Natural Hazards Flashcards
What are the causes of earthquakes?
They are caused by a sudden release in tension in the earths crust. Often subduction causes friction between plates which can be accredited for building up this tension.
What are intra and inter plate earthquakes?
An intra plate occurs within a plate whereas an inter plate occurs at a plate boundary.
Global distribution of earthquakes
pacific ring of fire. Alpine- Hymilaya collision zone. African rift valley. Mid Atlantic ridge.
Pacific ring of fire
A seismically active area around the edge of the Pacific Ocean.
What is the Alpine Himalaya collision zone?
Where content plates are crushing into themselves and causing seismicity over Western Europe.
African rift valley
An area in Southern Africa where part of the continent is pulling away from itself.
The mid Atlantic ridge
Underwater mountain range formed from a constructive plate margin.
What causes a volcano
Volcanoes are formed from a gap emerging in the crust where magma forces its way to the surface as seen in constructive volcanoes. The violence of a volcano is determined by the magma and how easily gasses can escape.
Distribution of volcanoes
Volcanoes are situated in linear clusters. There is a clustering of volcanoes around the edge of the pacific which is where 75% of the worlds volcinicity. This is the pacific ring of fire.
Sima
Oceanic plates- younger, heavier and denser.
Sial
Continental plates, thicker, heavier and lighter.
collision plate boundary
Plates of similar weight and size, through slab pushed, are thrust into each other. This causes the plates to buckle as they compress into each other, forcing earth upwards and creating fold mountains.
Constructive
when two oceanic plates move away from one another creating a gap. From this gap magma rises, cools and solidifies. As this process continues enough sediment is deposited that the, now shield volcano, breaches the surface.
Destructive
When a heavier and younger oceanic plate is forced under an older and lighter contental plate. In the subduction zone a sea trench is formed. As the plate is forced under it begins to melt in the magma and it is forced out as there is no room. It escapes through a composite volcano.
Conservative plate boundary
When two plates move in the same direction but at different speeds or when two plates move past one another, tension is accrued and eventually released in the form of earthquakes.
What is a mantle plume
A mantle plume in the mantle which then melts through the lithosphere. This is then a hotspot and this magma leaks through the crust and behaves as a constructive plate boundary. As the plate moves, as the plume is deeper, the plume remains and a chain of islands is created like Hawaii.
Who first proposed plate tectonic theory
Alfred Wegner
What is mantle convection?
when cool mantle sinks to the earth’s core as cool mantle is less dense. This mantle which then gets heated rises to the top in a circular fashion. The mantle is heated by the earth’s core which is heated by radioactive decay. As the convection currents reach the top of the current the current pulls down subducting plate creating slab pull.
What is paleo magnetism
confirmation of repeated reversals of the earth’s magnetic field in the geological past.
Sea floor spreading
Recycling of oceanic crust, the sea floor spreading theory. Underwater volcanoes create a constructive plate margin and magma rises and locks in the earths magnetism from the time this took place. This pushes apart the two plates when it cools and as the two plates are pulled apart a new gap is formed where more magma locks in the earth’s magnetism of the time in which it set. From this we can see changes in when the earths magnetism
Subduction
when 2 plates meet and the heavier one is pushed under the main plate. As this plate is pushed under it pulls the rest of the plate and the other side of the plate is pulled under.
Def Locked fault
A fault which is not slipping because the frictional resistance on the fault is greater than the shear stress across the fault
Destructive
Oceanic plate subducts where the continental plate is pulled further under by convection currents. Earthquakes take place at different depths. Convection currents push the plates. The plate that is subducting is being pulled the convection current which causes slab pull at the other end of the plate.
Constructive
palaeomagnetism is locked in as two oceanic plates are pulled away from one another.
Collision
2 continental plates are pushed into one another. As the plates are the same weight and density neither subduct nor they collide. Fold mountains and earthquakes are created but no volcanism takes place. Most violent earthquakes- alpine Himalaya collision zone.
Transform
(conservative) Slab push is taking place as one slab is pushed alongside one another. Either they are moving at different rates or in different directions. Friction builds up until it is released in the form of an earthquake.
