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Hazards - AQA Physical Geography, A-Level
Terms in this set (103)
What is Prediction?
Working out when and where a hazard is likely to occur - suggesting what might happen in the future. It is an attempt to modify vulnerability.
What is Adaptation?
Perspective that hazards are influenced by natural and human events, and their magnitude and frequency can be estimated based on experience.
What is Mitigation?
Actions aimed at reducing the severity of an event, often by direct intervention. It includes protection of natural barriers, e.g. coral reefs.
What 3 Phases does the Park Model Describe?
1. Relief - immediate response in the form of aid, expertise and search & rescue.
2. Rehabilitation - longer phase (weeks to months), restoring infrastructure and services.
3. Reconstruction - restoring to the same, or better, quality of life as before (often including mitigation strategies).
What are the 4 Aspects of the Hazard Management Cycle?
Explain the 'Preparedness' Stage of the Hazard Management Cycle
Education and awareness can reduce human causes and change behaviours, knowing what to do after an event can speed up recovery. Higher in areas of greater risk.
Explain the 'Response' Stage of the Hazard Management Cycle
Speed of response depends on effectiveness of the emergency plan. Immediate response = saving lives and co-ordinating medical assistance.
Explain the 'Recovery' Stage of the Hazard Management Cycle
Restoring the affected area to something approaching normality. Short term = restoration of services so long-term planning can take place.
Explain the 'Mitigation' Stage of the Hazard Management Cycle
Actions aimed at reducing the severity of an event, including direct intervention.
Describe the Characteristics of Oceanic Crust
Occasionally broken layer of basaltic rock known as sima (silica and magnesium). Sima = lower layer of crust, denser than sial.
Describe the Characteristics of Continental Crust
Bodies of mainly granitic rock known as Sial (silica and aluminium). Sial = upper layer of crust, forming continetal land masses. Thicker than oceanic sima but less dense.
Describe the Characteristics of the Earth's Core
Made of iron and nickel, 4x as dense as the crust. Has two parts - inner (iron) and outer (nickel-iron alloy). Major source of Earth's energy from radioactive decay within core.
What was Alfred Wegner's Theory?
Published in 1912. Theory that a single continent existed 300 million years ago - Pangea. It then split into Laurasia (N) and Gondwanaland (S). The theory of continental drift was supported by geological and biological evidence.
What Geological Evidence was there to Support Wegner's Theory?
1. The 'jig-saw fit' of S. America and Africa.
2. The same glacial deposits are found in S. America, Antarctica and India.
3. Striations on rocks in Brazil and W. Africa.
4. Rock formations in N. Scotland and E. Canada were likely laid under same conditions in one location.
What Biological Evidence was there to Support Wegner's Theory?
1. Fossil brachiopods in India limestone are comparable with similar fossils in Australia.
2. Fossils of the Reptile Mesosaurus are found in both S. America and S. Africa.
3. Fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica.
How did Wegner's Theory Develop in the 1940s?
1. The mid-Atlantic ridge was discovered and studied. A similar feature was later discovered in the Pacific Ocean.
2. Suggestion of sea-floor spreading either side of the mid-Atlantic ridge.
3. Alternating polarity of ocean crust rocks.
4. Iron particles in lava are aligned with the Earth's magnetic field at the ocean floor.
Explain the Theory of Ocean Floor Spreading
First identified in the 1960s by Harry Hess. Movement of the sea-floor due to convection currents in the mantle, with new rock forming at the surface as it rises and cools. This causes the other magmas that rises to pull the sea floor apart, moving the continents around.
What is Palaeomagnetism?
Iron particles in lava are aligned with Earth's magnetic field. Regularly the polarity of the Earth reverses; resulting in a series of magnetic stripes with the sea-floor rocks aligned alternately towards north and south poles. The striped pattern, mirrored exactly on either side of a mid-oceanic ridge, suggests that the ocean crust is slowly spreading away from the boundary. Also, the ocean crust gets older with distance from the mid-ocean ridge.
