Tectonics Flashcards
Where do the majority of tectonic hazards occur and what % of earthquakes are found in the Ring of Fire in the Pacific Ocean?
At plate boundaries, 70%
Why do most tectonic hazards take place at plate boundaries?
Plate boundaries can slide past or crash into each other so tectonic strain builds up between plates and when pressure exceeds friction, the rock fractures and huge amounts of energy released in form of seismic waves
What is ground-shaking in an earthquake?
Brittle crust either side of the fracture rebounding
What is the order of explosivity of different boundary types?
O-O –> O-C –> C-C
least explosive –> most explosive
What makes volcanoes more explosive at certain plate boundaries?
High silica content so high viscosity so high gas content
What are the case studies for an effusive, explosive, and very explosive volcano and what type of magma did each have?
Effusive: Iceland 2010 - basaltic
Explosive: Mt. St. Helen’s 2010 - andesitic
Very explosive: Mt. Pinatubo 1991 - rhyoltic
What was the VEI of the Icelandic eruption in 2010?
VEI 4
What was the VEI of the Mt. Pinatubo eruption in 1991?
VEI 6
Which type of plate movement has a shallow focal depth and why is this dangerous?
Conservative - seismic energy has less distance over which it can dissipate so higher magnitude earthquake due to tectonic strain
What is the case study for conservative plate movement, what was its focal depth, and what was its magnitude?
Haiti 2010, 13km, 7.0 magnitude
Which plates were involved in the 2010 Chile earthquake?
Nazca and South American plates
What was the magnitude of the 2010 Chile earthquake and how many people were killed?
8.8 magnitude, 525 people killed
What type of plate movement was involved during the 2010 Chile earthquake and why did this make it so dangerous?
Convergent, shallow focal depth so greater intensity ground-shaking
Where and how do intra-plate earthquakes occur?
Occur along ancient faults, slip easily to accommodate regional strain so forces exerted at all sides and strain on ancient fault produced which releases energy in form of seismic waves
Why are intra-plate earthquakes sometimes more dangerous than ones at plate boundaries?
Usually low level of preparedness as they are considered as low risk due to not being located at a plate boundary
What is the case study for an intra-plate earthquake?
Gujarat, India 2001
What was the magnitude and how many people were killed as a result of the 2001 Gujarat, India earthquake?
7.7 magnitude, 20,000 people killed
What is a volcanic hotspot?
Area of mantle
How can a volcanic hotspot create a volcanic island chain?
Heat rises as stationary thermal plume, high heat and low pressure at base of lithosphere melts rock so molten rock rises through cracks and erupts on Earth’s surface, tectonic plates move over stationary hotspot and oceanic volcanoes can cool, forming volcanic island chain
What is an example of a volcanic island chain?
Hawaii
How hot is the inner core and what is this caused by (convection currents)?
6000°C, caused by radioactive decay
What causes the mantle to become less dense and rise into the lithosphere (convection currents)?
Heat from the inner core radiates into the outer core and then the mantle
Which direction is the mantle forced in when it becomes less dense and rises into the lithosphere (convection currents)?
Sideways
What happens to the mantle after it is forced sideways in the lithosphere (convection currents)?
Cools down and becomes more dense so sinks back down to the core to form a convection current
What causes plate movement, what is this process known as, and what is the application for this (convection currents)?
Friction between slow-moving mantle and crust, convection traction, Nazca plate moves at 8cm/year
What drags the rest of the plate into the subduction zone (slab pull)?
Enormous weight of tectonic plates
What happens after the rest of the plate is dragged down into the subduction zone (slab pull)?
Plate is cooler as it is dragged down towards mantle so more dense than surrounding mantle which further facilitates plate movement
At which boundaries does slab pull take place and what is an example?
Oceanic-continental boundaries, Ring of Fire
Wadatti-Benioff Zone definition
Area of seismicity that corresponds with a slab being thrust downwards in the subduction zone
What is an example of a Wadatti-Benioff Zone?
Nazca plate subducting beneath South American plate
What generates varying focal depths in the Wadatti-Benioff Zone?
Different rates of movement of crustal rock at various points
What is the focal depth of a fracture also known as and what is it important in determining?
Focal point = hypocentre, important in determining surface magnitude
Which are the most dangerous seismic waves?
L waves - high amplitude
What are the 3 secondary hazards of earthquakes?
Landslides, liquefaction, tsunamis
Which communities are at risk to landslides?
Communities located at bottom of a steep slope comprised of unconsolidated sediment
How does a landslide occur?
Ground-shaking and gravity cause loosely-packed sediment to fall down slope
What is the case study for landslides and how many people were killed?
El Salvador 2001, killed 585 people
Which communities are at risk of liquefaction?