Benioff zone
The Benioff zone is an area of seismicity corresponding with the slab being thrust downwards in a subduction zone. The different speeds and movements of rock at this point produce numerous earthquakes. It is the site of intermediate/ deep focused earthquakes. This theoretical framework is an important framework in determining the position of the hypocentre. This is the zone of melting.
Focal depth
The depth at which the earthquake starts
Where do deeper earthquakes take place.
Subducting plates often lead to deeper earthquakes.
Composite volcano is destructive margin, and a shield volcano is a constructive margin.
P Waves
P waves are primary waves which are vibrations caused by compressions in the crust. They spread quickly from the fault at a rate of about 8 km/sec. these are body waves which pass along the crust. These waves travel the fastest and travel in longitudinal ways. Least destructive but they are the fastest.
S waves
S waves are secondary waves and are transverse (cross section of the wavelength looks like an S). These waves travel though the surface on the crust. Also, very destructive.
L Waves
L waves or love waves occur in the horizontal plane. These waves are the most damaging. These are surface waves
Seismic waves
Waves of energy that travel In all directions.
Liquefaction
Soil liquefaction is a phenomenon in which the strength and stuffiness of a soil is reduced by earthquake shaking or other rapid loading. This occurs in saturated soils, that is, soil which the space between particles is full of water. Before the earthquake the particles support the weight of the of the water however vibrations break down this structure which results in flooding and may leave cavities in the soil. Under the strong shaking of an earthquake this soil behaves and flows as water.
Landslides
where a mass of rock, soil or sediment moves down an angle. This starts where slopes weaken and fail. Rarely occur when the magnitude is less than four. Half the earthquake deaths in Japan are linked to earthquakes.
Lava flows
The faster moving this is the greater risk that is posed to human life. The viscosity of lava depends on the percentage of silicone dioxide it contains. On steep slopes some lava flows can reach 15m/ sec. The greatest lava flow was in 1873 in Iceland and following the eruption over 1/5th of the population died in the following famine.
Pyroclastic flows
These are responsible for most primary volcanic deaths. Pyroclastic flows are the result of a frothing of molten magma in the vent of the volcano. The bubbles burst explosively to eject hot gas and material such as pumice, crystals and ash. These clouds are most dangerous when they come out of the volcano sideways as famously happened in Pompeii. The temp of these clouds can be upwards of 1000 degrees.
Ash falls
When a volcano erupts it may eject material such as rock- this is called tephra. It can vary in size from bombs- >32mm to fine dust<4mm. This ash and larger material can cause rooves to collapse as well as start fires on the ground. Dust can reduce visibility and air travel- Iceland 2010.
Gas Eruptions
Gasses are associated with explosive eruptions and lava flows, the mix normally includes water vapour, sulphur dioxide, hydrogen, and carbon dioxide. Carbon dioxide is dangerous because it is heavy and so displaces oxygen. This can lead to suffocation.
Lahars
These are mudflows which are generally composed of fine particles like sand or silt. The severity of a Lahar depends on the steepness of the slope from which the lahar flows as well as the size of the particles. Lahars can be triggered by heavy rainfall after an earthquake which can trigger deposits of volcanic ash (tephra) released from a volcano in an eruption.
Jokulhlaups
Type of catastrophic glacial outburst flood, they are a hazard to people and infrastructure and through erosion and deposition they cause widespread landform modification. These floods occur rapidly with rapid discharge of water from a glacial source. They can occur anywhere where water accumulates in a subglacial lake beneath a glacier, the flood is usually initiated following the failure of an ice or moraine dam.
Secondary hazards
Lahars and Jokluhaps
Primary hazards
Lava Hazards, Pyroclasic flows, Ash falls, Gas eruptions.
Tsunamis
Tsunamis are the most distinct earthquake related hazard.
Tsunamis grow in height as the seabed becomes shallower, the wave train which is caused by seabed displacement. Waves from a tsunami can follow the ‘escalation effect’ which is when waves become increasingly larger.
