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Hazards - Coggle Diagram
Hazards
Volcanoes
Since 1982 they have been measured using the Volcanic Explosivity Index (0-8)
Magnitude
Volcanic events range from small, slow lava flows to huge eruptions of lava, ash and gas.
Measured by Volcanic Explosivity Index, grading on a scale of 0-8 based on ejected material and height.
Volcanic eruptions create primary hazards.
Pyroclastic flows are mixtures of heated gas, ash, volcanic rock travelling far and fast
Lahars (
secondary
) are mudflows combined with pyroclastic material, rocky debris and water.
Common causes include rapid melting of snow or ice on the volcano’s slopes, eruption induced heavy rainfalls mixing with loose material , pyroclastic flows entering streams.
Volcanic gases such as carbon dioxide and sulfur dioxide are released into the atmosphere which can be harmful to humans.
Acid rain (
secondary
) occurs when these gases react with water vapour which can damage ecosystems and cause stone and metal deterioration.
Tephra is solid material of varying grain size.
Composite (destructive) Volcanoes
: Rhyolitic/Andesitic
Formed from alternating eruptions of ash, tephra and lava.
Explosive
Highly viscous lava, high silica
Low temperatures
Shield (Constructive) Volcanoes
: Basaltic
Effusive
Fluid lava, low silica
Frequent
High temperatures
Frequency
Some active volcanoes erupt only once every 100,000 years, whereas some erupt every few months (tending to be less damaging with lower magnitude)
Randomness v Regularity
Some erupt regularly some may be dormant for periods of time, then erupt several times in quick succession.
Predictability
Regularity with which a volcano erupts can help scientists predict when it might erupt again.
Volcano monitoring (seismographic detection)
Changes in gas emission
Short-period earthquakes
Fracturing brittle rock as magma moves upwards.
Long period earthquakes
Indicate increased gas pressure in a volcano's plumbing system.
Harmonic Tremors
Result of magma pushing up against the overlying rock below the surface.
Responses
Hazard mitigation is anything that is done to reduce the severity or impacts of a hazard important as volcanic eruptions cannot be prevented.
Short-term responses
Normally occur immediately before, during or immediately after an event.
This includes evacuation methods and providing emergency food supplies.
Long-term responses
Designed to reduce the impacts of future eruptions by managing the risks
Prevention
It is not possible to prevent as volcanic eruption, but it is possible to prevent eruptions from posing a risk to people
Authorities can prevent the land around volcanoes from being developed.
Preparedness
What happens before an event before an eruption to minimise risk or vulnerability.
Authorities can install monitoring systems to predict when an eruption might occur.
Authorities cans top visitors from entering the area around the volcano.
Individual preparation (awareness of nearest shelter and kit)
-Community search and rescue teams or fire response units.
Adaptation
How people change their behaviour or surroundings to minimise the risk and maximise the benefits of living near a volcano.
Tropical Storms
Important in heat redistribution, transferring warm conditions from the tropics towards the poles
Characteristics
There is a degree of symmetry around its eye.
The eye wall is the most powerful part of a tropical storm which is a bank of cloud surrounding the eye.
No clear evidence that number or intensity of storms is growing as global temperatures increase.
Longer period of time needed for any long-term trends,
Warmer atmospheres do hold more moisture, but this is countered by increased wind shear acting as a negative feedback loop in nullifying tropical storm formation.
As they are mostly restrained to the tropics, they can be relatively predictable, late summer to autumn.
They are low pressure, swirling storms with high winds and torrential rain.
Prediction
They are mostly restricted to the tropics and do not usually occur close to the equator.
Indicators such as sea-surface temperatures, atmospheric conditions and short term climatic cycle.
Required Conditions
They do not occur randomly, most forming in the tropics
Oceans
Ocean temperatures have to be approximately 27 degrees and at least 50m deep, providing adequate energy for the storm.
Storms lose energy over land thus begin to dissipate, or at least in shallower waters.
Air Pressure
Areas where air pressure is unstable, convergence zones where areas of high pressure and low pressure meet.
Warm air rises more rapidly.
Intertropical convergence zone where two limbs of the Hadley Cell converge to form low pressure on the ground.
Rotation
A certain amount of spin is required for initiation of the motion of a tropical storm.
The influence of Earth's rotation on surface phenomena is known as the Coriolis effect, which increases from the equator, so tropical storms do not form at the equator.
Wind
Encourage swirling pattern, but must not be too strong to tear apart the storm.
Winds must exceed 75 mph to be classified as a tropical storm.
