Hazards Flashcards
Natural Hazard
A natural hazard is a perceived event that threatens both life and property. These forms of hazard thus pose a risk to human populations.
Adaptation
In the context of hazards, adaptaion is the attempts by people or communities to live with hazard events by adjusting their living conditions. Therefore people can reduce their vulnerability.
Fatalism
A view of a hazard event that suggests that people cannot influence or shape the outcome, therfore nothing can be done to mitigate against. People with such a attitude put in place limited or no preventative measures. In some parts of the world, the outcome of a hazard event can be said to be ‘Gods’ will.
Losses are inevitable
Perception
This is the way in which an individual or a group view the threat of a hazard event. This will ultimately determine the course of action taken by individuals or the response they expect from governments.
Influenced by religion, past experinces, socio-economic status , level of education and past experience.
Risk
This is the exposure of people to a hazardous event, presenting a potential threat to themselves, their possesions and the built enviroment in which they live.
Why do people put themselves at risk?
- Hazard events are unpredictable, difficult the frequency, magnitude or scale of a natural hazard scale.
- Lack of alternatives, due to social, political and economical factos people cannot simply uproot themselves from a place.
- Changing the level of risk, places that were once relatively safe may have become over time more at risk. Deforestaion for example may result in more flooding associated with tropical storms.
- Costs and benefits, if the benefits of a hazardous areas outweigh the risk that they are taking by being there. California cities.
Vulnerability
Vulnerebality to physical hazards means the potential for loss, varies over time and space, and losses vary geographically over time and among different social groups.
Fear
The perception of a hazard is such that people feel vulnerable to an event that they are no longer able to face living in the area and move away to regions percieved to be unaffected.
Risk sharing
This involves prearanged measuers that aim to reduce the loss of lifeand property damage through publiv education and awareness programmes, evacuation procedures, the provision of emergency medical, food and shelter supplies and taking out insurance.
Prediciton
The ability to give warnings so that action can be taken to reduce the impact of hazard events. Improved monitoring, information and communications technology have meant that predicitng hzards and issuing warnings have become more important in recent years.
Magnitude
The assesment of size and impact of a hazard
Primary and secondary effects
Primary effects are effects that are a result directly of that event, whereas secondary effects are those that result from the primary impacts of the hazard event.
Primary and secondary effects
Primary effects are effects that are a result directly of that event, whereas secondary effects are those that result from the primary impacts of the hazard event.
Resilience
The ability of individuals or communtiies to be able to utilise available resources to respond to, withstand and recover from the effects of natural hazards.
Protection
Protect the peopl and their possesions and the built enviroment from the impacts of hazards.
Park Model
Pre disaster - Relief, rehabilitation and reconstruction
Recovery can be a better quality of life or below the previous quality of life.
The Hazard manegement cycle
Mitigation
Preparedness
Response
Recovery
Earths structure
Mantle - This is made up of molten and semi-molten rocks containing lighter elements such as silicon and oxygen.
Crust - Even lighter because of the elements that are present, the most abundant being silicon, oxygen and aluminum, potassium and sodium.
Lithossphere - Consists of the crust and the rigid upper section of the mantle and is approximately 80-90 km thick. This is the section that consists of 7 large plates and a number of smaller ones.
Asthenosphere - Lies beneath this layer and is semi-molten on which the plates float and move.
Inner core - Solid ball of iron/nickel, very hot due to pressure and redioactive decay. Responsible for earths internal energy.
Outer core - Semi-molten
Oceanic crust
6-10km
Less than 200 million years
3.0 density
Mainly basalt, silicon, magnesium and oxygen
Continental crust
30-70km
Over 1.5 billion
2.6 density (lighter)
Mainly granite, silicon, aluminum oxygen
Plate tectonic theories of crustal evolution
1912 Alfred Wegener published his theory that a single continent existed about 300 million years ago.
In 1912 he noticed that the coastlines of the east coast of South America and the west coast of Africa appeared to fit together like jigsaw pieces.
