Hazards Flashcards
What is a natural hazard
A perceived event that threatens both life and property. They occur in the physical environments of the atmosphere, lithosphere and the hydrosphere
What do natural hazards result in
Disasters that cause some loss of life and/or damage to the built environment and create severe disruption to human activities
What do natural/environmental hazards include
Volcanic activity, seismic events and tropical storms
What are some examples of disruption to human systems
Death and injury, property and communication system damage and the disruption of economic activities
How is the risk of hazards posing a risk to human population increased
Because of built shanty towns on unstable tropical slopes, urbanisation of volcanic zones, people live in areas with active faults and also in coasts susceptible to hurricanes and tsunamis. The risk is also exacerbated by the failure to recognise a potential hazard and react accordingly
What are the 5 common characteristics of natural hazards and their effects on people
Origins are clear and effects they produce are distinctive.
Most only allow a short warning time before they hit.
Exposure to the risk is usually involuntary.
Most losses to life and damage to property occur shortly after the event.
The scale and intensity of the event requires an emergency response.
Where does the characteristic of the exposure to risk being involuntary apply to usually
To the populations of less well developed countries, people in developed areas who choose to live in hazardous zones are often well aware of the risks which they choose to minimise or even ignore
Examples of the effects of natural disasters being felt in communities a long time after the event has occurred
Disease, disruption to communities and economic activity
What is adaption in the context of hazards
The attempts by people or communities to live with hazard events. By readjusting their living conditions, people are able to reduce their levels of vulnerability.
Examples of adaption in the context of hazards
They may avoid building on sites that are vulnerable to storm surges but stay within the same area
What is fatalism
A view of a hazard event that suggests that people cannot influence or shape the outcome, therefore nothing can be done to mitigate against it. In some parts of the world, the outcome of a hazard event can be said to be ‘God’s will’
What do people who believe in fatalism do to mitigate the risks of a hazard
They put in place limited or no preventive measures
What is perception
This is the way an individual or a group views the threat of a hazard event. This will ultimately determine the course of action taken by individuals or the response they expect from governments and other organisations
What is risk
The exposure of people to a hazardous event presenting a potential threat to themselves, their passions and the built environment in which they live
What are 5 reasons people consciously put themselves at risk from natural hazards
Hazard events are unpredictable. There’s a lack of alternatives. Changing levels of risk. Cost/benefit analysis. Perception.
How is hazard events being unpredictable a reason for people choosing to live in hazardous areas
One can not predict the frequency, magnitude or scale of a natural hazard event
How is the lack of alternatives a reason for people choosing to live in hazardous areas
Due to social, political, economic and cultural factors, people cannot simply uproot themselves from one place and move to another, giving up their homes, land and employment
How is the changing level of risk a reason for people choosing to live in hazardous areas
Places that were once relatively safe may have become through time far more of a risk.
Example of changing levels of risk causing people to live in risky areas that once weren’t risky
Deforestation could result in more flooding from torrential rain associated with tropical storms and there could also be a greater risk from landslides
How is the cost/benefit analysis a reason for people choosing to live in hazardous areas
There are many hazardous areas that offer advantages that in people’s mind outweigh the risk that they are taking.
Example of the cost/benefit analysis causing people to live in risky areas
Californian cities for example have a high risk from earthquakes, but people see the many advantages of living there as greater than the potential risk
What does vulnerability to physical hazards mean
The potential for loss
Why does vulnerability vary over time and space
Since loses vary geographically, over time and among different social groups
Who came up with the model of vulnerability
Researchers at the University of South Carolina
What does the model of vulnerability look like
Risk and mitigation creates the hazard potential.
Hazard potential to geographic context and social fabric.
Geographic context to biophysical vulnerability.
Social fabric to social vulnerability.
Biophysical vulnerability and social vulnerability to place vulnerability.
Place vulnerability back to risk and mitigation.
What are some examples geographic context in the model of vulnerability
Physical setting
Proximity
What are some examples social fabric in the model of vulnerability
Experience
Perception
Built environment
What can effect the degree to which the hazard event will impact upon them
People wealth and the level of technology that they can apply
How can richer people and counties protect themselves from hazard
By building sea defences, constructing earth-quake resident buildings, providing better emergency services etc.
They can be better prepared by being made more aware of their risk through education
Why have more and more people been forced to live in hazardous areas
As urban areas have grown so has the population
What are low lying areas of cities at risk form
Tropical storms and tsunamis
Why do people react to the threat of hazards in different ways
Because of the way in which individuals receive and process information
What 7 factors effect perception
Socio-economic status Level of education Occupation/employment status Religion, cultural/ethnic background Family and marital status Past experience Values, personality and expectations
What do perceptions of hazards ultimately determine
The course of action taken by individuals in order to modify the event or the responses they expect from governments and other organisations
When is there often a greater difference in the perception of a hazard
Between people of differing levels of economic development
What is the idea that ‘in wealthier areas there is a sense that the better that you are prepared, the more you will be able to withstand the impact of a hazard’ based upon
Government and community action and is usually backed by capital that will fund technologically-based solutions
When does the sense of helplessness in the face of a natural hazard tend to increase
With the level of poverty and the deprivation of the people
What do disadvantaged people in wealthy counties usually see natural hazards as
Part of their way of life, unavoidable much like the bulk of people in poorer countries seeing the impacts of these events as being part of the conditions of overtly
What 3 ways may people perceive natural hazards
Fatalism (acceptance)
Adaption
Fear
How is the ‘adaption’ perception of a natural hazard carried out
People see that they can prepare for, and therefore survive the events by prediction, prevention and/or protection, depending upon the economic and technological circumstances of the area in question
How is the ‘fear’ perception of a natural hazard carried out
The perception of the hazard is such that people feel so vulnerable to an event that they are no longer able to face living in the area and move away to regions perceived to be unaffected by the hazard
What does community preparedness/risk sharing involve
Prearranged measures that aim to reduce the loss of life and property damage through public education and awareness programmes, evacuation procedures, the provision of emergency medical, food and shelter supplies and the taking out of insurance
What does frequency mean
The distribution of a hazard through time
What is the process of integrated risk management
Considering the social, economic and political factors involved in risk analysis; determining the acceptability of damage/disruption; deciding on the actions to be taken to minimise damage/disruption
What is magnitude
The assessment of the size of the impact of a hazard event
What is prediction
The ability to give warnings so that actions can be taken to reduce the impact of hazard events. Improved monitoring, information and communications technology have meant that predicting hazards and issuing warnings have become important in recent years
What are primary effects
The effects of a hazard event that result directly from that event. For a volcanic eruption these could include lava and pyroclastic flows. In an earthquake, ground shaking and rupturing are primary effects
What is community resilience
The sustained ability of individuals or communities to be able to utilise available resources to respond to, withstand and recover from the effects of natural hazard events. Communities that are resilient are able to minimise the effects of the event, enabling them to return to normal life as soon as possible
What are secondary effects
The effects that result from the primary impacts of the hazard event. In volcanic eruptions these include flooding (from melting ice caps and glaciers) and Lahars. In an earthquake, tsunamis and fires (from ruptured gas pipes) are secondary effects
Where can responses to natural hazards come from
Individuals, the local community with people working together, and from national governments and international agencies
What is a key feature of the modern approach to managing hazards
That hazards are best combated by efficient management
What do modern management techniques of natural hazards aim to do
Using their gathered information, careful analysis and deliberate planning, they aim to make the most efficient use of the money available to confront natural hazards
Example of a modern approach to managing natural hazards
Integrated risk management
What are the incorporated parts of the integrated risk management
Identification of the hazard.
Analysis of the risks.
Establishing priorities.
Treating the risk and implementing a risk reduction plan.
Developing public awareness and a community strategy.
Monitoring and reviewing the whole process.
What 3 ways do people and organisations try to manage natural hazards
Prediction
Prevention
Protection.
What is the key to predicting hazards in managing them
Improved monitoring in order to predictions which means the warnings can be issued
Example of agency that uses prediction depends upon monitoring information from satellites and recordings of land, sea and air
The National Hurricane Centre in Florida
For natural hazards, why is prevention unrealistic
Because it is too difficult to stop a natural disaster from occurring
Examples of prevention of natural hazards
Seeding clouds in potential tropical storms in order to cause more precipitation, which in theory would result in a weakening of the system as it approaches land
What is the aim of protection in managing natural hazards
To protect people, their possessions and the built environment from the impact of the event
What does protection in managing a natural hazard usually involve
Modifications to the built environment such as improved sea walls and earthquake proof buildings
What is one way in which governments can act, and people react, to help manage natural hazards
To try and change attitudes and behaviour to natural hazards which will reduce people’s vulnerability. Community preparedness.
