Flashcards
Tectonics
Flashcards do conjunto (43)
- 1Why are some areas at greater risk from tectonic hazards than others?Tectonic hazards occur in specific locations related to plate boundaries and other tectonic settings, their distribution is uneven with some high risk areas and some low risk areas, tectonic events can generate multiple hazards when they occur.
- 2How are tectonic hazards caused?Caused by earth’s internal heat engine- radioactive decay of isotopes such as Uranium 238 and Thorium 232 in mantle and core generate heat which moves towards the earth’s surface and generates convection currents in the mantle.
- 3What does plate boundary type depend on?Motion-whether or not the plates are moving apart, colliding, or sliding past each other, plate type, whether the tectonic plates are oceanic or continental, oceanic plates make up the ocean floor and are high density, basaltic rock but only 7-10km thick, continental plates are thicker at 25-70km thick but made of less dense, granitic rock.
- 4What are hotspots and how do they form?Some volcanic eruptions are intra plate- they occur at mid plate locations called hot spots, isolated plumes of convecting heat called mantle plumes bring heat towards the surface generating basaltic eruptions that erupt constantly, a mantle plume is stationary, but the plate will move over it creating a chain of volcanic islands.
- 5Using examples, describe the different plate boundary settings:Divergent – Oceanic-Oceanic- Mid Atlantic Ridge-Iceland- Rising convection currents bring magma to the surface which erupts with small, basaltic eruptions to form new oceanic plate, minor, shallow earthquakes
Divergent Continent-Continent- African Rift Valley – Caused by geologically recent mantle plume splitting a continental plate to create a new ocean basin, basaltic volcanoes and minor earthquakes
Convergent – Continent- Continent – Himalayas, The collision of two continental landmasses creating a mountain belt as the two landmasses crumple, infrequent major earthquakes distributed over a wide area.
Convergent- Oceanic-Oceanic – One oceanic plate is subducted bellow another, generating earthquakes and a curving arc of volcanic islands
Convergent Ocenic-Continental- A oceanic plate is subducted bellow a continental plate, creating a volcanic mountain belt, large earthquakes and violent eruptions
Conservative- Oceanic-Continent- Plates slide past each other along transform faults, frequent shallow earthquakes but no volcanic activity. - 6Outline a few of the discoveries that lead to the theory of plate tectonics:1912- Alfred Wegner’s theory of plate tectonics- all plates were once joined
1930’s Alfred Holmes suggested the earth’s internal radioactive heat engine was responsible for driving mantle convection that forms tectonic plates
1960’s – the discovery of the asthenosphere, a weak, deformable layer beneath the rigid lithosphere on which the lithosphere moves.
1965- discovery of transform faults - 7Describe what happens at constructive margins:Mantle convection forces plates apart, tensional forces open cracks and faults between the plates creating channels through which magma rises to the surface to erupt, creating new oceanic plate Eruptions are small and effusive due to erupted lava being basaltic and having a low gas content and high viscosity. Earthquakes are shallow at less than 60km and have a low magnitude of less than 5.0
- 8Describe what happens at destructive margins:One plate is subducted beneath another, mantle convection forces pull plates towards subduction zones, due to rising gas beneath them, constructive margins have elevated altitudes, causing oceanic plates to slope down towards subduction zones – gravitational slide, cold dense oceanic plate is subducted beneath less dense continental plate, the density of the plate pulls it downwards- slab pull. Earthquakes occur at a range of focal depths 10km-400km, following the subducting plate- the Benioff zone and can yield a major magnitude of 9.0. the descending plate begins to melt at a depth by a process called wet partial melting. This generates magma with a high gas and silica content which erupts with explosive force.
- 9Describe what happens at collision zones:Two continental plates meet at a convergent margin, as both are low density neither are subducted, instead the plates buckle to create huge tectonic uplift and form fold mountains, magma is generated at depth but cools before it reaches the surface, collision zones are cut by huge thrust faults so shallow, high magnitude earthquakes are very common.