Further examination of the globe revealed that all of the Earth’s continents fit together somehow and Wegener proposed an idea that all of the continents had at one time been connected in a single supercontinent called Pangaea.
He believed that the continents gradually began to drift apart around 300 million years ago. This was his theory that became known as continental drift.
Sea floor spreading
- The mid-atlantic ridge was discovered and studied along with a similiar feature in the Pacific ocean, examination of the crust either side of the mid-atalantic ridge suggested that sea floor spread was occuring.
- Movement of Oceanic crustal plates away from divergent/constructive plate boundaries such as in the middle of the Atlantic Ocean.
- Sea floor spreading implies that the earth must be getting bigger, as this is not the case then the plaes must be being destoryed somewhere to accomodate the increase in size at their midatlantic ridge.
- Plates diverge, magma rises up to fill the gap that is created, then cools to form new crust, over time the new crust is dragged apart and more forms between it, this creates mid ocean ridges
- Large areas of the oceanic floor were being pulled downward in process know as subduction.
Convection Currents
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 stinks. The edges of where plates meet are called plate boundaries.
- Heat from the innter core convects through mantle into asthenosphere.
- Hot magma rises because it becomes less dense with heat.
- Magma is cooler at the top as it is further away from heat source. Becomes more dense and sinks back down to bottom.
- Cooler magma is reheated and begins to rise again, creating a loop called a convection current.
These circular movements create drag on the base of the tectonic plates causing them to move.
Ridge Push/Gravatational sliding
At construtive boundaries the upwelling of hot material at ocean ridges generates a buoyancy effect that produces the ocean ridge which stands some 2-3km above the ocean floor. here oceanic plates experience a force that acts away from the ridge, known as ridge push, which is a result of gravtiy acting down the slope of the ridge.
The occurrence of the shallow earquakes, resulting from the repeated tearing apart of the newly-formed crust, indicates that there is also some frictional resistance to this force.
Slab pull
- At destructive plate boundaries, denser crust is forced under the less dense crust when they cinverge, the sinking of the plate edge pulls the rest of the plate towards the boundary and down into the mantle. This is called SUBDUCTION.
Destructive plate margin
- 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, friction with the upper mantle creates heat.
- Extra magma created causes pressure to build
- Pressurised magma forces through weak areas in the continental plate.
- Magma is also less dense than the continental crust and therefore will rise.
- Explosive, high pressure volcanoes erupt through the continental plate, known as composite volcanoes.
Constructive plate margin
- Two plates of the same type move away from each other.
- Magma rises between the gap left by the two seperating, forms new land when it cools.
- Volcanoes form where magma rises, magma is created by pressure release at the margin causing the mantle to melt.
Conservative plate boundary
- Between any crust the parallel plates move in different direction or at different speeds. No plates are destoryed so no landforms are created. When these plates move, a lot of pressure is built up.
- When pressure releases they jerk and release energy
Landforms associated with plate movements - Ocean ridges
- The longest continuous uplifted features on the surface of the planet, yet they are formed when plates move apart from each other in oceanic areas.
- The space between the plates is filled with basaltic lava upwelling from below to form a ridge. Volcanic activity occurs along these ridge lines, forming submarine volcanoes which can sometimes rise above sea level.
Construtive plates
Collision
- Two plates of the same density move towards each other.
- Due to their similiarty little or no subdiction will take place. The plates therefore come together and fold.
- This creates mountain ridges
Landforms associated with plate movements - Rift valleys
- Plates diverge at constructive boundarie, magma beneath the land causes the continental crust to bulge and fracture, forming fault lines.
- As the plates move apart the crust between the parallel faults drop down to form a rift valley.
- For example the east afrcian rift system is a series of rift valleys that strech from mozambique to the red sea.
Landforms associated with plate movements - Deep sea trenches
Where oceanic and continental plates meet, the denser ocean plate is forced under the lighter continental one, the downwarping of the oceanic plate forms a very deep part of the ocean known as a trench.
