Tectonics Flashcards
What is a hazard
A hazard is a potential threat to human life and property
A natural hazard can be either hydro-meteorological (Caused by Climate processes of Geophysical (Caused by Land processes)
Geophysical hazards occur near plate boundaries. These plates move at different speeds and directions which can cause collisions, earthquakes and volcanic activity.
What can the earths crust be divided into
- The earths structure can be divided into four sections: Inner core, outer
core, mantle and the crust - The earth’s crust then can then further divided into a series of plates: Oceanic (Thin and very dense) or Continental (thick and less dense)
Explain the three differences between plate boundaries
- Conservative – plates move past each other but at different speeds, causing
friction and collisions - Constructive – plates moving apart from one another, most clearly displayed
at ocean ridges - Destructive - plates move towards each other, colliding head on if both are
continental. If one is oceanic and the other oceanic, subduction will occur
where the oceanic plate is thrust under the continental plate as it is denser.
If there are two oceanic plates the heavier plate will be forced under the
other
Explain Plate Tectonic Theory
Plate Tectonic Theory is believed to be correct due to evidence from Wegner’s Continental Drift Theory which states that the shapes of South Africa seem to fit together so they were once part of a supercontinent. This is supported by similar rock types and fossils found on the east coast of South America and west coast of Africa.
What is a mid ocean ridge
An underwater mountain range, formed by the process of subduction where oceanic plates are pushed under continental as oceanic plates are heavier.
What is sea floor spreading
New crust rides formed when two oceanic plates move away from each other, allowing magma from the mantle to rise
What is Palaeomagnetism and explain the significance of
Palaeomagnetism is the magnetic patterns of cooled magma. A study of this phenomenon discovered that magnetic patters were arranged in the direction of the earth’s magnetic field which flipped every few million years. This was fundamental as it helps identify the age of the oceanic crust, by studying the youngest rocks at ridges and proves that the earth did once fit together.
What is the Benioff Zone
an area of seismicity corresponding with the slab being thrust downwards in a subduction zone. The different speeds and movement of rock at this point produce numerous earthquakes. It is the site of intermediate/deep-focused earthquakes
How do volcanoes form at constructive plate boundaries
At constructive margins, magma is less dense than the plate so rises above it, forming a volcano, such as those within the Rift valleys
How do volcanoes form at destructive plate boundaries
At destructive margins, subduction causes the melting of the oceanic plate, allowing for magma to rise on the crust to form a volcano. This produces explosive volcanos such as Mt St Helens.
Give the primary impacts of volcanic hazards
- Pyroclastic flows - hot gasses and ash ejected as the shaft of a volcano
collapses during an eruption – moves extremely fast - Tephra- volcanoes eject material such as rock fragments
- Lava flows- extremely hot liquid that is ejected from certain volcanoes during
an eruption – moves slow yet causes huge damage - Volcanic gasses - explosive eruptions - co2-carbon monoxide etc - most
deaths from this - colourless and odourless
Give the secondary impacts of volcanic hazards
Lahars - volcanic mudflows generally composed of relatively fine sand and silt material. The degree of the hazard varies depending on the steepness of slopes, the volume of material and particle size. As a secondary hazard, they are associated with heavy rainfall as trigger as old tephra deposits on steep slopes can be re-mobilised into mudflows
Jokulhlaups – type of catastrophic glacial outburst flood. They are a hazard to people and infrastructure and can cause widespread landform modification through erosion and deposition. These floods occur very suddenly with rapid discharge of large volumes of water, ice and debris from glacial source.
