Hazards: EGC All Quizlet Flashcards
Natural hazard
An event caused by natural processes that is a threat to people and property.
Natural disaster
A natural hazard becomes a disaster if there is a significant impact on people and property. According to the UN, this is when 10 or more people are affected, 100 or more people are affected, or the government declares a state of emergency.
Primary impacts
Have an immediate effect on the affected area and are a direct result of the event.
Secondary Impacts
Happen after the disaster has occurred or are a knock-on effect of the disaster.
Geophysical hazards
Driven by the earth’s own internal energy sources e.g., plate tectonics, volcanoes, seismic activity (earthquakes).
Atmospheric hazards
Driven by processes at work in the atmosphere e.g., tropical storms, droughts
Hydrological hazards
Driven by water bodies, mainly oceans, e.g., floods, storm surges, tsunamis.
Hazard perception
The way in which people receive and process information about a potential hazard and make sense of it. How people respond to a hazard links to their perception of the risk. Perception is influenced by a range of factors including socio-economic status, education, religion and cultural background.
Hazard risk
The probability/chances of a hazard event occurring and creating loss of lives and livelihoods.
Hazard vulnerability
The ability/inability to resist a hazard and respond when a disaster has occurred. Can be described as insecurity.
Economic determinism
The view that the wealth of an individual or community is the most significant factor in determining it’s capacity to cope with and withstand the impact of a hazard.
Cultural determinism
The view that cultural factors are significant in determining an individual’s or community’s capacity to cope with the impacts of a hazard. Cultural factors include a person’s values, beliefs and possibly their age and family situation.
Fatalism
An acceptance that hazards are a natural part of living in an area and that losses are inevitable. May be linked to a belief that they are ‘God’s will’.
Prediction
Improvements in technology, such as remote sensing and satellite images, have increased our ability to give advanced warnings of hazardous events. This allows for communities to take action.
Adaption
If we accept that natural events are inevitable, we can adapt/make changes to increase the level of protection and reduce risks. This may include making changes to the built environment
Mitigation
Actions aimed at reducing the seriousness of an event and lessening its impacts.
Management
Modern management techniques involve gathering accurate information, careful analysis and deliberate planning to make the most efficient use of the money and resources available.
Community Risk Sharing
One way of reducing people’s vulnerability. It involves public education and awareness programmes. It may include evacuation procedures and shelters as well as insurance (in richer areas).
Hazard Distribution
The spatial coverage of a hazard. The area affected by a specific hazard. Some events are localised, and some have a much wider effect.
Hazard Frequency
The distribution of a hazard through time. Some are very infrequent, and some are more regular.
Hazard Magnitude
The size of impact of a hazard. This can be given using a scale for example the Richter scale for earthquakes, the Saffir-Simpson scale for tropical storms and the Volcanic Explosivity Index (VEI) for volcanic eruptions.
The Park Model
Also known as the disaster-response curve. It show’s how people’s quality of life is likely to change through the five phases of a disaster.
The Hazard Management Cycle
This represents hazard response as a continuous process. The cycle has four stages: Preparation, Response, Recovery and Mitigation
Core
The densest, hottest part of the planet. Made of rocks rich in iron and nickel. Temperatures can exceed 5000oC. The heat is the result of primordial heat and radiogenic heat.
Primordial heat
Heat left over from the Earth’s formation.
Radiogenic heat
Heat produced by the radioactive decay of isotopes.
Mantle
Surrounds the core. The thickest layer made of silica rocks rich in iron and magnesium. The upper part of the mantle is semi-molten (plastic) and is known as the aesthenosphere. Convection currents occur here.
Crust
Thinnest outer solid layer. Two types of crust, oceanic and continental.
Oceanic crust
Found beneath the world’s oceans. Composed of relatively dense basalt and between 6-10km thick. Formed at spreading mid-ocean ridges at constructive margins.
Continental crust
Forms the continents. Is thicker and older, can be up to 70km thick. Composed of granite. Formed at subduction zones
Lithosphere
The crust and rigid upper mantle.
Aesthenosphere
The semi-molten, plastic upper mantle. The layer is below the lithosphere.
Plate tectonic theory
This theory has evolved over many years. It suggests that the crust is divided into tectonic plates that move due to convection currents in the asthenosphere. This movement creates distinctive features including mid-ocean ridges, ocean trenches and fold mountains, in addition to causing earthquakes and volcanic activity
Alfred Wegener
Published a theory in 1912 suggesting that there was once one supercontinent called Pangea and that over time the landmasses drifted apart until they reached their current positions. His theory was based on a range of evidence, including geological, climatological and biological. He could not explain how continental movement could have taken place.
Mid-Atlantic Ridge
A continuous uplift feature than runs down the centre of the Atlantic Ocean. The central part of the ridge is marked by a central valley. First seen in the 1940s when the ocean floor was first mapped. Since then, mid-oceanic ridges have been found in the other oceans.
