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.
