Tectonics Flashcards
Assess the significant of earthquake hazard profiles in relation to the effectiveness of management strategies. (12)
INTRO
Hazard profiles show the key characteristics of earthquakes, such as areal extent, magnitude, duration and predictability. Hazard management involves a range of strategies to reduce disaster impacts by managing before, during and after a hazard strikes.
Hazard profiles represent the physical characteristics of a hazard but these are not the only factor that determines the impact of management.
Assess the significant of earthquake hazard profiles in relation to the effectiveness of management strategies. (12)
Paragraph 1 magnitude
Magnitude is a key element of a hazard profile and, in general, larger magnitude earthquakes are more likely to overwhelm management strategies. HIgher magnitude events such as the 2011 Japanese earthquake and tsunami showed that even countries with high levels of economic development cannot successfully manage a mega disaster. Deaths amounted to 18,000 and economic losses over $300 billion. Low-magnitude earthquakes can be managed by land-use planning and aseismic buildings. However, in low-income countries such as Nepal, where an earthquake occured in 2015, poverty means that few people live in buildings that can resist ground shaking and secondary hazards such as landslides.
Assess the significant of earthquake hazard profiles in relation to the effectiveness of management strategies. (12)
Paragraph 2 areal extent
Immediate response and rescue is made easier if the areal extent of an earthquake is small. For instance, the sequence of shallow earthquakes in Christchurch and Canterbury in New Zealand in 2010-11 was limited in areal extent, whereas the Kashmir and Sichuan earthquakes in 2005 and 2008 affected much larger areas. However, size or area affected is only one factor. The terrain in the Himalayas hampered the relief efforts in 2005 and 2008 due to rugged mountains and isolated, inaccessible settlements.
Assess the significant of earthquake hazard profiles in relation to the effectiveness of management strategies. (12)
Paragraph 3 frequency
If earthquakes are infrequent, such as the Himalayan ones already referred to, there is a risk that community preparedness will be low because the risks are overlooked. In areas where there is a low collective memory of a recent disaster, preparation and education are likely to be more thorough. It could be argued that this is the case in Japan, where the memory of previous earthquakes such as Kobe in 1995 and the Okushiri tsunami in 1993 meant the preparation for 2011 was reasonable: tsunami sirens were heeded by many and the death toll could have been much worse.
Discuss evidence for plate tectonic theory? [12]
POINT 1 WEGENER
Alfred Wegener’s theory of continental drift from 1912 was based on physical evidence that continents were once joined. The most basic evidence is the ‘jigsaw fit’, best shown by the east coast of South America fitting into the coast of west Africa. This could be a coincidence, but geological evidence such as the Appalachian mountains of the USA being geologically related to the Caledonian mountains of Scotland confirms it. Identical fossil remains of reptiles are also found in South America and southern Africa.
Discuss evidence for plate tectonic theory? [12]
POINT 2 SEA FLOOR SPREADING
This early theory based on evidence needed more convincing material to provide an explanation. The theory of seafloor spreading was developed by Harry Hess in the 1960s. Hess showed that mid-ocean ridges were places where new seafloor was created by eruption at what became known as constructive plate margins. Vine and Matthews confirmed this through the discovery of magnetic strips on the seafloor. This paleomagnetic evidence proved that new oceanic plate close to mid-ocean ridges were younger than seafloor some distance away. This magnetism in basaltic rock recorded periodic magnetic reversals and is mirrored either side of ocean ridges.
Discuss evidence for plate tectonic theory? [12]
POINT 3 TUZO-WILSON
Tuzo-Wilson recognised that iland chains like Hawaii are produced as oceanic plates move over fixed mantle ‘hot-spots’ creating active volcanoes as well as chains of older, extinct ones. In the late 1960s, the idea of convection motion in the mantle was accepted as the power-source for moving tectonic plates. The geophysics of earthquakes and mapping of the sea floor has also helped explain the geology of subduction through the discovery of Benioff Zones (earthquake locations which reveal the form of subducting plates) as well as ocean trenches. Evidence gradually built over the last century to not only confirm the former position of continents, but also to provide an explanation for how they have moved.