Explain how an earthquake occurs
The movements are preceded by gradual build-up of tectonic strain, which stores elastic energy in its crustal rocks
When the pressure exceeds the strength of the fault, the rock fractures
This produces the sudden release of energy, creating a seismic wave that radiate away from the point of fracture
The brittle crust then rebounds either side of the fracture, which is the ground shaking, that us, the earthquake felt on the surface
What is the hypocentre
is the ‘focus’ point within the ground where the strain energy of the earthquake stored in the rock is first released. The distance between this and the epicentre is called the focal length
Explain the differences between the three different types of seismic waves produced by an earthquake
Primary waves: vibrations caused by compression, these waves can travel through fluids and solids and are longitudinal. This also means that they transfer energy parallel to the direction of the wave, so if a wave is travelling north to south, the energy will be transferred in this direction.
Secondary waves: S-waves cannot travel through air or water, only through solids, but they have a larger amplitude (this is the height of a wave, measured from the highest point to the middle line) so are more destructive in the case of an earthquake. They are transverse waves, meaning they transfer energy perpendicular
Love waves: The final type of seismic wave occurs along the boundary between two different substances (e.g. rock and air). They can be either longitudinal or transverse. These waves travel slower than both S and P waves but have a higher amplitude and so can be the most destructive of all the seismic waves.
Give the primary impacts on an earthquake
- Violent ground shaking
- Building collapse
- Ground splitting
Give and explain the secondary impacts on earthquakes
Soil liquification – This is the process by which water-saturated material can temporarily lose normal strength and behave like a liquid as a result of extreme shaking from an earthquake. The earthquake causes the water pressure to increase to the point where the soil particles can move easily, especially in poorly compacted sand and silt.
Landslides: Another important secondary hazard from earthquakes: where slopes weaken and fail. As many destructive earthquakes occur in mountainous areas, landslides can be a major secondary impact.
How are tsunamis formed
-Tsunamis are produced by sub-marine earthquakes at subduction zones, water
displacement and deep trough waves
- The movement of plates under the ocean causes an uplift of ocean water,
disrupting the sea bed
What physical and human factors does the impact of a tsunami depend on
The duration of the event
The wave amplitude, water column displacement and distance travelled
The physical geography of the coast
Timing of the event – quality of early warning systems
The degree of coastal development and its proximity from the coast
- However, the most serious events occur when the physical and human factors interact with each other to produce a disaster
What is a hazard
A perceived natural/geophysical event that has the potential to threaten both life and property.
What is a disaster
The realisation of a hazard, when it ‘causes a significant impact on a vulnerable population’. When 10 or more people are killed; when a 100 or more people are affected
Explain the complex relationship between risks, hazards and people.
Unpredictability - Many hazards are not predictable; people may be caught
out by either timing or magnitude of an event
lack of alternatives - People may stay in a hazardous area due to a lack of
options. This may be due to economic reasons, lack of space to move or a
lack of skills/knowledge
Dynamic hazards - The threat from hazards is not constant, it may increase
or decrease over time.
Cost-benefit - The benefits of a hazardous location may outweigh the risks
involved in staying there. Perception of a risk is also important here.
What is the hazard risk equation and what is the importance of it - giving examples
- The hazard risk equation helps explain why similar hazards cause disasters
at different degrees - For instance, both Izmit (Turkey) and Kashmir (Pakistan) had a similar size
earthquake in 1999 and 2005. However, Kashmir had 75,000 deaths whilst Izmit
had 18,000. This was because Kashmir is situated in a remote mountainous
location with poor access to services/infrastructure which hinder capacity to
cope. - Thus, impacts of disasters vary according to levels of development.
- For richer countries, there are high financial losses whilst poorer countries
are left with severe shocks to community wellbeing and infrastructure – the
poor are also vulnerable to secondary hazards, such as diseases, which may
arise from the inability to receive international aid quickly - For the emerging world, such as India and China, disasters can slow growth and
potentially destroy economic systems
What are the three scales used to measure earthquakes and explain their properties
Richter Scale - A measurement of the height and amplitude of the waves produced by an earthquake, it will measure the same on the Richter scale
Mercalli Scale - Measures the experienced impacts of an earthquake. It Is a relative scale, because people experience different amounts of shaking in different places. It is based on a series of key responses, such as people awakening, the movement of furniture and damage to structures
Moment Magnitude Scale (MMS) - A modern measure used by seismologists to describe earthquakes in terms of energy released. The magnitude is based on the ‘seismic moment’ of the earthquake, which is calculated from: the amount of slip in a fault, the area affected and the Earth-rigidity factor.