Sea floor spreading
Surveys of the ocean floor established that rocks found closest to mid-oceanic ridges were the youngest and rocks nearest the continental landmasses were the oldest. This supported the idea that the sea floors were spreading out from the mid-oceanic ridges where new crust was being formed as magma reached the surface as two oceanic plate moved apart at a constructive margin.
Palaeomagnetism
The rocks that form the ocean floor show stripes of alternating polarity. Lavas that erupt at the mid-oceanic ridges contain iron which aligns to the Earth’s polarity. This becomes fixed when the lava solidifies. The Earth’s magnetic field reverses, on average, 4 to 5 times per million years. These switches are recorded in the rocks of the ocean floor as aa series of ‘magnetic stripes’ with rocks aligned alternatively towards north and south poles. The pattern suggests that ocean crust is spreading out from the mid-ocean boundary.
Convection currents
High temperatures at the Earth’s core help to create continuous convection currents in the aesthenosphere that transfer heat from the core to the Earth’s surface. As the heated magma spreads out underneath the crustal plates it causes them to move due to traction. The magma then cools, becomes denser and sinks downwards again. In recent years the theories of ridge push and slab pull have been added to the theory of convection currents to help explain plate movement.
Ridge push
Also known as gravitational sliding. This occurs at mid-oceanic ridges where hot magma rises to the surface and the forces up the crust at constructive margin to form a slope on either side. As the new rock cools, it becomes denser and the weight causes it to ‘slide’ downwards away from the ridge, due to gravity. This results in a pushing force and in seafloor spreading.
Slab pull
At a subduction plate margin, the heavier plate, usually basalt, sinks down into the mantle. As the edge of the plate sinks it pulls the rest of the plate with it.
Collision plate margins
These occur where two continental plates converge (move together). This results in the plates buckling up and faulting and in the formation of young fold mountains.
Constructive plate margins
These occur where two plates diverge (move apart), and new crust is created. In the oceans this produces mid-ocean ridges. Shallow focused earthquakes and submarine (underwater) earthquakes can occur at these margins. Divergence can also occur within a continent, resulting in rift valleys and volcanic activity.
Conservative plate margins
These occur where two plates rub past each other or are side by side moving in the same direction but at different speeds. Earthquakes are a feature of these margins.
Ocean ridges
The longest continuous uplift features on the surface of the planet. Where two plates pull apart there is a weaker zone in the crust and an increase in heat near the surface. The hotter expanded crust forms a ridge. The central part of the ridge may feature a central valley where a section of the crust has subsided into the magma below.
Transform faults
Cracks in the Earth’s crust that form at right angles to constructive plate margins. As the plates pull apart the parts of the crust on either side of the fault move at different rates, leading to friction and, ultimately, earthquakes.
Young fold mountains
Fold mountains are formed at destructive plate margins, either subduction or collision. Young fold mountains are 10 to 25 million years old and include the Rockies, Andes and Himalayas. They form from sedimentary rocks which crumple and fold as plates push together, causing uplift.
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.
Deep-sea trenches
Found along the seaward edge of destructive margins. They are long, narrow, steep-sided depressions in the ocean floor. They mark where one plate begins to subduct beneath another.
Island Arcs
A slightly curving line of volcanic islands formed at a subduction destructive margin off the coast of a continental plate or in the ocean where two oceanic plates converge.
Benioff Zone
The area where friction is created between two plates as a result of subduction at a destructive plate margin
San Andreas Fault
A visible line in the Earth’s crust in California that marks an active conservative plate margin. Earthquakes occur here.
Magma Plumes
A huge upwelling of super-heated magma in the mantle that rises from a ‘hot spot’ and melts/pushes through the crust above causing lava to erupt at the surface.
Island Chains
A line of volcanic islands that form in the middle of an ocean plate from lava erupted when the plate moves over a mantle plume.
Vulcanicity
All volcanic activities related to magma being forced into the Earth’s crust.
Volcanoes
Openings in the Earth’s crust through which lava, ash and gases erupt. They mark the presence of magma within the Earth’s crust.
Lava
Once magma is ejected at the surface it is called lava.
Tephra
Rock fragments ejected as part of an explosive volcanic eruption. They can vary in size from fine ash to larger ‘volcanic bombs
Intraplate
In the middle of a tectonic plate
Lava flow
Molten rock flowing over the surface
Ash fall
Ash can be ejected high into the atmosphere and can cover a large area. Ash is highly abrasive, is heavy when it accumulates in layers and can obstruct sunlight
Pyroclastic Flow
A mixture of hot rock, ash and gases rising from a volcanic eruption that moves at a rapid speed (up to 200m/s) along the ground. Temperatures range from 350-1000oC.
Nuées Ardentes
A type of pyroclastic flow that contains more dense material and so doesn’t travel as far.
Lahar
Destructive mudflows formed when ash and other volcanic material are mixed with water. They flow at speeds of up to 60km/h and are highly erosive.
