Flashcards in Hazards- content Deck (223):
What is a hic?
A high income country
What is a lic?
A low income country
What is a nec?
A newly emerging country
Describe what a hazard is
"natural events that are perceived to threaten life/property/ the built environment and the natural environment
What is perception?
The way in which an individual or group views the threat of a hazard event
What is a disaster?
Exceeds the ability of the affected community to cope using its own resources
What are geophysical processes?
Processes that are driven by the earths internal energy
What are atmospheric processes?
Driven by processes that work in the atmosphere
What are hydrological processes?
Driven by water bodies (mainly oceans)
Give an example of atmospheric processes
-drought (leading to fires)
Give examples of geophysical processes
Give examples of hydrological processes
How do natural hazards share common characteristics?
-origins are clear and their effects are distinctive
-often they occur with little warning
-exposure to the risk may be involuntary especially in less developed areas
-most damage and loss of life occurs shortly after hazards but impact may last
-their scale and intensity requires an emergency response
What is risk?
"the exposure of people to a hazardous event presenting a potential threat to themselves, their possessions and the built environment in which they live
Why risk it?
1.)Hazards are unpredictable
2.)Lack of alternatives
3.)The level of risk changes
Why risk it? Describe how hazards are predictable
Cannot predict frequency, magnitude or scale of a natural hazard event
Why risk it? Describe how there are a lack of alternatives
People can't uproot themselves and move to another place
Why risk it? Describe how the level of risk changes
Places that were once relatively safe may have become more of a risk
Why risk it? Describe cost/benefit
May be advantageous e.g California
Why risk it? Describe perception
It is related to how much people view the threat of a hazard
Hazard risk, perception and vulnerability: What is popocatapeti?
A volcanic mountain less than 50 miles from Mexico City in Mexico. Mexico has a population of over 8.8m people
Hazard risk, perception and vulnerability: What is Mt. Vesuvius?
An active volcano near the city of Naples, Italy. It is a realistic threat for about 3 million people who live in Naples and surrounding towns
What is acceptable risk?
The level of potential losses that a society of community considers acceptable given existing social, economic, political, cultural, technical and environmental conditions
What is vulnerability?
The potential for loss- it is spatial, temporal and social
What are the 4 key approaches?
What is fatalism?
-natural events that are part of living in an area
-'gods will' (losses are inevitable)
-people remain where they are and any action is direct and concerned with safety but on the whole preventative measures are limited or non existent
What is adaptation?
people see that they can prepare and therefore survive the events by prediction, prevention and/or protection
What is fear?
Move away (no longer able to face living in the area)
What is domination?
-control is possible through engineering or use of technology
What factors affect people perception of a hazard?
-different cultures and nations
-the socio-economic situation of people
-trust we have in abilities of the responsible person
-individual values and personality
How does religion affect perception of a hazard?-give an example
-The people inhabiting tornado regions of Alabama, USA are largely convinced that what happens to them depends on God or good fortune.
-In contrast the inhabitants of Illinois, USA who are exposed to a similar threat believe it is all about their own behaviour that determines their fate. Accordingly they have implemented provocative measures that have considerably reduced the number of deaths caused by storm disasters in Illnois versus Alabama
Give an example of comparisons between different cultures and nations that have been made in the past
-Between Americans and Japanese
-Such studies revealed a difference in the perception of Japanese and Americans in relation to nuclear risks
-The Japanese tend to view nuclear risks as being higher, but the voluntariness to exposure to the risk is also viewed as being higher than it is by Americans
How does the socio-economic situation of people affect peoples perceptions of hazards?
Mexican field workers whose economic situation leaves extremely little leeway for action, have stated that they do not worry about health impairments caused by pesticides at work
How is media used as one of the main tools to amplify (inc.) or attenuate (reduce) a certain risk topic?
-if the media report a risk, many people become suddenly aware of it and start to worry
-if a risk topic appears in the media e.g news then the risk must be real because it has made it into the media
-in terms of numbers, a media-covered risk might be negligible, like the post-september 11 anthrax threats to US politicians and citizens if compared to other risks that are less extensively covered
What is preparedness?
Large scale events can be rarely prevented from happening, but education and raising public awareness can reduce the human causes and adjust behaviour to minimise the likely impact of the hazard. Knowing what to do can speed up the recovery process
What is response?
The speed of the response will depend on the effectiveness of the emergency plan that has been put in place. Immediate responses focus on saving lives and co-ordinating medical assistance. Damage assessment haps plan for recovery
What is recovery?
Restoring the affected area to something approaching normality
What is mitigation?
-Actions aimed at reducing the severity of an event and lessening its impacts
-This can involve direct intervention such as a building design that can withstand earthquakes or hurricanes
-Most desirable is the long term protection of natural barriers such as coral reefs which protect the shore against storm surges
-Support after a disaster in the form of aid and insurance can reduce long term impacts. Insurance may not be available in high risk areas.
What are the 4 elements of the disaster management risk cycle?
When was the park model established?
What are the uses of the park model?
-speed of response and the effectiveness of the response can be measured by the curve
-the model reflects the nature of how it recovers and when, this is important for future planners
-a park model curve allows for visual comparison between different places
-it's a versatile model, it can be used for an array of disasters
What are the limitations of the park model?
-the model does not take anything into account that happened before the event, for example any planning/mitigation/management. therefore it is hard to learn from the successes of planning as they are not visible on this model
-the curve reflects a single event for a single area and ignores the nuances nature of a disaster
-the model doesn't account for spatial variation as it assumes all parts of a country recover at uniform rate. Thus, the curve is not an accurate representation of the entire country
-no quantitative data is recorded (number of deaths/damage to the economy)
-the model can not be used effectively for more than 1 event. E.g hurricane Irma, the model requires multiple curves which is inconvenient
Why do rocks remain solid at depth?
