Edexcel A-level Geography - Tectonics

Tectonic location

Most earthquakes and volcanoes occur near plate boundaries

Divergent Plate Boundary

Cause effusive basaltic eruptions and rare shallow earthquakes (Mid-atlantic ridge - Iceland)

Convergent Plate Boundary

Cause violent andesitic eruptions and shallow, deep powerful earthquakes, volcanic cones, ocean trenches and mountains (Japan - Pacific plate moving NW under Okhotsk plate)

Conservative Plate Boundary

Cause powerful shallow earthquakes and diverted rivers along faults (San Andreas fault)

Infra-plate earthquakes

Caused by solid crust cracking over millions of years and primary collision at a plate boundary (New Madrid, Missouri)

Infra-plate volcanoes

Caused by hot spots from molten upwelling (Hawaii) or from mantle plume under crust (Cape Verde)

Convection currents

Caused by heat radiating outwards from core that occur due to mantle behaving like a viscous liquid

Earths structure

Core (Nickel/Iron), Mantle (870C solid and liquid), Crust (solid 1-75km)

Slab pull

When denser oceanic plates are subducted at cold downwellings by gravity

Ridge push

When magma rises at constructive margin and pushes the plates apart (Mid-atlantic ridge)

Paleomagnetism

Movement of plates apart identified by magnetic pattern caused by magnetic field reverse (every 4 million years). Mid-oceanic ridge contains iron that lines itself parallel to magnetic field and 'sets' after it cools, permanently marking magnetic field

Constructive processes

Activity = shallow, low magnitude earthquakes and effusive basaltic eruptions

Create = Rift valley, M.O.R, volcanic isle and transform faults

Destructive processes

Activity = shallow to 700km, high magnitude earthquakes (ocean-ocean plates)/ moderate magnitude (ocean-continent), explosive eruptions

Create = ocean trench, fold mountains (ocean-cont') or volcanic isle and ocean trench (ocean-ocean)

Transform processes

Activity = shallow, moderate magnitude earthquakes with usually no volcanic activity

Create = ridges and scars on the surface

Collision processes

Activity = shallow to middle, moderate magnitude earthquakes with usually no volcanic activity

Create = plateaus and fold mountains (Himalayas)

Magnitude factors

Seismic gap (time since last earthquake)

Depth of focus (0-75km)

Types of movement (subduction, collision, etc.)

Primary waves

Arrives first and fast, moves through rock and fluids whilst pushing and pulling (compresses) in travel

Secondary waves

Arrives second and slower than P waves, only move through rock in up and down movement

Love waves

Arrives last but moves fastest (only through crust surface), most damaging

Liquefaction

Earthquake secondary hazard; shaking sorts sediment that makes it act as a fluid

Landslides

Earthquake secondary hazard; mass material moves downslope (Kashmir 2005)

Tsunamis

Earthquake secondary hazard; water column displacement by plate thrust/volcano

Volcanic primary hazards

Lava flows, gas emissions, ash and pyroclastic flows

Lahars

Volcanic secondary hazard; mudflows

Jokulhlaups

Volcanic secondary hazard; meltwater floods

Basaltic lava

Hottest (1000-1200C), low silica/gas content, low viscosity (runny), gentle/effusive

Andesitic lava

Medium heat (800-1000C), intermediate silica/gas content, medium viscosity, violent

Rhyolitic lava

Coolest (650-800C), high silica/gas content, high viscosity, very violent

Hazard

Tectonic event with potential to threaten life and property

Disaster

When hazard causes significant impact (more than 10 deaths and over 100 affected)

Vulnerability

Ability to anticipate, cope, resist and recover

Resilience

Ability of a community to resist the impacts of a hazard by adapting and recovering

Factors affecting ability to cope

Location, resilience, preparedness, tech, knowledge of threat, community adaptation/ability to react and governance

Hazard risk equation

Risk = hazard x exposure x vulnerability / manageability (resilience)

Pressure and Release Model

New Zealand 2010

Event = 7.1 magnitude, 10km focus on Aus.- Pac plate boundary

Responses = 1 death and 2 major injuries, 16 operational ambulances, Hospital used emergency generators, 90% power back on by 6pm

Vulnerability/resilience = 14.3% elderly, GDP/C $30,500, reinforced houses, water boiled before use, $20 million spent on soil compaction 2005

Haiti 2010

Event = 7 magnitude, 13km focus on Carib - N.A plate boundary

Responses = 230,000 dead, all hospitals/services destroyed, roads damaged

Vulnerability/resilience = 34% 0-14 years, GDP/C $674, no reinforced buildings, high levels of poverty/disease, poor governance

Volcanic Explosivity Index

Measure explosiveness (1 = small and gentle ==> 8 = colossal)

Hazard Profiling

Resilience/vulnerability

Education, housing, healthcare, income, food, utilities/governance, age and disability

Haiti poor governance

61% school attendance

7% HIV

Poor sanitation (Diarrhoea)

90% capital buildings collapsed

Heimaey, Iceland 1973

Evacuation = 5,000 evacuated under 6 hours due to contingency plan

Dealt by = Lava stopped by spraying seawater, ash clearance from roofs, $2 million gov't funds, rebuilt property and monitoring seismometers

Bam, Iran 2003

Event = magnitude 6.6 at 5.52am, 7km focus

Response = 3 hospitals destroyed/services struggled and 70% houses gone

Governance = 1989 building code ignored as not enforced, lack of specialised medical training

Disaster trends since 1960

Steep exponential rise until decline 2000, most likely due to increased resilience and reduced vulnerability by government

Accuracy = most disasters recorded due to better global reporting network, ancient records less reliable, location may be remote/not reported

Spatial variation = Asia experienced far more disasters 2004-2013 (population)

Tectonic mega-disaster

Large scale by area or socio-economic impact - serious problems for management (may need international support)

High impact low probability event

Impossible to predict but very likely to occur over long time scales - require rapid global response and less resilience from globalisation

Multiple hazard zone

Philippines 2013, 2018:

Hazards = Earthquakes (7.2 2013), Typhoons (Haiyan 2013) and Volcanoes (Mayon 2018)

Resilience = stilt houses adapted for floods/storms but broken by earthquakes, buildings more resilient in capital

Vulnerability = hot and humid climate makes typhoons occur regularly, on active Philippine and Sunda plates, dense 102 million people, 74% vulnerable to multiple hazards, 18 active volcanoes

Tiltmeters

Earthquake indicator; react to change in ground levels

Gas measure

Earthquake indicator; radon gas can be released before 'quake

Parks Model

Mitigation

Land use zoning (California), Volcanic use zoning (New Zealand), Lava walls/channels

Preparedness

Modify vulnerability (monitoring systems, diverse economy, increase food production)

Response

After event; evacuation, immediate assistance and asses damage (by charity, services and insurers)

Recovery

After event; restoration of services, rebuilding infrastructure and socio-economic recovery

Micro management strategy

Strengthen individual buildings

Macro management strategy

Large scale protective measures

Hazard resistant engineering

Reinforced concrete and steel crossbracing

Internal Pendulum to decrease displacement

Base isolation, shock absorbers

Retrofitting old buildings

Cheap engineering

Lighter materials and single story (dome)

Sloped roofs to prevent ash build-up

Elevated buildings

Insurers

Protect economic livelihoods (compulsory in Turkey)

Emergency services

Reduce the loss after a tectonic event