What are mega disasters
Mega-disasters are large-scale disasters on either an areal scale or in terms of their economic and human impact.
They pose serious problems for successful management to minimise impact and mitigate the impact of the disaster.
They need often require international management both short term and longer term.
Extreme events are likely to pose serious challenges for any governance, however well-planned, e.g. the 2011 Japanese tsunami
Assess the importance of governance in the successful management of tectonic mega-disasters [12]
POINT 1 - PREPAREDNESS
PREPAREDNESS -
82% of earthquake damage comes from collapsed buildings
Twisting steel structure wrapped around building
Rubber shock absorbers in foundation that allows building to sway (Japan)
Base isolation (San Francisco City Hall)
Assess the importance of governance in the successful management of tectonic mega-disasters [12]
POINT 2 - RESPONSE TRAINING
RESPONSE TRAINING -
Japan school kids practice evacuation drill 1st September every year
Emergency services respond quickly with food, shelter and deal with issue swiftly
Services more advanced MEDCs than LEDCs.
Haiti 2010, no army and only 2 fire stations, roads and transport systems less advanced, 130,000 died
Assess the importance of governance in the successful management of tectonic mega-disasters [12]
POINT 3 - PREDICTION
PREDICTION -
Only partly effective with tsunamis where ocean monitoring equipment can detect open sea tsunamis. On the other hand, volcano detection is accurate where tiltmeters and strain meters record volcanoes ‘bulging’ as magma rises and seismometers record minor earthquakes indicating magma movement. . For instance, the Indian Ocean tsunami of 2004 had a magnitude of 9.2 and due to no ocean monitoring equipment being present in the Indian Ocean, there was no way of warning people and as a result there was 225,000 deaths. In comparison, the 2011 Tohoku earthquake which was magnitude 9.1 killed 21,000
Explain the difference between high and low resilience communities [12]
POINT 1 - INFRASTRUCTURE
The quality of infrastructure can have a large influence on how resistant a community is, with poor roads and housing not only posing a threat to those in and around them, but also making recovery efforts much longer and more arduous. In Port-au-Prince, Haiti (an LHD), 70% of the buildings collapsed including 60% of all administrative buildings severely hindering recovery efforts. As a result of this, it can be judged that on the front Haiti had an extremely low resistance. In contrast, New Zealand is a VHHD, so infrastructure in Christchurch was not hit so badly. However, damage is often unavoidable with earthquakes and 115 people were killed when the Canterbury Television Tower collapsed, more than half the total number of deaths from the whole event came from this. As a result the New Zealand government incorporated earthquake proof buildings in the rebuilding process. It is clear that in terms of infrastructure, Christchurch was much more resilient than Haiti.
Explain the difference between high and low resilience communities [12]
POINT 2 - POPULATION DENSITY
Population density also has a significant impact on resilience of communities. Those with a higher population density are likely to be much less resilient as more people are vulnerable and recovery and evacuation processes are likely to be are likely to be somewhat chaotic. The population density of Christchurch is 270/km2, a low density. This is one of the contributing factors to the relatively low death toll of 185. Port-au-Prince, however, has a population density of over 27,000/km2, contributing to the incomparable death toll of over 200,000 people. More people in a given area will mean more affected by a single event. The earthquake had a similar magnitude, yet the Haiti earthquake was still over a thousand times more deadly than Christchurch 2011, therefore Christchurch is more resilient.
Explain the difference between high and low resilience communities [12]
POINT 3 - HEALTHCARE
Healthcare can also have an impact on the resilience of communities. A prime example of poor healthcare having significant consequences is the outbreak of Cholera that occurred soon after the Haiti earthquake. Poor sanitation and a lack of good healthcare meant that the disease broke out, resulting in an additional 6,000 deaths in and around Port-au-Prince. Comparing this with the Christchurch 2011 earthquake, where there were no real issues with healthcare as good services could be found around the city. Therefore Christchurch is much more resilient in terms of sanitation and healthcare as well as a range of other factors.
Define what is meant by disaster (1)
A major hazard event that causes widespread disruption to a community or region that the affected community is unable to deal with adequately without outside help.
