Hazards Flashcards
Pyrophytic vegetation
Plants adapted to tolerate fire by having thick bark, high moistured soil content and underground storage structure
Retardants
Chemicals sprayed on to fires to slow them down
Reasons why wilfidres are getting worse
- Megafires being on the rise
- Result of western lifestyle
- Fire season getting 40-80 days longer each year
- 60% of all new housing in America built in the middle of forests
- ‘The Big Burn’ of 1910 in America shaping attitudes to wildfires
What is viscosity?
A measure of fluid’s resistance to flow
What is silica?
A natural sticky compound that determines how easily magma flows
- Magma with a high silica content is more viscous
Shield volcano characteristics
- Low viscosity
- Low silica content
- Flows quite far
- Typically formed at constructive margins or sometimes hot spots
- Effusive eruptions
- Low with gently sloping sides
Composite volcano characteristics
- High viscosity
- High silica content
- Flow not very far (hardens)
- Typically formed at destructive margins
- Steep sided cones formed from layers of ash and acidic lava
- Can rise over 8000 feet
- Explosive eruptions
Lava types
Balsatic, Andesitic, Rhyolitic
Balsatic lava
Low silica content and low viscosity so relatively fluid
Non explosive eruptions
Flow over long distances
Shield volcano
Andesitic lava
Intermediate content of silica and intermediate viscosity
Destructive eruptions
Rhyolitic
High silica content and high viscosity (sticky)
Less frequent, violent eruptions (highly explosive)
Slow flowing
Hazard management cycle
A disaster/risk managment cyclewhich illustrates ongoing processes that governoment, society and businesses plan for to reduce impacts
Hazard management cycle processes
- Preparation
- Event
- Response
- Recovery
- Mitigation
Preparation (HMC)
Focuses on ensuring emergency services and anyone at risk are aware of how to react in case of an event
- Community education
- Resilience building
Response (HMC)
After event, it is to deal with the immediate needs of population to protect life and property
- Emergency shelters
- Food and water
- Aid
Recovery (HMC)
Long term responses to an event such as the reconstruction of infrastructure and rehabilitating the injured
- City authorities focusing on rebuilding and cleaning up the affected area (may takes months or years)
Mitigation (HMC)
Acting the reduce the scale of next disaster in terms of impacts
- Rebuilding in a new, efficient method
- Reviewing and amending aspect of preparedness in light of sucessions of responses in previous hazard
Destructive plate boundaries
Occur when two lithosphere plates move towards one another with the nature of boundary depending on plates
- Continental and continental
- Oceanic and continental
- Oceanic and oceanic
Continental and continental destructive
- Two low density plates converging causing no subduction
- The increased build up of pressure can result in an earthquake
- When crust collides it folds forwards and upwards forming young fold mountains
The Himalayas
Oceanic and continental destructive
- The denser oceanic plate crust subducts under less dense crust to form a deep sea trench running parallel to boundary
- This causes accumulation of sediment at continental crust, folding upwards
- Plates may get stuck and so released pressure may cause an earthquake
- Subducted crust heated by friction and contact to upper mantle and so melts into magna which rising to the surface forming volcanoes
Marianas Trench
Oceanic and oceanic destructive
- Denser plate subducted and deep sea trenches may form as a result triggering earthquakes
- Along plate which hasn’t been subducted the magna from melted crust will rise and break through surface forming a chain of volcanoes known as island arcs
Guam Volcanic Islands
Formation of young fold mountains
Converging continental plates
-Two plates collide and so rock and debris compress and are forced upwards into rocky outcrops, hills and mountains.