- 10Describe what happens at transform zones:Conservative plate boundaries consist of transform faults, joining up sections of constructive plate boundary traversing the surface of the earth in a zig zag pattern, sometimes act like a plate boundary in their own right creating areas of significant tectonic activity – san andreas fault, earthquakes along conservative boundaries have shallow focus depths so high magnitude earthquakes can be very destructive.
- 11What are earthquakes?An earthquake is the release of seismic energy built up as tectonic plates slide past each other and inevitably stick, causing tension to build, and over time putting the plates under ever increasing stress, the sudden release of this stress causes earthquakes- stick-slip behaviour. A pulse of energy radiates out in all directions from the focus, in some places displacing the surface, causing a fault scrap to be seen.
- 12What are the different types of wave an earthquake can generate?P Waves- Fastest and first on the scene, cause little damage
S Waves- secondary waves, travel slower and arrive next, cause considerable shaking and BIG damage
L waves – Love waves travel the slowest because they only travel across the surface, have a large amplitude and so cause significant damage, including fracturing the ground surface. - 13Explain some secondary hazards of earthquakes:Frequently generate large landslides, especially true in geologically young and unstable mountains such as the Himalaya. Landslides accounted for up to 30% of deaths in the 2005 kashmir earthquake
Liquefaction: particular hazard in areas where the ground consists of loose sediment such as silt, sand or gravel that is also waterlogged, often found in areas close to the sea or lakes, intense earthquake shaking compacts the loose sediment, forcing water to move upwards between the sediment, undermines foundations causing buildings to sink, tilt and collapse. - 14Describe some volcanic hazards:Lava flow – Extensive areas of solidified lava, which can extend several kilometres away from volcanic vents if the lava is basaltic and low viscosity, it can flow up to 40mph- present at Hot spot and subduction zone volcanoes
Pyroclastic flow- Very large, dense clouds of hot ash and gas at temperatures of up to 600 degrees that can flow down the flanks of volcanoes and devastate large areas -present at subductive volcanoes
Ash fall – ash particles and larger tephra particles can blanket huge areas in ash, killing vegetation, collapsing buildings, and poisoning water courses – constructive and subductive
Gas eruption- The eruption of carbon dioxide and sulphur dioxide, which can poison animals and humans in extreme cases- Subductive and hot spots
Lahar: Volcanic mudflows, which occur when rainfall mobilises volcanic ash, travel down river systems and cause major destruction- subductive
Jokulhlaup: Devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of melt water. – constructive - 15Give some case studies for Tsunamis:2004, Indian ocean, 9.2mg earthquake, 24m waves, 230,000 dead, 2006 Java Indonesia, 7.7mg earthquake, 2-6m waves, 800 dead, 2009 samoa, 8.1mg earthquake, 14m wave height, 190 deaths, 2011 japan, 9.0mg earthquake, 9.3m waves, 16000 dead.
- 16How are Tsunamis formed?? Tsunami are generated when a sub marine earthquake displaces the sea bed vertically because of movement along a fault line at a subduction zone. The violent motion displaces a large volume of water in the ocean water column, which then moves outward in all directions form the point of displacement. The water moves as a vast bulge in open water rather than a distinct wave. In open water they are barely noticeable, as the waves approach shore they slow dramatically, wavelength drops but wave height increases. Tsunami usually hit coastlines in a series of waves the affect of which is more akin to a flood than a wave.
- 17How is a disaster different to a hazard?A tectonic hazard is a natural event with the potential to cause harm to people and their property, a disaster is the realisation of a hazard.