The impact of a tsunami depends on several human factors:
- Duration (waves can be over 1 hr apart)
- Wave amplitude, water column displacement, and the distance travelled.
- The physical geography of the coast
- The degree of physical ecosystem buffers such as coral reefs
- Timing of the event
- Degree of costal development
Sub marie earthquakes
Sub marine earthquakes result in the sima moving and slipping down. The water resting on the tectonic plate then rapidly drops with the plate and this results in water collecting, usually over the epicentre, and then surging outwards towards land. Not all earthquakes lead to tsunamis because the plate slipping is not guaranteed.
Natural Hazard
natural hazards are extreme natural events that can cause loss of life, extreme damage to property and disrupt human activates.
Disaster
a serious disruption of the functioning of a community or a society involving widespread human, material, economic or environmental losses and impacts, which exceeds the ability of the affected community or society to cope using its own resources.
Risk of hazard
- Unpredictability- many people may be caught out by the timing of an event.
- Lack of alternatives- people may stay in an environment because they have no other option. IE lots of the communities killed in Japan 2010 were coastal communities- there isn’t fish in the countryside.
- Dynamic Hazards- the threat from a hazard isn’t constant and it may increase or decrease over time. Human influence may also change the location of increase the frequency or magnitude of hazardous events.
- Cost benefit
- Acceptance of risk in the face of the reward for living in a geographical area- volcanic soils producing more fertile crop.
Resilience
in the context of hazards and disasters resilience can be thought of as the ability of a system, community or society exposed to hazards to resist, absorb and recover from the effects of a hazard. (ability to spring back after an event).
Risk
the exposure of people to a hazardous event. More specifically it is the probability of a hazard occurring that leads to the loss of lives and/ or livelihood.
Pressure release model
The basis for the pressure release model is that a disaster is the intersection of two processes.
- process of generating vulnerability
- Natural hazard event
Root causes generate risk.
Impacts of a tectonic hazard
The impacts of hazards vary by region and time. They may vary from minor nuisances to major disasters involving a considerable impact on people. The impacts are generally much greater than ones produced by volcanoes because they are more easily predicted as well as being easy to geographically avoid. The economic impacts are roughly proportional to the land area exposed to the relevant hazard. Economic hazards can include:
- Level of development
- Insured impacts vs non-insured impacts
- Total numbers of people affected and the speed of economic recovery for the event.
- Degree of urbanisation and level of independence
- Absolute impacts verses repetitive impacts on GDP higher relative impacts are more devastating.
Volcano eruption Iceland 2010
VEI 4, No deaths, 10 million passengers, 1.7bn in economic losses, flash floods.
Volcano eruption DRC 2002
147 dead, 1.2 bn in economic losses, lava flows and sediment made soils more fertile.
2010 New Zealand earthquake
0 deaths, 7.1 magnitude, 400m loss, liquefaction caused, damage to landscape.
2015 Nepal earthquake
7.6mg, 9000 deaths, fishing boats destroyed, 5bn losses and landslides.
2011 Japan tsunami
9.3m high, 16,000 deaths, 300bn losses, infrastructure damages, nuclear meltdown and fumashima.
2004 Boxing Day
230,000 deaths, people lost source of income, 15bn losses, landscape damage.
Mercalli scale
This scale measure earthquakes on scale between I-XII. This scale measures the felt impacts of an earthquake through measures like how many people moved or damage to homes. It is an intensity scale.
MMS (Moment magnitude scale).
This scale measures earthquakes on a scale of 0-9 to measure the amount of energy released. The magnitude is based in the ‘seismic moment’ of the earthquake which is calculated by the slip of the fault, area affected and the rigidity of the area. The USGS uses this on all major earthquakes. This scale is logarithmic which means that each increase in scale means ten times increase in size.
VEI (Volcanic explosively index)
This scale measures volcanic explosiveness on a scale of 0-8. Factors are amount of material produced, height of the eruption cloud and qualitative observations. This scale is logarithmic which means that each increase in scale means ten times increase in size.