- Rock at edge of crust typically weaker so more susceptible to folding that takes millions of years
The Alps, Europe
Formation of deep sea trenches
- Denser oceanic plate subducts under less dense crust
- Volcanic arcs may also form parallel to trench as some molten material may rise through near volcanoes
Peru-Chile Trench
Formation of island arcs
- Oceanic plate subducted benearth less dense oceanic plate
- Subducted lithosphere melts as it is pulled further into mantle and so molten material rises into crust to form a series of volcanoes
- Volcanoes form into chains of islands parallel to subducting slab
Mariana Islands
Ridge push
- Ocean ridges form high above the ocean floor at a constructive margin
- Hot magma melts to form molten magma which rises as plates move apart and cools to form a newer oceanic lithosphere
- As it gelts older and move denser it thickens and slides away from ridge down the sloping, semi molten asthenosphere
- Newer part of plate pushed in front due to gravity
Slab pull
- At destructive margins, the denser oceanic lithosphere is subducted under underlying mantle due to downward gravitational force
- This pulls the slabs of plate apart causing sea floor to spread/ rifts to form
Convection currents
- Heat is transferred from the core to the mantle where it is heated and rises
- When it reaches crust it is forced sideways as often, it cannot pass through friction between current and crust
- Causes the tectonic plates to move sinking and cooling liquid rock to core
- repeated the process
Theory of convection currents
As lithosphere plates are massive and require huge forces to move, convection currents were thought as a conveyer belt to drive plate movement
- The theory was discounted as most of mantle isn’t fluid and so is now believed to only play a supporting role
The Park Model
A disaster/response curve plotting quality of life after a disaster against the time of occurence, devised in 1991
Relief (TPM)
Medical attention, rescue services and overall care delievered lasting from a few hours to several days depending on scale of event.
- From this point quality of life begins to slowly increase
Rehabilitation (TPM)
People attempt to return to normality by providing food, water and shelter for those most affected lasting from days to weeks
Reconstruction (TPM)
Infrastructure and property repaired or rebuilt and crops are regrown as people use event experience to learn how to better respond to a next one lasting from weeks to many years
Tropical stoms characteristics
Low pressure systems over tropical or subtropical waters with organisied convections and winds at low levels, usually 200-700km in diameter
Formation of a tropical storm necessities
- Ocean temperatures above 27°C
- Ocean depth of at least 70m providing moisture and latent heat
- Location beyond 5° north and south of the equator where coriolis effect is at greatest
- Low level convergence of air
- Rapid outflow of air in upper atmosphere
Dreggs model
Demonstration of how a hazard can only be a disaster if vulnerable people are at risk
Disaster definition
Realisation of hazard to cause social and economic impacts
Vulnerability definition
High risk combined with inability for a place or individual to cope
Hazard definition
Events that are percieved to be a threat to people, the built environment and the natural environment
Distribution of volcanoes
Volcanoes are distributed along plate margins (constructive,destructive,convservative) however can also form at hot spots away from plate boundaries
Magnitude and frequency of volcanoes
Measurement of volcanoes used by Volcanic Explositivity Index (VEI)
Volcanic Explositivity Index (VEI)
Logarithmic scale measuring explositivty of volcanic eruptions by:
-Volume of ejected material
-Height of material thrown into atmosphere
-Duration of eruptions
Determining frequency of volcanic eruptions
Volcanologists interpret previous history using deposits associated to volcano and those within region it may effect
Constructive plate boundaries
- Two plates moving apart and the new lithosphere is created by molten magma rising through crust surface
- Plates moving at different speeds can build up pressure which when released produces a fault line causing an earthquake
Formation of ocean ridges
Constructive plate boundaries
- Plates move apart reducing pressure beneath them allowing upper mantle to melt forming magma which rises and erupts on sea floor
- Magma cools on surface forming new oceanic crust
Mid-Atlantic ridge
Formation of rift valleys
Constructive plate boundaries
- Lithosphere move apart causing it to fracture
- Land between faults collapse into deep wide valleys separated by upright land called hursts
- Volcanoes may be located around here
East African rift valley
East African rift valley
4000km from Mozambique to the Red Sea
Conservative plate boundaries
- Two plates slide past each other
- Crustal rocks are not being created or destroyed so volcanoes do not form however friction may be caused if plates get stuck building up pressure which may be released as shallow focus earthquakes