What scale is used to measure the size of a volcanic eruption
A relative measure of the explosiveness of a volcanic eruption, which is calculated from the volume of products, height of the eruption cloud and qualitative observations.
What is a tectonic hazard profile
- A technique used to try to understand the physical characteristics of different
types of hazards, for example earthquakes, tsunamis and volcanoes. - Hazard profiles can be used to analyse and assess the same hazards which
take place in contrasting locations or at different times. - Hazard profiles are developed for each natural hazard and are based on
criteria such as frequency, duration and speed of onset.
Giving examples explain how tectonic hazard profiles can be used to compare tectonic disaster
- Earthquakes, volcanoes and tsunamis have different characteristics on terms of magnitude, speed of onset, duration, frequency and special probability.
- Each disaster also varies in the destruction it causes. Impacts can either be social, economic or environmental as well as being direct/indirect, primary/secondary and long-term/short-term
- Generally, the less developed a country, the more likely it is to face more sever social and economic impacts of a tectonic hazard
For example, both California and the Philippines are disaster hotspots but whereas 40 to 60% lie below the poverty line in the Philippines, only 20% do in California. This means, in the case of a disaster, the Philippines will have greater social impacts (as most of the poorly built infrastructure will be damaged) whilst California will face larger economic losses
How can development be negative in causing the disaster risk
Development can be a cause of a disaster risk
• Unsustainable development practices that create
unsafe working conditions
and reduce environment quality
• Development paths generating inequality,
promoting social isolation or
political exclusion
How can development be positive in reducing the disaster risk
• Access to safe drinking water, food and secure
dwelling places increase community resilience
• Development can build communities and broaden the
provision of opportunities for participation and
involvement in decision making, recognising excluded
groups such as women, and enhancing education,
health and well-being
How can inequality drive the disaster risk nexus
- The social progress and power dynamics that drive
the disaster risk-poverty nexus is strongly linked with
inequality - In the context of tectonics, inequality has a number of
Impacts on disaster risk levels - Low income households are often forced to occupy
hazard-exposed areas where there are low land
values - Such places have poor infrastructure and social
protection; they are also likely to have high levels of
environmental degradation - People in such areas often have low resilience as they
have little voice in terms of political debate and
influence, as well as being socially excluded and
marginalised
What are the four different types of inequality that can effect the disaster risk nexus
o Asset inequality: relates to housing and security of tenure, as well as agricultural productivity (in farming communities) or goods and savings in trading communities
o Inequality of entitlements: refers to the unequal access to public services and welfare systems, as well as inequalities in the application of the rule of law
o Political inequality: unequal capacities for political agencies possessed by different groups and individuals in any society
o Social status inequality: is often directly linked to space and has a bearing on other dimensions of inequality, including the ability of individuals and groups to secure regular income and access to services.
How can disasters create development opportunities
Disasters create development opportunities
• Favourable environment for advocacy for disaster-risk
reduction measures
• Decision makers are more willing to allocate
resources in the wake of a disaster
• Rehabilitation and reconstruction activities create
opportunities for integrating disaster-risk measures
How can disasters limit or destroy development
• Destruction of physical assets and loss of production capacity, market
access and input materials
• Damage to infrastructure and erosion of
livelihoods and savings
• Destruction of health or education infrastructure
• Deaths, disablement and migration
How can Governance be a factor in contributing to a vulnerable population in terms of disaster risk
Economic Governance
Includes the decision-making processes that affect a country’s economic activities and its relationship with other economies. This has major implications for equity, poverty and people’s quality of life
Political Governance
Is the process of decision making to create policies, including national disaster reduction and planning. The nature of this process and the way it brings together the state, non-state and private-sector players/stakeholders determines the quality of the policy outcomes
Administrative Governance
Is the system of policy implementation and requires good governance at central and local levels. In the case of disaster risk reduction, it requires functioning enforcement of building codes, land use planning, environmental risk and human vulnerability monitoring and safety standards.