Communities located over loosely-packed, saturated ground
How does liquefaction occur?
Shaking causes ground to lose strength as friction between particles has been reduced so ground behaves like a liquid
What is the case study for liquefaction and how many houses were destroyed?
Niigata, Japan 1964, 3,500 houses destroyed
Which communities are at risk of tsunamis?
Communities located at O-C convergent coastlines
How does a tsunami occur?
Upward movement of ocean floor along boundary displaces low-lying column of water which creates ripple with long wavelength and small amplitude, amplitude increases as reaches land
What is the case study for tsunamis and how many people were killed?
Boxing Day Tsunami 2004, 225,000 died over 12 countries
What are the 4 primary hazards of a volcano?
Pyroclastic flows, tephra, lava flows, gas eruptions
What are pyroclastic flows?
Large, dense clouds of hot ash and gas that erupt out of side vents
How can pyroclastic flows destroy property?
Force of explosion causes material to travel downhill at high speeds and at temperatures of 1000°C
What is the case study for pyroclastic flows and how many people were killed?
Montserrat 1997, killed 19 people
What is tephra?
Rock fragments that can vary in size from ash particles to lava bombs and are ejected into atmosphere
Why is tephra dangerous?
Causes large areas to be blanketed in ash which kills vegetation, poisons water, and causes buildings to collapse
What is the case study for tephra, how big was the tephra cloud, and what did it cause?
Iceland eruption 2010, 10km tephra cloud, caused global flights to be cancelled
What are the 2 secondary hazards of a volcano?
Lahar, jokulhlaup
How is a lahar formed?
Particles of ash trigger heavy rain which remobilises fallen ash and causes volcanic mudflow
What is the case study for lahars and how much sediment destroyed farmland?
Mt. Pinatubo 1991, 3km³ of sediment
What does the Deggs Model show?
Shows interaction between geophysical hazard and vulnerable pop. - disaster occurs when vulnerable pop. exposed to hazard
What is the case study used for the Deggs Model?
Mt. Pinatubo 1991
How large was Pinatubo’s tephra cloud and why did this lead to disaster (Deggs Model)?
24km tephra cloud, vulnerable pop. didn’t have slanted roofs so ash accumulated and roofs collapsed
What is the Hazard-Risk Formula and what does it do?
Risk = hazard x exposure x vulnerability - breaks down the components of risk
What is the case study used for the Hazard-Risk Formula and what is the application for each component of risk?
Haiti 2010, hazard: 7.0 magnitude and 13km focal depth, exposure: 25% of pop. 20km from epicentre, vulnerability: brittle housing
What does the Disaster-Age Index show and what is the case study used for it?
Children and elderly more likely to suffer from hazards (weaker immune systems, less mobile), Tohoku 2011
How many people died as a result of the Tohoku 2011 earthquake and what % were aged 65+ (Disaster-Age Index)?
15,000 died, 55% aged 65+
What does the PAR model show and what is the case study for it?
Shows progression of vulnerability as a form of pressure, Haiti 2010
What was the root cause of vulnerability in Haiti (PAR model)?
Low levels of economic development
What % of Haiti’s population are living on less than $2/day (PAR model)?
72%
What was the dynamic pressure of vulnerability in Haiti (PAR model)?
Poverty - majority of residents couldn’t afford to build aseismic houses
What were the unsafe conditions in Haiti and what % of buildings were made of weak concrete (PAR model)?
Brittle housing, 90% made of weak concrete
What was the magnitude of the Haiti earthquake and how many people died as a result?
7.0 magnitude, 230,000 died
What is VEI a measure of, how is it calculated, what is the scale, and what kind of scale is it?
Explosivity, calculated by volume of ejected tephra and height of eruption cloud, 0-7, logarithmic (increase of 1 = explosion is 10x more powerful)
What is MMS a measure of, what is it based on, and what is the scale?
Seismic energy released, based on seismic movement of earthquake, 0-9
What are the 6 factors of a hazard that influence the scale of a disaster?
- Magnitude (LE: preparedness)
- Speed of onset (LE: magnitude)
- Duration (LE: mag.)
- Areal extent (LE: which hazard)
- Spatial predictability (LE: mag.)
- Frequency (LE: mag.)
What were the speeds of onset for the Haiti 2010 and Tohoku 2011 earthquakes?
Haiti: 0s
Tohoku: 60s
What were the durations of the Haiti 2010 and Tohoku 2011 earthquakes?
Haiti: 30s
Tohoku: 6 mins
Which human factors can increase vulnerability?
Education, income, housing, healthcare, nutrition
How many people died of cholera after the Haiti earthquake and how did this occur (poor healthcare increasing vulnerability)?
