Hazards Flashcards
What is a hazard?
A hazard is a potential threat to human life and property caused by an event. Hazards can be human caused or occur naturally. An event will only become a hazard when it is a threat to people.
What are the different types of hazard?
Geophysical - hazards caused by land processes, majorly tectonics (e.g. volcanoes)
Atmospheric - hazards caused by atmospheric processes and the conditions created because of these, such as weather systems (e.g. wildfires).
Hydrological - hazards caused by water bodies and movement (e.g. floods)
What is risk?
Risk is the exposure of people to a hazardous event presenting a potential threat to them and their property.
What is vulnerability?
Vulnerability is the potential for loss. Losses vary geographically, over time, and among different social groups.
What is risk perception?
Risk perception is how we view a hazard. How we receive and process information relative to the hazard, which then determines our reactions if any.
What determines hazard perception?
- wealth
- experience
- education
- religion and beliefs
- mobility
What is the passive response to hazards?
Fatalism - the viewpoint that hazards are uncontrollable natural events, and any losses should be accepted as there is nothing that can be done to stop them.
What are the active responses to hazards?
- Prediction - using scientific research and past events in order to know when a hazard will take place, so that warnings can be delivered and impacts of the hazard can be reduced. In some cases, hazards may also be prevented when predicted early enough (wildfires).
- Adaptation - attempting to live with hazards by adjusting lifestyle choices so that vulnerability to the hazard is lessened (earthquake proof buildings).
- Mitigation - strategies carried out to lessen the severity of a hazard (sandbags to offset flooding).
- Management - coordinated strategies to reduce hazards effects. This includes prediction, adaptation, and mitigation.
- Risk sharing - a form of community preparedness, whereby the community shares the risk posed by a natural hazard and invests collectively to mitigate the impacts of future hazards.
How does incidence effect responses to hazards?
Incidence - frequency of a hazard. This is not affected by the strength of a hazard, it is just how often a hazard occurs.
Low incidence hazards may be harder to predict and have less management strategies put in place, meaning the hazard could be more catastrophic when it eventually does occur. Also, low incidence hazards are usually more intense than high incidence hazards. For example, there are only 36 recorded earthquakes since 1500 above magnitude 8.5, but millions of earthquakes that are too weak to be recorded every year.
How does distribution affect responses to hazards?
Distribution - where hazards occur geographically.
Areas of high hazard distribution are likely to have a lot more management strategies, and those living in the area will be adapted to the hazardous landscape because it dominated the area more so than in places with low hazard distribution.
How do magnitude and intensity affect responses to hazards?
Intensity - the power of a hazard (how strong it is and how damaging the effects are)
Magnitude - the size of the hazard, usually a measure of intensity.
High magnitude, high intensity hazards will have worse effects, meaning they will require more management.
Magnitude and intensity are not interchangeable terms. The magnitude is usually definable and can be a number - this does not change. Intensity is the effects on the person, and can change depending on the distance from the hazard or the management strategies combating high magnitude risks.
How does level of development affect responses to hazards?
Level of development - economic development will affect how a place can respond to a hazard, so a hazard of the same magnitude may have very different effects in two places of contrasting level of development.
Even if the hazard is identical, an area with a lower level of development is less likely to have effective mitigation strategies as these are costly. Therefore, the effects of a hazardous event is likely to be much more catastrophic in a less economically developed area.
What is the park model?
The park model is a graphical representation of human responses to hazards. The model shows the steps carried out in the recovery after a hazard, giving a rough indication of time frame. The steepness of the curve shows how quickly an area deteriorates and recovers. The depth of the curve shows the scale of the disaster.
What are the stages of the park model?
Stage 1 - relief (hours-days)
- Immediate local response (medical aid, search and rescue)
- Immediate appeal for foreign aid (the beginnings of global response)
Stage 2 - rehabilitation (days-weeks)
- Services begin to be restored
- Temporary shelters and hospitals set up
- Food and water distributed
- Coordinated foreign aid (peacekeeping forces etc.)
Stage 3 - reconstruction (weeks-years)
- Restoring the area to the same or better quality of life
- Area back to normal (ecosystems restored, crops regrown)
- Infrastructure rebuilt
- Mitigation efforts for future events
What is the hazard management cycle?
The hazard management cycle outlines the stages of responding to events, showing how the same stages take place after every hazard.
What are the stages of the hazard management cycle?
Response - immediate action taken after event (evacuation, medical assistance, rescue)
Recovery - long term responses (restoring services, reconstruction)
Prevention - strategies to lessen effects of another hazard (barriers, warning signals developed, observatories)
Preparedness - being ready for an event to occur (public awareness, education, training)
What is the structure of the earth?
Inner core
- Solid ball of iron/nickel
- Very hot due to pressure and radioactive decay (contains elements such as uranium that give off heat when they decay)
- This heat is responsible for the earth’s internal energy.