What is Slab Pull?
At plate margins, dense crust is forced under less dense crust. The sinking of the plate edge pulls the plate towards the boundary.
What is Ridge Push/Gravitational Sliding?
Happens at constructive margins when magma rises forming new crust and heating the surrounding rocks. As the rocks get hotter they expand and rise above the surface forming a slop. The new crust cools, gets denser and moves downwards (gravity), away from the margin. This puts pressure on the plates, causing them to move apart.
Explain Sea-Floor Spreading
Tectonic plates diverge and magma rises to fill the gap, cooling and forming new crust. The new crust is then dragged apart and more new crust forms. When this happens under the sea, the floor gets wider.
What are Mid-Ocean Ridges?
Created by sea-floor spreading, they are ridges of high terrain on either side of the plate margin.
What are the 3 Destructive Plate Margins?
1. Oceanic meeting continental - e.g. Pacific coast of S. America.
2. Oceanic meeting oceanic - e.g. Mariana Trench, Western Pacific.
3. Continental meets continental - e.g. Himalayas.
What are the 2 things that happen at Constructive Plate Margins?
1. In oceanic areas, sea-floor spreading occurs either side of mid-ocean ridges, e.g. Mid-Atlantic Ridge.
2. In continental areas, stretching & collapsing of the crust creates rift valleys, e.g. Great African Rift Valley.
What happens at Conservative Plate Margins?
Two plates slide past each other. No crust is being destroyed, melted or rock being formed. Associated with powerful earthquakes.
What is the Difference between Constructive and Destructive Plate Margins?
Constructive plate margins are when two plates diverge/separate, whereas destructive plate margins are when two plates collide.
What are Mid-Ocean Ridges?
Oceanic divergence forms chains of submarine mountain ridges that extend for thousands of kilometers across the ocean floor.
What are Transform Faults?
Regular breaks cut across mid-ocean ridges. They occur at right angles to the plate boundary, separating sections of ridge. They widen at different rates and lead to frictional stress which is released through shallow-focus earthquakes.
How are Rift Valleys Formed?
Formed by continental divergence. The lithosphere stretches, causing it to fracture into sets of parallel faults. The land between the faults collapses into deep, wide valleys separated by upright blocks of land - 'horsts'.
Why is the Great African Rift Valley so Interesting?
Because it may eventually mark the formation of a new ocean as E. Africa splits away from the rest of the continent.
What is the Zone of Melting Called?
The Benioff Zone.
What 7 Geographic Features can be found at Constructive Plate Margins?
1. New oceanic crust is formed by basaltic magma rising.
2. New basaltic rocks
3. Mid-ocean ridges broken up by transform faults.
4. Shallow-focus earthquakes.
5. Basic volcanoes.
6. Volcanic islands.
7. Continental rift valleys.
What 4 Geographic Features can be found at Destructive Plate Margins Subduction Zones? (Oceanic V Oceanic)
1. Oceanic crust destroyed by subduction & melting.
2. Deep ocean trenches (Mariana Trench)
3. Shallow, intermediate and deep-focus earthquakes
4. Explosive, acid volcanoes (Merapi & Montserrat).
What 5 Geographic Features can be found at Destructive Plate Margins Subduction Zones? (Oceanic V Continental)
1. Oceanic crust destroyed by subduction & melting.
2. Deep ocean trenches (Peru-Chile trench).
3. Continental land mass is uplifted, compressed and buckled into fold mountains (Andes).
4. Intermediate and deep-focus earthquakes.
5. Explosive, acid volcanoes (Cotopaxi).
What 5 Geographic Features can be found at Destructive Plate Margins Collision Zones? (Continental V Continental)
1. Colliding plates, & sediment between, uplift & concertina into particularly high fold mountains (Himalayas).
2. Shallow-focus earthquakes.
3. Continued compression and overflowing can result in fracture creating a thrust fault and nappe.
What Geographical Features are found at Conservative Margins?