What must all attempts at managing natural hazards be evaluated in terms of
Their success
Example of successful schemes in managing natural hazards
Dynamite to divert lava flows on Mt Etna and pouring sea water on lava flows in Iceland
Example of an unsuccessful scheme in managing natural hazards
The Japanese felt they were well prepared for earthquakes and yet in 1995 the city of Kobe suffered the Great Hanshin earthquake, which destroyed over 100,000 buildings, a death toll over 6,000 and 35,000 injuries
What can be used to evaluate schemes to manage natural hazards
The disaster/risk management cycle
What does the disaster/risk management cycle illustrate
The ongoing process by which governments, businesses and society plan for and reduce the impact of disasters, react during and immediately following an event, and take steps to recover after an event has occurred
What do appropriate actions at all points in the disaster/risk management cycle lead to
Greater preparedness, better warnings and reduced vulnerability or the prevent of hazard events during the next cycle
What does the complete disaster/risk management cycle include
The shaking of public policies and plans that either modify the causes of the hazard events or mitigate their effects on people, property and infrastructure
What are the three parts to the disaster/risk management cycle
Pre-disaster: risk assessment, mitigation/preventing, preparedness
Response: warning/evacuation, saving people, providing immediate assistance, assessing damaging, ongoing assistance
Post-disaster: restoration of infrastructure, reconstruction, economic and social recovery, ongoing development activities, risk assessment, mitigation/ prevention
What is one of the main goals of disaster management (and one of its strongest links with development)
The promotion of sustainable livelihoods and their protection and recovery during such events
Where the goal of disaster management of ‘promotion of sustainable livelihoods and their protection and recovery during such events’ is achieved what happens
People have a greater capacity to deal with with disasters and their recovery is more rapid and long lasting
What is the Federal Emergency Management Agency (FEMA) main purpose
To co-ordinate the response to a disaster that has occurred in the United States and that has overwhelmed the resources of local and state authorities
What have FEMA created
Major analysis programmes for floods, hurricanes and earthquakes
Where are the operations by FEMA ferried our
Along the lines shown by the disaster/risk management cycle
What are the different ways of managing natural hazards
Community resilience
Integrated risk management
Prediction, prevention, protection
Community preparedness
What are the two ways attempts at managing hazards can be assessed
Disaster/risk cycle
Disaster/response curve
Who devised the disaster/response curve
Park
Why did Park devise the disaster/response curve
To show that hazard events can have varying impacts over time
What does the disaster/response curve show
An early stage, before the disaster strikes, where the quality of life is normal for the area. Here people try their best to prevent such events and prepare in case they should happen. When the event happens, the quality of life suddenly drops with people taking immediate action to preserve life and, if possible the built environment to bring the quality of life back to normality
What are the components in Parks disaster/response curve
Along the y axis: quality of life. Level of economic activity. Social stability communications/service level.
Along the x axis: time.
In the graph: the top is improvement in yellow, second section is normality and third section is deterioration.
The hazard event is the red line that usually starts in normality and drops due to disruption. The line then increases with recovery.
Pre-disaster: relief, rehabilitation, reconstruction. All along the x-axis
What is the stage in Parks model called relief
Starts as soon as the disaster strikes.
Relief is where medical attention, rescue services and overall care are delivered. This can last form a few hours to several days if the event has been damaging. From this point the quality of life of the people of the area starts to slowly increase.
What is the stage in Parks model called rehabilitation
Quality of life is still in the deterioration zone but it is rising.
Where people try to return the state or things to normal by providing food, water and shelter for those most affected. This period can last anything from a few days to weeks
What is the stage in Parks model called reconstruction
Quality of life is rising rapidly and is going back to the normality zone.
Where the infrastructure and property are reconstructed and crops regrown. At this time people use the experience of the event to try to learn how to better respond to the next one. This period can take from weeks to several years.
How can their be variations within the Park model
The model will be different due to different speeds of the drop in the quality of life, the duration of the decline and the speed and nature of recovery - e.g some places may never recover to their normal quality of life or some may recover to a better one.
What could variations within the park model be due to
It could be related to the type of hazard, the degree of preparedness or the speed of the relief effort and the nature of recovery and rebuilding
What is distribution
The spatial coverage of the hazard, this can refer to the area affected by a single event, which can have a localised effect, while others have a wider effect like tsunamis which can cross large oceans.
It can also refer to the areas where he particular hazard is likely to occur.
What have volcanic eruptions been known to have
A global effect with the spread of dust and the consequent short-term climatic change
What is the usual distribution of earthquakes and volcanoes
Generally they are associated with tectonic plate boundaries
What is the usual distribution of tropical cyclones
Usually between 5* and 25* north and south of the equator
At its most basic level, what does the frequency-magnitude principle lead us to expect
Many small insignificant events and, in the long term, increasingly fewer events as magnitudes rise
What would be the primary effects for an earthquake
Ground shaking and cracking
What would be the secondary impacts of an earthquake
Soil liquification, landslides, tsunamis and the effects on people and the built environment such as collapsing buildings, fires, flooding and the knock on effects which could be with the population for a long time
How may the legacy of a hazard event be around for years
Communication systems could be out of order.
The ability to produce food crops may take some time to be restored.
The economy of a region may be severely damaged for years.
Before the development of plate tectonic theory, what did the Earth scientists divide the interior of the earth into
3 layers: the crust, the mantle and the core
What is the core made up of
Dense rocks containing iron and nickel alloys
What is the core divided up into
A solid inner core and a molten outer one, with a temperate over 5000*C
How is the heat in the earths core produced
Mainly as a result of two processes: primordial heat and radiogenic heat
What is primordial heat
Heat left over from the earths formation
What is radiogenic heat
Produced by the radioactive decay of isotopes, particular uranium-238, thorium-232, potassium-40
What is the mantle made up of
Molten and semi-molten rocks containing lighter elements such as silicon and oxygen
Why is the crust light
Because of the elements that are present, the most abundant being silicon, oxygen, aluminium, potassium and sodium
How does the crust vary in thickness
Beneath the ocean it is only 6-10km thick but below the continents this increases to 30-40km and under the highest mountain ranges this can be as high as 70km
What has the theory of plate tectonics retained
The division of the 3 layers but new research suggests the crust and upper mantle should be divided into the lithosphere and asthenosphere
What does the lithosphere consist of
The crust and the rigid upper section of the mantle
How thick is the lithosphere approximately
80-90km thick
What is the lithosphere divided into
Seven large plates and a number of smaller ones
What are the two categories tectonic plates are divided into
Oceanic and continental, depending on the type of material from which they are made
Where is the asethenosphere
Lies beneath the lithosphere and is semi-molten on which the plates float and move
What is the thickness, age, density and composition of continental crust
30-70km
Over 1,500 million years
2.6 (lighter)
Mainly granite; silicon, aluminium, oxygen (SIAL)
What is the thickness, age, density and composition of oceanic crust
6-10km
Less than 200 million years
3.0 (heavier)
Mainly basalt; silicon, magnesium; oxygen (SIMA)
What is the basic earth structure
The inner core is solid and 5,100 km. The outer core is liquid and 2,900km. The mantle has 3 parts and includes the asthenosphere. Crust 0-100km thick. Lithosphere (crust and uppermost mantle)
What are the names of the tectonic plates
Eurasian plate. Indo-Australian plate. Pacific plate. North American plate: Nazca plate. South American plate. African plate. Antarctic plate
Describe the tectonic plates and their margins
The Eurasian plate contests of most of Europe and Asia (including Indonesia) and runs through Iceland as the mid-Atlantic ridge. It is on a convergent (destructive, subduction zone) fault line with the indo-Australian plate which surrounds India, Australia, Papua New Guinea and runs through New Zealand.
They both are on convergent (destructive, subduction zones) boundaries to the Pacific plate, which is all oceanic.
This has a transform fault and is divergent (constructive, sea floor spreading) boundary with the Antarctic plate.
The nazca plate lies between the Pacific plate, the Antarctic plate, the North American plate and the South American plate.
The nazca is divergent (constructive sea floor spreading) next to the Pacific, it is convergent (destructive) next to the South American plate.
The North American plate consists of North America and a small part of russia.
It forms a conservative zone with the Pacific plate and a divergent (constructive) boundary next to the Eurasian plate.
The South American plate is a convergent (destructive) boundary next to the African plate which is divergent (constructive) to the indo-Australian plate.
Where is the mid-Atlantic ridge
Runs between South America, Africa and North America and Europe, straight through Iceland
Where are the oceans
North Pacific Ocean by North America and Asia.
South Pacific Ocean by South America and Australasia.
