Hazards revision

Natural hazard

Natural event with potential to cause harm

Natural disaster

Natural event that actually causes harm

Risk

The likelihood of a hazard occurring combined with the potential severity of its impacts

Risk equation

Hazard frequency x vulnerability to a hazard

Vulnerability

Susceptibility of a population to impacts of a hazard

Mitigation

Addresses hazard causes

Hazard adaptation

Long term adjustments to reduce vulnerability to hazards

Factors determining hazard perception

Socio-economic status, education, employment, religion/culture, past experience

Hazard perception

Key factor influencing vulnerability, how a population perceives the threat posed by a hazard

Fatalism (hazard perception)

Acceptance of hazard, no action taken

Adaptation (hazard perception)

Significant action taken, prediction, protection, preparation

Fear (hazard perception)

Leaving the area in fear of a natural hazard

Risk sharing

Distributing the physical/economic burden of a hazard across many parties through insurance, education etc. to reduce individual vulnerability

Integrated risk management

Human response to hazard risk through analysis of interconnected social, economic, and political factors to reduce vulnerability

Hazard management cycle

Illustrates the ongoing process of all levels of society planning for and reducing the impacts of a disaster before, during, and after an event

Hazard management cycle leads to

Reduced vulnerability, better preparedness and warnings

Hazard management cycle main goal

Promotion of sustainable livelihoods and protection and recovery during natural disasters

Hazard management cycle benefits

Reduces vulnerability, promotes a shift from reactive to proactive hazard response, versatile - can be applied to many hazards, promotes community education and resilience, causes continuous improvement through evaluation of past performance

Hazard management cost effectiveness (benefit)

Studies show that money saved from future damages far exceeds money spent on resilience in relation to hazard management cycle

Hazard management limitations

Model heavily favours HICs which can afford all mitigation methods without considering LICs which lack resources and wealth to mitigate with, does not provide specific, realistic timeframes for recovery, implementation can receive public resistance and ignored warnings, argued to be too vague

Park model

Designed to show that hazard events have varying impacts over time in terms of quality of life

Park model benefits

Provides clear graphical representation of how quickly an area deteriorates and recovers to specific events, useful for comparing effectiveness of disaster responses, highlights when specific management strategies should be implemented in the response

Park model limitations

Lacks quantitative data such as death tolls, damage costs, specific magnitude of event, ignores preparation stage (adaptation and mitigation), assumes a linear/straightforward recovery - ignores potential aftershocks etc., provides little guidance to how governments and authorities should manage the disaster response

Core

Made up of solid inner section and molten outer section (5000+C)

Mantle

Thickest layer of Earth’s structure, made up of semi molten and molten rock

Crust

Outermost layer made of either thicker, older continental crust, or thinner, denser, younger oceanic crust

Plate tectonic theory

The lithosphere is able to slide over the asthenosphere allowing for plate movement which is driven by forces that are not yet fully understood

Evidence of plate tectonic theory

Similar glacial/fossil deposits found in different continents across the world

Continental drift theory

The theory that Earth’s continents were once joined into one single supercontinent (Pangaea) and have since drifted apart over geological time due to the plate tectonic theory

Lithosphere

Crust and rigid uppermost layer of mantle - roughly 100km deep - divided into today’s tectonic plates

Convection currents

Cells of heat transfer caused by uneven distribution of temperatures in the mantle that play a supporting role in tectonic plate movement

Ridge push (gravitational sliding)

The sliding away from a constructive boundary ridge caused by gravity of condensed, less young crust

Slab pull

The effect of a subducting oceanic plate pulling exerting a force of slab pull on the rest of the plate

Sea floor spreading

The process where tectonic plates diverge at mid-ocean ridges, allowing magma to rise, cool, and form new oceanic crust

Constructive (divergent) plate boundaries

Where rift valleys and mid ocean ridges are formed as new lithosphere is created as plates move apart

Rift valley

Linear shaped lowland regions formed by tectonic plate divergence where the continental lithosphere stretches, fractures, and sinks between parallel normal faults

Example of rift valley

Great Rift Valley of East Africa

Destructive (convergent) plate boundaries

Where subduction takes place, nature of the boundary depends on the types of tectonic plates involved

Destructive

Plate boundary associated with the most powerful earthquakes

Oceanic and continental plate destructive margin

Where subduction, young fold mountains, and deep sea trenches occur

Subduction

When the denser oceanic crust is forced under the lighter oceanic or continental crust and sinks into the mantle at destructive margins