Describe two areas of active volcanoes that are associated with plumes from hotspots rather than inter-plate boundaries.
Some volcanic eruptions are described as ‘intra-plate’. This means they are distant from a plate boundary at locations called mid-plate hotspots (such as Hawaii and the Galapagos Islands). At these locations:
• isolated plumes of convecting heat, called mantle plumes, rise towards the surface, generating basaltic volcanoes that tend to erupt continually
• a mantle plume is stationary, but the tectonic plate above moves slowly over it
• over millennia, this produces a chain of volcanic islands, with extinct ones most distant from the plume location.
Explain two secondary hazards caused by earthquakes (4)
- Tsunami when earthquakes displace the water column creating a bulge of water, waves ripple outwards
- Liquefaction, when ground shaking causes sediment to behave like a liquid/solid surface starts to slide or flow
Explain the tectonic hazards that may result from volcanic activity (6)
PRIMARY HAZARD - PYROCLASTIC FLOW
-Fast-moving current of hot gas and volcanic matter (collectively known as tephra)
PRIMARY HAZARD - ASH FALLS/GASES
-The wide variety of material that a volcanic eruption releases into the atmosphere. Material varies in size with larger fragmentation likely to cover the surrounding environment and result in crop and agriculture damages.
SECONDARY HAZARD - LAHARS
Volcanic mudflows, which occur when rainfall mobilises volcanic ash. They travel at high speed down river systems and cause major destruction
SECONDARY HAZARD - JOKULHLAUPS
Catastrophic glacial outburst flood. Can cause widespread landform modification through erosion and deposition.
Which type of plate boundary that does not lead to tectonic activity. (1)
Conservative, no subduction zone.
Explain the causes of tsunamis. (6)
Tsunami waves are caused by the displacement of large quantities (columns) of water
Earthquakes displace water when movement causes the seabed to thrust upwards, undersea landslides displace water when material falls from a continental shelf on to the seabed
Volcanic eruptions displace water when material ejected from the volcano falls into the sea
Landslides displace water when large quantities of water are displaced by land falling into the sea
The displaced water becomes tsunami waves and as the waves reach shallow water in coastal areas (as the topography of the seabed changes) the waves become higher In shallower water the friction between the tsunami wave and the seabed increases and the tsunami wave slows down, decreasing wavelength but increasing wave height.
Explain the causes of tsunamis. (6) part 1
Tsunami waves are caused by the displacement of large quantities (columns) of water
Earthquakes displace water when movement causes the seabed to thrust upwards, undersea landslides displace water when material falls from a continental shelf on to the seabed
Volcanic eruptions displace water when material ejected from the volcano falls into the sea
Explain the causes of tsunamis. (6) part 2
Landslides displace water when large quantities of water are displaced by land falling into the sea
The displaced water becomes tsunami waves and as the waves reach shallow water in coastal areas (as the topography of the seabed changes) the waves become higher In shallower water the friction between the tsunami wave and the seabed increases and the tsunami wave slows down, decreasing wavelength but increasing wave height.
Assess the factors which influence the effectiveness of responses used by different groups of people to cope with tectonic hazards [12]
POINT 1 ACCESSIBILITY
ACCESSIBILITY
- Rural communities are more difficulty to rescue in times of tectonic hazard due to the poor transport links making rescue efforts more difficult
- e.g. Kashmir 2005 where road closures completely cut off land access to the Jhelum, Neelum, and Kaghan alleys. Landslides were the predominant cause of the closures. The problem was so severe that the army was forced to use 12 tanks purely to address this issue. This also meant efforts from emergency aid such as UNICEF was more difficult
- led to more than 80,000 deaths from the 7.6 magnitude earthquake. Comparatively, the 6.2 magnitude Christchurch earthquake whilst smaller only had 185 deaths due to far better transport in place
- TIES TO GOVERNANCE AND DEVELOPMENT SO NOT AS IMPORTANT FACTOR
Assess the factors which influence the effectiveness of responses used by different groups of people to cope with tectonic hazards [12]
GOVERNANCE/DEVELOPMENT
-Development is the most important factor affecting tectonic hazard vulnerability. Development links to a country’s ability to afford tectonic proof defences. For instance, Japan is a highly developed nation that has the procedures in place to cope with a tectonic event. Every Japan resident practices an evacuation drill on the 1st September each year. Moreover, the country has spent heavily “earthquake-proofing” their buildings and putting strict infrastructure legislation in place. E.g. 54 story Mori Tower in Tokyo has earthquake resistant features including reinforced steel piping, motion absorbing technology and 192 shock absorbers. Whilst such defence systems are an essential form of protection they are also too expensive for less developed countries. As a result, the infrastructure of these less wealthy countries will be unable to cope with the strain of tectonic events and are more vulnerable to the threat.
