Tectonics Flashcards
What is a tectonic hazard?
A natural event formed by tectonic processes which has the potential to threaten both life and property.
What are the three types of plate boundary?
- Divergent
- Convergent
- Conservative
Example of divergent plates
North American and Eurasian
Example of convergent boundary
Nazca and South American
Example of conservative boundary
North American and Pacific
Features of a divergent boundary
- Shallow earthquakes
- Volcanic is the eruptions - effusive
- Rift valleys
- Runny basaltic lava
- Gassy eruptions
- Mid Ocean Ridge
- Transform faults
- Island volcanoes
Features of a convergent boundary
- Medium to deep earthquakes
- Fold mountains
- Ocean trenches
- Explosive volcanoes (oceanic to continental)
- Batholiths - a mass of intrusive igneous rock (continental to continental)
- Dangerous eruptions of viscous lava
- Pyroclastic flows
- Slab pull
Features of a conservative boundary
- Medium to shallow earthquakes
* Some show a pattern of earthquakes - transform faults
Why is the lava viscous at a convergent oceanic to continental boundary?
- Introduction of silica from millions of years of sediment and sand deposited onto the ocean bed.
- The partial melting of the continental crust.
What is the Benioff Zone?
Area of seismicity that relates to the slab pull of a plate as it subducts below another
Why is there no volcanic activity at a continent to continent convergence?
The lava is too viscous
Why is there no ocean trench at a continent to continent convergence?
There is almost no subduction due to buoyancy of the continental crust
What are intraplate earthquakes?
They occurs in the middle of tectonic plates where the pressure of the plate being squashed and forced to move builds up and is released through the cracks in the rocks associated with fault zones.
This results in an earthquake.
Example of intraplate earthquake
New Madrid between 1811-1812 4000 earthquakes were recorded.
1811 - 7.5
1812 - 7.3
1812 - 7.5
Earthquakes at the North American plate
Faults were left after North America split from Rodina.
When the plate is under strain as the plates move, the fault zone takes some of the brunt and releases strain energy in the form of earthquakes.
The crust
- The thinnest layer - 75km
- Relatively cold
- Solid but brittle
- Oceanic and continental
The lithosphere
Top layer of crust
The Asthenosphere
- Top layer of crust
* Where the convection currents are
What is rheid?
Molten/semi solid
The core
Mostly nickel and iron
The inner core
- Solid
* Under intense pressure
The outer core
- Liquid/molten
* 4000 - 6000 ‘C
The mantle
The largest section
The inner mantle
- Mostly non metals
- Solid because of high pressures
- 3000’C
The outer mantle
- Bottom layer is liquid rock - 1400-1300’C
* Upper layer is rheid - lower temperature
What is ridge push
Magma that rises pushes the plates apart.
It is a continuous process which is thought to have lead to sea floor spreading.
What is slab pull?
- Gravitational pull of subducted lithosphere is a driving force of plate movement
- Cold, dense lithosphere sinks at an ocean trench, pulling the rest of the plate with it
What is sea floor spreading?
When convection currents force the plates to move apart and material rises
Fissure eruptions
Evidence of active rifting on MOR.
The lava is basalt
What is palaeomagnetism?
- The earth traps any iron and lines itself with the north pole at that time
- Magnetic field reverses roughly 4 times every million years
- A striped pattern is left behind - white stripes showing the reversal
What is happening to the MOR?
- The crust either side of the MOR is moving apart
* Radiometrically date them to calculate the rate of spreading
What is magnitude?
The size or extent of an event.
Each unit releases about 32 times more energy.
Hotspot volcanoes
- Occur in the centre of plates
- The surface expression for a mantle plume in the centre of a plate
- E.g. Hawaii
What is a mantle plume?
Stationary area of high heat flow from the mantle, which rises from depth and produces magma that feeds a hot spot volcano.
Factors affecting magnitude
- Seismic gap
- Types of movement/boundary
- Depth of the focus
What is a seismic gap?