1. Shallow-focus earthquakes (Haiti & San Andreas Fault system).
What is the Exception to Plate Margins?
Hotspots near the centre of a plate cause basic volcanoes, e.g. Yellowstone and Kilaue.
Explain Magma Plumes
If radioactive decay is concentrated, hotspots will form around the core which heat the lower mantle creating localised thermal currents where magma plumes rise vertically. They are usually found close to plate margins, e.g. Iceland.
How many of the Earth's Volcanoes and Earthquakes are Located along Plate Margins?
How do Magma Plumes create Volcanic Activity on the Earth's Surface?
They occasionally rise in the centre of plates and 'burn' through the lithosphere. The hotspots remain stationary, but the moving overlying plate results in a chain of active volcanoes. As the plates move away from the hotspot, the volcanoes will become extinct.
What are the 6 Primary Hazards of Volcanoes?
1. Lava flows.
2. Pyroclastic flows.
4. Nuees ardentes.
5. Ash fallout.
6. Volcanic gases.
What are Pyroclastic Flows?
A Mixture of hot rock, lava, ash and gases arising from a volcanic eruption, moving at a rapid speed along the ground.
What are Nuees Ardentes?
Dense, rapidly moving clouds of hot gases, ashes and lava fragments.
What are the 4 Secondary Hazards of Volcanoes?
2. Volcanic landslides.
4. Acid rain.
What are Lahars?
Destructive mudflows occurring as a result of a volcanic eruption.
What is the Volcanic Explosivity Index?
A scale of 0 to 8 based on the amount of material ejected and how high the material is blasted.
What is the Frequency of Volcanic Hazards?
This depends on the type of volcano. For example, Kilaue, Hawaii is an active shield volcano that has erupted basaltic lava continuously since 1983. In contrast, the Yellowstone Caldera has erupted 3 times in the last 2.1 million years.
Define the Term 'Hazard'?
A hazard is the threat of substantial loss of life, substantial impact upon life or damage to property that can be caused by an event.
What is a Disaster?
A disaster occurs as a result of a hazard. For example, living on a fault line is a hazard, whereas an earthquake on the fault line with enormous impact on people and property is a disaster.
What are Geophysical hazards?
Driven by the Earth's own internal energy source, t.g. plate tectonics, volcanic eruptions, landslides and seismic activity.
What are Atmospheric Hazards?
Driven by processes at work in the atmosphere. E.g. tropical storms, droughts, extremes of hot and cold weather, wildfires.
What are Hydrological Hazards?
Driven by water bodies, mainly the oceans. E.g. floods, storm surges and avalanches.
What affects Perception of Hazards?
Wealth, religion, education, past experience, personality.
What is 'Fatalism'?
An acceptance that hazards are natural events, that we can do little to control. Losses have to be accepted. View that the interference with the natural processes can have a detrimental effect on ecosystems.
What would be a Fatalistic Approach to Wildfires?
Whilst wildfires can be hazardous to human activity, they are also a natural regenerative process within forest ecosystems and should be allowed to take their course.
What is La Nina?
Where the waters of the tropical Eastern Pacific are colder than usual and winds blow stronger.
Shows periods of below average sea surface temperatures across the East Central Equatorial Pacific. During a La Nina year, winter temperatures are warmer than normal in the South East and cooler than normal in the Northwest.
It causes cooler water so their is less likelihood of cloud formation.
What are the Primary Impacts of Volcanic Hazards? (4)
1. Lava and pyroclastic flows - destroy roads and buildings.
2. Ash fall - damages crops and contaminate water.
3. Tephra, lava and pyroclastic flows can kill people.
4. CO2 gases can cause suffocation.
What are the Secondary Impacts of Volcanic Hazards? (3)
1. Lahars can kill people and destroy roads, blocking emergency service routes.
2. People can experience physcological problems.
3. Food shortages.
What are the Social Impacts of Volcanic Hazards?