North Atlantic Ocean between North America and Europe.
South Atlantic Ocean by South America and Africa.
Southern Ocean by Antarctica.
Indian Ocean between Africa and Australia.
Arctic Ocean above Asia by the Arctic.
When maps of The Atlantic Ocean were first produced what did people notice
That the continents either side seemed to fit together remarkably well - the bulge of South America fitting into the indent below west Africa
Who noted the fact that the continents seem to fit together in the seventeenth century
Francis Bacon
Why did Francis Bacon not attract any serious attention
No one thought the continents could move
In 1912 who published the theory of a single continent existing 300 million years ago
Alfred Wegener
What did Alfred Wegner publish
The theory of Pangea that existed 300 million years ago.
He maintained that it later split into the two continents of Laurasia in the north and Gondwanaland in the south.
It was the theory of continental drift and claimed it was supported by several pieces of evidence that these areas were once joined.
What are the3 bits of geological evidence for the theory of continental drift
The fit of South America and west Africa.
Evidence of a late-Carboniferous glaciation (290 million years ago).
Rock sequences in northern Scotland closely agree with those found in eastern Canada.
Where were deposits of evidence of a late-Carboniferous glaciation found
In South America, Antarctica and India.
There were also striations on rocks in Brazil and west africa.
How is the evidence of a late-Carboniferous glaciation evidence for the theory of continental drift
The formation of these deposits cannot be explained by their present position; they must have been formed together and then moved.
How can the rock sequences in Scotland and Canada be used as evidence for continental drift
It indicates that they were laid down under the same conditions in one location
What are the 3 pieces of biological evidence for the theory of continental drift
Fossil brachiopods found in Indian limestone are comparable with similar fossils in Australia.
Fossil remains to the reptile Mesosarus are found in both South America and Southern Africa.
Fossilised remains of a plant.
Why is the fossil remains of the reptile Mesosaurus being found in South America and Southern Africa evidence for the theory of continental drift
It is unlikely that the same reptile could have developed in both areas or that it could have migrated across The Atlantic
How does the fossilised remains of a plant act as evidence of the theory of continental drift
The fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica
Why did Wegeners ideas gain little ground
Because they were unable to explain how continental movement took place
When did evidence begin to accumulate to show that Wegeners theory could have been correct
1940s onwards
What was discovered in the 1940s that gives evidence of continental drift
The mid-Atlantic ridge was discovered and studied with a similar feature in the Pacific Ocean. Examination suggested that sea-floor spreading was occurring.
What is the evidence for sea-floor spreading in the mid-Atlantic ridge
The alternating polarity of the rocks that form the oceanic crust
How do magnetic ‘stripes’ in The Atlantic Ocean floor occur
Iron particles in lava erupted in the ocean floor are aligned with the earths magnetic field. As the lavas solidify these particles provide a record of polarity at the time of eruptions. However the earths polarity reverses at regular intervals. This results in a series of magnetic ‘stripes’ with rocks aligned alternately towards the north and south poles.
How often does the earths polarity reverse
Approx every 400,000 years
What is the record of the earths polarity at times of eruptions called
Palaomagnetism
Where is the striped pattern of magnetic ‘stripes’ found
Mirrored exactly on either side of a mid-oceanic ridge
What does the magnetic ‘stripes’ on either side of a mid-oceanic ridge suggest
The oceanic crust is slowly spreading away from this boundary
Beside the magnetic ‘stripes’ on either side of mid-oceanic ridges, what else helped to develop the theory of continental drift
The fact that oceanic crust gets older with distance from the mid-oceanic ridge
What does sea-floor spreading imply
That the earth must be getting bigger, as this is not the case however it must be that plates are being destroyed somewhere to accommodate the increase in their size at mid-Oceanic ridges
What is evidence that plates are being destroyed to accommodate the growth from constructive sea-floor spreading
The discovery of huge oceanic trenches where large areas of ocean floor were being pulled downwards in a process known as subduction
Describe the process of constructive plate boundaries
Hot spots around the core of the earth generate thermal convection currents within the asthenosphere, this causes magma to rise towards the crust and then spread before cooking and sinking. This circulation of magma is the vehicle upon which the crustal plates move.
What can crust be thought of doing
Floating on the denser material of the asthenosphere
What are constructive boundaries
Plates moving away from each other - divergent
What are destructive boundaries
Plates moving towards each other - convergent
What is a conservative plate boundary
Where two crustal plates slide past each other and the movement of the plates is parallel to the plate margin
Why is there volcanic activity at conservative margins
There is no subduction
What 5 landforms are associated with plate movements
Ocean ridges Rift valleys Deep sea trenches Island arcs Young fold mountains Volcanoes
How are Ocean ridges formed
When plates move part in oceanic areas. The space between the plates is filled with basaltic lava upwelling from below to form a ridge.
What is the longest continuous uplifted form on the surface of the planet
Ocean ridges
What can form on ocean ridges
Volcanoes - submarine volcanoes which sometime rise above sea levels
Example of submarine volcano that rose above sea level
Surtsey to the south of Iceland
When do rift valleys form
When plates move apart on continental areas. The crust fractions as the plate moves apart and the broken crust drop down between parallel faults to form the ridge
Example of Rift Valley
In East Africa, the brittle crust fractures as sections of it move apart
What is a Horst
An area between two parallel rift valleys hat forms an upstanding block
What is the line of the African rift thought to be
An emergent plate boundary
What is an emergent plate boundary in Africa
The beginning of the formation of a new ocean as Eastern Africa splits away from the remainder of the continent
How do deep sea trenches form
Where oceanic and continental plates meet, the denser oceanic plate is forced underneath the lighter continental one (subduction).
The downwarping of the oceanic plate forms a very deep part of the ocean known as a trench.
Example of a deep sea trench
Off the western coast of South America, the Nazca plate is subducted under the South American plate forming the Peru-chile trench
Example of a deep sea trench formed by two oceanic plates
On the western side of the Pacific Ocean, the Pacific plate is sub-ducted beneath the smaller Philippine plate forming the very deep Marianas trench
How do Island arcs form
During subduction, the descending plate encounters hotter surroundings, and this coupled with the heat generated from friction, begins to melt the plate. As this material is less dense than the surrounding asthenosphere, it begins to rise towards the surface as plutons of magma. Eventually these reach the surface and form complex, composite and explosive volcanoes. If the eruptions take place offshore, a line of volcanic islands forms. These are known as island arcs.
Examples of island arcs
The Mariana’s islands and Guam form a good example, running parallel to the Marianas trench.
How do young fold mountains occur
The plates forming continent crust have a much lower density than the underlying layers so there is not much subduction when such plates meet. As such plates move towards each other, their edges and sediments between them are forced up into fold mountains
Why is there no volcanic activity near fold mountains
Because there is little subduction
How are deep mountain roots created
During the process of forming fold mountains, some material is forced downwards
Examples of young fold mountains
The previous intervening Ocean, known as the Sea of Tethys, has had its sediment forced upward in large overfolds to form the Himalayas, a process which is continuing today.
Currently, where is it likely the next set of fold mountains will occur in the future
The indo-Australian plate is moving northwards into the Eurasian plate
Why can sediment that has accumulated on the continental shelf, along the edge of a plate, be uplifted
As the plate edges buckle during the subduction of a denser oceanic plate
Examples of where subduction causes fold mountains
The Andes, running down the area where the nazca plate is being subducted beneath the lighter South American plate. This is because sediment that accumulates in the continental shelf can be uplifted
What causes a number of explosive volcanoes in the Andes
Molten magma rising from the depths
For a long time the generally accepted view of plate motion was convection currents. What is now believed
That forces behind plate motions are not as simple as would be explained entirely by convection currents
How can different forces, that aren’t convection currents, work on plate boundaries
These forces can push from the ridge, drag the plates down at the trenches, or act along the sides of plates at conservative boundaries
What does the force ‘ridge push’ occur
At constructive boundaries, the upwelling of got material at ocean ridges generates a buoyancy effect that produces the ocean ridge which stands some 2-3km above the ocean floor. Here, oceanic plates experience the force that acts away from the ridge
What is ridge push the result of
Gravity acting down the slope of the ridge
What indicates there is some frictional resistance to the force ‘ridge push’
The occurrence of shallow earthquakes, resulting from the repeated tearing apart of the new-formed crust
What do some experts prefer ‘ridge push’ to be called
The process ‘gravitational sliding’
What is the force ‘slab pull’
The situation at destructive plate boundaries. A major component is the downward gravitational force acting on the cold and dense descending plate as it sinks into the mantle. This gravity-generated force pulls the whole oceanic plate down as a result of the negative buoyancy of the plate. This is called ‘slab pull’
What happens due to the pushing of the sub-ducting plate through slab pull against the overriding plate
There is frictional resistance that gives rise to both shallow and deep earthquakes in subduction zones
What does the fact that each plate moves at its own rate suggest
That the relative importance of the driving and retarding forces must vary from plate to plate. It is therefore unlikely that any single agent is the sole driving mechanism of plate motion; plates are therefore controlled by a combination of forces
What are lahars
There are formed by volcanic ash mixing with water and flowing downhill. Essentially they are volcanic mudflows
Examples of where lahars can occur
In the Philippines if a typhoon occurs after a volcanic eruption, then lahars can be the result
What is lava
Molten rock (magma) flowing onto the surface. Acid lava solidifies very quality but basic lava (basaltic) tends to flow some distance before solidifying
Example of a place with basic lava
On the Hawaiian islands
What is the lithosphere
The layer of the earth which consists of the crust and the upper section of the mantle. It is this layer which is split into a number of tectonic plates
What are pyroclastic flows also known as
Nuées Ardentes
What are pyroclastic flows
Formed from a mixture of hot gas (over 800*C) and tephra. After ejection from the volcano they can flow down the sides of a mountain at speeds of over 700km per hour. Some volcanologists apply the term nuées ardentes when the cloud is formed int from hot
What is tephra
The solid matter ejected by a volcano into the air. It ranges from volcanic bombs (large) to ash (fine)
What is most volcanic activity associated with
Plate tectonic processes
Where are most volcanic activities located
Along plate margins
Where 4 places is volcanic acidity found
Along oceanic ridges.