Landforms associated with plate movements - Island arcs
- During subduction the descending plate encounters hotter surroundings and this coupled with heat generated from fiction begins to melt the plate, as this material is less dense that the surrounding asthenosphere it begins to rise towards the surface as plutons of magma.
- This rise to the surface to form complex, composite an explosive volcanoes.
- A line of volcanic island can form if this happens of shore.
Landforms associated with plate movements - Young fold mountains
- Collison boundaries, two plates of continental crust, same density means there is no subduction.
- As plates move towards each other the edges and sediments are forced into fold mountains. Very little subdiction can occur so not volcanism.
Where can volcanoes form
- Oceanic ridges
- Rift valleys
- Subduction zones (destructive boundaries)
- Hot spots
Volcano formation - Oceanic ridges
- Plates moving apart at constructive boundaries, magma forces its way to the surface and cools creating new crust, as the plates move away this new crust is carried away from the ridge (sea floor spreading).
- Volcanoes here are fairly gentle, low viscosity, basaltic. Frequent but effusive.
Volcanic formation - Subduction zones
- Oceanic plate subducts and decends under the continental plate, the deeper it goes the hotter surroundings become, this together with heat generated from friction begins to melt the oceanic plate into magma.
- This magma is less dense than its surrounding material and therefore rises as plotuns of magma, they reach the surface and form volcanoes.
- Andesitic lava, high viscosity, composite and more explosive volcanoes.
Volcanic formation - Rift valleys
- At constructive margins in continental areas such as east africa, the brittle crust fractures as sections of it move apart. Areas of crust drop down between parallel faults to form rift valleys, the crust here is much thinner suggest that the tension is causing the plate to thin as it sarts to split, as the crust gets thinner magma can more easily force its way to the surface.
For example Mount Kenya in the East African Rift system
Volcanic formation - Hot spots
- A high concentration of magma below the crust is called a hotspot, a plume of magma rises to towards the plate above, heating the crust and causing it to fracture and thin, forcing its way up anf forming volcanoes.
- Forms shield volcanoes, baslatic lava, effusive.
- The hot spot is stantioanry so as the plate moves over it a chain of islands is formed.
Fissure volcano
- Basaltic lava
- Lava can pour out in a number of places and in multiple directions, flat gentle slope.
- Construtive boundary
- Low silica content, low viscosity, this allows bubbles to escape and therefore pressure cannot build and they arent explosive.
- Effusive, gentle and frequent
Shield volcano
- Result of constructive plates and hotspots.
- Basaltic lava
- Single vent, gentle slope byt steeper than fissure and taller.
- Basic, low silica content, low viscosity, bubbles cant be trapped, pressure doenst build, effusive and frequent.
Dome
- Destrutive boundary
- Explosive
- Andesitic/Rhyollitic
- Can be very acidic, high silica content and more visocus if it is rhyolitic, trapping gass and building pressure.
- Steeper sides and more unstable.
- little lava flow
Ash-Cinder
- Ash/TEPHRA more common
- Deposited erupted material
- Andesitic, between basaltic and rhyolitic.
- Steep sided, smaller, conical.
- Destructive boundary
- Explosive
Composite
- Steeper sides, much larger .
- Destructive
- Andesitic or Rhyolitic
Caldera
- Rhyolitic and Andositic
- Much larger, form when the crater collapses, forms a caldera out of the old cone.
- Steep rimmed
Silica content
- Destrutive plate boundaries have higher silica content as they become contaminated with this and other sediment as they move up through the continental crust.
- Contiental crust is HIGH silica content.
Magnitude
VEI Volcanic expolsivity index
Primary impacts
- TEPHRA
- Proclastic flows
- Lava flows
- Volcanic gases
- Land slides
TEPHRA - Primary impact VOLCANO
- Volcanic material ejected into the atmosphere including ash and volcanic bombs.
- Bombs can fall to the ground within 2 miles of the vent.
- Eruption columns of gas can reach more than 12 miles into the air.