Assess the factors which influence the effectiveness of responses used by different groups of people to cope with tectonic hazards [12]
POPULATION DENSITY
- Harder to evacuate due to the number of people that need to be moved
- e.g. Gujarat earthquake of 2001, 797 per square mile, resulting in 20,000 deaths. Sumatra 7.6 magnitude 2009 resulted in 1,115 deaths largely due to the lower population density off 272 square mile.
Earthquake waves?
Earthquakes generate three types of seismic wave:
• P-waves, or primary waves, are the fastest. They arrive first, and cause the least damage
• S-waves, or secondary waves, arrive next and shake the ground violently, causing damage
• L-waves, or Love waves, arrive last as they travel only across the surface. However, they have a large amplitude and cause significant damage, including fracturing the ground surface. Earthquakes cause crustal fracturing within the Earth, but also buckle and fracture the ground surface.
Assess the physical and human factors which cause some tectonic hazards to have a more disastrous impact than others [12]
POINT 1 - PHYSICAL 1 - LOCATION
The Pacific Ring of Fire is the meeting point of the Pacific, Nazca, Eurasian, Antarctica and Australian plate and is home to over 450 volcanoes and 90% of the world’s earthquakes. However, this factor is not as significant as development as whilst tsunami prediction is only partly effective where ocean monitoring equipment can detect open sea tsunamis. On the other hand, volcano detection is accurate where tiltmeters and strain meters record volcanoes ‘bulging’ as magma rises and seismometers record minor earthquakes indicating magma movement. Furthermore, gas spectrometers analyse gas emissions which can point to increased eruption likelihood. Areas which are still recovering from a previous event are unlikely to have rebuilt effectively and therefore are less likely to have the precautions in place to respond appropriately. For instance, Haiti was still recovering from 2008 Hurricane Gustav which killed over 150 people. Therefore, when the 2010 earthquake hit over 100,000 people died from the 7.0 event. In comparison, the 2017 Papua New Guinea earthquake was 7.9 magnitude and killed only 3 people.
Assess the physical and human factors which cause some tectonic hazards to have a more disastrous impact than others [12]
POINT 2 - HUMAN 1 - GOVERNANCE/DEVELOPMENT
Development is the most important factor affecting tectonic hazard vulnerability. Development links to a country’s ability to afford tectonic proof defences. For instance, Japan is a highly developed nation that has the procedures in place to cope with a tectonic event. Every Japan resident practices an evacuation drill on the 1st September each year. Moreover, the country has spent heavily “earthquake-proofing” their buildings and putting strict infrastructure legislation in place. E.g. 54 story Mori Tower in Tokyo has earthquake resistant features including reinforced steel piping, motion absorbing technology and 192 shock absorbers. Whilst such defence systems are an essential form of protection they are also too expensive for less developed countries. As a result, the infrastructure of these less wealthy countries will be unable to cope with the strain of tectonic events and are more vulnerable to the threat.
Assess the physical and human factors which cause some tectonic hazards to have a more disastrous impact than others [12]
POINT 3 PHYSICAL 2 - POPULATION DENSITY
- Harder to evacuate due to the number of people that need to be moved
- e.g. Gujarat earthquake of 2001, 797 per square mile, resulting in 20,000 deaths. Sumatra 7.6 magnitude 2009 resulted in 1,115 deaths largely due to the lower population density off 272 square mile.