One or near subduction zones.
Associated with rift valleys.
Over hot spots.
Why are volcanoes found along ocean ridges
Because the plates are moving part and magma is forcing its way to the surface, cooking and forming new crust.
What is Sea-floor spreading
As plates move far apart, the new crust is carried away from the ridge
Best example of nature and distribution of volcanoes along ocean ridges
The mid-Atlantic ridge where Iceland represents a large area formed by volcanic activity.
Volcanoes formed here have fairly gentle sides because of the low viscosity of the basaltic lava.
Eruptions are frequent but relatively gentle (effusive).
E.g Eyjafajallajökull.
What are eruptions that are frequent but relatively gentle called
Effusive
What are the components in a cross section of the mid-Atlantic ridge
Asthenosphere. Lithosphere. Oceanic crust. Transform fault. Central rift. Sea level.
How do volcanoes form on or near subduction zones
The deeper the oceanic plate descends, the hotter the surroundings become. This, together with the heat generated form friction, begins to melt the oceanic plate into magma in part of the subduction zone known as the Benoit zone. As it is less dense than the surrounding material, this molten magma begins to rise as plutons of magma. Eventually they reach the surface and create composite and explosive volcanoes.
What is the Benioff zone
The part of the subduction zone where the oceanic plate begins to melt
What is the ring of fire
The line of volcanoes that surround the Pacific Ocean associated with plate subduction
What are volcanoes on subduction zones composite and explosive
Because of the andesitic lava
What is the nature of andesitic lava
Viscous (flows less easy)
What is the lava type of volcanoes on constructive margins
Basaltic (less viscous)
How do island arcs appear
If the eruptions in subduction zones take place offshore
Which plates are creating island arcs on the western side of the Pacific Ocean
The Pacific plate is being dragged beneath the smaller Philippines plate - the Guam and the Marianas have been formed form magma upwelling form the Benioff zone
What landforms are there near subduction zones
Trench
Marginal geosyncline
Mountain chains
Volcanoes
How do volcanoes form in rift valleys
When the areas of crust drop down between parallel faults to form the Rift Valley. The crust here is much thinner than neighbouring areas, suggesting that tension in the crust is causing the plate to thin as it starts to split. Through this thinning crust, magma forces its way up to the surface to form volcanoes.
Example of a volcano on a Rift Valley
Mt Nyiragongo
What causes a hot spot to develop
A concentration of radioactive elements below the crust
What is a hot spot
Small area of earths crust where an unusually high heat flow leads to volcanic activity
Where are hot spots located
Away from plate boundaries - creating a challenge for plate tectonic theory
Example of hot spot volcanoes
Hawaiian islands (kauai is the oldest at 3.8 million years and Hawaii is the active, Liohi underwater volcano will eventually form the next succession)
How do hot spot volcanoes form
A plume of magma rises from the core of the hot spot. This creates a column of upwelling lava which breaks through the surface causing an active volcano to form.
What volcanoes are created at hot spots
Huge (but relative to the area) flattish volcanoes called shield volcanoes
How is a succession of volcanoes in hot spots formed
The hot spot is stationary so as the plate moves over it, a line of volcanoes is created. (Volcanic island chain)
How do the oldest volcanoes in an island chain become seamounts below the level of the ocean
Because they had put so much pressure on the crust that subsidence has occurred. This, together with marine erosion replacing eruptions as the dominant process, causes them to get smaller
In a hot spot volcanic chain, why may a volcano that’s not directly above the mantle plume still erupt
As the plate moves it drags the head of the thermal plume with it
Examples of volcanic eruptions having an enormous variation
They can involve the tranquil effusion of a sluggish lava; one the other hand they can take the form of huge explosions that eject gas and dust and can blot out the sun for many years, bringing on global climatic change
What is the main measurement of magnitude of volcanoes
The volcanic explosively index (VEI)
What is the volcanic explosively index (VEI)
A logarithmic scale from 0 to 8.
Quiet lava-producing eruptions score 0-1 on the index whereas the more colloidal eruptions are nearer the high end.
9-8 eruptions occur very infrequently
What was the VEI of the eruption of Mr St Helen’s and Pinatubo
5 and 6
What do volcanologists estimate the last eruption at 7 in the VEI was
Tambora (Indonesia) in 1815
When was the last eruption which graded 8 on the VEI
73,000 years ago in Toba (indionesia)
What do critics of the VEI point out
It does not take into account gas emissions or the atmospheric/climatic impact of eruptions
How do volcanologists determine the frequency of eruptions of specific volcanoes
It’s previous history of activity can be interpreted by volcanologists using the deposits associated with the volcano itself and those within the wider region it can effect
Where the effects a volcanic event range from
The area immediately around the volcano to the whole planet
What can the impact presented by a volcanic eruption be categorised into
Primary and secondary education
What are primary effects in a volcanic eruption brought about by
Material ejected from the volcano
What are the four primary effects of a volcanic eruption
Tephra
Pyroclastic flows
Lava flows
Volcanic gases
What is the global distribution of active volcanoes
Mostly around plate boundaries, especially the Pacific ring of fire and on the Mid-Atlantic ridge in Iceland. The SAN Andreas fault in North America also has a few.
One volcano in the middle of northern Russia and one in the middle of the Pacific Ocean, not on a fault. One in Africa on the west coast.
Example of a pyroclastic flow destroying a city
The Roman City of Pompeii (Italy) was destroyed in 79 AD From flows from Mt Vesuvius
What are volcanic gases
Carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine.
Example of volcanic gases killing people
In 1989, carbon dioxide emissions from the lake in the crater of Nyos (Cameroon) killed 1,700 people
What are the 6 secondary effects of volcanic eruptions
Lahars Flooding Volcanic landslides Tsunamis Acid rain Climatic change
What are lahars
Volcanic mud flows. Melted snow and ice as a result of the eruption combined with volcanic ash forms mud flows that can move down the course of river valleys at high speeds
Example of lahar
In 1985, a lahar restores the Colombian town of Armero after an eruption of the volcano Nevado del Ruiz. Only a quarter of the 28,000 population survived
How is flooding a secondary effect of a volcanic eruption
When an eruption melts glaciers and ice caps, serious flooding can occur
Example of flooding after a volcanic event
In Iceland in 1996 when the Grimsvotn volcano erupted
How are tsunamis a secondary effect of volcanic eruptions
Sea waves can be generated by violent eruptions
Example of a tsunami as an effect of an eruption
In 1883, Tsunamis after the eruption of Krakatoa (Indonesia) killed 36,000
How is acid rain a secondary effect of volcanic eruptions
Volcanoes emit gases which include sulphur. When this combines with atmospheric moisture, acid rain occurs
How is climatic change a secondary effect of a volcanic eruption
The ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to have been an agent in past climatic change
When do volcanic events become hazardous
When they impact upon people and the built environment, killing and injuring people, burying and collapsing buildings, destroying infrastructure and bringing agricultural and other economic activities to a haunt
Why isn’t prediction a great management strategy of volcanic hazards
It’s difficult to predict when activity will take place.
How can prediction be a management strategy of volcanic hazards
A study of the previous eruption history of any volcano is important, along with an understanding of the type of activity produced.