San Andreas Fault
San Andreas Fault
Conservative plate boundaries
- North American and Pacific plates moving north west
- 750 miles through California
Earth’s structure
Crust
Inner Core
Outer core
Mantle
Crust
15-20km thick - continental
5km thick - oceanic
relatively thin lithosphere layer
Inner core
1250 thick
solid
80% iron, 20% nickel
centre of the earth
Outer core
2200km thick
liquid molten rock
80% iron, 20% nickel
Mantle
Largest layer of earth
2886 km thick
semi molten liquid known as magma
upper part is asthenosphere
Lithosphere
- On top of asthenosphere
- 90km thick
- Composed of solid upper part of mantle and the crust
- Made up of continental and oceanic plates
Asthenosphere
- Heat from core keeps it malleable
- Generates convection currents
- Semi molten
Continental crust
30-70km thick
over 1500 million years old
density of 2.6
composition of granite, silicon, alumunium and oxygen
Oceanic crust
6-10km thick
less than 200 million years old
density of 3.0
composition of balsatic, silicon, magnesium and oxygen
Plate tectonic theory
Hypothesis that the earth’s external shell is separated into a few plates that float over the mantle developed in the 1960’s however emerged from Alfred Wegener in 1912
- It suggests that one giant continent existed about 300 million years ago (pangea) yet have drifted apart since then through ‘continental drift’
Evidence of the Plate Tectonic theory
Geological evidence
- ‘Jigsaw fit’ of South America and Africa
- SImiliar geology strata in northern Scotland and Canada
Biological evidence
- Fossil remains of reptile mesosaurus found in both South America and southern Africa
- Identical plant fossils found in coal deposits of India and Antartica
Crustal evolution
- Oldest rocks around 4 billion years old
- Plate movement developed around 750 million years ago
lithosphere made up of crust and rigid mantle dividing into seven large continents and oceanic plates
Paleomagnetism
The alternating polarisation of new land created. As magma cools, the magnetic elements within will align with the Earth’s magnetic field, which can alternate over thousands of years.
Evidence of paleomagnetism
Mid Atlantic RIdge
Record of the history of Earth’s magnetic field
- Polarity of rock either side of ridge alternated in striped pattern
- Oceanic crust slowly move away from plate boundary
- Oceanic crust got older with distance from mid oceanic ridge (200 million years)
Different types of hazards
Geophysical
Hydrological
Atmospheric
Geophysical hazards
- Caused by earthly processes
Can be internal processes by tectonic activity
Can be external process of geomorphological origins involving mass movement
Landslides, earthquakes, tsunamis
Hydrological hazards
- Caused by occurrence, movement and distribution of surface and underground water
Flooding
Atmospheric hazards
- Processes operating in the atmosphere resulting in extreme weather
Tropical storms, droughts, wildfires
Common nature of hazards
- Clear origins and effects produced are distinctive
- Short/no warning
- Involuntary exposure to risk causing loss to life
- Emergency response
Reasons people live in areas of risk
Unpredictability, lack of alternatives, changing level of risk, cost benefit
Impacts of perceptions to living in vulnerable areas
- Level of education
- Socio economic status
- Past experience
- Religion, culture, ethnicity
- Personality and values
- Occupation status
Views and interpretations of hazards
Fatalism
Adaptation
Domination
Fatalism
Optimisitc approach accepting that hazards are apart of life or ‘Acts of God’ which are inevitable
Adaptation
Attempting to live with natural hazards by adjusting life style choices to reduce impacts
Domination
Using scientific research and past events to better understand and predict a natural hazard
Mantle plumes theory
In 1970, a theory was composed to explain the presence of volcanic activity away from the plate boundaries by John Tuzo-Wilson
Example of mantle plumes
Hawaiian islands
- Hot spot active for around 70 million years created a 6000km long chain of volcanic islands in north west Pacific ocean
- Youngest is Hawaii of 0.7 million years old
Formation of a mantgle plume
- Heating at the mantle causes a plume of magma to rise through surface crust above hot spot melting lithosphere
- Where lava broke through active volcanoes have formed and hot spot remains fairly stationary
- Tectonic plates move away from hot spot inside athenosphere carrying volcanoes away
- This movement causes volcanoes to become extinct and so new island will form in its place forming another plume
- Creates a chain of islands with oldest volcano being furthest from plume and youngest being directly over it
Volcanic hazards
Pyroclastic flows (nuees ardentes)
Tephra
Lava flows
Volcanic gases
Lahars (volcanic mudflows)
Flooding
Tsunamis
Acid rain
Climate change
Pyroclastic flows (nuees ardentes)
Primary hazard
- Mixture of hot rock fragments, lava particles, ash and hot gases in a turbulent fast moving cloud which hugs the ground.