Evaluate what happened in the Icelandic Volcanic Ash Hazard of 2010
Why is Iceland a hotspot for Volcanic activity?
- Iceland is located in a tectonically active area
- The island is bisected by the northern part of the Mid-
Atlantic Ridge, a constructive plate margin which
diverging by about 23 mm per year. - Magma periodically rises between the plates at the
surface as basaltic lava flows.
What happened in Spring 2010?
- Volcano under the Eyjafjallajökull ice cap in south east
Iceland erupted - The strata-volcano is a cone composed of alternating
layers of ash and lava - There were two eruptions (March and April), with the
second eruption occurring under the icecap which
increased the explosivity of the event – 9km into
atmosphere
Primary Impacts of the eruption
- Flooding: heat from the eruption melted vast amounts
of ice under the ice cap - meltwater subsequently
emerged from the edge of the ice cap as a glacial
burst - Airport closure: Ash-fall closed Reykjavik airport for
several days - Mudslides (lahars): ash mixed with meltwater and rain
created mudslides or lahars
Secondary Impacts of the eruption
- Overtime the ash spread onto Europe – causing
widespread disruption to the European and North
American Airspace - Entire UK airway system had to be closed
- 100,000 flights cancelled
- 10 million people stranded
- 1.7 billion in losses for airlines – 5 billion to the
European economy - Airports across Europe lost over 250 million
Responses
- Further research into the effects on ash on aircraft.
- Reconstruction of roads, local flood defences needed
reconstructing.
Evaluate the Nyirangongo volcanic eruption in 2002
The volcano
- Mount Nyriragongo is an active stratovolcano with an
elevation of 3,470m in the Virunga Mountains
associated with the Albertine Rift.
- It is located inside Virunga National Park, In the
Democratic Republic of Congo
What happened in 2002?
- After several months of increased seismic and
fumarolic activity. A 13 km fissure opened in the south
flank of the volcano, spreading in a few hours from
2800 m to 1550 m elevation and reaching the
outskirts of the city of Goma - Lava streamed from three spatter cones at the end
of the fissure and flowed in a stream 200 to 1000 m
wide and up to 2 m deep through Goma.
Impacts
- 147 people killed, 45 of which in the first 24 hours of
the eruption killed by roofs crashing down due to the
heavy ash, lava flows, and toxic gas - 14 villages were destroyed - Goma split in half by lava
flows. - 4500 buildings destroyed, making up 40% of Goma
- Very large number lost their workplace, their
employment and their income, as well as assets and
savings (increase vulnerability no income) - 20,000 people left homeless – 300,000 evacuated
Secondary Impacts of the eruption
- The volcano still emits gases which have reportedly killed children
Evaluate the Nepal Earthquake of 2015
- Nepal is a developing country with a population of
about 26.5 million people. - On 25 April 2015 a magnitude 7.8 earthquake struck
Nepal - Nepal is a multiple hazard zone, with a steep
mountainous landscape
Primary impacts
- Approximately 9000 people lost their lives
- More than 22,000 people were injured
- More than half a million houses collapsed
- Kathmandu airport shut
Secondary effects
- Violence against women soared
- Thousands of refugees
- Starvation due to the limited supplies
- Small outbreaks of cholera
Evaluation
- The low level of development means that much of the
local science is out of date - Nepal’s population is vulnerable. Poor and socially
excluded groups are less able to absorb shocks than
well-positioned and better-off households - Because of poverty, many people build their own
houses, which are often built without the correct
building codes
Evaluate the New Zealand earthquake of 2010
- Magnitude 7.1 earthquake
- Epicentre 40km from Christchurch
- Lasted 40 seconds
Primary impacts
- 1 person died
- Sewers damaged
- Electrical grid disrupted
- Rail lines buckled