- 18What does the hazard risk equation show:The hazard risk equation links vulnerability, hazard and capacity to cope, to show how each of these factors contribute to the overall risk level of a tectonic hazard
- 19Describe Haiti as a case study:2010 earthquake port au prince Haiti, low magnitude of 7.0 but still 160,000 deaths. Low access to resources, rapid population chance and urbanisation, poor, unsafe construction standards, weak infrastructure, poverty, lack of social safety net, lack of education, training and investment, limited decision making of general populace, poor governance and weak economic system, 50% of population under 20, port au prince, a city of 3.5 million, has no sewer system. 80% of prot au prince’s housing is unplanned informal slums
- 20How are earthquakes measured:Earthquakes are measured using the moment magnitude scale, a revised version of the richter scale, this measures the energy released by earthquakes, relating to the slip along a fault plane and the area of movement along a fault plane. It uses a logarithmic scale
The Mercalli scale also measures earthquake intensity on a scale of 1-12, this older scale measures what people feel during an earthquake, ie the intensity of ground shaking. This cannot be used to compare earthquakes because the shaking experienced during earthquakes is affected by building design/quality, ground conditions and other factors. - 21The relationship between magnitude and death toll is a weak one because:Some earthquakes cause serious secondary impacts such as landslides and Tsunamis, earthquakes hitting urban areas are likely to have greater impacts than those hitting rural areas, level of development and level of preparedness affect death tolls, isolated hard to reach places could have a higher death toll because rescue and relief take longer
- 22How are volcanoes measured:Volcanoes are measured using the volcano explosivity index which scores eruptions on a scale of 0-8 based on eruption height, volume of material erupted and the duration of an eruption.
Volcanoes with eruptions between 0-3 are associated with shield volcanoes and basaltic eruptions at constructive plate margins at mid plate hotspots. VEI eruptions from 4-7 occur at destructive plate margins, erupting high viscosity, high gas, high silica andesitic magma. - 23Give case study examples for volcanic eruptions in developing countries, developed countries and emerging countries:Developed: 2010: Eyjafjallajökull- Iceland, constructive margin, mid ocean rift, VEI=4, no injuries or deaths, major disruption to European air travel affecting ten million passengers and costing 1.7 billion dollars in economic losses, some flash flooding caused by ice melt
Emerging: 2010 Merapi Indonesia, destructive margin subduction zone, VEI=4, 353 deaths and 500 injured, 350,000 successfully evacuated, US$0.6 billion in losses, loss of rice harvest due to ash fall and some destruction of forests due to pyroclastic flows.
Developing: 2002 Nyriagongo (DRC) constructive margin, continental rift zone, VEI=1, 147 deaths, 120,000 made homeless, 15% of the city of Goma destroyed by lava flows, major international aid response launched, US$1.2 billion in economic losses. - 24Give case studies for an earthquake in a developed, emerging and developing countries:Developed: Canterbury (New Zealand), Magnitude 7.1, subduction zone, focal depth=10km, 100 injuries, no deaths, major building damage due to liquefaction, a magnitude 6.3 aftershock in 2011 killed 185, total costs= US$40 million
Emerging: Sechuan China, Magnitude 8.0, focal depth= 19km, continent-continent collision zone, 69,000 deaths, 370,000 injured, at least five million homeless, more than $140 billion in economic losses, about one third of deaths due to landslides - 25Give examples of a Tsunami in developed, emerging and developing countries:Developed: Tohoku (Japan) 2011, magnitude 9.0 earthquake, 9.3m wave, megathrust subduction zone, 16,000 thousand deaths, 6000 injured, US$300,000 billion in economic losses, 46,000 buildings destroyed, 146,000 damaged, huge damage to infrastructure, ports, water and electricity supply.
Emerging: 2010, Talcahuano Chile, magnitude 8.8 earthquake, 2.6m wave height, 525 deaths, 370,000 houses destroyed, US$15-30 billion in economic losses. Overall the earthquake was more damaging than the accompanying earthquake.
Developing: 2004 Indian Ocean, magnitude 9.2, 24m wave height, megathrust subduction zone, 230,000 dead, 125,00 injured, 1.7 million displaced across 15 countries, US$15 billion in economic losses. - 26What are hazard profiles and what do they show?Hazard profiles are tools used to compare tectonic hazards allowing for a better understanding of the risks associated with each. They show magnitude, speed of onset, spatial predictability, frequency, duration and areal extent of the hazard.
- 27Explain the influence of development and governance on the size of a disaster:The impacts of tectonic events are very much influenced by the level of development, both the 2015 earthquake in Nepal and the 2007 earthquake in chilie had magnitudes of 7.7, however, chilie has a HDI of 0.83, whereas Nepal’s was 0.55, 9000 people were killed in Nepal, only 2 died in Chile.