- Associated with andesitic and rhyolitic volcanic eruptions
- Move up to speeds of 700km per hour extending 40km with temperatures varying from 100°c to 700°c
Mount Pelee May 8th 1902- 190km per hour
Tephra
Primary hazard
- Solid material ejected by volcano into the air varying from fine ash to volcanic bombs
- Larger tephra particles the less further they travel and so less damage to people
- Ash fallout can cause exposure to respiratory systems causing emphysema or asthma etc
- Damage agricultural land destroying crops and closing airspaces
Eyjafjallajokull 2010 - cancellation of 100,000 flights
Lava flows
Primary hazard
- Molten rock erupting onto rock’s surface
- Different volcanoes producing different types varying in temperature and silica content
- Rarely injure people due to relatively low velocity yet can be unstoppable damaging crops and buildings
Andesitc/rhyolitic/balsatic
Volcanic gases
Primary hazard
- CO2, carbon monoxide, sulphur dioxide, hydrogen sulphide can cause breathing problems and exposure to high levels of health risks
Lake in Crator of Nyos emitted a lot of co2 killing 1700 people
Lahars (volcanic mudflows)
Secondary hazard
- Mixture of water and rock fragments from unconsolidated ash flowing down river valleys or volcano in form of a hot, dense, fast moving mudflow
- Speeds of around 50km per hour
- May be water from rain or melting snow and ice
Nevada del Ruiz, Colombia 1985- 22000 killed with speeds up to 45km
Flooding
Secondary hazard
- Hot ash or lava from eruption melting snow and ice which can cause dangerous flooding
- Can travel up to 50 miles away from volcano
Iceland 1996- Grimsvotn eruption
Tsunamis
Secondary hazard
- Large sea waves generated by violent volcanic eruptions displacing large volumes of water due to size, speed and extensive reach
- Very destructive to properties and life
Krakatoa 1883- 35 metre high waves killed 36000 people
Acid rain
Secondary hazard
- Volcanic eruptions release slow moving molten lava and toxic gas into air, this combined to atmospheric moisture results in acid rain
- Can cause respiratory problems and rusts metal objects like cars
Hawaii led to lost crops and temporary relocating
Climate change
Secondary hazard
- Particles from eruptions can cool planet by shading solar radiation
- Also cause global warming due to release of greenhouse gases in eruption
What is a volcano
An opening in the Earth’s crust where magma, rock fragments and dissolved gases from inside planet erupts onto surface
Active volcano
Historically active volcano that has erupted in the last 10,000 years
- holocene period
Dormant volcano
An active volcano that hasn’t erupted for an extended period of time yet expected to
- no time period
Extinct volcano
No longer active and hasn’t erupted in historical times
Example of a shield volcano
Mount Kilauea
Example of a composite (strato) volcano
Mount Fuji
Causes of wildfires
Ignition source
Fuel
Ignition sources
- Lightning is the main course of natural fires, with the climate affecting frequency of electrical storms
- Falling power lines
- Discarded cigarettes and barbeques
- Arsonists, specifically known around Brazil and Australia
Fuel sources
- Sufficient quantity of dry fuel
- Climate affecting frequency and duration of droughts
- Types of plants that grow
- Rate of plant litter produced
Distribution of wildfires
Most susceptible- Mediterranean and tropical wet seasons/ dry seasons of savanna climates
Mediterranean- Australia, California, Southern Europe
Savanna- Northern Australia, north eastern India, tropical regions of Africa and South America
Impacts of wildfires
Primary:
Loss of crops, timber and livestock
Loss of life
Loss of property
Loss of wildlife
Release of toxic gases
Damage to soil structure
Secondary:
Evacuation
Flood risk
Preparedness of wildfires
Education-
- Department of Homeland Security in California has warning and educational systems for residents in case of an event.