- Soil liquification caused flooding
Secondary effects
- Disruption to industrial production, goods exports and
activity – however, this was relatively short lived as
the region’s manufacturing hub escaped significant
damage - Tourism industry suffered badly. The city of
Christchurch had been the hub of tourist activity and
many of its attractions were demolished
Evaluation
- Indicators suggest that business activity had been
quite resilient. Although business confidence dropped
nationwide in the immediate aftermath of the 2011
quake, they recovered quickly - Financial markets largely ignored he earthquake
impact - Agricultural sector was largely unaffected
Evaluate the Indian ocean tsunami of 2004
Context
- Subduction caused by indo-Australian plate under
Eurasian plate - 9.1 mag caused 20metre uplift in sea bed
Primary impacts
- 14 countries affected
- 250,000 killed
- In Sumatra alone 130,000 were killed and 30,000 still
missing - Thousands of villages destroyed
Secondary impacts
- Diseases such as cholera spread quickly, especially in
refugee camps
Evaluation
- No early warning systems in place – as it occurred in
a relatively impoverished area - Huge amounts of poverty – very few structures could
withstand the tsunami
Explain the trends in Tectonic disasters
- At a global scale, deaths have decreased whilst
economic losses have risen. This is because the
global economy and wealth is greater than what it was
before - The use of international aid and preparedness means
that less people are affected by disasters now than in
1960. - The number of tectonic hazards has fluctuated having
peaked in 1997 and 200, reaching an all-time low in
the early 1980s and 2012
What are Hydro-meteorological Hazards
‘a process or phenomenon of atmospheric, hydrological or oceanographic nature that may cause loss of life, injury or other health impacts, property damage, loss of livelihoods and services, social and economic disruption, or environmental damage
(includes tropical cyclones, thunderstorms, hailstorms, tornados, blizzards, heavy snowfall, avalanches, coastal storm surges, floods including flash floods, drought, heatwaves and cold spells).’
What are multiple hazard zones
- Multi-hazard zones are where a number of physical
hazards combine to create an increased level of risk
for the country and its population - For the Philippine’s, there is a complex mix of
geophysical and hydro-meteorological hazards as the
plate boundaries intersect a major storm belt in an
area of high population density - The Philippine’s
faces explosive volcanic threats, landslides,
earthquakes, typhoons, tsunamis, drought and
flooding. - These locations are often seen as disaster hotspots
Explain why earthquakes are difficult to predict
- Prediction accuracy depends on the type of tectonic
hazard; a volcano can be monitored for likely eruptions,
but tectonic plates move randomly so earthquakes
cannot be predicted accurately
Evaluate the importance of a communities resilience to a natural hazard - include Parks model
The United Nations Office for Disaster Risk Reduction stresses on the importance of improving a community’s resilience to natural hazards. They highlight the vitality of adopting multiple management techniques to prevent hazards from becoming disasters (these include preventing flooding by utilising sandbags on coasts, whilst improving warning systems)
- Parks disaster response curve can be used as a
framework to better understand the time dimensions
of resilience - 4 stages: Pre-disaster, Relief, Rehabilitation and
Reconstruction - In the event of a tectonic disaster these four factors will
define a communities future resilience - It takes into account that different hazard events have
different impacts so vary in their duration, speed and
destruction of quality of life. - The less developed a country, the greater the impacts
and destruction of quality of life – the disaster onset is
slower as secondary hazards worsen the death tolls.