What are the ways in which volcanologist are seeking to give accurate timings of an eruption
The monitoring of land swelling, changes in the groundwater levels and the chemical composition of groundwater and gas emission. It is also possible to monitor seismic activity looking for the shock waves that result from magma moving towards the surface, expanding cracks and breaking through other areas of rock
What does protection mean as a management of a volcanic hazards
Preparing for the event
How is protection a management of a volcanic hazard
Monitoring a volcano will possibly identity a time when the area under threat should be evacuated. The government of several counties with volcanoes, such as New Zealand, have made risk assessments and from them produced a series of alert levels in order to warn the public of the threat
What provides evidence for hazard assessment as a management strategy of volcanic hazards
Geological studies of the nature and extend of deposits from former eruptions and associated Lahars and floods
What do hazard assessments allow to happen in the management of volcanic hazards
They allow for the identification of areas at greater risk and land use planning can be applied to avoid building in high risk areas
Examples of protection strategies for managing volcanic hazards
Once the lava has started to flow and is fairly viscous, it may be possible to divert it from the built environment.
On Mt Etna in Italy: digging trenches, dropping blocks into the lava steam and using explosives have been successful in slowing down the flow.
Why do many devastated areas in poorer counties require aid for considerable periods of time after a volcanic hazard
Volcanic events can be prolonged and very damaging to the local economy
Why do many counties need aid after a volcanic hazard
Aid is needed for monitoring, evacuation, emergency shelters and food, long-term resettlement of the population and the restoration of the areas economic base and infrastructure
What are immediate responses to volcanic hazards
Those which take place just before or after the volcanic event such as warnings, evacuation and attempts to stop lava flows
What do long term responses of volcanic hazards include
The monitoring of a volcano, research into finding new methods of prediction and even building barriers in anticipation of the direction of lava flows and Lahars
What is an earthquake
As the crust of the earth is constantly moving, there tends to be a slow build up of stress within the rocks. When this pressure is released, parts of the surface experience, for a short period, an intense shaking motion - an earthquake
What is retrofitting
In earthquake prone areas building and other structures can be fitted with devices such as shock absorbers and cross-bracing to make them more earthquake proof
What is a tsunami
Giant sea waves generated by shallow-focus underwater earthquakes, violent volcanic eruptions, underwater debris slides and landslides into the sea
What is the focus of an earthquake
The point at which this pressure release occurs within the crust
What is the epicentre
The point on the earths surface immediately above the focus of an earthquake
What are the three broad categories of earthquakes
Shallow focus (0-70km deep) - these tend to cause the greatest damage Intermediate focus (70-300 km deep) Deep focus (300-700km)
What percentage of all the earthquake energy released is caused by earthquakes with shallow focus’
75%
Where does the most damage in an earthquake occur
The nearer to the epicentre
What is sent out during an earthquake
Shock waves
Where do the vast majority of earthquakes occur
Along plate boundaries
Where do the powerful earthquakes occur
Destructive marine
At conservative margins how are earthquakes created
The boundary is marked by a fault, movement along which produces the earthquake
What is the most famous conservative margin that creates earthqkadsn
San Andreas fault in California, which represents the boundary between the North American and Pacific plates. In reality the San Andreas system consists of a barrier complex zone in which there are a number of fractures of the crust
What are some earthquakes associated away from plate boundaries associated with
The reactivation of old fault lines
What has been suggested as the cause of some minor earthquakes
Human activity
How can human activity cause minor earthquakes
Through building large reservoirs which puts pressure on the underlying rocks, or subsidence of deep mine workings.
What is the global distribution of earthquakes
Around plate boundaries (ring of fire, mid Atlantic ridge, San Andreas fault) and some midland of the Eurasian plate, African plate, Pacific plate.
In recent times, what have people been worried about
The process of fracking (hydraulic fracturing of rock in order to release gas)
What are the ways in which the magnitude of earthquakes is measured
The Richter scale
The moment magnitude scale (MMS)
The Mercalli scale
What is the Richter scale
A logarithmic scale - an event measured at 7 in the scale has an amplitude ten times greater than one measured 6 on the scale. Energy release is proportional to the magnitude, so that for each unit increase on the scale, the energy released increases by approximately 30 times
Why do some geologists use the moment magnitude scale now
Because they have been unhappy with the fundamentals of the Richter scale for some time
What does the MMS identify
Energy release. It’s scale is the same as that of the Richter 1-10.
What was the largest earthquake ever recorded by the MMS
The Valdivia (Chile) event in 1960 at 9.5 MMS
Examples from the Richter scale
1-3 : normally only detected by seismographs, not felt.
4: faint tremors causing little damage.
5: widely felt, some structural damage near epicentre.
6: distinct shaking, less well-constructed buildings collapse.
7: major earthquake causing serious damage.
8: great earthquake causing massive destruction and loss.
9-10: very rare great earthquake causing major damage over a large region and ground seen to shake.
What does the mercalli scale measure
The intensity of an event and its impact. It is a 12-point scale where level 1 is approximate to 2 on the Richter scale. It goes up to level XII (approximately 8.5 on Richter)
What are some examples of the mercalli scale according to the USGS
I: not felt (not felt except by a very few under especially favourable conditions)
II: weak (felt only by a few)
III: weak (felt quite noticeably by persons indoors, vibrations)
IV: light (felt indoors by many and outdoors by few, dishes, windows, doors disturbed)
V: moderate (felt by nearly everyone, some dishes and windows broken)
VI: strong (felt by all, many frightened. Damage slight)
VII: very strong (damage negligible in buildings of good design and construction)
VIII: severe (damage slight in specially designed buildings. Considerable damage in normal buildings)
IX: violent (damage considerable in all buildings)
X: extreme (buildings destroyed, rails bent)
XII: extreme (bridges destroyed, underground pipeline completely out of service)
XIII: extreme (damage total, waves seen on ground surface, lines of sight and level distorted, objects thrown upwards in air)
What do seismic records enable
Earthquake frequency to be observed
What is a fault of seismic records
They only date back to 1848 when an instrument capable of recording seismic waves was first developed. Before that we have to consult historical records as to the date and the effects of the identical event
What are the primary effects (impacts) of an earthquake
Ground shaking
Ground rupture
What does the severity of ground shaking depend upon
The magnitude of the earthquake, it’s depth, the distance form the epicentre and the local geological conditions
What were the seismic waves that devastated Mexico City in 1985 amplified by
The ancient lake sediments upon which the city is built
What is ground rupture
The visible breaking and displacement of the earths surface, probably along the line of the fault
What does ground rupture pose a major risk for
Large engineered structures such as dams, bridges and nuclear power stations
What are 5 secondary effects of seismic hazards
Soil liquefaction Landslides/avalanches Tsunamis Fires Effects on people and the built environment
How is soil liquefaction a secondary effect of seismic hazards
When violently shaken, soils with a high water content loses their mechanical strength and start to behave like a fluid
How are landslides/avalanches a secondary effect of seismic hazards
Slope failure as a result of ground shaking
How are tsunamis a secondary effect of seismic hazards
Giant sea waves generated by shallow-focus underwater earthquakes involving movements of the sea bed, or landslides into the sea
How are fires a secondary effect of seismic hazards
They result from broken gas pipes and collapsed electricity transmission systems
Examples of the effects on people and the built environment being a secondary effect of seismic hazards
Collapsing buildings; destruction of road systems and other forms of communication; destruction of service provisions such as water, electricity and gas; flooding; disease; food shortages; disruption to the local economy, either subsistence or commercial.
What will some of the effects on the human environment from seismic hazards depend on
The ability of the area to recover
What are the characteristics of tsunamis
Very long wavelength (sometimes over 100km)
Low wave heigh (under one metre) in the open ocean
Travel at speeds of over 700km per hour
How long do some tsunamis take to cross the Pacific Ocean
Less than a day
What happens to tsunami waves when they reach shallow water bordering land
They increase rapidly in height
What is the first warning given to coastal populations about an oncoming tsunami
The wave trough in front of the tsunami which results in a reduction in sea level, known as a drawdown.
Behind this comes the tsunami itself.
How high can tsunamis reach
An excess of 25m
What do tsunami events usually consist of
A number of waves, the largest not necessarily being the first
How far did the Indian Ocean tsunami reach
Started in the West coast of Indonesia and spread through Kenya, bangladesh and throughout the whole of Indonesia
When a tsunami reaches land, what 5 things will it’s effect depend upon
The height of the waves and the distance they have travelled.
The length of the event (at source).
The extent to which warnings could be given.
Coastal physical geography, both offshore and on the coastal area.
Coastal land use and population density.