Young fold mountains

Formed by either sediment accumulating at the edge of the continental plate in a subduction zone and being deformed by folding and faulting and uplifted to form mountains often with active volcanoes, or by sediment being forced up at a destructive margin between 2 continental crusts causing no volcanic activity but shallow focus earthquakes

Andes

Example of young fold mountains

Deep sea trenches

Long, narrow V shaped depressions in the sea floor formed in the subduction zone

Oceanic and oceanic plate destructive margin

Where island arcs and deep sea trenches are formed

Island arcs

Chains of volcanic islands formed by magma upwelling from the Benioff Zone

Continental and continental plate destructive margin (collision boundary)

Where young fold mountains occur. No subduction takes place

Magma plumes

A theory suggesting that localised heating at the core/mantle boundary causes a plume of magma to rise through the mantle and eat into the plate above forming a hotspot where lave breaks through the surface forming active volcanoes forming chains of volcanic islands as the crust above slowly moves

Effusive volcano

Produce gentle, frequent eruptions of low viscosity basaltic lava, common at constructive boundaries and hotspots, typically form shield volcanoes

Distribution of volcanoes

Typically formed at destructive and constructive plate boundaries as well as hotspots such as Hawaii

Explosive volcano

Produce violent, infrequent eruptions of high viscosity andesitic lava and high gas content, common at destructive boundaries, typically form stratovolcanoes

Nature of lava and its viscosity

Main factor in determining the type of volcano and volcanic activity

Tephra

Solid material of varying sizes from ash to volcanic bombs that are ejected into the atmosphere

Less viscous lava

Tends to cause less intense, more frequent eruptions as less gas is able to build up - often forms shield volcanoes with gentle slopes

More viscous lava

Tends to cause more intense, less frequent, but more widespreading eruptions, as huge amounts of gas and hence pressure is able to build up

Pyroclastic flows (nuees ardantes)

Extremely hot (800+C) gas charged, high velocity flows made up of a mixture of gas and tephra that usually hug the sides of volcanoes at up to 700kmh

Lava flows

Virtually unstoppable low velocity flows of lava that rarely injure people due to its speed but severely damage anything in its path unless diverted

Volcanic gases

CO2, carbon monoxide, sulfur dioxide etc.

Lahars (volcanic mudflows)

When unconsolidated ash combines with water and sweeps down river valleys as a hot, dense, fast moving mudflow which is generally caused by heavy rain post eruption - secondary effect of volcanic eruptions

Volcanic flooding

Secondary effect of volcanic eruptions when the eruption causes melting of glaciers/ice caps

Volcanic landslides

Secondary effect of an eruption where great momentum carries huge amounts of rock and soil often across valleys and up slopes

Acid rain

Secondary effect of volcanic eruptions where sulphur emitted combines with atmospheric moisture

Volcanic climate change

Rare secondary effect of the most extreme volcanic eruptions where huge amounts of ash released into the atmosphere block out sunlight and reduce global temperatures - believed to have caused historical climate change

Signs that a volcanic eruption may be imminent

Increased release of various gases, upwards bulging of surrounding land due to pressure from below, increased number of small earthquakes caused by rising magma, rise in the level of lava lakes in volcanic craters

Volcanic hazard mitigation

Risk assessments (before), diverting viscous lava (during)

Earthquakes

A build up of stress between masses of rock that is suddenly released causing a shaking motion

Focus

The specific point in the ground below the epicentre where earthquake pressure is released from

Shallow focus

Causes most dangerous and destructive earthquakes - between 0-70km deep

Moment Magnitude Scale (MMS)

Measures the size of an earthquake in terms of energy released in a logarithmic scale

Human activity

Potential emerging cause of some minor earthquakes caused by building large structures such as reservoirs or mining

Mercalli scale

Measures the intensity of an earthquake event and its impact (I-XII)

Most dangerous and deadly impacts of earthquakes

Primary and secondary factors such as roof collapse, tsunamis and landslides rather than the ground shaking/earthquake itself

Soil liquefaction

When soils with high water content lose their mechanical strength after ground shaking and start to behave like a fluid, can lead to mudflows and sinking of buildings/infrastructure - secondary effect of earthquakes

Pacific Basin

Where around 90% of tsunamis are generated, typically at destructive plate boundaries where subduction occurs, disrupting the sea bed

Preparedness for an earthquake

Storing items at a low level, establishing emergency plans, ensuring buildings are structurally sound, specialised earthquake insurance