- 28List some factors increasing risk and how they can be mitigated:Population growth: Warning and response systems, Urbanisation and Urban sprawl: Economic wealth, Environmental degradation: Economic wealth, loss of community memory of hazards: government assistance programmes, very old/young population: Insurance- wow, ageing, inadequate infrastructure: community initiatives, greater reliance on water, power and communication systems: Scientific engineering, hazard engineering.
- 29Why is vulnerability unusually high in some areas?In some areas with low HDI rankings (bellow 0.55) there is an unusual level of vulnerability because: people lack basic amenities (water, food) in normal times, housing is informal, made without care of hazard resilience, access to healthcare is poor so disease spreads easily. Education levels are poor, so there is little knowledge of the risks posed by hazards. Low income families may lack a safety net of personal savings or a government one so have few resources after a disaster.
- 30What is governance and how can it link to the impacts of a hazard?Governance is the process by which a country/region is run. The effectiveness varies between locations: Meeting basic needs: areas with food supply water supply and health surfaces are likely to fare better than those without them, Planning: land use planning- not building habitation on the side of steep slopes, areas prone to liquefaction or volcanic risk areas, Environmental management: planting of forests can reduce landslides, the right monitoring equipment can help to warn of hazards, Preparedness: education and community preparedness programmes raise awareness and teach people how to prepare, act and respond, corruption – siphoning off ear-marked money for hazard management or bribes allows the construction of unsafe buildings and increases vulnerability. Open-ness governments with open, free media and press can be held to account, increasing the likelihood that preparation and planning take place.
- 31How can geographic factors affect the impacts of a hazard?Population density: highly populated areas are much harder to evacuate than low density areas, degree of urbanisation: highly urban areas are likely to have much higher death tolls and damage than rural ones, isolation and accessibility, often rural areas take much longer to reach due to limited access or isolation so rescue/relief operations can be delayed, less assets: healthcare, transport links, food stores, emergency services too.
- 32Why is disaster context important?Developed countries offer widespread insurance, allowing people to recover in the long term, government funded preparations such as Japan’s disaster preparation day – September 1st every year, and public education about risk, coping, response and evacuation, sophisticated monitoring of volcanoes, and where possible, construction of sea walls, regulated local planning systems which use land use zoning and building codes to ensure buildings can withstand hazards and aren’t built in unsafe locations.
- 33Describe some tectonic disaster trends:Hydro-met disasters such as floods, storms, cyclones and drought appear to have become more common over time, because of climate change and environmental issues such as deforestation. Tectonic hazards have not increased over time. Deaths have fallen due to better management , preparation and prediction, mobile communications allow people to warn people of disasters, number of reported disasters has stabilized as improvements in data coverage and accuracy of databases have increased. Number of people affected by disasters is increasing due to growing populations in dangerous areas.
- 34Outline the impacts of some mega disasters:2004 Asian Tsunami- 14 countries surrounding the Indian Ocean, thousands killed economic losses in Thailand, Indonesia, sri lanka and Somalia.
2011 Japanese Tsunami- only japan directly but had global consequences, disruption of ports, factories had impacts for global car production supply chain, and those of boeing jets
2010 Eyafjallajokul – over 20 European countries were affected by total or partial closure of their airspace. The ash-cloud from the eruption had a disruptive effect on air travel, over 10,000 cancelled flights, and £1 billion in losses. - 35Describe some characteristics of multiple hazard zones:Prone to regular earthquakes, tectonically active locations, geologically young with unstable mountain ranges prone to landslides, often in major storm tracks, may suffer from global climate perturbations
- 36Describe how tectonic hazards can be predicted:Earthquakes- no way of predicting, however areas of high risk can be identified- risk forecasting, areas that are prone to liquefaction or severe ground shaking, this can be used for land zoning purposes, seismic gaps- areas that have not experienced an earthquake for some time, and are overdue another one.
Volcanic eruptions- Volcanic eruptions, sophisticated monitoring equipment can measure changes as magma chambers fill and eruption nears, Tiltmeters and strain meters record volcanoes bulging as magma rises and seismometers record minor earthquakes that indicate an eruption is near. Gas spectrometers analyse gas emissions which can point to increased chances of eruption.