- Volcanic ash in cloud can pose a hazard to aviation, last 15 years 80 commercial jets have been damaged through inadvertantly flying into ash.
- Finer pieces of TEPHRA can kill vegetation and cause long term health impacts to people.
Pyroclastic flows - Primary impact VOLCANO
These are very hot, over 800 degrees celcius, gas charged, high velocity flows that make up a mixture of gas and TEPHRA. They usually flow down the sides of the volcano at speeds of around 700km per hour.
Mount Unzen 1991 killed 43 people
Volcanic gases - Primary impact VOLCANO
These include carbon dioxide, carbon monoxide and sulphur dioxide.
Dangerous to people as they are toxic.
Cracks in teh ground allow for gases to reach the surface.
Carbon dioxide is heavier than air and can be trapped in low areas in high concentrations.
E.G
1986 carbon dioxide emission from the lake in the crater of Nyos cameroon killed 1,700 people.
Secondary impacts - Volcanoes
- Lahars
- Flooding
- Tsunamis
- Acid rain
- Climate change
Landslides - Primary imapact volcanoes
- Rapid downhill movement of rocky material, snow and ice.
- They can be entire collapses of the volcanoes sumit.
- Heavy rainfall, large earthquakes or volcanic events can cause them. SO COULD BE SECONDARY
Mount rainer, washington
Mount st helens eruption 1980, washington
Lahars - Secondary impact VOLCANO
- Melted snow and ice as a result of the eruption comined with volcanic ash forms mud flows that can move down the course of rivers and valley at high speeds.
- 20-40 kph
- It can orginate from melting snow/ice, water from a glacier melted by a pryoclastic surge.
- Can happen when the volcano is quite.
Flooding - - Secondary impact VOLCANO
When a eruption melts glaciers and ice flooding can be a result.
E.G
Iceland in 1996 when the Grimsvotn volcano erupted melting a glacier.
Tsunamis - Secondary impact VOLCANO
Sea waves generated by violent volcanic eruptions.
E.G
Krakatoa in 1883, tsunami was estimated to kill 36,000 people.
Acid rain - Secondary impact VOLCANO
- Sulfure emitted from eruiptions can react with water droplets in the atmosphere to create acid rain, this can cause corrosion and harm vegetation.
Climate change - Secondary impact VOLCANO
The ejection of huge amount of debris into the atmosphere can reduce global temperatures.
Prediction of volcanoes
- Locating volcanoes is straightforward but prediction is difficult.
- Colomibian volcano, Nevado del ruiz in 1984 came to life with small scale activity, volcanologists were unable to predict the scale of the event.
- When the final violent event took place after several months of small scale activity, Lahars swept down the valley killing over 20,000 people and resulting in over $6 billion n property damage.
- You can study previous eruption history of a volcano.
- Monitor land swelling
- Gas emissions and the chemical compostion of water.
- Measure seismic activity that are found through shock waves of magma moving towards the surface, expanding cracks and breaking through other areas of the rocks.
Protection
- In this case this usually means preparing for the event, monitoring the volcano will indeitfy the time and area which is under threat.
Enviromental impacts of volcanos
- Ecosystems can be damaged or destoryed by flows and fallout of material.
- Acid rain can cause acidification of aquatic ecosytems, killing plants and animals.
- Volcanic gases contribute to the greenhouse effect and add to global warming.
- CLouds of ash and volcanic debris can decrease temperatures and reduce sunlight reaching earth
Social impacts of volcanos
- People are killed, buildings are destoryed by mudflows, pyrcolcalstic flows, ash fallout and rockfalls.
- Fires can be started.
- Mudflows and flooding from ice melt can cause damage and death.
Montserrat 1997 (DESTRUCTIVE) 19 dead, 100s without homes, 8000 people left after the eruption, poppulation decline.
Economic impacts of volcanos
- Eruptions can destory businesses and ash clouds can prevent aircraft flying and damage crops. ECONOMIC DAMAGE.