Assess the different challenges tectonic activity poses for the communities who experience its effects [12]
POINT 1
Firstly, tectonic activity brings huge economic consequences both during an event and after an event. Tectonic disasters pose huge threats to infrastructure such as homes, businesses and public buildings, especially large events. For example, after the New Zealand earthquakes of 2010 and 2011, economic losses were around NZ$20 bn due to loss of buildings which had to be rebuilt. The tourism industry in New Zealand suffered by 40% during 2011 and 2012 period, due to worries of another earthquake by tourists. However, in Iceland after the Eyjafjallajokull earthquake in 2010, initially tourism dropped but now tourism has rose to 1.8 million in 2016 from 450,000 in 2010, as people want to visit the tectonic spots such as the volcanoes as well as visiting geysers and hotsprings. Overall, economic costs can be huge for communities but can also use tectonic activity to attract visitors and rebuild from disaster.
Assess the different challenges tectonic activity poses for the communities who experience its effects [12]
POINT 2
Secondly, social costs are large. Social costs relate to the number of deaths and injuries, as well as, disruptions to daily life such as health services and housing. The extent to the social cost depends largely on the size of a disaster or the vulnerability of a location. For example, Haiti suffered widespread social issues due to a relatively small quake of 7 magnitude in 2010. 160,000 died, 1.5 million were made homeless and 250,000 homes were destroyed. Haiti also suffered from an outbreak of cholera where 9,000 people died. Haiti has a low human developed and this caused huge social costs. There are usually some sort of social cost with all sizes of events and the extent to social costs depends on the vulnerability of a place. Means a community can reduce social effects by increasing human development and reducing risks to the tectonic activity.
Assess the different challenges tectonic activity poses for the communities who experience its effects [12]
POINT 3
Lastly, environmental costs of tectonic activity pose challenges to communities. Volcanic and earthquake activity causes lots of challenges such as lava flows destroying and covering areas of land or ash causing the collapse of buildings and covering crops and earthquakes destroying areas of land possibly due to landslides caused by earthquakes. An example of volcanic activity causing environmental challenges was seen in the Democratic Republic of Congo where when Mt. Nyiragongo erupted poisonous gases were released which caused acid rain which affected farmland and cattle. Also during the Eyjafjallajokull eruption 30000 tonnes per day of CO2 were released which has negative impacts on soils and water as the CO2 is sequestered.
Explain the processes that lead to deep ocean trenches at destructive plate boundaries? (6 marks)
Ocean trenches are steep depressions in the deepest parts of the ocean, where old oceanic crust from one tectonic plate is pushed beneath another plate, raising these underwater mountains, causing earthquakes, and forming volcanoes on the seafloor and on land. With depths exceeding 6,000 meters, the vast underwater slopes and steep walls of trenches make for unique habitats across a range of depths and are caused by tectonic activity and convection currents.
The ocean trenches are formed by subduction, a geophysical process in which two or more of Earth's tectonic plates converge and the older, denser plate is pushed beneath the lighter plate and deep into the mantle, causing the seafloor and outermost crust (the lithosphere) to bend and form a steep, V-shaped depression. This process makes trenches extremely prevalent in terms of seismic activity and are frequently the site of large earthquakes, including some of the largest earthquakes on record. Subduction also generates an upwelling of molten crust that forms mountain ridges and volcanic islands parallel to the trench, these areas are often found in the pacific ‘ring of fire’
Describe how ocean ridges are created by tectonic forces? (6 marks)
A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. This uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary. The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every ocean, making the mid-oceanic ridge system the longest mountain range in the world, with a believed total length of about 60,000KM2
There are two processes, ridge-push and slab-pull, thought to be responsible for the spreading seen at mid-ocean ridges, and there is some uncertainty as to which is dominant. Ridge-push occurs when the weight of the ridge pushes the rest of the tectonic plate away from the ridge, often towards a subduction zone. At the subduction zone, "slab-pull" comes into effect. This is simply the weight of the tectonic plate being subducted below the overlying plate dragging the rest of the plate along behind it. The other process that are believed to contribute to the formation of new oceanic crust at mid-ocean ridges is the "mantle conveyor". However, there have been some studies which have shown that the upper mantle (asthenosphere) is too flexible to generate enough friction to pull the tectonic plate along.
