Hazards (Mostly Volcanic) Flashcards
What are five things that Natural Hazards have in common?
- No Warning
- Involuntary exposure in LICs
- Clear Origins
- Losses shortly afterwards
- Emergency response
What three ways do people perceive natural hazards?
- Fatalism
- Adaption
- Fear
What are the four parts of the disaster management cycle?
- Mitigation
- Response
- Recovery
- Preparedness
Give two strengths and two weaknesses of the disaster management cycle?
Strengths
- Evaluate Response
- Not place specific
Weaknesses
- No data
- Ignores Individuals
What evidence supports Seafloor Spreading?
The mirrored magnetism on either side of an ocean ridge.
What theory did Alfred Wegener suggest?
Continental Drift (Pangea - all, Laurasia- North, Gandwanaland - South)
Give three features of a hotspot.
- Stationary
- Thin Crust
- High heat flow (magma plume)
What are the six parts of the risk disc model?
- Disaster response
- Disaster recovery
- Mitigation
- Adaption to climate change
- Disaster preparedness
- Development
What is the lithosphere?
Rigid part of the mantle. Crust
What is the asthenosphere?
Semi-molten part of mantle.
How do constructive/ divergent plates move?
Apart.
How do destructive/convergent plates move?
Towards each other.
How do conservative plates move?
Side by side.
For each plate boundary are there: Earthquakes, Volcanoes or both?
Constructive: Both
Destructive: Both
Conservative: Earthquakes
What are the three types of destructive plate boundary?
- Oceanic/ Oceanic
- Oceanic/ Continental
- Continental/ Continental
What landforms are found at Destructive plate boundaries?
Ocean trench : Oceanic/ Oceanic
Fold Mountain : all types possible
Island Arcs: Oceanic/ Oceanic
What landforms are found at Constructive plate boundaries?
Ocean Ridge: Oceanic/ Oceanic
Rift Valley: Continental/ Continental
What is a natural hazard?
Events that are seen as a threat to people and the built environment. Occur in the lithosphere, atmosphere and hydrosphere.
What is meant by fatalism in the context of hazards?
Cannot influence shape of outcome, nothing can be done.
Why is perception important in the context of hazards?
It will decide the course of action or the response from governments or organisations
Why do people consciously put themselves at risk from natural hazards?
- Lack of alternatives
- Changing level of risk
- Cost/ benefit
- Perception
- Unpredictable
What factors influence people’s perception of natural hazards?
- Socio-economic status
- level of education
- occupation
- religion, culture
- Family status
- past experience
- personality
What is community preparedness/ risk sharing?
Prearranged measures to reduce loss of life.
The distribution of a hazard through time is called….
Frequency
The assessment of the size and impacts of a hazard event is known as the…
Magnitude
What is meant by the term resilience?
Ability to utilize resources to respond and recover.
What is a primary hazard event?
Directly related to the hazard event e.g. lava flows & ash
What is a secondary hazard event?
Occur due to the occurance of a primary hazard
What are the differents layers of the Earth’s structure?
Inner core, Outer core, Mantle, crust
What are the two different layers of the mantle?
Lithosphere, Asthenosphere
What are the two layers of the crust?
Oceanic & Continental
How was the Earth formed?
- Accretion
- Gravitational compressions, radioactive decay
- Heavier metal sinking, lighter rising
- Temperature rise above 2000 C and layers formed as it cooled
What evidence did Alfred Wegener use to support his theory?
Geological evidence (glacial striations, rock sequences, continents fit together) Biological evidence (fossil evidence- brachiopods, fossil remains of plants, mesosaurus in S America and S Africa)
What did Frederick Vine & Drummond Matthew add to the theory of continental drift?
Sea floor spreading. Supported by the evidence of mirrored magnetism on either side of an ocean ridge.
What did John Tuzo Wilson add to the theory of continental drift?
The theory that plates move over fixed ‘hotspots’ in the mantle.
What are two reasons that the Earth’s core is so hot?
- Primordial heat
- Radiogenic heat (radioactive decay)
What is a mid-ocean ridge?
Undersea line of volcanoes forming at constructive plate boundaries.