Richter scale
Measures earthquakes on a scale of 0-9. This is a measure of the amplitude of an earthquakes wave which makes it an absolute scale which means that any earthquake- anywhere- will measure the same. This is a magnitude scale. This scale is logarithmic which means that each increase in scale means ten times increase in size.
Tectonic hazard profile
Tectonic hazard profile: A technique used to understand different types and characteristics of hazard- Tsunami, volcano, earthquake. They can be used to analyse and assess the same type of hazard taking place in different places or at different times. Profiles are developed for each natural hazard and area based on relevant criteria such as magnitude, speed of onset, duration and areal extent. Only compares physical processes and helps rank hazards into different categories to try to determine which ones should be given resources and attention.
Hazard profiles cannot easily compare different types of hazards as shared characteristics differ.
Root causes of PAR Model
In the ‘root causes’ of the PAR model- 1.4B- the most important causes are those which have an economic, demographic or political foundation. Developing countries tend to have less wealth which can be expended to deal with disasters. Therefore, vulnerability increases as these factors decrease.
People in developing countries have access to resources which are insecure and vulnerable.
Hazard mitigation is likely to be low priority for the government.
People who are economically and politically on edge are less likely to trust local knowledge and are more likely to rely on local government for help.
Lack of education, secure housing, healthcare and secure income all reduces a community’s ability to react to a disaster.
Hati earthquake: see case study sheet.
Governance and geographical factor
Governance encompasses several formal and informal arrangements and procedures, which can change over time. This also varies from national to local levels.
Governance should be considered through several forms including economic activity, political activity internationally, spread of technology. Positive governance results in significant response effectiveness and preparation efforts.
Population density
The higher the population density is the greater the risk presented to citizens.
Isolation and accessibility
A more remote population is more challenging to rescue- Nepal 2015- helicopters were used in recovery efforts.
Degree of urbanisation
The more urbanised a place is the more people will be concentrated- high urbanisation is synonymous with high population densities- Asan cities. On the other hand, as, multiple people live in one building mitigation strategies like earthquake resistant buildings can become cheaper per capita and be more effective.
Charachteritic of a natural hazard
The characteristic of a natural disaster is the result of a changing pattern of social and physical factors that influence the event and their degree of intervention. Disasters need to be viewed through a lens of both human and physical factors when understanding the scale of disaster.
See case study sheet for examples.
Trend of natural disasters
- Number of disasters seems to be falling. With deaths following this trend except for mega disasters.
- due to inflation and the emergence of wealthy nations the cost of hazards is increasing.
- Deaths globally are and are continuing to fall which is credit to the development of resistance technologies
Mega disasters
Tectonic mega disasters are often classified as high impact, low probability events. Japan 2011 saw the Fushimi nuclear plant meltdown cause the reduction of nuclear power globally.
For case studies see the case study sheet attached separately.
Multiple hazard zone
A multiple hazard zone is an area which is at threat from several hazards- volcanoes and earthquakes- earthquakes and tsunamis. Hydrological hazards like tsunamis often can contribute to the devastation of their own creator- the earthquake. As seen in Japan 2011 the earthquake which caused its own level of devastation was the first step in the devastation deriving from the consequent tsunami.
Prediction and forecasting of Tsunami
Only certain coastal areas are at risk and forecasting can be effective because underwater earthquakes can result in tsunamis, so prediction is effective.
Prediction and forecasting earthquakes
Risk prediction focuses on an earthquake happening at a certain area. Long term forecasts are more accurate than week by week forecasting.
Location of earthquake can be unpredictable and so prediction efforts can be ineffective.
Verry few signs that an earthquake may take place.
Prediction and forecasting volcanos
Because only certain areas are at risk from volcanoes there is less space to monitor. Many signals can indicate for effective forecasting- St Helens.
Responce as a stage in the hazard management cycle
Response includes taking primary and secondary responses to try to minimise the loss following an event.
Recovery as a stage in the hazard management cycle
Reconstruction is a key part of hazard recovery to ensure that economies and communities recover to be more resilient and better react to the onset of another disaster.