- Expensive to repair damage to buildings
HOWEVER volcanoes can attract toursists.
Montserrat 1997 (DESTRUCTIVE) total loss was around 1 billion, 2/3 of buildings destoryed by Pyroclastic flows. The Port along with schools and hospitals destoryed.
Political impacts of volcanos
- Damage to agricultural land can cause food shortages, leading to conflcit and political unrest.
- Governments may have to spend money on reprairing damage to buildings and roads, instead of devotion to education and health.
Preparedness VOLCANO
- Monitoiring 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 a eruption.
- Authorities can stop people entering the area around the volcano.
- Trained response teams and evacuation procedures planned.
Prevention VOLCANO
They cannot be rpevented, Risk to people can be prevented.
Mitigation volcano
- Direct inertvention to the volcano, concrete blocks steer lava away from areas at risk.
- Strengthening builiding that are at risk from mudflows and ash pile up.
- Evacuation zones
- Emergency aid on the ready.
Adaptation volcano
- Capatalise on oppurtunities such as encouraging tourism.
- Move away from at risk areas.
Mt Nyiragongo 2002, congo IMPACTS
- Lava flows destoryed much of a nearby town.
- 147 people were killed, poisonous gasses, collapse of buildings and lava flows.
- Water and power facitlities destoryed along with the medical facilities.
- Several earthquakes accompanied the eruption.
- Eye irritation and repitory issues from smoke and fumes from the eruption.
White Island Background 2019
Phreatic eruption, release of steam and volcanic gases.
It was caused by water coming in contact with hot magma as it rose upwards, soil and ash trapped the steam in and allowed pressure to build, eventually it erupted in ash, steam and rock.
Located in New Zealand
Prepardeness to White Island
GeoNet monitors the volcano, there had been reports of increased earthquake activity, gas release and mud eruptions in the months before.
Three weeks previous the alert level rose from level 1 to level 2
However even closly monitoored volcanoes are unpredictable, however tourists were still allowed onto the island.
White Island primary impacts
- Rock and ash was launched 3km into the air.
- 18 people were killed and 26 were injured
- However White Island is located around 48km out in the Bay of Plenty so the primary impacts were relatively localised.
Background of the Iceland eruption 2010
Iceland is positioned on the mid atlantic ridge, seperating the Eurasian plate and the North American plate, on a conservative plate boundary.
Magma fills the magma chamber has the plates move apart through ridge push.
Preparedness of the Iceland Eruption 2010
In early 2010 seismic sctivity was detected in the area of Eyjafjallajokull, this gave volcanologists evidence that magma was puring from under the crust into the volcanoes magma chamber, a few minor eruptions followed.
However it went quite for a short moment before the main eruption.
1,000 people were evacuated in response to flood risk.
Primary impacts of Iceland 2010
- Huge amounts of ice melted causing floods
- Large quantaties of ash pured from the volcano, it was picke up by the Jet stream and blown towards europe, this meant that all airspaces were shut costing airlines around £130 million a day.
- Rescuers were forced to wea masks to avoid the toxic clouds of ashes.
- Homes and roads were destoryed and cops damaged.
- No human fataities were incured, risk was relatvely low, only a VEI 4.
Secondary effects of Iceland 2010
Impacts were felt as far as Kenya where farmers laid off 5000 workers as crops were left to rot at airports.
Kenya exports were down 97%.
Responses to the Iceland eruption 2010
- European Red Cross mobilised volunteers, staff and resources to aid those directly impacted by the earthquake.
- 600 more people were avcuated in 2 hours, 120 were given accomadation.
- Iceland declared a state of emergency
Response to Montserrat eruption 1997
- UK provided £17 million in aid
- £41 million in long term aid committed to development of the north of the island.
- Montserrat Volcano Observatory set up to predict in the future.
Seismic hazards relation to plate tectonics
As the crust of the earth is mobile, there tends to be a slow build up of stress ithin the rocks, when pressure is suddenly released, parts of the surface experience an intense shaking motion.
