definition
Factors of resilience
How well a population can recover from a disaster
- metabolic flows (supply/consumption chains)
- governance networks (institutional structures / organisations)
- social dynamics (demographics, inequity)
- built environment (ecosystem services)
How to build resilience
- good international relationships
- good governance
- thorough training / awareness
- pre-planned conversations
Scales used to measure magnitude & intensity of tectonic hazards
- Mercalli = measures intensity of shaking produced by earthquake
- Moment Magnitude Scale (MMS) = measures earthquake magnitude based on seismic movement
- Volcanic Explosivity Index (VEI) = measures explosiveness of volcanic eruptions
The Pressure and Release Model (PAR)
Used to analyse factors which cause vulnerability (inter-relationships between hazards & wider context)
- root causes
- dynamic pressures
- unsafe conditions
Root causes
Economic, demographic and political processes which affect large populations or entire country
- weak governance
- mismanagement of industry
- high reliance on products/industries easily affected by hazards
Dynamic pressures
Local economic or political factors that can affect a community or organisation
Due to:
- lack of basic services (health, education, police)
- lack of training & education for locals
- poor communication between gov & locales
- rapid urbanisation
- deforestation
Unsafe conditions
Physical conditions that affect an individual
- informal settlements
- lack of health & safety
- poor education
- poor infrastructure (electricity, sewage removal)
- unsafe building (disease/fire can spread easily)
- low income
(Kashmir)
Park model disaster response curve
Graphical representation of human responses to hazards
- steepness of curve shows how quickly an area deteriorates & recovers
- depth of curve shows scale of disaster
(More developed - less steep on deterioration, more steep on recovery & less deep)
Stages of Park model
Stage 1 - pre-disaster (modify cause & event)
Stage 2 - Relief (immediate local response - medial aid, search & rescue, appeal for foreign aid)
Stage 3 - Rehabilitation (foreign aid, modify the loss - temporary housing / services, food & water distributed)
Stage 4 - reconstruction (permanent rebuilding of physical & social infrastructure, reduce vulnerability to prevent further disasters (mitigation))
(Christchurch EQ, New Zealand)
Earth internal structure
- inner core = solid due to extreme pressures & high temp: produced by radioactive decay
- outer core = semi-molten rocks containing iron & nickel alloys, flows to create magnetic field
- mantle = semi-molten, temp gradient towards core creates convection currents - may contribute to lithosphere plate tectonic movement
asthenosphere = weakest part of upper mantle, lies beneath lithosphere - crust (Lithosphere) = thinnest, least dense & lightest layer of earth we live on made up of tectonic plates, oceanic crust a lot thinner than continental crust
Mantle convection
- mantle heated from below (core)
- in areas that are hotter it rises upwards (closer to core), area that are cooler sink down (near lithosphere)
- results in convection currents in mantle
- produces horizontal motion of mantle material close to Earth’s surface
Types for plate boundaries
- Destructive = move towards each other (earthquakes, volcanoes, ocean trenches)
- Constructive = away from each other (earthquakes, volcanoes, rift valleys, ocean ridges)
- Conservative = slide past each other in same direction at different speeds or opposite direction (friction overcome & plates slip past in sudden movement, shockwaves produce EQ)
What occurs at constructive plate boundaries
- sea floor spreading (paleo magnetism)
- ridge push & slap pull
Sea-floor spreading & paleo magnetism
Paleo magnetism = study of past changes in earth magnetic field, reverses every 200,000 years
- tectonic plates split apart from each other as magnetic field reverses & new rock comes from underneath
- as a result of mantle convection (less dense material rises, forming mountain/elevated area of sea floor)
- creates mid ocean ridges between 2 oceanic plates / rift valleys between 2 continental plates
Ridge push & slab pull
- driving force of plate tectonics
- mid-ocean ridges fall away under gravity, pushes plates further apart, widening the gap
- as plate is pulled at other end by gravity fed subduction, sinks into mantle
Volcano primary & secondary hazards
Primary hazards:
- lava flows
- pyroclastic flows
- ash falls
- gas eruptions
Secondary hazards:
- lahars
- jokulhlaup
(Mt Nyiragorgo in republic of Congo)
Lava flows
- molten magma flows on earth surface
- viscosity determined by amount of silicon dioxide
- buildings burnt / covered
Pyroclastic flows
- frothing bubbles of molten magma in volcano vent
- volcano bursts explosively to eject dense mixture of hot gases & pyroclastic material (glass shard, pumice, crystals, ash)
- can reach up to 1000C
- moves rapidly down volcano
- everything destroyed
- leaves behind volcanic deposits (up to 200m thick)
- causes floods (secondary hazards)
Ash falls (tephra)
most ash fall locally
- roof collapse
- choke machinery/electronics
- ppl/animal breathing difficulties
- bury crops & vegetation
- disrupts flight paths of planes
Lahars
Water mixed with volcanic deposits flows rapidly along existing valley
- caused by heavy rainfall from volcanic ash / volcano water vapour
Jokulhlaup (glacial run)
Glacial outburst floods
- where water accumulates in subglacial lake beneath glacier
- breaches damn & drains
Strategies to modify an event (reduce risks)
- land use zoning (keep residential/commercial areas away)
- engineering defences (sea walls, mangroves)
- diversion of lava flows (use seawater to solidify lava)
- hazard resistant designs (retrofit/aseismic buildings)
Tsunamis
result of sea bed & large water column displacement
- caused by sub-marine earthquakes at subduction zones, earthquakes movement causes seabed to thrust up = displaces water