What are some effects of tsunamis
The wave will wash boats and wooden coastal structures inland, and the backwash may carry them out to sea. People are drowned or injured by the tsunami as both the water itself and the debris that it contains are hazards. Buildings, roads, bridges, harbour structures, trees and even soil are washed away.
What do most tsunamis have an effect on depending upon the coastal geography
At least 500-600m inland
What percentage of all tsunamis are generated within the Pacific basin
Around 90%
What are the tsunamis in the Pacific basin associated with
The tectonic activity taking place around its edges
What plate boundaries generate the most tsunamis
Convergent plate boundaries where subduction is taking place, particularly on the western side of the Pacific and the bordering eastern side of the Indian Ocean
What percentage of all tsunami events take place on the eastern side of the Indian Ocean
25%
Which areas do the geological record indicate that huge tsunamis have affected
The Mediterranean Basin (the Santorini eruption around 1450 BC) and the North Sea (for example the Storegga slide, around 7240 BP) resulting from huge submarine debris slides off Norway which produced tsunamis of over 6m in height in Scotland and other areas bordering the North Sea. It is believed these tsunamis continued across The Atlantic to hit the coastlines of Spitsbergen, Iceland and Greenland
What are the 3 ways to manage seismic hazards
Prediction
Prevention
Protection
What is the prediction of earthquakes
Very difficult
How can regions at risk from seismic hazards be identified
Through plate tectonics, but attempts to predict a few hours before the event are questionable
What are attempts at prediction seismic hazards based upon
Monitoring groundwater levels, release of radon gas and unusual animal behaviour. Fault lines such as the Sans Andreas can be monitored and the local magnetic fields measured
How can producing a hazard zone map predict the impact of an earthquake
Areas can be mapped on the basis of geological information and studies made into ground stability. The map can be acted upon by local and even national planners
What can close studies of fault lines sometimes indicate
The point along the fault line where the next earthquake could be due
What did a study of the pattern of the seismic events along the San Andreas fault between 1969 and 1988 indicate
The existence of a ‘seismic gap’ in the area of Lona Prieta (that is, the area had not had any real seismic activity for the past 20 years)
When do seismic surveys not work
For events which take place on unknown fault lines
What is trying to prevent an earthquake thought to be
Almost impossible
Some studies have looked at the feasibility of schemes to keep plates sliding past each other (rather than sticking and then releasing) as a management of a seismic hazard, what are some examples
Lubricating the movement by focusing on water and oil. Some have even gone as far to suggest nuclear explosion
Why is it essential for everyone from civil authorities to individuals to be prepared for a seismic hazard
Since earthquakes strike suddenly, violently and without warning
Example of a programme to protect places from seismic hazards
In the USA, the Federal Emergency Management Agency (FEMA)
What are the 4 objectives of FEMA
To promote understanding of earthquakes and their effects.
To work to better identify risk.
To improve earthquake-resistant design and construction techniques.
To encourage the use of earthquake-safe policies and planning practices.
What does protection from a seismic hazard mean
Preparing for the event by modifying the human and built environment in order to decrease vulnerability. Includes attempts to modify the loss by insurance and aid.
What are the 8 ways to protect a place as a management of a seismic hazard
Hazard-resistant structures Education Fire prevention Emergency services Land-use planning Insurance Aid Tsunami protection
How can hazard resistant structures be used as management of a seismic hazard
Buildings can be designed to be aseismic, in that they can be earthquake resistant
What are the three main ways that buildings can be designed to be aseismic
By putting a large concrete weight on top of the building which will move, with the air of a computer programme, in the opposite direction to the force of the earthquake in order to counteract stress.
Putting large rubber shock absorbers in the foundation which will allow some movement of the building.
By adding cross-bracing to the structure to hold it together better when it shakes.
What can happen to older buildings and structures, such as elevators and motor ways, to make them more earthquake proof
They can be retrofitted with devices
Example of a comparison which shows the effects of different types of buildings on earthquakes
Comparison between the 1989 Loma Prieta earthquake (6.9 MMS) and the 1988 event in Armenia (6.8 MMS).
Greater earthquake proof buildings of California resulted in 63 deaths whereas in Armenia, over 25,000 people died, many buildings collapsed as a result of soft foundations and no earthquake proof features.
For many areas what’s the main way that loss of life from seismic events can be minimised
Education
How does education help protect from a seismic event as a management strategy
Instructions are issued by the authorities in how to prepare for such events by securing homes, appliances and heavy furniture, and assembling ‘earthquake kits’.
Example of education as a management strategy for seismic events
Children having earthquake drills at school as do people in offices and factories.
How does fire prevention help protect from a seismic event as a management strategy
‘Smart metres’ have been developed that can cut off the gas if an earthquake of sufficient magnitude occurs.
What do emergency services need
Careful organisation and planning
How do emergency services help protect from a seismic event as a management strategy
Heavy lifting gears need to be available and many people should be given first aid training, as it could be some time after the event that trained medical personnel arrive. Much of the preparation in California involves the establishment of computer programs that will identity which areas the emergency services should be sent to first
How does land use planning help protect from a seismic event as a management strategy
The most hazardous areas in the event of an earthquake can be identified and then regulated in terms of land use. Certain types of buildings should be put in areas of low risk, such as schools and hospitals. It’s also important to have sufficient open space, as this forms a safe area away from fires and aftershock damage to buildings
How does insurance help protect from a seismic event as a management strategy
In richer areas, people are urged to take out insurance to cover their losses, the only problem being that for individuals, that is expensive. In the Kobe earthquake in Japan in 1995 only 7% of the people were covered by earthquake insurance
How does aid help protect from a seismic event as a management strategy
Most aid to poorer countries has generally been to help in the few days after the event, providing medical services, tents, water purification equipment, search and rescue equipment etc.
Why is aid over the long term problematic
Because it is something which is needed for the reconstruction of the built environment and redevelopment of the economy
How does tsunami protection help protect from a seismic event as a management strategy
They cannot be entirely predicted, even if the magnitude and location of an earthquake is known. Certain automated systems can be installed to give warnings, the best of which uses bottom pressure sensors, attached to buoys, which constantly measure the pressure of the overlying water column.
What do regions with a high tsunami risk use to warn people of a tsunami
Warning systems (such as a klaxon) to warn the population before the wave reaches the land
What is mitigation
Mitigation strategy is designed to reduce or eliminate risks to people and property from natural hazards. Money spent prior to a hazardous event to reduce the impact of it can result in substantial savings in life and property following the event
What is a storm surge
A rapid rise in sea level in which water is piled up against a coastline to a far excess of the normal conditions at high tide. Usually produced during the passage of a tropical storm when wind-driven waves pile up water against a coastline combined with the ocean bracing upwards as a result of much lower air pressure
What are tropical revolving storms (hurricanes, cyclones, typhoons)
Intense low-pressure weather systems that develop in the tropics, between the tropics of Cancer = 23* north and the tropical of Capricorn = 23* South. They are huge spinning storms with strong winds and torrential rain.
What is the usually diameter of tropical storms
200-700km
How do tropical revolving storms develop
They begin with an area of low pressure, resulting from surface heating, into which warm air is drawn in a spiralling manner. Such small-scale disturbances can enlarge into tropical depressions with rotating wind systems and these may continue to grow into a much more intense and rapidly rotating system - the tropical revolving storms.
What isn’t clear about the formation of tropical storms
Why they become so intense
What 5 conditions need to be present for a tropical storm develop
Oceanic location with sea temperatures above 27C.
Ocean depth of at least 70m.
A location at least 5 north or south of the Equator.
Low level convergence of air in the lower atmospheric circulation system.
Rapid outflow of air in the upper atmospheric circulation.
What are the 3 different names for tropical storms
Hurricanes
Cyclones
Typhoons
Why is the condition of ‘Oceanic location with sea temperatures above 27*C’ needed for tropical cyclones to occur
It provides a continuous source of heat in order to maintain rising air currents
Why is the condition of ‘an ocean depth of at least 50m’ needed for tropical cyclones to occur
This moisture provides latent heat; rising air causes the moisture to be released by condensation and the continuation of this drives the system
Why is the condition of ‘a location at least 5* north or south of the equator’ needed for tropical cyclones to occur
Because this means the Coriolis force can bring about the maximum rotation of the air (the coriolis force is weak at the equator and will stop a circular air flow from developing so tropical storms don’t form between 0-5* north and south of the equator)
Why is the condition of ‘low level convergence of air in the lower atmospheric circulation system’ needed for tropical cyclones to occur
Winds have to come together near the centre of the low-pressure zone
Why is the condition of ‘rapid outflow of air in the upper atmospheric circulation’ needed for tropical cyclones to occur
This pushes away the warm air which has risen close to the centre of the storm
When does the tropical revolving exist
While there is a supply of latent heat and moisture to provide energy and low frictional drag on the ocean surface
How does the central eye of a storm develop
When the tropical revolving system reaches maturity
What is the central eye of a storm
An area 10-15km in diameter in which there are calm conditions, clear skies, higher temperatures and descending air
What have been observed around the eye of a storm
Wind speeds of more than 300km/hour
What is low pressure in an area
An area in which there is less air than in surrounding areas. This means that the air here rises because there is less air pressing down on it from above. Air moves from an area of high pressure to areas of low pressure. This movement of air is felt as wind.