-despite the fact that as temperature rises with depth, rocks reach temperatures that would cause them to melt if they were at the surface, the rocks remain solid at depth because of the extreme pressure acting upon them
-however they do become plastic, subjected to vast amounts of time, such rocks will flow
Give an example of solid creep
-Substances like plasticine will flow under gravity, especially when warm
-In the upper mantle, peridotite (a type of rock) will also display the property of solid creep, this occurs when peridotite reaches 1300 degrees and gives rise to a layer called the athenosphere where the rock is weaker than both overlying and underlying mantle
Describe how rocks 'behave mechanically as one' and compromise the lithosphere
The rocks above the asthenosphere, being the uppermost mantle plus the overlying crust behave mechanically as one and compromise what geologists call 'the lithosphere'. The lithosphere moves as one over the weaker, plastic asthenosphere
What are the 4 pieces of evidence that continents were once joined
1.) Continental fit
Evidence that the continents were once joined: describe continental fit
-Alfred Wegener noticed a fit between the coasts of South America and Africa
-Continents look like they could be part of a giant 'Jigsaw puzzle'
Evidence that the continents were once joined: describe the biological evidence
-Wegener also noticed that there was a link between fossil types either side of the Atlantic
-Fossil branchiopods found in Indian limestone are comparable with similar fossils in Australia
Evidence that the continents were once joined: describe the geological evidence
-same rock patterns found in South America, India, Africa, Antarctica and Australia
-rock sequences in Scotland similar to this in Eastern Canada
-many minerals and natural resources also matched and similar striations on rocks in Brazil and West Africa
Evidence that the continents were once joined: ancient climates
-tropical plant remains (coal deposits) found in Antarctica
-glaciation in Africa, South America, India and Australia during the same time (290 million years ago)
What are hot spots
-A concentration of radioactive elements below the crust causes a hot spot to develop
-From this a plume of magma rises to eat into the plate above
-when the lava breaks through to the surface, active volcanoes form above the spot
-the basaltic lava flows slowly and forms huge flattish volcanoes, sometimes referred to as 'shield' volcanoes
What is the hottest part of earths surface?
-because it receives intense solar radiation
What is global, atmospheric circulation?
-the atmosphere is a highly complex swirling mass of gases, liquids and solids
-these include water droplets, water vapour, ash, carbon dioxide and oxygen
How does global, atmospheric circulation work?
-air that is sinking towards the ground surface forms areas of high pressure (e.g North Pole). Aims on the ground move outwards from these areas
-air that is rising from the ground surface forms areas of low pressure on the ground, for example the equator. Wind from the ground move towards these areas of low pressure
-winds on the ground are distorted by the earths rotation. They curve as they move from areas of high pressure to areas of low pressure
-surface winds are very important in transferring moisture from one place to another
-The patterns of pressure belts and winds are affected by seasonal changes. The seasonal changes cause pressure belts and winds to move north during our summer and south during our winter
What is capacity?
Resources, means and strengths which exist in households and communities that enable them to cope with, withstand, prepare for, prevent, mitigate and/or quickly recover from a disaster
What is community preparedness/risk sharing?
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 is frequency
The distribution of hazards through time
What is integrated risk management?
The process of considering the social, economic and political factors, involved in risk analysis, determining the acceptability of damage/disruption and deciding on the actions to be taken to minimise this damage/destruction
What is magnitude?
The assessment of the size of the impact of a hazard event
What is mitigation?
Any sustained action taken to reduce or eliminate the risk to life/property
What is monitoring?
The observations and measurements associated with natural evens. Undertaken via specialist data gathering and communication systems, geological exploration, site visits and collaborative studies of current and historical events
What is reconstruction?
The resettlement or relocation of people and ongoing development activities centred on improving not only the built environment and the infrastructure networks but economic and social systems too
What is rehabilitation?
The process of helping communities and individuals to achieve the highest levels of function, cohesion and all round recovery as possible. Actual process will be place-specific but often includes a combination of relief, reconstruction and integrated risk management.
What is relief?
Refers to the process of responding to a hazard/ disaster by providing aid to individuals and communities who have suffered some type of loss. This 'aid' can be varied and focusses on dealing with risks as well as preparing, supporting and rebuilding communities. Relief can last from a few hours to several weeks
What is 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
What is mohorivic discontinuity?
Starp divide forming the boundary between the upper mantle and the crust
What is the athenosphere ?
Lies beneath the lithosphere and is semi-molten on which which the plates float and move
What is the lithosphere?
Crust and rigid upper section of the mantle, it is the section of the earth that is divided into the plates
How thick is the lithosphere
approximately 80-100km thick
What does primordial mean?
heat left over from the initial collision of rocks/objects in space during the formation of the earth
What does radiogenic mean?
heat produced by the radioactive decay of isotopes (particularly uranium -238, Thorium -232 ad potassium -40), this material was delivered via the collisions
What are the problems with Wegener's theory?
-no mechanism for movement of continents
-wind and currents could possibly move continents
What is oceanic crust made up of?
Basalt, silicon, magnesium and oxygen
What is continental crust made up of
Granite, silicon, aluminium, and oxygen
Compare oceanic and continental crust
-more dense (3.0g/cc)
-young (under 2m years)
-thin (0-10km thick)
-flat ocean plains, trenches and mountains
-less dense (2.7g/cc)
-older (over 1,500m years)
What is basaltic magma like?