- ‘Smokey the Bear’ is an American campaign of the US forest service in WIldfire Prevention Service on the human dangers causing fires
- Computer modelling to understand and predict fire behaviour
Mitigation of wildfires
- The Colorado State Forest Service encourage creation of ‘fire adapted communities’ to increase fire resilience, providing advice on how to reduce and prevent damage through rise resistant landscaping and fire protection measures in homes
Prevention of wildfires
- Awareness on discarded cigarettes, barbeques and arson
- ‘Smokey the Bear’ controlled burning to create firebreaks
- Land use planning ensuring houses are built 30m from forests
- Spray water of roofs to prevent them catching on fire
- Retardents uses during wilfdires to further prevent it
Adaptation of wildfires
- Using technology such as satellites, infrared sensors and lightning detection
- Training citizens as auxillary firefighters to know first safety steps
- Centre for Climate and Energy Solutions cost USA $24 billion in 2018 to put measures in place to adapt hazard
Measuring tropical storms
Saffir- Simpson scale
- five point scale
- based soley on wind speed
Impacts of climate change
- Increase in ocean temperatures causing air temperature above warmer water to increase leading to an enhanced uplift and local lowering of atmospheric pressure
- Increase in ocean evaporation and a corresponding increase in atmospheric water vapour content
Predictions for 2100 by climate change
2-11% increase in average intensity of storms
6-34% decrease in total number of storms
Substantial rise in frequency of intense storms
Impacts of tropical storms
- Intensity of storm
- Distance from sea
- Preparations
- Speed of movement
- Warnings and response
- Winds
- Heavy rainfall
- Physical geography
- Storm surges
Impacts of tropical storms
- winds
Often exceed 150km/hr causing structural damage to tall buildings and roads, bridges
Able to bring down electricity transmission lines and devastate agricultural areas
Huge debris flung around are huge threats
Impacts of tropical storms
- heavy rainfall
May exceed to 200-300mm causing severe floods, landslides and mudslides
Rainfall may rise to 500mm/day in a high relief coastal area
Impacts of tropical storms
- storm surges
Lower atmospheric pressure may cause oceans to heave up and wind-driven waves to pile up leading to high sea levels
Can cause majority of deaths especially on low lying coastal areas like river deltas
Also damage agricultural areas by sea water contamination
Preparedness of tropical storms
- National Hurricane Centre (Florida, USA) forecast tropical storms in the Atlantic and Eastern Pacific basins in North America
- USA use satellites to track intensity, size and structure across 280 miles of coast
- Land based radar monitoring precipitation and wind velocity controlled by the Tropical Analysis and Forecast Branch (TAFB)
- ‘Project Safeside’ in Florida, Hurricane drills
- Correct warnings, costs $2.3m to evacuate per km in Georgia
Mitigation of tropical storms
- USA’s Federal Emergency Management Agency (FEMA) has handbooks on how to reduce damage to infrastructure. Also has a factsheet for homeowners on how people protect their homes from floods and wind damage
- Bangladesh built cyclone shelters on stilts with reinforced concrete and storm shutters which residents can use in event
Adaptation of tropical storms
- Land use planning to identify areas at greatest risk and limit development
- Building sea walls, breakwaters and flood barries (Bangladesh cyclone shelters)
- Retrofitting structures to be resistant to events (Dominica retrofitting buildings by Organisation of the America states and government of Dominica to withstand Hurricane Marilyn)
Prevention of tropical storms
- Cannot be prevented
- Unsuccessful attempts over last 80 years include cooling oceans with icebergs to reduce evaporation
- Seeding clouds with dry ice so storms lose waters and has less latent energy
- Blowing black soot into storm to change radiation balance
- Use hydrogen bombs to explode storm away
- Blow storm away using giant fans
Management of natural hazards
- Intergrated risk management
- Mitigation
- Prediction
- Protection
- Prevention
Management of natural hazards
- intergrated risk management
More than one organisations working together to deliever an effective response to a hazard by sharing knowledge and human response strategies
Management of natural hazards
- mitigation
Actions taken to reduce or eliminate any long term risks to human life and property from natural hazards, this can be before, during or after an event
Management of natural hazards
- prediction
Giving warnings to improve menitoring of a hazard. The ability to know when and where a hazard strikes on a spatial and temporal scale
Management of natural hazards
- protection
Aim to protect people, their possessions and the built environment from impacts of an event- such as modifications to infrastructure. Another way to protect loss can be through insurance and international aid
Management of natural hazards
- prevention
Actions taken to avoid a natural hazard from having any harmful effects on people and economy. Not very realistic for natural hazards