- volcanic eruptions eject material into sea = displaces water
- landslides cause land to fall into sea = large quantities of water displaced
displaced water becomes tsunami waves as waves reach shallower water in coastal areas = waves become higher
Shallower water = friction between tsunami waves & seabed increases, tsunami wave slows down = decreased wavelength but increased wave height
Subduction zone
Where dense oceanic crust descends under less dense crust and melts into mantle at Benioff zone
destructive plate boundary
Shield volcanoes
- at constructive plate boundary (diverging)
- lower silicates & gas content in magma
- continuous eruption
- calmer eruption
- runny basaltic lava
- gentle slope & short volcano
Composite volcanoes
- at destructive plate boundaries (subduction)
- higher silicates & gas content in magma
- longer dormancy (less frequent eruptions = pressure builds up = explosive eruption)
- viscous (thick) andesitic lava
- steep slopes & tall
Landslide stresses
- angle of slope
- rainwater/saturation (encourages soil movement)
- vibration (less consolidated area)
- cliff erosion (creates stealer slope & less stable rock)
Landslide strengths
- less lubricant layers
- tree/vegetation roots (bind soil together)
- more consolidated material (rock type = less likely to move)
- porosity of soil (less permeable = more surface run off = less saturated so stronger)
Hydrometeorological hazards
- floods
- droughts
- hurricanes
- tornadoes
- landslides
Caused by extreme meteorological/climate events
Stages of hazard management cycle
Response (protection, evacuation, close transport)
Recovery (insurance, political alliances, scientists)
Mitigation (land use zoning, healthcare services, rebuilding)
Preparedness (evacuation, training, land use zoning)
Earthquake waves primary & secondary hazards
Primary:
- ground shacking (infrastructure collapses)
- crustal fracturing (energy released causes crust to crack)
Secondary:
- liquefaction (surface rocks shake violently & become liquid, lose ability to support building foundations)
- landslides (violent shaking creates stress)
What influences vulnerability & resilience
Development/social
Inequality of access to
- education
- housing
- healthcare
- income opportunities
(DWAGES)
What influences vulnerability & community resilience
Geographic
governance
geographic factors
- population density
- isolation
- accessibility
- degree of urbanisation
Strategies to modify (change) vulnerability & resilience
- education (drills, training)
- high tech monitoring (sensors, computer models)
- community preparedness (towns work together, prepare alert systems)
- adaptation (EOC, seismic retrofits: pump stations, police stations)
- models forecasting disaster impacts
- prediction (early warning systems)
Strategies to modify loss
- emergency aid (navy, volunteers, EOC)
- short term / long term aid (charities, insurance companies)
- insurance (insurers/NGOs)
- actions of affected communities
Hot spots
Cause intra-plate volcanoes/earthquakes
- mantle plumes occur at areas where heat rises
- high heat/low pressure at base of lithosphere = rock melts
- magma rises & volcano formed
- volcanoes move away as tectonic plates move over hotspot which remains stationary
- volcanic island formed
Hazard profile (definition & aspects)
Compares all physical process to help decision makers identify, rank hazards & decide how to allocate resources
- magnitude
- speed of onset
- duration
- areal extent
- spatial predictability
- frequency
Global distribution of volcanoes
- majority at destructive plate boundaries - melting magma at subduction zones, rend to be more violent
- pacific, dominated by subduction zones = lots of volcanoes
- some at constructive plate boundaries, plates pull apart & magma rises - less violent
- none at conservative plate boundaries
- hot spots cause intra-plate volcanoes eg. Hawaii, mantle plumes create mid plate eruptions
Earthquake waves:
P waves
- short wavelength
- travel fast through solid & liquid
- waves push & pull in direction of travel = creates compression & extension zones
S waves
- longer wavelength
- slower waves
- only moves through solid rock
- move at 90 to direction of travel
L waves
- longest wavelength
- slowest waves
- only move at surface
- most destructive waves
- largest amplitude
- shake ground from side to side as travels
Types of natural hazards
Geophysical hazard
- earthquake
- volcano
- landslide
(Hydro)Meteorological hazard:
- cyclones
- hurricanes
- typhoons
Hydrological hazard:
- tsunami
- drought
- flood
- avalanche
Why might more powerful hazards not cause the most deaths in some regions
- better transport links (aid arrives faster, decreases injuries becoming fatalities)
- richer / more developed (better infrastructure, aseismic buildings decrease deaths)
- lower population density (fewer people exposed to hazards, less chance of being trapped by collapsing buildings or landslides)
Why have the no. of reported hazards increased
- increased no. of recording stations = more detected in remote areas
- higher population density = more reporting (migration)
- more reliable & accurate detection equipment tech (smaller magnitude earthquakes detected)
- greater variety & coverage of media
How do insurance losses differ in developed countries
Developed countries have more financial vulnerability (high value of insured property)
Eg. USA = large population size (310 million) &high GDP = high value residential properties in Florida around San Andreas fault
Why no. of people affected by tectonic disasters have increased
- global population growth
- increased urbanisation = increased density
- many of poor live in vulnerable shanty towns unprotected from hazards
- improved incomes = more travel for leisure / business (people go to risky locations)
- increased economic development = gov & cities can invest in adaptation strategies (ppl live in vulnerable locations which may be damaged)