-low in silica (below 55%)
-gases easily escape, lava is fluid and very hot and flows for long distances before cooling. Only lava is ejected
-lava has not mixed with other materials through subduction, comes directly from mantle at hot spot or spreading ridge
-Hawaii or Iceland-forms shield volcanoes (2-20 degree slopes) or lava plateau's
-Frequent or regular plateaus
What percentage of basaltic magma is silica?
What degree slopes do shield volcanoes have?
2-20 degree slopes
What is acidic lava like?
-either rhyolite or andesite type of lava, high in silica (55-70%)
-andesitic (intermediate) lavas are typical of destructive margins
-rhyolitic (acid) lavas are found at destructive and collision margins
-gasses are trapped, they are viscous and sticky and explosive, can shatter into bombs and shards or to ashes and dust
-magma comes through subduction zone (at destructive boundaries)
-non-frequent eruptions, forms composite stratovolcanoes or acid domes (steep sides)
What percentage of acidic lava is made up of silica?
What 5 pieces of supporting evidence are there for plate tectonic theory
1.) Convection currents
3.)Sea floor spreading
4.)Distribution of earthquakes
5.)Thickness and age of ocean basin sediments
What process happens at constructive margins?
plates diverge-move away from each other
What geographical features are found at constructive plate margins?
-new oceanic crust is formed by by basaltic magma rising from the athenosphere
-new basaltic rocks
-mid-ocean ridges broken up by transform faults (mid-atlantic ridge)
-basic volcanoes (eyjafjallajokull)
-continental rift valleys (the great African Rift Valley)
What process happens at destructive margins
Plates converge-move towards each other
What geographical features are found at destructive margins?
-oceanic crust is destroyed by subduction and melting at depth
-deep ocean trenches (Mariana Trench)
-Island arcs (West Indies)
-shallow, intermediate and deep focus earthquakes
-explosive, acid volcanoes (Krakatoa)
-oceanic v continental
-continental v continental
Destructive margins: what happens when oceanic plates and continental plates collide?
-oceanic crust is destroyed by subduction and melting at depth
-deep ocean trenches formed (e.g Perth-Chile trench)
-continental land mass is uplifted, compressed and buckled into fold mountains (e.g Andes)
-intermediate and deep focus earthquakes formed, they are explosive, acid volcanoes
Destructive margins: what happens when two continental plates collide?
-colliding plates, and any sediments between them, uplift and concertina into particularly high fold mountains (Himalayas)
-continued compression and overflowing can result in fracture creating thrust fault and nappe
What process happens at conservative margins?
Plates move sideways past each other
What geographical features occur at conservative margins?
-shallow focus earthquakes (Haiti)
Give examples of exceptions to plate margins
-Hot spots near the centre of a plate
-Basic volcanoes (Yellowstone)
How are ocean ridges formed?
-when plates move apart in oceanic areas. The space between plates is flooding with basaltic lava upwelling from below to form a ridge
Constructive margins: What geographical features also form at ocean ridges
-volcanic activity also occurs along these ridges forming submarine volcanoes which sometimes rise above sea level, such as Surtsey at the south of lceland
Destructive margins: how do island arcs form?
-during subduction the descending plate encounters hotter surroundings and this this coupled with the heat generated from friction begins to melt the plate
-as the material is less dense than the surrounding athenosphere, it begins to rise towards the surface as plutons of magma
-eventually these reach the surface and form complex, composite and explosive volcanoes
-if these eruptions take place offshore a line of volcanic islands form-known as island arcs
Give an example of island arcs
The Marinaras islands, running parralel to the Marinaras trench
Desctructive margins: how do ocean trenches form?
-when oceanic and continental plates meet the denser oceanic plate is forcedunderneath the lighter continental one (subduction) . The downwarping of the oceanic plate forms a very deep part of the ocean known as a trench
Constructive margins: how are continental rift valleys formed?
-these plates form when plates move apart in continental areas
-In East Africa for example the brittle crust fractures as sections of it move apart
-areas of crust drop down between parallel faults to from the valley
-an area between two parallel rift valleys forms an upstanding block known as a horst
-the line of African rift is thought to be an emergent plate boundary, the beginning of the formation of a new ocean as Eastern Africa splits away from the remainder of the continent
Destructive margins: how are young fold mountains formed?
-the plates forming continental crust have much lower density than the underlying areas, so there is not much subduction when plates meet. As such when plates move towards each other,
Describe the formation of mid ocean ridges
-they are formed when plates move apart in oceanic areas
What is the thickness of the crust
*5-10km under oceans
*up to 70km under continents
What are the two types of crust?
Describe oceanic crust
Broken layer of basaltic rocks known as sima
What is sima made up of?
Silica and magnesium
Describe continental crust
Bodies of mainly granite rocks known as sial
What is seal made up of?
Silica and aluminium
-upper layer of the earths crust and forms the continental land masses
-much thicker than oceanic sima but less dense
-lower layer of the earths crust and is found in the oceans as well as grading into the lower part of the sial into the continents
-much thinner than sial but more dense
What is formed in the lithosphere?
How thick is the mantle?
2900 km thick
Why are many of the silicate rocks in the mantle in a thick liquid state?
-due to the great heat and pressure within this zone
Describe the rocks in the upper mantle and how they change towards the lower mantle
-the rocks in the upper mantle are solid and sit on top of the athenosphere, a layer of softer, almost plastic type riock
-the athenosphere can move very slowly, carrying the lithosphere on top.
-densities within the mantle increase as you go down into the lower mantle
What can temperatures reach at the core?