Seismic hazards mitigation

Early warning systems before shockwaves radiate out from the focus, earthquake resistant buildings, tsunami protection

Earthquake resistant buildings

Achieved through rubber shock absorbers on foundations, adding cross bracing to buildings, retrofitting, or putting a large concrete weight on top to counteract stress using computer assistance

Tsunami protection

Pressure sensors attached to buoys which can give early warnings of intensity and direction of tsunamis, prevention walls of up to 12m high have been proven ineffective against severe tsunamis that smash through them

Adaptation to seismic hazards

Land use/planning regulations in areas most at risk, putting key buildings such as hospitals in low risk open spaces, including open spaces in design plans to escape from falling debris, emergency services equipped with heavy loading gear and first responder trained for trapped individuals

Where tropical storms are formed

5-20 degrees north or south of the Equator over seas of 27C+ and 70m+ deep where the coriolis force can act on converging winds to create accelerating air spirals around a depression of low pressure

Westwards

The direction that tropical storms tend to travel in the vast majority of the time due to prevailing winds

Saffir Simpson scale

The scale measuring the category of tropical storms based purely on wind speed (suggested to be changed as 90% of USA tropical storm deaths in recent years were not the result of wind, instead water - storm surges, flooding etc.)

Impacts of climate change on tropical storms

Causing them to decrease in overall frequency but significantly increase the frequency of the most intense events due to increased ocean temperatures, causing them to last longer on average, causing them to move slower on average due to warming of polar areas decreasing the difference in pressure and hence reducing wind speeds that carry tropical storms - causing storms to drop more rainfall as they move away slower

Preparedness for tropical storms

Prediction is increasingly sophisticated and accurate allowing for evacuations, drills are practised and education is improving, evacuation/response plans are made

Adaptation for tropical storms

Increasingly important due to increased frequency of extreme events due to climate change: Land use/planning restrictions in vulnerable areas, building sea walls, breakwaters, and flood barriers to weaken impacts of storm surges, retrofitting structures to become more wind resistant

21,400

Amount of tropical storm related deaths recorded in the 2010s after it was over 200,000 in the 1990s (most of the reduction has taken place in LICs)

Mediterranean climate

The type of climate that the most susceptible areas to wildfires possess: Winter rainfall which encourages vegetation growth (fuel), and hot, dry summers with occasional lightning storms that can result in a fire hazard (e.g. California, SE Au, Southern EU)

Natural benefits of fires

Can clear vegetation, aid new seed germination, stimulate the growth of certain plants, and rid an area of insects/parasites

Pyrophytic vegetation

Plant species that have evolved to tolerate or in some cases depend on wildfires to reproduce due to adaptations such as fire resistant bark

Primary effects of volcanic hazards

Tephra, pyroclastic flows, lava flows, volcanic gases

Secondary effects of volcanic hazards

Lahars, flooding (melting of glaciers/ice caps), volcanic landslides, tsunamis, acid rain, climate change (large amounts of ash released into atmosphere can lower temperatures by blocking the sun - believed to have caused past climate change)

Primary effects of seismic hazards

Ground shaking caused by shock waves radiating out from focus, ground rupture - visible breaking/displacement of Earth’s surface (poses major risk to large man-made structures such as dams, bridges, and nuclear power stations)

Secondary effects of seismic hazards

Soil liquefaction, Landslides/avalanches, fires (caused by broken gas pipes or collapsed electricity systems), tsunamis

Primary effects of tropical storms

Wind causing structural damage and carrying debris in the air dangerously, heavy rainfall, storm surgesS

Secondary effects of tropical storms

Contamination of soil in agricultural areas (can take a long time to recover from), landslides after heavy rainfall, contaminated water supply

Primary effects of wildfires

Loss of crops/timber/livestock, loss of life (generally avoided unless fire moves unusually fast causing people to be trapped), loss of property, release of toxic gases and particulates, loss of wildlife, damage to soil structure and nutrient content

Secondary effects of wildfires

Evacuation (people are often not allowed back into damaged areas for a long time), increased flood risk due to loss of vegetation and hence interception of rainfall, large amounts of carbon emissions exacerbating climate change

Hazard nature

The physical characteristics of a hazard including its causes and processes

Hazard incidence

The number of hazard events occurring in a given area over a specific period of time

Hazard resilience

The ability of people or systems to absorb, recover from, and adapt to hazard impacts