Winds must be in a uniformed direction, as different directions at altitude prevent a tropical storm attaining height and intensity.
Associated Hazards
This is exacerbated by a growing population, especially in coastal regions.
Strong winds
Capable of causing significant damage and disruption
Storm surges
Surge of water typically up to 3m, sweeping inland from sea, flooding low-lying areas.
Combination of low atmospheric pressure of the tropical storm together with the powerful, driving surface winds.
Major cause of widespread devastation and loss of life, coastal erosion.
They inundate agricultural land with saltwater and debris, pollute fresh water supplies and destroy housing and infrastructure,.
Coastal and river flooding
Warm, humid air associated with a tropical storm can generate torrential rainfall, which can trigger flash flooding at the coast, particularly in urban areas where surface water can overwhelm the drainage system.
Landslides
Up to 90% of landslides each year are caused by heavy rainfall, many triggered by tropical storms.
Reducing the impacts of tropical storms
Behavioural
Structural
Plate Tectonic Theory
Hess found that the youngest rocks on the Atlantic Ocean floor were in the middle, with he oldest near the USA., proving sea-floor spreading due to palaeomagnetism.
Tectonic plates diverge, magma rises, then cools to form new crust.
The new crust is dragged apart over time so the sea floor gets wider.
Creates a structure such as mid-ocean ridges where ridges of higher terrain on either side of the margin.
Tectonics are driven by radioactive decay causing immense temperatures in the mantle, causing convection currents.
However, there are multiple convection cells under the pacific plate, moving in different directions, so this is implausible.
Plate Margins
Constructive
The mantle is under pressure from the plates above causing the mantle to melt, producing magma.
The magma is less dense than the plate so it rises and can erupt to form a volcano.
Plates do not form in a uniform manner which means some move faster than others.
This causes a buildup of pressure, which when it becomes too much, the plate cracks, creating earthquakes.
Constructive Landforms
Ocean Ridge
Mid-Atlantic Ridge
When two oceanic plates diverge.
Underwater volcanoes erupt, and can eventually build up to sea level.
Iceland
Rift Valley
East African Rift System Mozambique
Two plates diverge beneath land, rising magma makes continental crust bulge and fracture.
Volcanoes are found at rift valleys
Mt Kilimanjaro in the East african Rift System
Destructive
Oceanic- Continental
Continental and oceanic crust converges, so the most dense oceanic crust subducts the continental crust.
This forms a deep sea trench
Peru-Chile trench in the Pacific Ocean
Fold mountains are also created, made up of sediments accumulated on the continental crust folded upwards along the edge of the continental crust.
Oceanic crust is heated by friction and contact with the upper mantle melts into magma.
Magma is less dense than the continental crust above so rises to form volcanoes at the surface.
One plate moves under the other, they can get stuck, causing pressure to build up.
When this becomes too much the plates jerk past each other, causing an earthquake.
Oceanic-Oceanic
Most oceanic-continental processes occur here, where the denser of the two oceanic plates subduct, forming a deep sea trench
Triggers earthquakes and volcanoes.
Volcanic eruptions that take place underwater create island arcs (clusters of islands sitting in a curved line).
Mariana islands (Guam)
Continental- Continental
As neither plate is subducted, there are not any volcanoes, but the pressure building up does cause earthquakes.
Fold mountains form when continental crust converges
The Himalayas
Conservative
Only earthquakes occur at conservative plate margins.
Two plates are moving past each other
They can get locked in places and pressure builds up, energy is released as an earthquake.
San Andreas fault in California (Pacific and North American)
Magma plumes
Most volcanic activity occurs at plate margins, but some intense volcanic activity occurs nowhere near boundaries.
A magma plume is a vertical column of extra-hot magma that rises up from the mantle, where volcanoes form above.
The magma plume remains stationary, so the plates move over it
Volcanic activity of the part of the crust previously on the plume decreases as it moves further away.
New volcanoes form over the magma plume, which creates a chain of volcanoes
Hawaii
Slab pull is when the lithosphere sinks into the mantle under its own weight following subduction
Occurs at destructive margins
(Constructive) Upwelling of hot material generates a buoyancy effect so the ocean ridge stands higher than the ocean floor.
Oceanic plates experience a force acting away from the ridge known as
ridge push
or
gravitational sliding
Gravitational sliding involves the thickening of the lithosphere over the asthenosphere away from the mid-ocean ridge, so this slopes away from the ridge.
Gravity causes the denser rock to move downslope away from the plate margin.