Time period since last earthquake
Earthquake waves
- Primary waves
- Secondary waves
- Love waves
Primary waves
- Arrive first
- Compression and extensional movement
- Travel within the Earth
Secondary waves
- Arrive second
- Up-down movement
- Travel within the earth
Love waves
- Arrive last
- Long waves
- Surface waves
- Most damaging waves
Secondary hazards of earthquakes
- Liquefaction
- Landslides
- Tsunamis
Liquefaction
- Waves cause water pressures to increase in sediment and grains to lose contact with each other
- Water saturated sediment temporarily loses strength and acts as a fluid
- The most vulnerable areas are bays or marshland that we’re pumped with material
Landslides
- Large mass of material moves downslope
- Can be triggered by liquefaction
- 87,000 killed in Kashmir in 2005
Tsunami
- Wave of water which is usually caused by an earthquake.
* Usually caused by a dislocation of a larger section of crust on the sea floor, causing displacement of water.
Primary hazards of volcanoes
- Lava flows
- Pyroclastic flows
- Ash flows
- Gas eruptions
Secondary hazards of volcanoes
- Lahars
* Jokulhaups
Lava
- Viscosity is determined by temperature and chemical composition
- Hotter, low-silica lava flows fastest
Basaltic lava
- Hottest lava - 1000-1200’C
- Low silica
- Flows readily and travels far
- The Hawaiian islands were built up from the sea floor from successive basaltic lava flows, forming large shield volcanoes
Rhyolitic laval
- Lower temperatures - 800-1000’C
- Highly viscous - slow
- Produces explosive volcanic domes
Andesitic lava
- Viscosity depends on quantity of sediment subducted
- Eruptions are characterised by a mixture of explosive activity and lava flows
- Very dangerous
Effusive eruption
- Non explosive release of lava
- Lava gently wells up from the ground and overflows, cooling on its way down the slope
- Common in a Hawaiian type event
Peléan eruption
- Type of explosive eruption
- Large amount of gas, dust, ash, and lava fragments are blown out of the volcano and the andesite lava dome collapses
- Pyroclastic flows
- Landslides
- Andesitic lava
- Very dangerous
Plinian/Vesuvian eruption
- Eruptive columns reach up to 2-45 km into the atmosphere
- Can last days
- Regions affected are subjected to heavy pumice/ashfall - which eventually settles in a thick layer on the ground
- E.g. Mt St Helens
Pyroclastic flows
- Most dangerous eruptive feature
- Move down side of the mountain at extreme speeds
- Incredibly hot - can melt snow Bank and ice deposits, which mixes with tephra to form lahars
Lahar
- Fast moving mudslides
* E.g. Nevada Del Ruiz, 1985
Haiti earthquake 2010 information (developing example)🇭🇹
- Magnitude of 7.0
- Large seismic gap - 1770
- Epicentre 16 miles west of the capital, Port au Prince
- Shallow focus - 13km
- Had been hit by a storm in 2008 which killed 800 people
- Country has national debt and poverty
- GDP per capita $674
- Doctor:patient - 1:4000
- High risk of water and vector borne diseases
Social impacts of the Haiti earthquake🇭🇹
- 230 000 deaths
- 300 000 homeless
- Crush injuries - gangrene -amputation
- No utilities
- Gangs - unfair distribution of resources
- Lack of ongoing education
- Mass burials and burnings create risk of disease spreading
- Lack of organisation lead to cholera outbreak which killed 7000
Environmental impacts of the Haiti earthquake🇭🇹
- Damaged infrastructure
- Hospitals collapsed
- 20 million cubic metres of rubble and less than 5% was cleared
- 100 000 damaged buildings that are still usable but many can’t afford them
Cause of Nevado Del Ruiz event, 1985🇨🇴
- An eruption released ash and pyroclastic material
- This melted 5-10% of snow and ice on the Arena Crater
- This mixed with ash to form a lahar
Social impacts of Nevado Del Ruiz, 1985🇨🇴
- 23,000 deaths
- 10,000 homeless
- Many traumatised - bodies discovered a week after the event
Environmental impacts of Nevado Del Ruiz, 1985🇨🇴
- 85% of the town of Amero covered
- Roads and bridges destroyed which made aid supplies and access difficult
- Water contaminated with materials such as lead
- 1000 head of cattle killed
- 30,000 cattle stressed which decreased milk production
What is a jokulhlaup?