What is a rift valley?
Deep valley with steep sides, forming at constructive plate boundaries, caused by sinking land between fault lines e.g. African Rift Valley. Continental/continental.
What is an ocean trench?
Deep valley where an oceanic plate is subducted at a destructive plate boundary, causing downwarping. E.g. Marianas trench
What is an island arc?
Volcanoes form on the oceanic plate, not subducting. E.g. Mariana islands.
What are fold mountains?
Crumpling and uplifting of the less dense plate at destructive plate boundaries. E.g. Himalayas
What is the Benioff zone?
Area of high friction and heat between subducting and non-subducting. This melts the subducting plate and causes earthquakes.
What is a tectonic plate?
Part of lithosphere moving on top of the asthenosphere.
What is a hotspot?
A small stationary area of the Earth’s crust with high heat flow due to a rising magma plume
What is a magma plume?
A stationary area of high heat flow, that is formed due to intense radioactivity.
What is a seamount?
A seamount is an eroded extinct volcano that has sunk under the water due to erosion and subsidence.
Three types of hazard?
- Geographical
- Atmosphere
- Hydrological
Vulnerability in context of hazards
How susceptible the area is to damage and potential for loss
Risk in context of hazards
Likelihood of harm
Multi hazard environment
Place at risk of two or more different hazards that may interact
Adaption in context of hazards
Living with hazards, by adjusting their living conditions
Mitigation
Lessen severity of hazards
Fatalism
Nothing can be done. Limited or no prevention measures against the hazard.
Socio-economic status
Wealth determines how much control they have over the hazard damage & risk. Wealthy areas are more protected in ways poorer areas can’t afford.
Level of education
If people are uneducated on hazards they aren’t aware of the risk or believe that they are unable to reduce risk.
Religion
They believe that their god will deal with the hazard and therefore don’t mitigate.
Past Experience
They are more prepared and feel like they know how to handle it as they expect it to be similar to past experience. May have a ‘lightning never strikes twice’ approach.
Community Preparedness/ Risk Sharing
Prearranged collective methods to reduce loss of life.
Integrated Risk Management
Social/ political/ economic factors of risk analysis. Decides acceptability of damage. Decides plan to minimise damage.
The park model shows changes of ______ over time?
Quality of life
Five stages of the Park Model
- Pre disaster
- Disruption
- Relief
- Reconstruction
- Rehabilitation
What does the Park Model tell us about a country’s disaster response?
Depth of curve- intensity of impacts
Steepness of upward curve - They were well prepared and immediate response was successful
Steepness of downward curve - Type of hazard (rapid or slow onset)
Positive and negatives of Park Model
+
- Compares effectiveness of recovery between events
- Predict resources
- Plan for future
- No spacial variation
- No quantitative data
- Only single event on single area
- Doesn’t show pre-onset mitigation
Rehabilitation stage of park model
Solve longer term problems after immediate impacts are controlled
Ability of individuals to withstand and recover from a disaster is known as…
Resilience
Methods of prediction
- Scientific Research
- Tsunami Warning System
- National Hurricane Centre (Florida)
Factors that are needed to make prediction an effective management technique
- Information must be accurate
- Must be trustworthy
- Information must be distributed
Three ways people and organisations manage natural hazards
- Prediction
- Protection
- Prevention
Differences between oceanic and continental crust
Oceanic
- More dense
- Thinner (6-10 km thick)
- Younger (less than 200 million years)
- Basalt & SIMA
Continental
- Less dense
- Thicker (30-70 km thick)
- Older (over 1500 million years)
- Granite, SIAL
Describe each layer of the earth
Inner core
- Iron & nickel
- Solid
- Over 6000 C
Outer core
- Iron & nickel
- Liquid
- 4000-5000 C
Mantle
- SIAL & SIMA
- Semi molten
- 3000 C
Crust
- SIAL & SIMA
- Solid
Process of convection currents in the asthenosphere
- Hot spots in the Earth’s core cause thermal plumes in the asthenosphere
- Hot magma rises as it is less dense and when it reaches the lithosphere, it moves sideways
- This basal drag moves the plates
- The magma cools becoming more dense and sinking
- This is a continuous cycle
Process of gravitational sliding at ocean ridges
- Magma rises to the surface
- This heats the surrounding rocks, creating a slope
- As the new crust cools, gravity moves it, creating a downslope
- There is a lot of pressure on the plates, causing them to move apart
Process of slab pull at ocean trenches
- Destructive oceanic plate subducts
- Dense plate pulled down by gravity
- Pulls the rest of the plate behind it
Formation of ocean ridges
- Plates diverge in oceanic areas
- This creates fissures, which magma escapes through
- Magma fills gaps, erupts onto the surface and cools as new land
Formation of rift valleys
- Plates diverge. Magma rising causes crust to fracture, forming fault lines
- Crust between faults drops down, forming a rift valley
- The crust here is thinner due to tension. Magma forces its way through these areas. These reach the surface to form volcanoes
Formation at oceanic-continental destructive plate boundaries.