10,000 killed, contamination of water sources by UN peacekeepers so water-borne diseases arose and poor healthcare so less likely to recover
What % of school-aged children attend school in Haiti and why is this an issue (poor education increasing vulnerability?
50%, less qualified so less earning potential so decreased ability to afford aseismic housing OR less knowledge of what to do in event of an earthquake so less likely to evacuate
What % of Haiti’s population face food insecurity and why is this an issue (poor nutrition increasing vulnerability)?
42%, weaker immune systems due to malnutrition so less likely to survive spread of disease in aftermath of a hazard
What are mega-events?
High impact, low probability events
Why was the Boxing Day 2004 tsunami classed as a mega-disaster?
Many countries affected and long-term economic impacts - 90% drop in hotel bookings
Why was the Iceland 2010 earthquake classed as a mega-disaster?
Had impacts on global economy and supply chain - 100,000 air journeys were cancelled which cost airlines £130m/day
What are multiple hazard zones?
Areas where a number of physical hazards combine to create an increased level of risk
Which areas are generally classed as disaster hotspots?
Located at a plate boundary, high density of people (urban), developing countries
What are the 4 stages of the hazard management cycle?
- Response
- Recovery
- Mitigation
- Preparation
How much did the EU pledge to help Haiti in providing food and shelter after the 2010 earthquake (response)?
£122 million
Who aided reconstruction of key infrastructure in Haiti after the 2010 earthquake (recovery)?
World Bank
What are carried out and built in the mitigation stage of the hazard management cycle?
Risk assessments carried out, hazard-proof buildings built
What national day does Japan hold on 1st September every year (preparation)?
National Disaster Prevention Day
What is an evaluation of the hazard management model?
Researchers argue that cycle is too generic and unquantifiable
What does the Parks model help us to understand and what is it useful for?
The time dimension of resilience, useful to compare events
What are the 4 stages of the Parks model?
- Hazard
- Deterioration from normality
- Response and hazard management (length depends on governance)
- Recovery - normality and improving infrastructure
What is an evaluation of the Parks model?
Researchers argue that it doesn’t account for different models of economic, social, or political development
Forecasting definition
Providing % chance of a hazard occurring based on past events
Prediction definition
Knowing when and where a hazard will occur on a spatial and temporal scale
Which natural hazards can be predicted and which can’t?
Can be: Volcanoes (but not magnitude), tsunamis (partially)
Can’t be: Earthquakes (but can forecast risk)
Which 2 pieces of equipment can be used to predict a volcano and what do they do?
- Tilt meters - record volcano “bulging” as magma rises
- Gas spectrometer - analyses gas emissions
What formed before the Mt. Pinatubo 1991 eruption occurred and how many were evacuated?
Bulge and lava dome, 25,000 evacuated
How can an earthquake event be managed?
Base isolation
How does base isolation manage an earthquake event?
Building is built away from ground on flexible pads known as base isolators so building shaking is reduced or doesn’t happen
What % does base isolation reduce damage to key structures by and how many buildings in Japan use base isolation?
80%, 9,000 buildings
What is an evaluation for base isolation in managing an earthquake event?
Expensive so unlikely to be an option for a developing country
How are tsunami events managed?
Sea walls prevent tsunami from travelling inland by slowing the flow
How many km of sea walls have been built in Japan since 2011 and how much did this cost?
395km, cost £9.1 billion
What is an evaluation for sea walls managing tsunami events?
Provides a false sense of security as magnitude of tsunami may overcome sea wall and prevents residents from being able to see ‘natural’ warning sign of water retreating
How are volcanic eruption events managed?
Diverting lava flow
How does diverting lava flow manage a volcanic eruption event?
Lava sprayed with sea water which solidifies and creates a wall which leads to a diversion
What is an evaluation for diverting lava flows managing a volcanic eruption event?
Dependant on location (can only be used at coastal regions)
How can vulnerability in an earthquake event be managed?
Preparedness and education
How does preparedness and education manage vulnerability in an earthquake event (Japan application)?
Preparedness - 5pm every day Tokyo plays song on loudspeakers to test earthquake warning systems
Education - National Disaster Prevention Day
What is an evaluation for preparedness and education managing vulnerability in an earthquake event?
Warning systems need to be inclusive for old/young/disabled people
How can vulnerability in a tsunami event be managed?
Networks of sensors can be used to detect a tsunami and communications infrastructure can be used to alert coastal areas
What is an evaluation for managing vulnerability in a tsunami event?
Elderly may not have access to phones or internet data so don’t receive tsunami alerts
How can loss from a natural hazard event be managed?
International aid e.g. UN peacekeepers in Haiti
What is an evaluation for international aid managing loss from a natural hazard event?
UN peacekeepers caused the spread of cholera in Haiti by contaminating water sources so a further 10,000 people were killed