Wegener- continental drift
The Park Model
Represents the varying impacts of natural hazardous events over time
Describes the phases following a hazard event
Relief
Immediate local and possible global response in the form of aid, expertise and search and rescue.
Rehabilitation
A longer phase lasting weeks and months, when infrastructure and services are restored (possibly temporary) to allow reconstruction to resume as soon as possible.
Reconstruction
Restore to the same if not exceed the quality of life before the event took place . Usually involves methods of mitigation
Disruption
During and directly after an event, involving primary effects such as destruction of property, loss of life
Pre-disaster
Before the event, the situation is normal.
The type of disruption depends on
Type of hazard
Intenisty or magnitude
Immediate environment
Infrastructure.
The steepness of the downward curve during disruption depends on the nature of the event.
Tsunamis and earthquakes due to their unpredictable nature have immediate disruptive impacts so the disruption of curve downwards
Volcanoes may give weeks of warning during which, mitigation techniques can be employed.
Hazard Management Cycle
Each part of the cycle correlates to part of the ongoing cycle
Preparedness
Focus on ensuring emergency services and people at risk are aware of how to react during an event.
Response
Focused on the immediate needs of the population such as the protection of life and propoerty and includes firefighting, emergency medical response, evacuation and transportation, decontamination and the provision of food, water and shelter to victims.
Recovery
Long term response- where city authorities focus on clean-up and rebuilding
Mitigation
Authorities look at the impact of the hazard and rebuilding in a better way to reduce similar impacts from a future hazard. Earthquake proofing buildings.
The hazard management cycle is widely employed, however there are alternative frameworks
The Park Model allowed for providing room for improvements to the landscape- hazards can be turned into an opportunity for development.
Advantages:
Aknowledging management operates as a cycle, it identifies that living in a hazardous environment requires constant management for inhabitants to be safe from negative effects.
Disadvantages:
Hazards largely cannot be prevented.
Disadvantages:
Not a clear time scale, no statistics, does not clarify the hazard.
Advantages:
Adapted to compare different hazards; forecasted and up forecasted hazard; same hazard in LEDC vs MEDC; events before and after mitigation strategies.
Earthquakes
Some plate margins are more seismologically active than others - they show no predictability
An understanding of seismological activity means scientists know where most are at risk, but when and where specifically are impossible.
Can be humanly induced such as mining, building large reservoirs putting pressure on underlying rocks.
Some old fault lines can be reactivated as in September 2002 in the midlands, the Malvern lineament.
Plate movements produce energy of extraordinary proportions.
Friction along plate margins builds and stresses in the lithosphere.
Impacts depend on
magnitude of earhtquake
geological conditions
distance from epicentre
population density
design of buildings
impact of indirect hazards
Secondary Impacts
Landslides, tsunamis, suspended education, fires, hindrance of emergency services, disease, NGO provide aid, buildings foundations subside, power cuts, civil disorder, looting.
Primary Impacts
Include buildings and bridges to collapse, windows to shatter, schools, colleges destroyed, immediate death and injury from falling objects , shock, hunger, displaced, liquefaction
Long Term Impacts
Include higher unemployment, lost generation, repair and reconstruction, temporary prefabricated homes become permanent fixture, loss of farmland products results in poor food production, restoration of trust.
Prediction of earthquakes:
micro quakes, ground bulging, decreasing radon gas concentrations in groundwater, raised groundwater levels, curious animal behaviour.
Protection of earthquakes:
Preparing via modifying built environments to decrease vulnerability.
Hazard resistant structures
Large concrete counter weight
Shock absorbers
Cross bracing
Retrofitting of older buildings
Education
Japan observes a Disaster Prevention Day on September 1.
Fire prevention
Smart meters can cut off electricity in the event of an earthquake
Land use planning
Most hazardous areas can be identified and regulated in terms of land use, schools and hospitals should be built in low risk areas with sufficient open space.
Insurance
Aid
Even where earthquakes are expected, such flimsy evidence could never be risked due to resulting panic and chaos.
Geographic Information Systems are used to prepare hazard maps showing areas of greater risk.
Modified Mercalli Intensity
Actual intensity of damage, using observations on the ground of the impact of the earthquake on a twelve point scale.
Breaking point is called the focus, the epicentre is the point on the surface directly above the focus (most intense ground shaking)
Seismic Shockwaves
There are different types of shockwaves.
Primary
waves are the fastest to the surface, they are high frequency, pushing through the crust, mantle and core.
Secondary
waves are half as fast and reach the surface next, also high frequency, cannot travel through the core.