What is the cyclonic flow
As the air rises, the water vapour within it condenses forming clouds and often precipitation too. Because of earths spin and the Coriolis effect, winds of a low pressure system swirl counterclockwise north of the equator and clockwise south of the equator - the cyclonic flow
Characteristics of tropical storms
Winds of 120km/he to over 250km/hr. Torrential rain. Circular in shape. Hundreds of kilometres wide. Usually last 7-14 days. Develop over warm water (above 27*C)
What is the Coriolis effect
A force caused by the earths rotation. It reflects the path of the converging winds causing the winds to rotate.
Why do tropical storms loose strength when they move over land (landfall) or they reach colder waters polewards
As the source of heat and moisture is removed
Where provides the perfect condition for the formation of tropical storms
The Inter Tropical Convergence Zone (ITCZ) where two limbs of the Hadley cell converge to form low pressure on the ground
Once generated, where do tropical storms tend to move
Westwards
What is the distribution of tropical storms
In the Caribbean Sea/gulf of Mexico On the western side of Central America In the Arabian Sea/bay of Bengal Off Southeast Asia Off Madagascar Off north western and north-Easten Australia
In the Caribbean Sea/ Gulf of Mexico what are tropical storms known as and what percentage of all tropical revolving storms occur here
Hurricanes and 11%
In the Western side of Central America (eastern Pacific) what are tropical storms known as and what percentage of all tropical revolving storms occur here
Hurricanes and 17%
In the Arabian Sea/bay of Bengal what are tropical storms known as and what percentage of all tropical revolving storms occur here
Cyclones and 8%
Off Southeast Asia what are tropical storms known as and what percentage of all tropical revolving storms occur here
Typhoons (1/3 of all storm events every year occur here)
Off Madagascar (Southeast Asia) what are tropical storms known as and what percentage of all tropical revolving storms occur here
Typhoons and 11%
Off northwest and northeaster Australia what are tropical storms known as and what percentage of all tropical revolving storms occur here
Willy-Willies and 20%
What is the magnitude of tropical storms measured on
The Saffir-Simpson scale
What is the Saffir-Simpson scale
A five point scale based upon central pressure, wind speed, storm surge and damage potential.
What does a scale 5 event on the Saffir-Simpson scale have
Central pressure at 920mb or below.
Wind speeds at 250km/hr or greater.
Storm surge at 5.5m or greater.
Damage potential that refers to ‘complete roof failure of many buildings with major damage to lower floors of all structures lower than 3 meters above sea level, evacuation of all residential buildings on low ground within 16-24km off coast is likely.
Every year how many tropical storms form
Around 80-100
What percentage of tropical storms go on to become a revolving tropical storm
80%
What 5 factors does the vulnerability of people to tropical storms depend upon
The intensity of the storm. Speed of movement: the length of time over the area. Distance from the sea. Physical geography of the coastal area. The preparations made by a community. Warnings and community response.
How does the physical geography of the coastal area alter people’s vulnerability to tropical storms
Width of the coastal plain or size of delta, and location of any mountain ranges relative to the coast
Why do many tropical storms not develop into a hazard
They don’t reach land (don’t evolve into a revolving tropical storm)
When are storms more frequent in the northern hemisphere
Between June and novermber
When are tropical storms more frequent in the Southern Hemisphere
Between November and April
What is the impact wind from a tropical storm can have on an area
Scale 5 events can cause structural damage to buildings (even collapse) and roads, bridges etc. They can bring down electricity transmission lines and devastated agricultural areas. The huge amounts of debris that are flung about are a serious threat to people’s lives.
What is the impact heavy rainfall from a tropical storm can have on an area
They can bring about severe flooding, landslides and mudslides.
What can rainfall from a tropical storm exceed
200 to 300mm. If there is high relief near the coastal area, rainfall could increase over 500 mm/day
What is the impact storm surges from a tropical storm can have on an area
They can have devastating effect on low-lying coastal areas such as river deltas where the flooding can extend a long way inland.
They cause the majority of deaths in such events and agricultural areas can suffer for a long time as soil is contaminated by sea water.
What are the four ways of managing the tropical revolving storm hazard
Prediction
Prevention
Protection
Preparedness
What is wildfire a natural process in
Many ecosystems, it can be necessary and even beneficial
What does the prediction of tropical cyclones depend upon
The state of monitoring and warning systems
Example of a weather bureaux for tropical storms
The National Hurricane Centre in Florida (USA)
What do the USA do
They are able to access data from geostationary satellites and from both land and sea based recording centres. They maintain a round the clock surveillance of tropical storms that have the potential to become hurricanes by the use of weather aircraft
Why is information from weather bureaux useful
The information they collect can be compared with computer models so that a path can be predicted and people warned to evacuate an area
Why is it essential that information from weather bureaux correct
There is a high economic cost associated with evacuation, and as with all false alarms, people may become complacent and refuse future advice.
What is the estimation of cost to evacuate the coastal areas in the USA
One million dollars per kilometre of coastline due to losses in businesses and tourism and the provision of protection
Why is it not always possible to give more than 12-18 hours warning of cyclones
Because they tend to follow an erratic path
What does the fact that it’s not always possible to give more than 12-18 hours of cyclones mean for poorer places
Where communications are poor, this is insufficient time for an evacuation
What have some high income places established to give people a chance to evacuate in case of a tropical storm
Warning systems
While tropical storms can’t be prevented, what can be done
Research into the effect of cloud seeding in order to cause more precipitation. The theory is that if the cyclone could be forced to release more water over the sea, than this would result in a weakening of the system as it approaches land.
Why has research into cloud seeding to prevent cyclones not been continued
There was some concern expressed over the effects of this on the global energy system
What does ‘protection’ as a managment strategy of cyclones mean
Being prepared
What will predicting the landfall of a tropical storm enable
Evacuation to take place, together with the emergency services being put on full alert.
What happens if evacuation because of a cyclone does take place
Protection units, such as the National Guard in the USA, have to be called in to prevent homes and commercial properties from being looted.
Why are people made aware of how to strengthen their homes and properties in case of a cyclone
So they can withstand high winds
Example of cyclone/hurricane drill that is practiced
In Florida, ‘Project Safeside’ which is a hurricane awareness programme that is composed of precautionary drills for use in schools and the emergency operations centre of the state
What are the 5 ways protection as a management strategy of a cyclone occurs
Cyclone/hurricane drills Land-use planning Sea walls Breakwaters Flood barriers Retrofitting
When storm surges are a problem because of cyclones what can be used to protect the area
Land-use planning which csn identify the areas at greater risk and certain types of development can be limited in such areas.
What can houses be put on to protect against flooding from a cyclone
Stilts
In the USA, how are local authorities required to address the problem of storm surges
By limiting expenditure on developments in high-risk areas and directing populations away from them, as well as having sound plans to reduce evacuation times and for post-disaster development
When does land-use planning not always work
In poorer areas where the need for land outweighs any considerations
How can some structures be retrofitted as a management of a tropical storm
By adjusting the buildings to make it resistant to wind to ensure greater safety during an event
What is a way people can use their abilities to mitigate the effects of tropical storms
Through preparedness
Examples of preparedness in Outerbanks
Local communities have got together to put into a practice the Outer Banks Mitigation Plan. It aims to make as much information as possible available to the people of the outer banks area
On the eastern seaboard of the USA, what is an area susceptible to the dangers brought by hurricanes
Part of the state of North Carolina, a group of barrier islands known as Outer Banks
What are the aims of the Outer Banks Mitigation Plan in managing tropical storms
It’s aims are to save lives and money, property and natural resource protection, reduce future vulnerability, speedy recorders from the effects of hurricanes and post disaster funding.
Why is damage to the economic base of a poor area likely to last for years after a tropical storm
Becsuse, as with other phenomena, rich people are urged to take out insurance, whereas in poorer countries this is not always possible
What is important following a cyclonic event
That aid is available in the short term and long term
What do people’s abilities to resist natural hazards depend upon
That aid is available in the short term and long term
Why do poorer areas suffer more because of natural hazards
Because land-use planning, warning systems, defences, infrastructure and emergency services are inadequate and this usually results in a higher death toll.