Outer core
- Semi-molten
- iron/nickel
Mantle
- Mainly solid rocks, and the rocks are high in silicon
- The very top layer of the mantle is semi-molten magma, which is known as the asthenosphere
Asthenosphere
- Semi-molten layer that constantly moves due to flows caused by convection currents.
- Movements are powered by heat from the core
Lithosphere
- Broken up into plates
- Majority of the lithosphere is within the mantle
- The top of the lithosphere is the crust which is the land and sea we live on
Crust
- The thin top of the lithosphere
- Oceanic crust is dense and is destroyed by plate movement, continental crust is less dense and is not destroyed.
What is plate tectonic theory?
The lithosphere is broken up into large slabs of rock called tectonic plates. These plates move due to the convection currents in the asthenosphere, which push and pull the plates in different directions. Convection currents are caused when the less dense magma rises, cools, then sinks. The edges of where plates meet are called plate boundaries.
What happens at destructive plate boundaries for continental and oceanic plates?
- Denser oceanic plate subducts below the continental
- The plate subducting leaves a deep ocean trench
- Fold mountains occur when sediment is pushed upwards during subduction
- The oceanic crust is melted as it subducts into the asthenosphere
- The extra magma created causes pressure to build up
- Pressurised magma forces through weak areas in the continental plate
- Explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes
What happens at destructive plate boundaries for oceanic and oceanic plates?
- Heavier plate subducts leaving an ocean trench. Fold mountains will also occur
- Built up pressure causes underwater volcanoes to burst through the oceanic plate
- Lava cools and creates new land in the form of island arcs
What happens at destructive plate boundaries for continental and continental plates?
As neither plate is very dense, pressure builds
Ancient oceanic crust is subducted slightly, but there is no subduction of continental crust
Pile up of continental crust on top of the lithosphere due to pressure between plates
Fold mountains formed from piles of continental crust
What happens at constructive plate boundaries for oceanic and oceanic plates?
- Magma rises in between the gap left by the two plates separating, forming new land when it cools
- Less explosive underwater volcanoes formed as magma rises
- New land forming on the ocean floor by lava filling the gaps is known as sea floor spreading
What happens at constructive plate boundaries for continental and continental plates?
- Any land in the middle of the separation is forced apart, forming a rift valley
- Volcanoes form where the magma rises
- Eventually the gap will most likely fill with water and completely separate from the main island
- The lifted areas of rocks are known as horsts whereas the valley itself is known as a graben.
What happens at conservative plate boundaries?
Between any crust, the parallel moves in different directions or at different speeds. No plates are destroyed so no landforms are created. When these plates move, a lot of pressure is built up. On an oceanic crust, this movement can displace a lot of water. On continental crust, fault lines can occur where the ground is cracked by the movement.
What are young fold mountains?
Large mountain ranges where the layers of rock within them have been crumpled as they have been forced together. They can be formed at destructive or collisional plate boundaries, where tectonic plates are moving together forcing layers of rock to be crumpled upwards.
What are rift valleys?
Occur at constructive margins in continental areas. The heating and up-doming of the crust leads to fracturing and rifting. As the sides of the rift move apart, central sections drop down to form rift valleys. Active volcanoes are surface evidence of volcanic activity beneath the rift valley.
What are ocean ridges?
Long ridges of mountains created by 2 plates moving apart at a constructive plate margin. The rising convection currents in the asthenosphere push up the crust and cause rifting or cracking. This forces the two plates to diverge creating a central rift. New crust is created as the plates diverge because magma rises to the surface along this fissure from the asthenosphere. The lava which erupts is low viscosity basaltic lava so creates gentle sided shield volcanoes as it can flow a long way before it cools. Occasionally the submarine volcanoes may grow above sea level to form volcanic islands. Iceland is the largest example on the Mid-Atlantic Ridge.
What are deep sea trenches?
Deep water areas that run along a coastline which has a destructive plate margin. They are created by subduction, and mark the point where the Oceanic crust is being pushed under the Oceanic crust. There is often quite a large section of continental crust between this margin and the ocean’s edge, and sometimes a volcanic island arc such as Japan or the Aleutian Islands can be found in between the trench and the continental shelf.
What are island arcs?
Where two oceanic plates converge the denser crust subducts the other. This creates a trench. As the oceanic plate descends it melts, and the magma rises forming a volcanic island chain, known as an island arc.
What is ridge push?
Ridge push - the slope created when plates move apart has gravity acting upon it as it is at a higher elevation. Gravity pushes the plates further away, widening the gap. As this movement is influenced by gravity, it is known as gravitational sliding.
What is slab pull?
Slab pull - when a plate subducts, the plate sinking into the mantle pulls the rest of the plate with it, causing further subduction.
What are hotspots?
Hotspots are areas of volcanic activity that are not related to plate boundaries. Hot magma plumes from the mantle rise and burn through weaker parts of the crust. This can create volcanoes and islands. The plume stays in the same place but the plates continue to move, which sometimes causes a chain of islands (Hawaii).