- Oceanic plate subducts as it is more dense. Causes downwarping, forming a trench
- Friction at benioff zone causes the subducting plate to melt
- Magma rises through fissures in crust as it is less dense than surrounding asthenosphere. This creates composite volcanoes
- Sediments crumple and uplift to form fold mountains
- Plates can become stuck due to friction. Plates release seismic energy as they slip past each other.
Formation at oceanic-oceanic destructive plate boundaries.
- Denser plate subducted. Forms a deep ocean trench and triggers earthquakes & volcanic eruptions
- Volcanic eruptions take place underwater
- This creates volcanic island arcs
Formation at continental-continental destructive plate boundaries.
- Plates crumple & uplift as they are similar densities. Forms fold mountains
- No volcanoes form as neither subducts. Pressure can cause earthquakes.
Formation at conservative plate boundaries.
- Plates move alongside each other in opposite directions or at different speeds.
- Plates get stuck due to friction & pressure build up
- Plates jerk past each other or crack, forming fault lines. This releases pressure, sending shockwaves through the crust in the form of earthquakes
Three features of a hotspot
- Stationary
- Thin crust
- High heat flow (plume)
Formation of a hotspot
- Intense radioactivity forms magma plume.
- Plume reaches the asthenosphere. High heat & low pressure of plume melt the lithosphere above.
- Lava breaks through, forming active volcanoes
- Plume remains stationary but plate moves, creating chain of volcanoes. Volcano above hotspot is active but the remainder are extinct
- Extinct volcanoes put pressure on crust which causes subsidence and erosion, creating seamounts
Differences between shield & composite volcanoes
Shield
- Wide base & sloping sides
- Frequent & not explosive
- Basaltic lava
Composite
- Steep sides
- Explosive & infrequent
- Andesitic & rhyolitic lava
Examples of hotspots
- Reunion hotspot (deccan traps)
- Hawaii hotspot
What is VEI?
Volcanic Explosivity Index
What does VEI measure?
- Volume of ejecta
- Height of eruption column
- Qualitative observations
Criticisms of VEI
- Doesn’t account for climate change
- Doesn’t account for gas emissions
- Considers all tephra the same
Five ways volcanic eruptions vary
- Magnitude
- Frequency
- Predictability
- Regularity
- Duration
What is a super volcano?
An unusually large volcano with the potential to produce an eruption with major effects on global climate & ecosystems
Tephra
Solid material of varying sizes (primary hazard)
Pyroclastic flows (nuees ardentes)
Super heated, high velocity & density flows of gas and tephra which flows down the side of volcanoes (primary hazard)
Lava flows
Melted down magma that flows down the side of the volcano. Speed depends on temperature, viscosity and steepness. (primary hazard)
Volcanic gases
Carbon Dioxide, Sulphur Dioxide, Hydrogen Sulphide, Carbon Monoxide and Chlorine. (primary hazard)
How does incidence affect level of management?
The more frequently an area experiences a hazard, the more it’s expected so more management is in place. These hazards also tend to be less intense so less large management.
How does intensity affect level of management?
High intensity have worse affects and require more management.
How does distribution affect level of management?
high hazard distribution have less management. Those living in those areas will be more adapted to the hazardous landscape.