Tsunami- Partially- An earthquake induced Tsunami cannot be predicted, however seismometers can detect earthquakes and locate it then ocean monitoring equipment can detect a Tsunami in the open sea, this information can be relayed to coastal areas that can be evacuated. - 37What does the hazard management cycle show?The different stages of managing hazards in an attempt to reduce their impacts
Preparedness- community education and resilience building, including people know how to act before, during and after a disaster, prediction, warning and evacuation technology systems.
Mitigation- Acting to reduce the scale of the next disaster, land use zoning, hazard resistant buildings and infrastructure.
Response- immediate help in the form of emergency services/rescue to save lives and provision of aid to keep people alive: water, food, shelter.
Recovery: rebuilding infrastructure and services, rehabilitating injured and helping people to rebuild their lives. - 38Describe the ways a disaster can be modified:Disasters can be managed by modifying impacts, modifying the event, modifying the vulnerability and modifying the loss. Modifying the event is the most desirable, but isn’t always possible.
Modifying the event takes place before the event strikes, and seeks to reduce the scale of the event in terms of it’s aerial extent and magnitude
Modifying vulnerability: this involves getting people away out of the hazard and helping them to cope with the impacts Modifying the loss: This takes place after the disaster, reducing the short and long term losses by acting to aid recovery and reconstruction. - 39Describe some different ways to modify the event:Land use zoning: preventing building on low lying coasts, close to volcanoes and areas of high ground shaking and liquefaction risk. – Low cost, can save lives by removing them from high risk areas, but prevents economic development on some high value land, requires strict laws and enforcementAseismic building, cross bracing, counter weights, deep foundations – widely used technology can prevent collapse, protects both people and property, however at high costs for tall buildings, older buildings and low-income families are rarely protectedTsunami defences: tsunami walls and breakwaters prevent waves from traveling inland. This dramatically reduces damage and provides a sense of security but can be overtopped and comes at a very high cost. They are also ugly.Lava diversification channels, barriers and water cooling -diverts lava out of harms way, relatively low cost. This only works for low basaltic magma; the majority of killer volcanoes are not of this type.
- 40Describe some ways to modify vulnerabilityHi-tech scientific monitoring, used to monitor volcano behaviour and predict eruptions. -in most cases predicting an eruption is possible, warnings and evacuations save lives but costly so not all volcanoes in developing countries are monitored, does not prevent property damageCommunity preparedness and education- low cost, often implemented by NGO’s, can save lives through small actions. But does not prevent property damage and is hard to implement in isolated rural areas.Adaption: moving out of harms way and relocating to a safe area- would save both lives and property. High population densities prevent it, disrupts people’s local homes and traditions
- 41Describe some ways to modify the loss:Short term emergency aid- reduces death toll by saving lives and keeping people alive until longer term help arrives-high costs and technical difficulties in isolated areas Emergency services are limited and poorly equipped in developing countries Long term aid- reconstruction plans to rebuild an area and improve resilience – reconstruction can build in resilience. Through land use and better planning methods, very high costs, needs are quickly forgotten by the media. Insurance- compensation given to people to replace their losses-helps people to recover economically, does not save lives, few people in developing countries have access to insurance.
- 42Describe the process of seafloor spreading:In the middle of the oceans are huge mid ocean ridges, these are formed when magma is forced up from the asthenosphere and hardens forming new oceanic crust. The new oceanic crust pushes tectonic plates apart in a process called seafloor spreading. This theory was confirmed in 1950, when scientists linked the minerals inside the rock with the earth's magnetic field direction.
- 43Give a case study for a multiple hazard zone:The Philippians is a country consisting of over 7000 islands, of which 1000 are inhabited. population is settled along the coast- access to fishing, population=102 million, located in the pacific ring of fire- subduction of Philippians plate and sunda plate, 37 volcanoes, 18 are active, Most significant earthquake in 1976, 8.0Mg, killed 6000 people, 85% of which due to a Tsunami, 74% of population exposed to multiple hazards.