How much more dense is the core than the crust
Almost 4 times as dense
What is the core mostly made up of?
Iron and nickel
What are the two parts of the core?
Describe the inner core
-made up of an iron-nickel alloy
Describe the outer core
What is a major cause of the earths activity?
-where may some of this heat be from?
The cores internal heat
-some of this heat may be primeval, retained from the ball of dust and gas from which the earth evolved
-but we now know that by far the greatest source of heat energy from the earth is derived directly from radioactivity
-natural radioactive decay of uranium, thorium, potassium and other elements provides a continuous but slowly diminishing heat supply
How does the core contribute towards the movement of tectonic plates?
-the radioactive decay at the core generates exceptional temperatures. Hot spots around the core heat the lower mantle creating convection currents. These currents spread very slowly within the athenosphere then cooling and sinking again, they are important but not solely responsible for the movement of tectonic plates
What is magma?
Molten rock, gases and liquids from the mantle accumulating in vast chambers at great pressures deep within the lithosphere. On reaching the ground surface magma is known as lava
What are igneous rocks?
Rocks formed by the cooling of molten magma, either underground (intrusive) or on the ground surface (extrusive)
What does intrusive mean?
Magma that cools, crystallises and solidifies slowly before the surface is intrusive. It forms coarse-grained igneous rocks such as granite and dolerite. Vertical dykes and horizontal or inclined sills may only become part of the landscape once erosion removes the overlying rocks
What does extrusive mean?
Lava that is in contact with the air or sea. It cools, crystallises and solidifies far quicker than magma that is still underground. The resulting igneous rocks such as basalt tend to be fine grained with small crystals ,
When was Alfred Wegener theory of continental drift?
Describe the plate tectonic theory of crustal evolution and sea floor spreading: Harry Hess: 1962
1.)Hess studied the age of the rocks on the floor of the Atlantic Ocean finding the the youngest rocks were in the middle and the oldest near the USA and the Caribbean, with the newest rocks still being formed in Iceland-this was compelling evidence that the Atlantic sea floor was spreading outwards from the centre, a concept known as sea-floor spreading
2.)The rate of spreading was estimated at about 5cm a year which was confirmed by studies of the earths magnetic field in rocks- paleomagnetism. Every 400,000 years or so the Earths magnetic fields switch polarity causing the magnetic north and South Pole to swap. Magnetite (iron oxide) in lava erupted onto an ocean floor records the earths magnetic orientation of that time. Sea-floor spreading from ocean ridges is shown by mirror-imaged patterns of 'switches' or reversals
3.)Sea floor spreading and paleomagnetism would suggest that the earth would be getting bigger, were it not for the discovery of deep ocean trenches where the ocean floor was being pulled downwards (subjected) and destroyed.
What explains oceanic plates relatively young age in contrast to continental plates?
-Continental plates are permanent and may extend far beyond the margins of current land Masses, they will not sink into the asthenosphere because of their relatively low density
-In contrast denser oceanic plates are continuously being formed at mid ocean ridges and being destroyed at deep ocean trenches- hence their young age
Describe gravitational sliding
-explanation for plate movement
-the lithosphere thickens with distance (and time) away from the mid-ocean ridge, this is because it cools with distance and the boundary between the solid lithosphere and plastic asthenosphere becomes deeper
-the result of this thickening with distance from the ridge is that the lithosphere/asthenosphere boundary slopes away from the ridge
-gravity acting on the weight of the lithosphere near the ridge 'pushes' the older part of the plate in front (ridge push)
-furthermore following subduction the lithosphere sinks into the mantle under it's own weight, helping to pull the rest of the plate with it (slab pull)
What is ridge push?
where gravity acting on the weight of the lithosphere near the ridge 'pushes' the older part of the plate in front
What is slab pull?
following subduction, the lithosphere sinks into the mantle under the mantle helping to 'pull' the rest of the plate with it
What happens when two separate plates diverge?
they form a constructive margin
Constructive (divergent) plate margins: What are the two types of divergence?
-in oceanic areas sea floor spreading occurs on either side of mid-ocean ridges (e.g Mid Atlantic ridge)
-in continental areas, stretching and collapsing of the crust creates rift valleys (e.g the great African Rift Valley)
Constructive plate margins: What are mid ocean ridges?
-oceanic divergence forms chains of submarine mountain ridges
-regular breaks called transform faults cut across the ridges, these faults occur at right angles to the plate boundary separating sections of the ridge
-they may widen at different rates which leads to frictional stresses building up with shallow focus earthquakes releasing the tension
-mid ocean ridges can rise up to 4000m above the ocean floor, the middle of the ridges is marked by deep rift valleys
-over centuries the rift valleys are widened by magma rising from the asthenosphere which cools and solidifies to form new crust
-volcanic eruptions along the ridges can build submarine volcanoes
What classifies a shallow-focus earthquake?
Earthquakes that occur at a depth of less than 70km
Constructive plate margins: what are rift valleys?
-continental divergence forms massive rift valleys
-these valleys are formed when the lithosphere stretches, causing it to fracture into sets of parallel faults
-the land between these faults then collapses into deep, wide valleys that are separated by blocks of land called horsts
-the Great American Rift Valley is interesting as it may eventually make the formation of a new ocean as eastern Africa splits away from the rest of the continent
Destructive (convergent) plate margins: what are the three types of convergence possible?
1.) Oceanic plate meets continental plate
2.)Oceanic plate meeting oceanic plate
3.)Continental plate meeting continental plate
Give an example of an oceanic plate meeting a continental plate
Along the pacific coast of South America
Give an example of an oceanic plate meeting an oceanic plate
Along the Mariana Trench in the western Pacific
Give an example of a continental plate meeting a continental plate
Destructive plate margins: what happens when an oceanic plate meets a continental plate?