Glacial outburst floods when a volcano erupts underneath a glacier
How were the impacts of the 1996 joklhlaup in Iceland reduced?🇮🇸
The government had an effective hazard plan and had already evacuated nearby areas, preventing any deaths
Impacts of the 1996 joklhlaup in Iceland🇮🇸
- Destruction of the southern road in Iceland which left problems for many months as there was no alternative road
- 1 billion kroner to repair the road but with a low population of 265,000, the countries had a lower GDP to pay for it
New Zealand earthquake 2010 information🇳🇿
- Magnitude of 7.1
- Shallow focus of 10km
- Epicentre was 40km from Christchurch
- GDP per capita was $30,500
- Large seismic gap - 1922
Impacts of New Zealand earthquake🇳🇿
- 1 death and 2 major injuries
- Private insurance prices rose as high as $4 billion
- Damaging aftershocks up to Magnitude 6.3
How were the impacts of the New Zealand earthquake reduced?🇳🇿
- Most buildings were under reinforced construction
- $20M was spent on soil compaction previously to reduce chance of liquefaction
- Residents were asked to boil water until no contamination was found
- 16 ambulances operational within 30 minutes of the earthquake
- Hospital has emergency generators
- 90% of electricity was restored on the same day
- The army was deployed to the worst affected areas
What is a disaster?
When a hazard causes significant impact on a vulnerable population
What is a vulnerable population?
- A population that wouldn’t be able to deal with the hazard.
- Factors are: finance, governance, dealing with a prior event, emergency services, population density and preparation and education
What is the pressure release model?
Risk = hazard + vulnerability
Hazard risk equation
Risk = hazard x exposure x vulnerability/manageability
What is the resilience of a country?
- The ability to recover from a disaster
* Factors are: community cohesion, GDP, insurance and governance
Sichuan, China earthquake 2008 information (emerging example)🇨🇳
- Population of 15 million
- Magnitude of 7.9
- Epicentre 80km from capital city
- Shallow focus of 19
- Highly industrial region
Social impacts of Sichuan earthquake 2008🇨🇳
- 69,000 deaths
- 4.8 million homeless - 1 million tents, water and medical supplies provided by government
- Most schools collapsed
- 3 year rebuild
Economic and environmental impacts of Sichuan earthquake 2008🇨🇳
- 40% of chemical factories damaged
- 80 tonnes of ammonia leaked, causing major water contamination
- $137.5 billion spent on rebuilding
Japan earthquake 2011 information (developed example)🇯🇵
- Magnitude of 9
- Triggered tsunami
- Fukushima Daiichi nuclear power plant was hit
Impacts of Japan earthquake 2011🇯🇵
- 16,000 deaths from tsunami (60% elderly)
- Some cracking and liquefaction
- High radioactive releases which contaminated water in the ocean and fishing grounds
- Liquefied natural gas prices rose
- Other countries shut down some of their nuclear reactors
How were the impacts of the 2011 Japan earthquake reduced?🇯🇵
- Land use zoning
- Earthquake proof buildings
- Text message system
- Regular earthquake drills
Haiti - potential factors🇭🇹
- 61% attend school
- Gangrene caused over 1000 deaths
- 7% have HIV
- Few have access to good healthcare
- 47% vaccinated against tetanus which has a high fatality rate of 70-100%
- 16% of secondary deaths from diarrhoea
- 90% of buildings in Port au Prince collapsed or were severely damaged due to no building regulations
- Weak government neglected building standards and agricultural- cash crops
Heimeay, Iceland 1973🇮🇸
- In 6 hours, 5,300 residents were evacuated
- Icelandic State Civil Defence Organisation had an evacuation plan ready
- Sprayed sea water onto lava flows
- No deaths or panic
- National bank released funds
- Parliament increased taxes
- Government gave $2 million
Measuring earthquakes
- Moment Magnitude
- Size of waves
- Amount of rock moved
- Area of the fault broken by earthquake
- Resistance of the affected rocks
Duration of an event
- How long it will last
* Volcanic events typically last longer than earthquakes
Speed of onset
How much warning time before an event occurs
Areal extent
Area that the event has affected
Spatial predictability
How predictable the event is likely to be
Difficulties of hazard profiling
- Consider comparability of hazards
- Consider scale
- Can suggest severity but does not always relate to death rate
Hazard profiling
- Magnitude
- Duration
- Speed of onset
- Areal extent
- Spatial predictability
- Frequency
Natural factors of the Bam, Iran earthquake🇮🇷
- Shallow focus of 7km
- Directly under city
- Shaking vertically
- 5.26 am - early morning
- Cold January temperatures
Human factors of the Bam, Iran earthquake🇮🇷
- Recent construction was of poor quality
- Wooden structures had already been weakened
- Buildings were unstable and had old heavy roofs
- The 3 main hospitals were destroyed
- Emergency services struggled - facilities and infrastructure destroyed
- Lack of specialised medical training
Natural factors
- Magnitude
- Depth of focus
- Distance from coastline
- Tile of day and year
- Recent floods
- Steep relief
Why might death rate data be unreliable?