Surface love
waves are the slowest, causing most of the damage, entirely horizontal motion, amplitude largest at the surface.
Rayleigh
waves radiate from the epicentre in low-frequency rolling motions.
Wildfires
Uncontrolled rural fire.
Conditions for a Wildfire
Supply of fuel influences the intensity of the wildfire and the rate of spread.
Finer vegetation causes fire to spread quickly, but thicker vegetation burns more intensely.
Plants with oils such as eucalyptus cause more intense fires.
Vegetation should be dry for it to catch.
Weather conditions means heatwaves and droughts provide favourable conditions.
Strong dry winds from continental interiors exacerbate the drying process.
However, areas need to have experiences enough rainfall to promote vegetation growth.
Dry seasons in California
Can be natural (lightning) or human (discarded cigarettes or campfires)
Wildfire mitigation
Short term mitigation
Focus on extinguishing and diverting the fire.
Long term mitigation
Controlled burnings remove flammable material
Fire breaks provide a physical boundary of fire spreading.
Smokey Bear Mitigation (US)
Flammable objects should be kept away from the house.
Flammable vegetation should be kept away from the house.
Keep lawns watered and mowed.
Wildfire Prediction
Red flag warnings are used to predict wildfires by warning when wildfire conditions are optimal.
Evacuation zones can be set up
Used in Wildfore Alberta, resulting in 0 fatalities.
Thermal imaging enables government to see where wildfires are currently occurring and predict their path based on many factors such as the green density.
Fires do not spread in grassland but in thick, dense forestry.
Public awareness can prevent ignition
Smokey Bear in the US for the last 70 years providing information on wildfire prevention.
Wildfire adaptation
Insurance (dependent on wealth of the area)
Measures taken to reduce the impact of enhanced greenhouse effect
Fatalists argue that wildfires should not be attempted to be managed as they will only start again
Personal and government resources can be used elsewhere, away from recovery.
There are ecological benefits to wildfires such as eradication of disease and enhanced seed germination.
A hazard is the threat of substantial loss of life, or impact of life or damage to property caused by an event.
3 Main types of hazard:
Geophysical
Atmospheric
Hydrological
How we perceive hazards is based on the effect it may have on our lives, effected by direct experience and duration of effects.
A natural event only becomes a hazard in the presence of people.
More people live in at risk areas due to increased demand for land by an increasing population.
Risk and Vulnerability
There are many reasons why people put themselves at risk of a potential natural disaster
Unpredictable
Alternatives
Change in level of risk
Benefits such as fertile soil.
A disaster is a sudden, calamitous event that causes serious disruption of the functioning of a community or a society.
Responses to Hazards
Try to reduce vulnerability to reduce its impacts, success depends on hazard incidence, magnitude and distribution and level of development.
Prevent or reduce magnitude
Not possible for some but risk sharing (insurance)
Mitigate and adapt impacts
This could be a prediction working out where is likely to be affected, allowing people to respond.
Governments
Coordinate responses to hazards to manage it effectively.
Fatalism
The belief that hazards cannot be avoided , so must be accepted.
For some, the benefits of living near the threats of hazards outweigh the risk. E.g soil fertility on floodplains and in the vicinity of volcanoes.
Human response is also a determining factor:
fatalism
adaptation
prediction
Affected by economic, social and cultural background
Wealth- richer people able to move to areas less prone to hazards or build their homes to withstand hazards, so may perceive a smaller risk.
Religion- some people view hazards as acts of God to punish people.
Education- people with more may have a better understanding of the risks and hazards, or believe they are able to reduce the risks or mitigate the impacts.
Past experience- people who live in hazard-prone areas may have experienced hazards before.
Personality- some people fear hazards, whereas some think of them as exciting.
Tsunamis
Unrelated to tides and winds, but usually generated by seismic activity
Ocean floor earthquakes
Submarine volcanic eruptions
Differ from normal ocean waves
Low wave height until they nearly reach the shore where they can rise to over 25m.
The wavelength is very long
They travel very quickly
They usually consist of a series of waves, the first is not always the biggest.
The wave period is very long ranging between 10 and 60 minutes.
They slow down before reaching the shore, especially funnelling into an inlet, wavelength gets shorter.
Up to 90% of tsunamis related to seismic activity occur along the 'Pacific Ring of Fire'
Effective warning systems do exist
Pacific Tsunami Warning System based in Hawaii
Without this, the first sign is
drawdown
which is the apparent draining of the sea in front of the tsunami.
Ocean floor earthquakes are more dangerous than tsunamis related to submarine volcanoes.