-the colliding of oceanic plate with continental plate is associated with subduction (one is destroyed by melting)
-oceanic plate is denser than lighter continental plate and so subjects underneath it
-the exact point of collision is marked by the bending of the oceanic plate to form a deep ocean trench e.g the Peru-chile trench along the pacific coast of South America
-as two plates converge, the continental land mass is uplifted, compressed, buckled and folded into chains of fold mountain such as the Andes
-as compression continues folding can become asymmetrical then overflowed (making a recumbent fold). Increasing the compression yet further would make the middle section so thin that it might break, creating a nappe
-the descending oceanic plate starts to melt at depths beyond 100km and is completely destroyed by 700km, this zone of melting is called the Benoiff zone
-melting is caused by both increasing heat at depth and also friction, this friction may also lead to tension (stresses) building up which may suddenly released as intermediate or deep focus earthquakes.
-the melted oceanic plate creates magma, which is less dense than the surrounding asthenosphere, and as a result, rises in great plumes. Passing through cracks (faults) in the buckled continental plate, the magma may eventually reach the surface to form explosive volcanic eruptions
Where the oceanic plate starts to melt at depths beyond 100km and is completely destroyed by 700km, what is this zone called?
-what is melting here caused by?
-the benoiff zone
-both increasing heat and depth and friction
Destructive plate margins: what happens when oceanic plates meet an oceanic plate
-when two oceanic plates collide, one plate (the faster, or denser) subjects beneath the other. This leads to the formation of a deep ocean trench and melting.
-the resulting rising magma from the benoiff zone forms crescents of submarine volcanoes along the plate margins which may grow to form island arcs
-the Mariana Trench and the Marianas islands in the Western pacific show this particularly well
Destructive plate margins: what happens when a continental plate meets a continental plate?
-continental plates are of lower density than the asthenosphere beneath them. This means that subduction does not occur
-the colliding plates, and any sediments deposited between them, simply become uplifted and buckle to form high fold mountains such as the Himalayas. Volcanic activity does not occur at these margins because there is no subduction but shallow focus earthquakes can be triggered
-young fold mountains such as the Himalayas are continually compressing and growing higher Everest is growing 5mm every year
Destructive plate margins: what happens when a continental plate meets a continental plate: what rate is Everest growing at?
5mm every year
What occurs at conservative plate margins?
Give examples of earthquakes occur at conservative plate margins?
-powerful shallow focus earthquakes such as in Los Angeles and San Francisco
-these earthquakes occurred along Californias infamous San Andreas fault system
Why is there no volcanic activity at conservative plate margins?
-crust is not being destroyed by subduction, there is no melting of rock and therefore no formation of new crust and no volcanic activity
What is seismicity?
What is vulcanicity?
Magma plumes: how are the volcanic Hawaiian islands formed?
-radioactive decay within the earths core generates very hot temperatures
-if the decay is concentrated, hot spots will form around the core
-these hot spots will heat the lower mantle, creating localised thermal currents where magma plumes ride vertically
-although usually found close to plate margins such as beneath Iceland these plumes occasionally rise within the centre of plates and 'burn' through the lithosphere ot create volcanic activity on the surface
-as the hot spot remains stationary, the movement of the overlying plate results in the formation of a chain of active and subsequently extinct volcanoes as the plate moves away from the hot spot
What are mudflows/lahars?
Flows of ash, cinder, soil and rock that have been changed to clay by acids in volcanic gases and hot spring waters
What are the common causes of mudflows/lahars?
-eruptions ejecting water directly from a crater lake or through the broken crater walls
-rapid melting of ice or snow onto the volcanoes slopes
-euption induced heavy rainfall mixing with loose material on the volcanoes slopes
-pyroclastic flows (nuees ardentes) entering streams
State 5 different types of volcano
1.)fissure eruptions of basic lava can create extensive lava plateaus
2.)Basic shield volcanoes
3.)Acid dome volcanoes
4.)Composite cones (strato volcanoes)
What are the impacts of fissure eruptions of basic lava
-basic lava such as blocky or smooth and ropy can create extensive lava plateaus. Hollows in the existing landscape are filled to create flat, featureless basalt plains such as the Deccan traps in Central India
-fissure eruptions are the largest contributors to global climate change and large-scale landscaping
What are the impacts of basic shield volcanoes?
-basic shield volcanoes are shallow sided and broad
-they are formed by relatively pure basalt that cools as it runs down the summit crater
-typical of constructive plate margins, rift valleys and hot spots their impact is most obvious by the vast scale of the resulting volcanic cones
-eruptions are gentle enough however to become tourist attractions, such as in Hawaii
What are the impacts of Acid dome volcanoes?
-steep sided, convex cones associated with thick (viscous) silica-rich gaseous lava that solidifies before running down the slope
-associated with destructive margins, their explosive eruptions of pyroclastic flows have a deadly impact e.g in 1902 when Mount Pelee's pyroclastic flows in the Caribbean island killed 30,000 people just after erupting
How are composite cones formed?
-formed when alternating eruptions of ash, tephra and lava build up the volcanoes in layers, the layering produces weaknesses which can be exploited by the magma
-consequently the classic conical shapes relatively rare compared to the irregular shaped composite volcanoes covered by numerous (parasitic) cones and fissures, such as mount Etna
how are calderas formed and what are their impacts?