People are killed, buildings and infrastructure destroyed, gas lines break and water supplies can be damaged.
What are the Environmental Impacts of Volcanic Hazards?
Ecosystems damaged, acid rain causes acidification of aquatic ecosystems and removes soil nutrients, volcanic gases contribute to greenhouse effect and ash clouds can reduce sunlight, decreasing temperatures.
What are the Economic Impacts of Volcanic Hazards?
Businesses destroyed, crops destroyed, aircraft cannot fly and repair is very expensive. However, in the future the volcanoes can become tourist attractions, boosting the economy.
What are the Political Impacts of Volcanic Hazards?
Food shortages can lead to conflicts and political unrest and governments have to spend money on repairs instead of investing it in the development of the country.
What are the Short Term Responses to Volcanic Hazards?
Evacuation of people at risk from further eruptions, deploying of emergency services and emergency food supplies.
What are the Long Term Responses to Volcanic Hazards?
1. Prevention - e.g. authorities banning development of land around volcanoes.
2. Preparedness - e.g. monitoring systems, evacuation plans and emergency kits.
3. Adaptation - e.g. buildings can be strengthened and people could capitalise on opportunities such as farming on the fertile soils.
Where Do Shallow Focus Earthquakes Occur?
1. Constructive plate boundaries - often at mid-ocean ridges.
2. Collisional plate boundaries.
3. Conservative margins.
Where Do Deep Focus Earthquakes Occur?
1. The Benioff Zone - compressional forces as oceanic crust subducts under continental.
Where do the Majority of Earthquakes Occur in General?
90% at plate boundaries, 10% are intra-plate.
What are the Primary Hazards of Earthquakes?
1. Body Waves.
2. Surface Waves.
Describe the 2 Types of Body Waves
1. Primary (P) Waves - travel through solids and liquids at 5 km/s (faster, detected first).
2. Secondary (S) Waves - Don't travel through liquids. 3km/s.
What are Surface Waves?
They travel along the Earth's surface and cause the most damage to buildings.
What are Love Waves?
They are a form of surface waves. They shake the ground at right angles to the direction of movement.
What are Rayleigh Waves?
Surface waves that move in a rolling motion.
What are the 3 Secondary Hazards of Earthquakes?
What is Liquefaction?
Unconsolidated sediment saturated with water acts as a liquid when the ground shakes, causing the subsidence of building foundations or destruction of utility pipes.
What is the Richter Scale?
First used in 1934, it is a logarithmic scale. It is more useful for smaller earthquakes, there is no upper scale but major earthquakes are classified as a '7'.
What is the Modified Mercalli Intensity Scale?
Uses observations of people to determine damage caused by an event. Its a 12 point scale and ranges from 'earthquake not felt' to 'damage is total, objects thrown in air'.
Explain the Quote 'Earthquakes Don't Cause Death, Buildings Do'
3/4 of all deaths during an earthquake are caused by collapsing buildings, rapid urbanisation has increased earthquake risks. Low cost, poorly built housing is a particular hazard, people in slums are disproportionately vulnerable.
What are the Short Term Impacts of Earthquakes?
1. Destruction of infrastructure and roads.
2. Rescue efforts hindered.
3. Water pipes bursting causing contamination, leading to disease.
What are the Long Term Impacts of Earthquakes?
1. Infrastructure problems.
2. Disruptions to supply lines and the economy.
What are the Social Impacts of Earthquakes?
1. Buildings collapse killing people and leaving others homeless.
2. Gas and power lines break = fires and flooding.
3. Lack of clean water = disease.
4. Tsunamis = flooding and further damage.
What are the Environmental Impacts of Earthquakes?
1. Industrial units and power plants damaged causing leaks of chemicals and radioactive material.
2. Fires destroy ecosystems.
3. Tsunamis flood freshwater ecosystems and salinise water.
What are the Economic Impacts of Earthquakes?