What is a volcanic hazard?
Volcanoes occur on plate boundaries where plates melt and magma erupts through a plate, or on a hotspot. A volcanic hazard is any volcanic activity or process that poses a threat to human life, livelihoods, and infrastructure. Most of these hazards are harmful and destructive to the surrounding area of a volcano, but some are long reaching and can affect distant places.
What hazards are associated with volcanoes?
- lava flows
- lahars
- glacial floods
- tephra
- acid rain
- pyroclastic flows (nuees ardentes)
What are lava flows?
lava can flow quickly or slowly depending on its viscosity. Silica makes lava viscous and slow, which is common in explosive eruptions.
What are lahars?
mudflows usually caused by melting ice at high latitudes.
What are lahars?
mudflows usually caused by melting ice at high latitudes.
What are glacial floods?
when temperatures are high from magma, glaciers or ice sheets at high temperatures quickly melt and a large amount of water is discharged.
What is tephra?
any type of rock that is ejected by a volcano
What are toxic gasses?
Released during some eruptions, gases like C02 can be toxic as they are heavier than oxygen so suffocate people
What is acid rain caused by a volcano?
caused when gases such as sulphur dioxide are released into the atmosphere.
What are pyroclastic flows?
clouds of burning hot ash and gas that collapses down a volcano at high speeds.
What is the spatial distribution of volcanoes?
Along constructive or destructive plate boundaries, or on hotspots. The ring of fire is an area of high volcanic activity and earthquake activity located in the pacific, and the majority of large volcanoes occur within this 25,000 mile belt.
How is the magnitude of eruptions measured?
Vulcanicity is measured using the Volcanic Explosivity index (VEI). The more powerful, the more explosive. The scale is logarithmic from VEI 2 onwards. Multiple features are considered when calculating the VEI, including how much tephra is erupted, how long it lasts, how high the tephra is ejected, etc. Intense high magnitude eruptions are explosive whereas calmer, lower magnitude eruptions are effusive.
How is the magnitude of eruptions measured?
Vulcanicity is measured using the Volcanic Explosivity index (VEI). The more powerful, the more explosive. The scale is logarithmic from VEI 2 onwards. Multiple features are considered when calculating the VEI, including how much tephra is erupted, how long it lasts, how high the tephra is ejected, etc. Intense high magnitude eruptions are explosive whereas calmer, lower magnitude eruptions are effusive.
How is the frequency of volcanoes classed?
Frequency of eruptions varies per volcano. Volcanoes are either classed as active, dormant, or extinct. 50-60 volcanoes erupt each month, meaning volcanic eruptions are always frequent. Usually, a higher frequency eruption means that the eruptions are effusive whereas low frequency means the eruptions are explosive.
How predictable are volcanoes?
Regularity of eruptions can help estimate when eruptions take place. Seismic activity, gases releasing, elevation etc. can all all indicate an imminent eruption, but there are no definite predictions to a volcanic eruption.
What are the primary impacts of volcanic eruptions?
Social
- People killed
- Homes destroyed from lava and pyroclastic flows
Economic
- Businesses and industries destroyed or disrupted
Environmental
- Ecosystems damaged through various volcanic hazards
- Wildlife killed
Political
- Government building and other important areas destroyed or disrupted
What are the secondary impacts of volcanoes?
Social
- Fires can start which puts lives at risk
- Mudflows or floods
- Trauma
- homelessness
Economic
- Jobs lost
- Profit from tourism industry
Environmental
- Water acidified by acid rain
- Volcanic gases contribute to greenhouse effect
Political
- Conflicts concerning government response, food shortages, insurance, etc.
How do people respond to hazards?
prevention, preparedness, mitigation, adaptation
How can volcanic hazards be prevented?
Volcanic eruptions cannot be prevented. Only the risk to people can be prevented by not allowing people near volcanic hazards.
How can volcanic hazards be prepared for?
Monitoring increases the notice of volcanic eruptions, meaning warnings can be given out.
Education on volcanoes in areas of risk so people know what to do if there is an eruption.
Evacuation procedures planned.
Training response teams.
How can volcanic hazards be mitigated against?
Direct intervention to the volcano (concrete blocks to steer lava away from at risk areas)
Strengthening buildings that are at risk of mudflows or ash pileup.
Evacuation and exclusion zones.
Mitigating effects on health by having emergency aid and rescue.
How can volcanic hazards be adapted to?
Move away from areas at risk.
Capitalise on opportunities, such as encouraging tourism.
Change profession so it is less likely to be affected by volcanic hazards.
When was the Nyiragongo 2021 eruption?
22 May 2021
What were the primary impacts of the 2021 eruption?
- At least 32 people died
- An estimated 450,000 were displaced or evacuated
- 17 nearby villages were badly affected by the fast flowing lava
- Hundreds of homes, a school and three health-care centres were destroyed
- A lot of the people who lived in the suburbs were farmers - they lost their homes and only source of income in one night