While not monetarily, the simple dwelling of the inhabitant of a poor country may suffer a huge loss, taking into account the time invested in it and the years of irreplaceable and uninsured savings that it represents.
How are richer counties better prepared in the case of a natural disaster
They have some planning systems in place, sophisticated warning arrangements, better defences and infrastructure and emergency services that are much more comprehensive
Why do HICs like the USA bear much greater monetary loss after a tropical storm event, even though they are better prepared
Becsuse of the damage to the built environment, however this damage is usually covered by insurance e.g house insurance
What are surface fires
Fires that sweep rapidly over the ground, consuming plant litter, grasses and herbs, and scorching trees, and it is possible for ground temperatures to rise over 1000*C
What are crown fires
Fires at a higher level than surface fires that spread through the canopy of trees
What does the nature of fire depend upon
The types of plants involved, strength of the winds, topography of the area in question and the behaviour of the fire itself
Once vegetation has dried out, what does the nature of fire largely depend on and why
The wind because wind drives the fire forward and burning embers that ignite more vegetation are more easily spread in windy weather
Where do the largest wildfires occur
In dry windy weather with low humidity
What are the 2 key factors in a fire
The climate and nature of the plants
What is a retardant
Chemicals sprayed on the fires in order to slow them down. They are composed of nitrates, ammonia, phosphates, sulphates and thickening agents
What is pyrophytic vegetation
Pyrophytes are plants adapted to tolerate fire. Methods of survival include thick bark, tissue with a high moisture content and underground storage structures
What 2 things are needed for a natural fire to occur
An ignition source
Fuel
What is the main ignition sources of natural wildfires
Lightning (electrical storms)
What affects the frequency of electrical storms
Climate, particularly when there is no rainfall
Where are fires that are the result of human intervention particularly situated
In and around settlements
How are human fires started
Falling power lines Carelessly discarded cigarettes Children playing with matches Camp fires Agricultural fires (controlled burning) which get out of hand And in some cases arson
Which places have an increased danger of fires because of access to wild areas by tourists
The USA and Australia
What 2 conditions of fuel (wood) is needed for a wildfire
Sufficient quantity and dry enough to burn
How does fuel dry out to cause wildfires
Climate affects the frequency and duration of droughts during which the vegetation and litter has an opportunity to accumulate and dry out
How does climate affect the fuel of a wildfire
Affects the frequency and duration of droughts which dries out vegetation.
It also affects the type of vegetation that will grow in an area and the rate at which litter can be produced.
What kind of hazard are wildfires
A rural hazard
Where do wildfires occur
Most environments although with the continued expansion of human habitation, wildfires now occur within the boundaries of even substantial settlements
Where is the world do wildfires occur
California, Australia, Florida and the countries of Southern Europe like France, Italy, Greece, Turkey and Mediterranean islands duh as Sicily, Cyprus, Corsica and Sardina
Which areas are most susceptible to wildfires
Those with a combination of dry vegetation and lightning strikes.
Areas with a dry season are most likely to be affected as are those regions of the world with a semi-arid climate and susceptible to drought
Example of fires and natural ecosystems being linked
Mediterranean climate regions and the savannah grasslands
What are some good impacts of wildfires
They can clear vegetation and aid new seed germination, stimulate the growth of certain plants and rid of an area of insects and some parasites
examples of pyrophytic vegetation
Baobab tree has resistant bark.
In Australia, plants such as banksia need fire for their woody fruit to open and thus regenerate.
Why are fires not a real hazard of tropical rainforests
Due to the humid climate
What has recent burning for forest clearance in tropical rainforests that has gotten out of hand resulted in
Widespread fires that burned out of control for long periods
Which rainforests have suffered from fires in recent years
Amazon Basin (Brazil) and south-east Asia (Indonesia)
What is drought-resistant chaparral
Scrub vegetation
In Los Angeles what is the Santa Ana
A dry wind that descends from local mountains and increases the dryness of the vegetation to the point where a small spark can cause a major fire
What are the 6 primary effects of wildfires
Loss of crops, timber and livestock. Loss of life. Loss of property. Realise of toxic gases and particulates. Loss of wildlife. Damage to soil structure and nutrient content.
How can the loss of crops, timber and livestock be an effect of wildfires
Forest fires can have a huge impact in timer producing areas, with the loss of trees taking many years to replace.
In the US what is the estimated price spent fighting wildfires
$10 million
How can the loss of life be an effect of wildfires
Although many fires are events from which people can get out of the way, some fires move so fast that people can be trapped although this is not usual
How many people lost their lives in the Victorian (Australia) bushfires of 2009
173 people
How can the loss of property be an effect of wildfires
At one time, only a few rural communities were at risk from fires, but with urban expansion, the fringes are now susceptible. The cost of damage and of fighting the fires can run into hundreds of millions of dollars. After such events, large numbers of people can be left homeless
How can the damage to soil structure and nutrient content be an effect of wildfires
With the intense heat generated at ground level, wildfires can destroy many soil nutrients and lead to an alteration in the soils structure
What are the two secondary effects of wildfires
Evacuation
Increased flood risk
How is evacuation a secondary effect of wildfires
Many people will flee from the area of the fire. Such people will not be allowed back into the affected area, often for a long period, if not forever. Emergency shelters/accommodation will have to be found along with food etc
How can the increased flood risk be an effect of wildfires
In certain environments, where rain comes in heavy bursts, the loss of so much vegetation, and the consequent decrease in interception, can lead to increased flooding
What are the 3 main ways of dealing with the fire hazard
Planning to mitigate the effect of an event.
Coping with the wildfires.
Addressing the effects.
What are the 7 in which the fire hazard can be managed before the event occurs
Managing the vegetation. Managing the built environment. Modelling. Education. Warning systems. Community action. Being well insured.
How is managing the vegetation a way to manage a wildfire before the event occurs
This is done by controlled burning to get rid of much of the litter and by creating firebreaks in the vegetation in advance rather than during the event
How is managing the built environment a way to manage a wildfire before the event occurs
This is done by increasing the gap between houses and vegetation and by incorporating more fire-resistant methods in construction (using more stone and brick rather than the wood; fitting spark arresters to chimneys)
How is modelling a way to manage a wildfire before the event occurs
This involves studying the ways in which fires behave with computer simulations in order to comprehend and predict fire behaviour
How is education a way to manage a wildfire before the event occurs
In areas susceptible to wildfires, it is important to make people aware with regards to home safety and how to avoid starting fires
How are warning systems a way to manage a wildfire before the event occurs
These can be put in place by establishing lookout towers and even air patrols. In tourist areas, notice boards at strategic locations could carry warnings of the fire hazard
How is being well insured a way to manage a wildfire before the event occurs
In wealthier counties, residents are urged to take out insurance against fire-damage, although this can be very expensive in fire-prone areas
What does the fire propagation model
The ‘fire start.’
The ‘propagation axis’ (wind) goes through the middle.
The ‘left front’ is above the ‘propagation axis’ (wind).
The ‘right front’ is above the ‘propagation axis’ (wind).
The ‘head of the fire’ is at the end of the ‘propagation axis’(wind)
What does dealing with the fire hazard event as it happens involve
Fighting the fires as they happen, which can be a very dangerous operation and it is not unknown for firefighters to suffer fatalities when they are involved in this action.
How do firefighters deal with wildfires
Spraying with water and chemicals from the ground and in the air (which can be costly).
They also work on the ground beating out the flames and bulldozing large breaks in the vegetation.
Retardants are also used.
How does firefighters beating flames and bulldozing large breaks in the vegetation help deal with wildfires
This prevents the fire jumping in certain directions
How do retardants deal with wildfire events
They flow the pace of the wildfire, they are often sprayed on fires in areas which are fairly inaccessible or when human safety and structures are endangered
Once the fire has been extinguished, what is needed
In the short term, communities and governments need to try and repair the damage caused by the fire.
In the long term, action will mean that attention will be directed towards making sure that areas are well prepared for the next fire.
What are the two ways of addressing the effects of wildfires
Replanting trees
Preparedness
What are the two ways that replanting trees address the effects of wildfires
Particularly in commercials forestry areas this improves the economy of areas devastated by fires.
After vegetation has been removed by fire, there is a great danger of flash flooding and mudslides on, what are now, unprotected slopes. Planting trees should stabilise slopes and should also lead to an improvement in water quality.
What does preparedness in address the effects of wildfires mean
This means making sure that people are better prepared for the next fire by having emergency supplies ready, along with survival kits, etc, and by setting up community groups such as that in Victoria.