Acid rain
Volcanoes emit sulphurous gases, which can result in acidic rainwater when combined with atmospheric moisture.
Volcanic Explosivity Index (V.E.I.)
A logarithmic scale from 0-8 which measures the magnitude of a volcanic eruption. The scale uses several volcanic characteristics to judge the size of an eruption, including eruption cloud height and volume of material erupted.
Seisometer
A device that measures tremors in the Earth’s crust. These occur when rising magma cracks and fractures overlying rocks.
Tiltmeter
A device that measures changes in the angle of the slope of a volcano’s sides. The sides of a volcano deform and bulge out as it fills with magma.
Seismic
Relating to earthquakes or other vibrations of the Earth and it’s crust.
Faults
When rocks of the Earth’s crust come under stress, they can fracture along cracks called faults. Plate movement creates such stress.
Earthquakes
Tremors that result from the release of pressure that builds up in the Earth’s crust due to plate movement.
Focus
Also known as hypocentre. The breaking point of an earthquake, within the Earth’s crust. Shallow focus earthquakes (0-70km) have a higher impact than deep focus earthquakes (300-700km)
Epicentre
The point on the surface directly above the focus. Ground shaking is most intense here.
Body Waves
Shockwaves that travel through the earth
Primary (P) waves
Body waves that travel from the focus through both liquids and solids and are the fastest waves. They are compressional waves, which means that they compress and expand any material they move through.
Secondary (S) Waves
Body waves that travel through the Earth but cannot travel through solids like the core. They are half as fast as Primary waves and are transverse waves, which means that they shake the ground at right angles to the direction of the wave
Surface waves
Travel along the Earth’s surface and arrive after body waves.
Love (L) Waves
Surface waves that travel out from the epicentre and shake the ground from side to side. They are the slowest waves but are the most destructive which can cause significant damage to buildings and infrastructure.
Rayleigh (R) Waves
Surface waves that move in a rolling motion and can break up the surface.
Tsunamis
Giant sea waves generated by shallow-focus underwater earthquakes involving movements of the seabed e.g., when subduction occurs offshore. Secondary earthquake hazards. They travel at speeds of over 700km/h
Liquefaction
When saturated unconsolidated sediments/soils are shaken by shockwaves their strength can fail causing them to behave more like a liquid. This secondary hazard can result in objects and buildings sinking into the sediments/soils.
Landslide
A type of mass movement involving the rapid movement of soil and boulders down a slope. A secondary earthquake hazard.
The Richter Scale
A logarithmic 10-point scale used to measure the magnitude of earthquakes. Earthquakes above scale 6 are considered destructive.
Moment Magnitude Scale
An adaption of the Richter Scale that uses complex mathematics to calculate the total amount of energy released in an earthquake. Its values also range from 1-10 and it is more reliable than the Richter scale when measuring the largest earthquakes
Mercalli Scale
Measures the intensity of an earthquake event and its impact, rather than its magnitude. It is a 12-point scale.
Tropical Storms
Intense low-pressure systems that develop in the tropics. These violent revolving storms usually measure some 200-700km in diameter. Known as hurricanes, cyclones and typhoons.
Coriolis Effect
The Earth’s rotation causes objects not connected to the ground to deflect, including currents of air. The effect is responsible for the spin of tropical storms and is at its strongest either side of the equator at around 5o north and south.
Intertropical Convergence Zone (ITCZ)
The region near the equator where trade winds from the northern and southern hemispheres come together. The intense sun warms the surface at the equator causing the air to heat and rise, creating an area of low pressure and high precipitation.
Storm ‘eye’
Central point of a storm, 10-15km in diameter, where air sinks giving calm conditions and clear skies.
Storm Surge
A rise in sea level that occurs during low pressure storms. The low pressure ‘sucks up’ the surface of the water and the storms produce strong winds that pile water against the shore, which can lead to flooding.
Saffir-Simpson Scale
A 5-point scale that measure the magnitude of a tropical storm. The scale is based on measurements of central pressure, wind speed, storm surge and damage potential.
Wildfire
An uncontrolled rural fire, known as bushfires in Australia and North America.
Ground Fire
A slow smouldering fire that burns organic matter in the soil, such peat. They spread slowly at fairly low temperatures for long periods of time. There may be no flame.
Surface Fire
The burning of leaf litter and low-lying vegetation. The most common type of fire. Can be low or high intensity. They cool quickly and are relatively easy to control.
Crown Fire
A fire that moves rapidly through the canopy (top layer of vegetation). This type of fire has a dramatic effect on forested areas. The hottest type of fire. Very difficult to contain.
Ladder effect
When fires spread from the ground to the tree canopy
El Niño
A climate pattern that describes the unusual warming of surface waters in the eastern tropical Pacific Ocean. It can lead to drought conditions in SE Asia and eastern Australia, which increases the risk of wildfires.