How does level of development affect level of management?
LICs are less able to afford management strategies and hazards are therefore more disastrous.
How do multi hazard environments affect level of management?
Lack of money to manage multiple hazards so may lack management.
Prediction in the context of hazards
Using scientific research to forecast when and where hazards will occur and to provide warnings
Protection in the context of hazards
Protect people from the impact of the event by modifications to the built environment
Examples of secondary volcanic hazards
- Lahars
- Flooding
- Volcanic landslides
- Tsunamis
- Acid rain
- Climate change
Sea Floor Spreading
Theory that the ocean floor was created at mid-ocean ridges and has expanded due to volcanic activity. Plates must be destroyed somewhere to accommodate their size increase.
Characteristics of basaltic lava
- 45-55% silica content
- 1050-1200 C
- Low viscosity
- Low gas content
- Shield volcano
- Constructive plate boundaries
- Gentle, effusive explosion
Characteristics of rhyolitic lava
- 65-75% silica content
- 650-800 C
- High viscosity
- High gas content
- Composite volcano
- Destructive plate boundary
- Explosive, infrequent
- Ash, rocks, gases and lava ejected
Characteristics of andesitic lava
- 800-1000 C
- 55-65% silica content
- Medium viscosity
- Medium gas content
- Composite volcano
- Destructive plate boundary
- Explosive, infrequent & short-lived
- Ash, rocks, gases and lava ejected
How are lahars formed?
melted ice & snow or heavy rainfall due to eruption, mixes with volcanic ash and forms mud flows.
How are tsunamis formed?
Waves are generated by violent volcanic eruptions or pyroclastic flows/lahars displacing water. Often leads to much more widespread impacts than the explosion itself.
How is acid rain formed?
The gases emitted by the volcano, such as sulphur, combine with atmospheric moisture.
How does volcanic activity cause climate change?
Huge amounts of volcanic debri into the atmosphere can cause global temperature reduction.
Impact of lahars (with case study)
1985, Nevado Del Ruiz, Colombia. 23,000 people killed Destruction of natural habitats, settlements. Economic benefits of lahar deposits. Can have impacts years into the future.
Impact of tsunamis (with case study)
2018, Anak Krakatua volcano, Indonesia - landslide triggered a tsunami which killed 400 people. Widespread destruction.
Impact of acid rain
- Damages and kills trees
- Leaches toxic metals from soil
- kills fish stock and damages ecosystems
- damages buildings and monuments by accelerating weathering
Impact of climate change
Unusually cold weather. Crop failure and food shortages.
How can the four volcanic hazard warning signs be predicted?
Sulphur/ radon gases: spider robots/ gas trapping bottles
Ground deformation: tiltmeter. gravity changes
Energy release: infrasound. seismometers
Surface temperature changes: thermal heat sensors
Methods of preparedness to reduce volcanic hazard risk
- Hazard mapping: plotting predicted levels of risk. People are less vulnerable as they are removed from high risk areas
- Authorities limit access to hazardous areas and create evacuation routes.
- Preparing emergency kits
- Installing monitoring systems
- Search and rescue teams
- Educate residents on preparation measures
Three things that affect speed of lava flow
- Temperature (Higher temperatures flow further)
- Viscosity (low viscosity flow further)
- Steepness of slope (steeper slopes flow further)
Methods of diverting lava flows
- Creating earth trenches
- Bombing lava tubes
- Use of ice water/ cooling the lava
How might people adapt to the risks of volcanic activity?
- Strengthening buildings to reduce chance of collapse from ash on the roof
- Capitalise on the opportunities of living near volcanoes e.g. farming fertile soils or tourism
Primary impacts of volcanic activity
- People killed and buildings destroyed by pyroclastic flows
- Ash causes damage to agriculture
- Flights suspended by ash
- Death from volcanic gases
Secondary impacts of volcanic activity
- Acid rain acidifies ecosystems
- Volcanic debris reflects sunlight and kills crops from cold winters
- Flash floods from glaciers melting
- Tsunamis due to volcanic landslides displacing water
- Death from lahars