-Calderas result from violent eruptions that blow of the volcanoes summit. This empties the magma chamber causing the sides of the volcano to collapse inwards
-The resulting vast Pitt crater can be many kilometres in diameter and is left to be flooded by the sea or fill as a lake
-In Santanorini the sea has broken through the walls of the caldera and produced an impressive ring of all islands
What are human causes of seismicity?
How do plate tectonics cause seismicity?
-friction along plate margins builds stress in the lithosphere
-when the strength of the rock under stress is overcome they fracture along cracks called faults, sending a series of seismic shockwaves to the surface
-the breaking point is called the focus (hypocentre) of the earthquake
-the epicentre is the point on the surface directly above the focus
-further from the epicentre the less severe the shaking
What are the 4 different types of seismic waves?
1.)Primary or pressure
2.)Secondary or shear
What are primary or pressure waves?
-the fastest waves that reach the surface first
-high frequency and push like balls in a line
-they travel through both the mantle and the core to the opposite side of the Earth
What are secondary or shear waves?
-these are half as fast to pressure waves and reach the surface next
-like P waves they are high frequency but shake 'like a skipping rope'
-they can travel through the mantle, but not the core, so cannot be measured at a point opposite the focus or epicentre
What are surface love waves
The slowest waves and cause most of the damage
What are Rayleigh waves?
They radiate from the epicentre in complicated low-frequency rolling motions
What are the causes of tsunamis?
seismic activity such as ocean floor earthquakes or submarine volcanic eruptions
-massive landslides into the sea, submarine debris slides, or even meteor or asteroid strikes can also cause them
In what ways do tsunamis differ from normal ocean waves?
-the wave height is very low (less than 1m but on reaching the shore they can reach 25m)
-the wavelength (distance between crests) is very long. In open water the wavelength can be anything from 100 to 1000 km
-they travel quickly, reaching speeds of up to 960km per hour
-usually consist of a series of waves
-a long time between each wave (up to 60 minutes)
-on approaching the coast, especially if funnelled into an inlet, they will slow down, and pile up as a massive wall of water before breaking
What events occur before an earthquake strikes allowing us to mitigate?
-microquakes before the main tremor
-bulging of the ground
-decreasing radon gas concentration in groundwater
-raised groundwater levels
-electrical and magnetic changes within local rocks
-increased argon gas content in the soil
-curious animal behaviour
Give examples of how buildings can be made earthquake-proof
-rolling weights on roof to counteract shock waves
-panels of marble and glass flexibly anchored to steel superstructure
-reinforced lift shafts with tensioned cables
-'birdcage' interlocking steel frame
-reinforced latticework foundations deep in bedrock
-rubber shock absorbers between foundations and superstructure
What are the primary impacts of seismic activity?
-ground shaking causing buildings and bridges to collapse, windows to shatter, power lines to collapse, road and railway damage and water/gas mains and sewers to fracture
-schools, colleges, universities to be dstroyed
-immediate deaths from crushing, falling glass, fire and transport accidents
-shocked, hungry people to sleep outside
-slope failures sett off landslides and avalanches
-liquefaction of saturated soils
-damage to power stations
-panic, fear and hunger
What are the secondary impacts of seismic activity?
-fires caused by broken gas pipes and power lines are difficult to put out
-emergency services are hindered
-diseases spread from contaminated water
-education suspended for immediate future
-bodies not buried or cremated spread diseases such as cholera
-injuries may result in a long term disability or death if not treated properly
-non-governmental organisations provide tents, water and food
-flooding from blocked rivers creating 'quake lakes'
-powercuts affect medical supplies, restricting immediate medical care
-buildings subside as a result of liquefaction
-panic leads to civil disorder, lotting and direct intervention by civil authorities such as police and authority
What are the long-term impacts of seismic activity?
-higher unemployment as not all business recover
-repair and reconstruction of buildings may take months or years
-immediate suffering leading to longer term illness/ or reduced life expectancy
-trauma and grief
-disability resulting from injury and reduced life expectant
-emergency prefabricated homes may become permanent fixtures
-loss of farmland and food production
-permanent disruption to natural drainage patterns
-problems restoring trust in neighbours and civil authorities after looting
What are the three different words for a tropical storm in different countries?
-Hurricane (North Atlantic)
-Typhoon (south-east Asia)
How far can tropical storms extend in diameter?
What wind speeds must tropical storms have to classify as a tropical storm?
Average wind speeds in excess of 120km/h
What is the most damaging part of a tropical storm?
-the menacing bank of cloud that rings the central eye (eye wall)
What often form in tropical storms ?
-why are they difficult to predict
-because they have a highly localised nature
Give 5 factors that are important in affecting the distribution of tropical storms
-rotation of the earth
-uniform wind direction at all levels
How to oceans affect the distribution of tropical storms?
-tropical storms derive their moisture (through the transfer process of evaporation) and energy (in the form of latent heat) from the oceans, there is a clear link with the water cycle
-this explains why tropical storms form and continue to develop over ocean areas and then Peter out on reaching land
How do high temperatures affect the distribution of earthquakes?
-a sea surface temperature in excess of 26 degrees is required for tropical storm formation, which is why they are formed in low latitudes during the summer, when temperatures are at their highest
What temperature should the sea's surface be for a tropical storm to form?
How does atmospheric instability affect the distribution of earthquakes?
-tropical storms are most likely to form in areas of intense atmospheric instability, where warm air is being forced to rise
-the ITCZ (intertropical convergence zone) where two limbs of the Hadley cell converge to form low pressure on the ground is a perfect spawning ground for tropical storms
How does rotation of the earth affect the distribution of tropical storms?