1. Destroy business premises damaging the economy.
2. Damage to industry means the country may have to rely on expensive imports.
3. Damage is expensive to repair.
What are the Political Impacts of Earthquakes?
1. Shortages of food and water = political unrest.
2. Governments may have to borrow money.
3. Governments can no longer invest in countries development.
How can Earthquakes be Prevented?
1. Stop land thats prone to liquefaction being developed on.
2. Build sea walls for tsunamis.
How can People be Prepared for Earthquakes?
1. Earthquake warning systems.
2. Plans and drills.
4. Tsunami warnings.
5. Evacuation routes.
Where do Most Tropical Storms Originate?
In the tropical convergence at latitudes of between 5° and 25° north and south of the equator.
What are the Specific Conditions Required for a Tropical Storm to Form?
Warm, deep oceans with temperatures of 27°C to a depth of at least 70m, the increased importance of the Coriolis force and the creation of a circular pattern of winds and unstable air with high humidity.
What is the Coriolis Force?
A force caused by the Earth's rotation deflecting the path of winds. It is weak at the equator but need to be increased for tropical storms to accelerate the spinning of the original depression.
Explain Tropical Storms Seasonality
* Northern hemisphere = June to November.
* Southern hemisphere = November to April.
Where do Tropical Storms Occur?
* Caribbean sea - 'hurricanes'.
* Bay of Bengal - 'cyclones'.
* China sea - 'typhoons'.
* Northern Australia.
How are Tropical Storms Measured?
On the Saffir-Simpson Scale. Category 5 = strongest (winds over 250km/h), category 1 = weakest (120km/h).
What are the Primary Hazards of Tropical Storms?
1. High winds - destroy buildings, uproot treesm carry debris.
2. Storm surges - large rise in SL caused by high winds and low pressure of storm.
3. Heavy rain - warm moist air rises, cools and condenses = torrential rain.
What are the Social Impacts of Tropical Storms?
1. People may drown, be injured or killed.
2. Destroyed houses = homelessness.
3. Electricity cables damaged, supplied cut off.
4. Flooding causes overland sewage flows = contamination.
5. Lack of clean water = disease.
6. Food shortages.
What are the Environmental Impacts of Tropical Storms?
1. Beaches eroded and coastal habitats damaged.
2. Environments polluted.
3. Landslides can block watercourses.
How are Tropical Storms Predicted?
In the USA, the National Hurricane Centre and joint Typhoon Warning System provide coverage of the Atlantic and Pacific Oceans. They use geostationary and orbiting of satellites to provide data about storm structure, rain, wind speed and direction.
What are Wildfires?
Uncontrolled fires that destroy forests, grassland and other areas of vegetation. Usually occur in rural areas, but can reach inland destroying agricultural land and settlements.
What are Surface Fires?
The most common type of wildfire. They burn leaf litter and low-lying vegetation. They cool quickly and are relatively easy to control.
What are Ground Fires?
Fires that burn organic matter in the soil, such as peat. It is a slow, smouldering fire with no flame and little smoke.
What are Crown Fires?
They burn through the canopy and up tree trunks into the crown. They affect the whole forest and are the fastest, most intense wildfires.
What are the 3 Favourable Conditions for Wildfires?
1. Vegetation type - thick undergrowth, oily plants.
2. Fuel characteristics - fine dry material.
3. Climate and weather - rainfall that has allowed vegetation to grow followed by warm, dry weather.
What is the Global Early Warning System for Wildfires (Global EWS)?
Proves 1-7 day forecasts using satellite technology to help those assessing the fire hazard in their decision making.
What are the Main Methods for Fighting Fires?
1. Spraying fire with water or chemicals from the ground or air.
2. Creating firebreaks.
3. Beating the flames.
What Building Codes Have Susceptible Communities Developed for Wildfires?
1. Considering site layout - e.g. patios may act as firebreaks.
2. Fire-resistant roofing.
3. Roll down metal fire doors and window shutters.
4. Sprinkler systems.
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