What are micro and macro hazard management approaches
Micro: strengthening individual buildings and structures against hazardous stress
Macro: large-scale protective measures designed to protect whole communities
Give methods of hazard management approaches for earthquakes
o Hard resistant designs: Hospitals, police stations, pipelines, schools and factories have been strengthened with improvements such as cross-bracing, deep foundations and resistant materials
o Land-Use Zoning: Create policies on where it is the safest to build infrastructure
Give methods of hazard management approaches for volcanos
o Diversion flows: Lava can be diverted by spraying sea water to cool and solidify the flow – this was achieved in Iceland in 1973, saving the fishing port and harbour that were the economic lifelines of the populations
Give methods of hazard management approaches for tsunamis
o Tsunami walls: work for a given amplitude or threshold of the wave
o Mangrove restoration: slow the speed of the wave. 70,000 trees were planted after the 2004 tsunami
What strategies can be used in terms of modification of a hazard in terms of vulnerability
- Modification of a hazard can involve a number of
approaches and adaptions including:
Prediction, forecasting warnings
Improvements in community preparedness
Working with groups and individuals to change
behaviours
- High-Tech Monitoring: international satellites and aircraft monitor changes in the earth, for instance GNS Science in New Zealand use light detection and ranging to create 3D data pieces of the Earth’s surface. Changes to the surface pinpoint the likelihood of a disaster
- Prediction: Observing changes in volcanic shapes or low magnitude earthquakes could suggest whether a disaster is likely
- Education: Teaching communities about hazards and protection enables the community to gain strength and withstand shock better
- Community preparedness: Earthquakes drills and alarms prepare communities for how best to protect themselves in a disaster
How can loss as a result of a tectonic disaster be modified
Disaster aid
- Aid flows to countries and victims via governments,
NGOs and private donors. In the longer-term aid is used
for relief, rehabilitation and reconstruction. - This type of aid is often appropriate to middle- and lower-
income countries
Internal governmental aid
- This is typically used in emerging and developing
countries where the disaster mitigation is achieved by
spreading the financial load throughout the tax payers of
the country. - This may include a national disaster fund and release of
funds may require a political declaration.
What is the equation for a hazard
Risk=hazard × exposure × vulnerability/(manageability )
Philippines 1991 (lahars impact case study)
- Annual rainfall at Mount Pinatubo ranges from 80 inches
(2,000 millimeters) on the volcano’s northeast flank to
more than 160 inches (4,000 millimeters) on its summit
and southwest flank. - Ash and other deposits from Mount Pinatubo’s 1991
eruption destroyed or buried much of the lush
vegetation that had covered the volcano. - When rainfall in Pinatubo exceeded about 0.5 inches (12 millimeters) in 30 minutes, rapid runoff down the still
bare slopes quickly grew into torrents that became lahars by eroding these deposits. - When the largest and fastest lahars reach the lowlands surrounding Pinatubo, they have speeds of more than
20 miles (32 kilometers) per hour, are as much as 30 feet (10 meters) thick and 300 feet (100 meters) wide, and
can transport more than 35,000 cubic feet (1,000 cubic meters) of debris and mud per second. - Since the 1991 eruption, lahars from Pinatubo have destroyed the homes of more than 100,000 people. With
most old stream channels filled, lahars can now spread widely on the gentle slopes and lowlands surrounding
Mount Pinatubo, threatening successors to the early dams and levee
How prepared is Japan for an earthquake
Japan’s P-wave system includes more than 1,000 seismometers, which are instruments designed to detect and record earthquakes.
At the mouth of Kamaishi Bay on the northeast coast stands the a 20-metre-thick barrier, which is 2 km long. It rises to 8 metres above the water and is anchored to the sea floor 63 metres down and Completed in 2008 after 30 years, it cost of more than US$ 1.4 billion.
How much of Tokyos buildings are earthquake proof
In Tokyo, 87% of buildings are reportedly built to withstand earthquakes.
1906 San Fran Cisco earthwyake
The 1906 San Francisco earthquake struck the coast of Northern California
Devastating fires soon broke out in the city and lasted for several days. As a result, up to 3,000 people died and over 80% of the city of San Francisco was destroyed.