- Location - did it occur in a remote place?
- Political bias - over or understate death rate
- Level of development - LIC of high density
- Time - data collection methods change
What is a HILP event?
High impact, low probability event
Local human impacts of 2010 mega hazard in Eyjafjallakull🇮🇸
Grounded flights
Global human and economic impacts of 2010 mega hazard in Eyjafjallakull🇮🇸
- 100 000 cancelled flights
- Produce from Africa rotted-$65 million
- Imports and exports were affected
Local human and economic impacts of 2011 mega hazard in Japan🇯🇵
- 16,000 dead
- 4,000 missing
- 63% of dead were 60 or over
- Disabled power supply
- Nuclear energy became less trusted
- Contaminated fishing grounds
Global human and economic impacts of 2011 mega hazard in Japan🇯🇵
- Reduced availability and affordability of LNG
- Less people trusted nuclear energy and many plants were shut down
- Contaminated fishing grounds
- Asian market affected
- Increasing costs for new, safe nuclear reactors
What is a multiple hazard zone?
An area in the world where there are a number of different physical hazards that combine to create and increased level of disaster
What is a disaster hotspot?
A country or area extremely prone to disasters due to its range of physical hazards
Hazards in California🇺🇸
- Earthquake: active faults
- River flooding: winter storms and deforested hillsides
- Coastal flooding: subsiding area
- Drought: Mediterranean climate - Lack of water for rising population
- Wildfires: LA expanding into rural areas
- Landslides/mudslides: winter storms and burnt and eroded hillsides
- Fog/smog: cold sea air meets warm air and car pollution
Signs of an earthquake
- Changes in ground level
- Measurement of gases
- Changes in water levels
- Coloured skies
- Animal behaviour
The stages of the hazard management cycle
- Mitigation (prevention)
- Preparedness
- Response
- Recovery
What are players?
- The different groups of people who are involved in a hazard
- E.g. governments, NGOs, private donors
What is the Park’s Model?
It shows the stages of recovery from disruption based on development
What is the difference between micro techniques and macro techniques?
- Strengthen individual structures
* Large scale protective measure
What’s the difference between hazard mitigation and hazard adaptation?
- Strategies to avoid/delay/prevent
* Strategies to reduce impact
What is land use zoning?
- Local governments use a GIS map to consider areas at risk
* They can them decide what it is safe to use that area of land for
Diverting lava flows
- Building barriers and digging channels
- Usually unsuccessful as lava is unpredictable, landscape may not be suitable and stopping lava in one area may put others at risk
Building design
- Reinforced concrete
- Cross braved steel frames
- Steel pendulum
- Bass isolation
- Retrofitting - fitting after it has been built
Modifying vulnerability
- Prediction and warnings
- Improved community preparedness
- Changing a populations behaviour
Modifying the loss
- Emergency services
- Insurance
- NGOs/charities
Negatives of disaster aid
- Poor or corrupts distribution systems could be present
* Doesn’t encourage self help
What is the VEI?
- Volcanic explosivity index
* Relative measure of the explosiveness of volcanic eruptions
Why is it difficult for buildings to remain intact during an earthquake?
- Each type of seismic wave moves through the ground differently
- The waves all arrive within seconds of each other
- Anything attached to the ground would also move
Explain the geographical criteria that can be used to decide if a tectonic event is a hazard, disaster or mega disaster
- Definitions by the UN
* Suggestions if impacts contained within the scales for measuring volcanoes, tsunamis and earthquakes
An example of a multiple hazard and risk zone
- Vanuatu - 65 Pacific islands
- Vulnerable due to cyclones earthquakes, volcanic eruptions and the fact that they are isolated islands spread over a large area
Developed examples
- New Zealand🇳🇿
- Japan🇯🇵
- Iceland🇮🇸
Developing examples
- Iran🇮🇷
* Haiti🇭🇹
Emerging examples
- Colombia🇨🇴
* China🇨🇳