-a certain amount of 'spin' is needed to initiate the characteristic rotating motion of a tropical storm
-the influence of the earths rotation on surface phenomena is called the Coriolis effect
-this increases with distance away from the equator and explains why tropical storms do not usually form in the region between 5 degrees North and 5 degrees south (close to the equator)
Where do tropical storms not usually form?
-between 5 degrees North and 5 degrees south (close to the equator)
-due to the Coriolis effect which increases with distance away from the equator
How does uniform wind direction at all levels affect the distribution of tropical storms?
-winds from different directions at altitude prevent a tropical storm from attaining height and intensity
-the vertical development is effectively 'sheared off' by multidirectional winds
How does a tropical storm form?/ why do they look like they do?
-warm air rises rapidly in its centre to be replaced by air drawn in at the surface
-a central vortex will develop as more and more air is drawn in and rises
-the very centre of the storm (the eye) is often characterised by a column of dry sinking air
-as the air rises it rapidly cools, leading to condensation and the formation of towering cumulonimbus clouds
-sometimes a number of isolated thunderstorms will coalesce to form a single giant storm, when condensation occurs, latent heat is released, which effectively powers the storm
-a tropical storm continues to grow and develop as it is driven by prevailing winds across the oceans. Only when it reaches land and the supply of moisture and energy is cut off will the storm start to decay, should it move back the ocean it will become reinvigorates
Give 4 hazards associated with tropical storms
-coastal and river flooding
How do strong winds associated with tropical storms pose a hazard?
-a tropical storm has average wind speeds in excess of 120km/h with gusts of 250km/h being recorded at the eye wall
-the strong winds are capable of causing significant destruction and damage by tearing off roofs, breaking windows, and damaging communication networks
-debris forms flying missiles whisked up by the wind
-damaged power lines often lead to widespread electricity cuts and even fires
-debris strewn over roads can cause major transport disruption
How do storm surges associated with tropical storms pose a hazard?-give examples
-Hurricane Katrina in the USA in 2005 recorded a storm surge of 7.6 metres
-In addition to loss of life, storm surges inundate agricultural land with saltwater and debris, pollute freshwater supplies, and destroy housing and infrastructure
-Enhanced coastal erosion can lead to the undermining of buildings and highways
What is a storm surge?
-a huge of high water, typically about 3m in height which sweeps inland from the sea, flooding low lying areas
-it is caused by a combination of the intense low atmospheric pressure of the tropical storm (enabling the sea to rise vertically) together with the powerful, driving surface winds
How does coastal and river flooding associated with tropical storms pose a hazard?-give examples
-the warm, humid air associated with a tropical storm can generate potential rainfall, often in excess of 200mm in just a few hours
-this can trigger flash flooding t the coast, particularly in urban areas where surface water can overwhelm the drainage system, this exacerbates the flow hazard by encouraging rapid overland flow
How do landslides assisted with tropical storms pose a hazard?
-it is estimated that up to 90% of landslides each year are caused by heavy rainfall and many are triggered by tropical storms
-the intense rainfall increases pore water pressure (hydrostatic pressure within a slope) which weakens cohesion and triggering slope failure, the additional weight of the water exacerbates erosion
-there is also some evidence that load release caused by tropical storm induced landslides may trigger earthquakes in tectonically stressed regions
When does fire occur?
When oxygen combines with carbon, hydrogen and other organic materials in a rapid chemical reaction
What is a wildfire
The generic name for any uncontrolled fire
What are the 3 types of forest fires?
What are ground fires?
They burn organic matter in the soil such as peat and spread slowly at fairly low temperatures (around 540 degrees) for long periods of time
What are surface fires?
Most common type of wildfire, they sweep rapidly over the ground, burning plant litter, grasses, herbs and scorching trees. Typically burn around 900 degrees but ground temperatures may rise above 100 degrees. They cool quickly and are relatively easy to control
What are canopy/ crown fires?
Spread through the canopy of the trees, loose bark can allow fire to spread up the trunk of trees and into the crown. Combustion of the foliage can generate temperatures in 1100 degrees. Crown fires are the most intense and difficult to contain
What is the only continent that wildfires do not occur in?
What makes us more vulnerable to wildfires?
-population growth and more people in rural areas means that the risk is increasing
-we are living in more vulnerable areas and also offer greater opportunities for ignition (power lines, machinery)
What are human causes of wildfires?
-poorly controlled campfires
-increased access of tourists to wild areas increases risk. Known as 'woodland urban interfaces', this is woodland close to urban areas e.g LA
-urban areas e.g fallen power lines
-agricultural fires that get out of hand
What are natural causes of wildfires?
-burning fragments of vegetation (firebrands) carried ahead on the fire front lighting isolated 'spot fires'
-sparks from rock falls
-gravity (responsible for spot fires), firebrands role down slope and start fires in the distance
What are the two types of lightening ?
-which tend to cause wildfires?
hot-lower voltage, long duration
cold-intense electrical current, short duration
-hot usually cause wildfires
What are the majority of fires that threaten life and residential areas caused by?
Human actions such as discarded cigarettes and poorly controlled campfires
What are the most common areas for wildfires to start?
'wildland-urban interfaces' that are closed to large urban areas such as Sydney and Los Angeles
What causes wildfires?
-heat transfer processes (essentially radiation, conduction and convection) preheat vegetation ahead of the flames and prepare them for ignition and rapid spread of fire. These processes are most effective in preheating material that is above the fire (hot air rises) thereby causing advance of the fire front vertically, this is why fires advance more rapidly up aslope than on level ground
-burning fragments of vegetation (called firebrands) can be carried ahead of the fire front by convection currents and strong winds igniting isolated spot fires, their randomness presenting a specific a significant hazard
-gravity is also responsible for spot fires, firebrands can roll downslope and start fires some distance from the fire front
What are the primary environmental impacts of wildfires?