Mitigation
This stage occurs prior to an event taking place. The aim of this stage is to reduce the extent of damages done by future hazard events. Infrastructure can be built so that it is hazard resistant. Buildings can also be constructed so they are shock absorbent.
Preparedness as a stage in the Harvard magagent cycle
Aims to help people be prepared for an event if one were to occur if managed appropriately this should mean that people know how to respond to the onset of a hazard event so that the risk of damages can be prevented or reduced. Preparedness includes monitoring, early warning systems and education.
Parcs model
This can be used to better understand the time dimensions of resilience. Each stage shows the different stages of time during which relief, rehabilitation or reconstruction is started. The words on the y- axis describe quality of life, stability and infrastructure. The model can be used to plan and understand risk and resilience as well as to better prepare for future events.
Japan 2011- improvement took place with reconstruction and tsunami walls being improved unlike in Hati 2015 where citizens have never recovered.
land use zoning as a strategy to modify the event
Land use zoning is a method used by the government to classify parcels if land and restrict the physical development or use of certain parcels of land. Zones include commercial, industrial, residential, agricultural. The most at-risk land is used for unimportant processes while the most important and functional land is used for the most important efforts- housing.
Hazard resistant design as a strategy to modify hazard design
Hazard resistant design incorporates designing structures and infrastructure to withstand pressure from natural hazards. This allows homes to withstand earthquakes which results in reduced cost of earthquakes or other natural hazards. An example of this are houses built with steel rods running down the building to reduce the impact of hazards.
Engineering defences to modify the event
This involves hands on infrastructure which can reflect tsunami waves- post 2011 Japan installed tsunami defences. Infrastructure can also direct lava flow.
Diversification of lava flow to reduce the impact of the event.
The diversification of lava flow can undertake sacrificial protection, whereby cars are used sacrificially to divert lava flow or diggers are utilised to direct lava flow away from highly valuable infrastructure or interests like homes.
Hi tech monitoring as a strategy to modify vulnerability
Hi- tech monitoring is using intelligence software to track changes in the activity of a volcano or other cause of natural hazard. As was seen in the eruption of Mt st Helens, many people were able to survive through the evacuation which took place. This made the community more resilient.
Predictions as a strategy to modify vulnerability
Earthquakes cannot be predicted. Volcanic eruptions can be predicted, sophisticated infrastructure can be installed in a volcano which then allows for accurate inferencing of when a volcano may erupt. Tsunamis can be partly predicted. Those stemming from an earthquake cannot be predicted however once one has occurred the tsunami can be predicted.
Education as a strategy used to modify vulnerability
Education of natural hazards can go a long way to reduce vulnerability. For example, in 2004 Asian tsunami, before the waves hit, the sea retreated, and many fish were beached onto the seabed. This resulted in local people going to investigate which however resulted in more people being in the firing line of the tsunami when it hit. If this population was educated about the potential risk, then they would have evacuated. This would have resulted in many people surviving the event who did not.
Community preparedness as a strategy to reduce vulnerability
Community preparedness is crucial in modifying resilience because the actions of a community after the event in the immediate search and rescue response stage is critical to saving lives as official emergency response teams have not yet shown up.
Adaptation as a strategy to reduce hazard vulnerability
Adaptation is also highly important at reducing the impact of natural hazards. Efforts like constructing houses onto stilts or living further away from volcanoes or living at a higher altitude instantly reduces the risk posed to citizens making them less vulnerable and more resilient.
Short term aid as a method to modify loss
Short term aid- like the sheltering of 810,000 thousand people after Haiti 2010- reduces loss because these people who are now incredibility vulnerable are protected which reduces any further deaths.
Long term aid as a strategy to modify loss
Long term aid- the rebuilding of schools- helps to bounce back and results in many pupils not being held back by this disaster. This reduces the loss of the future economy of a country by having an under- educated workforce. This was seen in Hati 2010 with the erection of temporary schools.
Insurance as a strategy to modify loss
Insuring assets protects and reduces the vulnerability of a community because the communities’ assets are protected. Therefore, loss is modified because over a short period of time the house or insured item has been replaced and life goes on.