-destruction of habitats of ecosystems
-death and injury of animals which impacts on food chains and food webs
-short term surge of carbon dioxide due to the burning of carbon stores (trees)
-atmospheric pollution resulting from smoke and water pollution as toxic ash gets washed into the water sources
What are the secondary environmental impacts of wildfires?
-lack of trees and vegetation causes depletion of nutrient sources, leading and increased risk of flooding
-increased carbon emissions impact on the greenhouse effect and climate change
-effects on ecosystem development (secondary succession)
What are the primary social impacts of wildfires?
-loss of life and injury
-displacement (people being forced to temporarily live elsewhere)
-disruption to power supplies if power lines are damaged by strong winds
-damage to mobile phone stations and telephone exchanges affecting communications
What are the secondary social impacts of wildfires?
-possible need for new employment and income stream
-behavioural adaptions based on wildfire experience
-people may have to abide to new rules and regulations
What are the primary economic impacts of wildfires?
-damage/ destruction of structures (homes, public buildings such as schools fences and field boundaries)
-financial loss (loss of earnings, damage costs)
-destruction of businesses
-loss of crops and livestock
What are the secondary economic impacts of wildfires?
-costs of building or possible relocation
-replacement of farm infrastructure, crops, fruit trees & livestock
-cost of future preparedness and mitigation strategies
What are the political primary impacts of wildfires?
-actions of emergency services
-responses of local and national government (state of emergency etc.)
-pressure on local authorities and emergency services to coordinate and prioritise responses in the immediate aftermath
What are the secondary political impacts of wildfires?
-develop strategies for preparedness and mitigation
-decisions about replanting forests, compensation, future regulations etc.
-review laws/advice regarding use of countryside for leisure
Describe how vegetation type fuels a fire
-fires are most likely where vegetation has been dried out by the climate change which makes it susceptible to burning
-this susceptibility increases if the quantity of vegetation is high (dense vegetation)
-pyrophitic vegetation: plants that have adapted to tolerate fire. Adaption such as thick bark, tissue with high moisture content and underground storage systems allow for survival. The Baobab tree is an example
-In Australia, pants such as the banksia need fire so that their woody fruit opens and generates
The type and amount of fuel available (living and dead vegetation) influences the intensity of the wildfire (output of the heat energy) and the rate of spread (degree of threat)
Describe how topography fuels a fire
-wildfires travel fastest uphill (20 degree slope increases the rate of advance by 4 x in Australian research
-this is due to the heat transfer process (radiation, conduction and convection)-vegetation is preheated (often above as air rises) which advances the fire vertically
-also the fire travels in the direction of the ambient wind which is normally uphill
What 3 climate basics affect fires?
How do winds 'favour' fires?
Winds fan the flames of a fire and also drive the flaming front (front edge of the fire). This rate of movement increases with wind velocity. Winds also pick up embers that ignite more vegetation which spreads the fire
How does humidity 'favour' fires?
Determines the rate of moisture in the air, if this is above 15% the risk of fire is low, below 7% it is much higher. Relative humidity varies during the day but is its lowest in the afternoon which explains occurrences of fires at this time
How does climate 'favour' fires?
Affects the frequency and duration of droughts during which vegetation and litter has the opportunity to accumulate and dry. It also affects what can grow in the first place
How can we prepare for a wildfire?
-community preparedness is vital (early detection and suppression needed, rural fighting teams staffed by volunteers)
-warnings- increasingly given by social media e.g USA national weather service issue warnings after critical weather (strong winds, dry fuels, dry lightening possibility)
-red flag warning-extreme fire behaviour within 24 hours (extreme caution at highest level of warning)
-fire weather watch
-defensible fire space-establish fire brake around property
e.g FEMA advice is to call emergency services if you discover a wildfire and to protect property with water containers, put lights on so that house is visible in smoke and place ladder at the side of the house, then evacuate and await emergency services
Give an example of how a house could protect itself from wildfires
-prune branches to 10ft above ground
-stack firewood away from home
-mow dry grasses and weeds to keep soil wet and saturated
-remove leaves and other litter around house
How can we mitigate for wildfires?
-recent technology has allowed mitigation for fires to improve such as through satellites or infrared sensors which can detect thermal variation, cameras can also detect the early ignition of fires
-NASA is developing drone technology for surveying vast areas such as the Great Dismal swamp on the Virginia North Carolina border in the USA. A fully equipped drone with a 2m wingspan has a range of about 13 km and can fly for about an hour
-disaster aid and fire insurance can mitigate the effects of wildfires e.g disaster aid following the 1983 ash Wednesday fires in Australia raised A$12 million to those affected
How can we prevent wildfires in nature? (prevention)
-wildfires need fuel. In forested areas this is often dead vegetation that has collected as litter on the ground
-controlled burning reduces the amount of fuel but there is always a danger that it may get out of control. They also impact on the natural ecosystem by reducing the litter store as well as releasing carbon dioxide into the atmosphere
-public awareness is also important, especially in campsites and public areas where rules regarding the use of campfires and barbecues have to be strictly enforced. Many countries operate 'fire bans' during times of high risk
-since 1944 smokey bear has been urging Americans to behave responsibly to fires, with good results (96% of Americans recognise him)
-however is school of thought that fires are a natural regenerative process within forest ecosystems that should be allowed in certain circumstances that should be allowed to take their course