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103 Cards in this Set
- Front
- Back
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What are 4 factors that influence perception of risk of natural disasters?
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1. Many are killed at once
2. Victims seem vulnerable (very young or very old, pregnant) 3. Victims lack illusion of control 4. We hear about it a lot through the media As a result, we tend to overestimate the perceived risk of natural disasters |
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What is risk?
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The probability of a disaster affecting people
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What is perception of risk?
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Subjective perceived likelihood of being affected by a disaster
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What are hazards?
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Processes capable of causing loss of life, damage to property or damage to the environment.
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What are geohazards?
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A geological process that can threaten people or property (e.g. earthquake, tsunami)
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What are natural disasters?
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Specific natural events that harm people and property and significantly disrupt civil and economic function (e.g. Japan Tsunami 2011, Hurricane Katrina)
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What is the relationship between population growth and hazard risks?
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As populations grow, more people are affected by geohazards. Specifically, population growth prompts people to settle in hazardous areas and build structures that can harm humans in a natural disaster. Urbanization and megacities.
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How can economic development decrease risks associated with geohazards?
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Economic development can increase building construction and planning, increase public awareness and education, increase resources to deal with disasters
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How can economic development increase risks associated with geohazards?
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Results in environmental degradation, especially in highly urbanized megacities, causing regions to become more sensitive to geohazards
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What is an Order of Magnitude scale?
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A scale used to measure the intensity (in earthquakes, shaking) of a geohazard. Magnitude 1 is 10 times less intense than Magnitude 2, and 1000 times less intense than Magnitude 3.
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What is a logarithmic scale?
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Graphs by powers of 10, so order of magnitude easier to interpret
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What is a return period?
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The average number of years between disaster events of a given magnitude
RP(M) = Time span of data/cases of M |
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How are energy sources related to natural disasters?
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1. Gravity: form of potential energy converts to kinetic energy. Powers landslides and impacts.
2. Solar radiation: differences in heat from the sun related to atmospheric phenomena (waves, storms) 3. Remnant heat: heat from the formation of the earth, powers volcanos and earthquakes, pushes mountains to form landslides |
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What is a rock?
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A solid aggregate or mass of minerals
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What are the 3 categories of rocks?
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1. Igneous: formed from magma within the earth (intrusive) or on the surface (extrusive)
2. Sedimentary: formed at the surface of the earth through a variety of methods 3. Metamorphic: formed by temperature, pressures and/or chemical conditions on existing rock into another |
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What is the rock cycle?
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The worldwide recycling of the three major groups of rocks, driven by Earth's internal heat and by energy from the Sun
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What is the association between seismic events and plate margins?
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Earthquake epicentres are primarily located at plate margins
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What is oceanic crust?
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Dense, thin crust; part of the lithosphere
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What is continental crust?
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Less dense, thick crust; part of the upper lithosphere
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What is the lithosphere?
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Outermost surface layer of the earth above the asthenosphere; composed of crust and upper mantle; strong and rigid
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What is a logarithmic scale?
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Graphs by powers of 10, so order of magnitude easier to interpret
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What is a return period?
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The average number of years between disaster events of a given magnitude
RP(M) = Time span of data/cases of M |
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How are energy sources related to natural disasters?
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1. Gravity: form of potential energy converts to kinetic energy. Powers landslides and impacts.
2. Solar radiation: differences in heat from the sun related to atmospheric phenomena (waves, storms) 3. Remnant heat: heat from the formation of the earth, powers volcanos and earthquakes, pushes mountains to form landslides |
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What is a rock?
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A solid aggregate or mass of minerals
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What are the 3 categories of rocks?
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1. Igneous: formed from magma within the earth (intrusive) or on the surface (extrusive)
2. Sedimentary: formed at the surface of the earth through a variety of methods 3. Metamorphic: formed by temperature, pressures and/or chemical conditions on existing rock into another |
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What is the rock cycle?
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The worldwide recycling of the three major groups of rocks, driven by Earth's internal heat and by energy from the Sun
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What is the association between seismic events and plate margins?
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Earthquake epicentres are primarily located at plate margins
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What is oceanic crust?
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Dense, thin crust; part of the lithosphere
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What is continental crust?
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Less dense, thick crust; part of the upper lithosphere
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What is the lithosphere?
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Outermost surface layer of the earth above the asthenosphere; composed of crust and upper mantle; strong and rigid
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What are lithospheric/tectonic plates?
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Large broken fragments of floating lithosphere that move relative to one another
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What are the 3 types of plate tectonics?
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1. Divergent: two plates move away from each other and new lithosphere is produced
2. Convergent: two plates collide head on (subduction: higher density ocean plate drawn beneath a lower density continental plate) Transform: Two tectonic plates slide horizontally past each other |
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What drives hot spots?
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Convection inside the mantle heats the lithosphere, can create a line of volcanos as lithospheric plate moves over it and melted rock is propelled through surface
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Why do plates move?
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Changes in density brought on by differences in heat result in hot material rising to the lithosphere and cold, dense material falling into the core. These changes in density drive plate movements.
Gravity: when dense crust falls to the core, it pulls the plate with it |
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What are 3 types of stress?
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1. Compressive: forces act toward each other
2. Tensional: forces act away from each other 3. Shear: forces are parallel but move on opposite sides of a plane |
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What is strain?
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A change in the shape or size of a body because of the application of a stress
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What are the 3 types of deformation?
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1. Elastic: temporary changes in shape that go back to original shape when stress is removed
2. Plastic: permanent change in shape or size that results in folding of rocks 3. Brittle: permanent breaking, resulting in faults |
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How can plastic deformation result in earthquakes?
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Compressive stress acts to create folding of rocks. Eventually, rocks lose cohesion due to stress and result in faults and/or earthquakes.
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What are the 3 main types of faults?
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1. Normal (tension): rocks pull away from each other, hanging wall moves down relative to the footwall
2. Reverse (compressive): rocks push toward each other, hanging wall moves up relative to footwall 3. Strike-slip (shear): rocks move past each other laterally at a vertical fault (right or left lateral) |
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How are earthquakes distributed globally?
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Faults are concentrated in certain regions due to movement between plates.
- Divergent: small quakes - Convergent: very large quakes - Transform: moderate to large quakes - Intraplate: can be large |
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What is elastic rebound theory?
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- Describes how earthquakes build and release energy
- Elastic stress builds at plate boundaries, resulting in a buildup of energy. Energy is released through earthquakes, and then slowly accumulates again. |
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What are seismic waves?
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Energy movements in wave form that release from the focus through the earth
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What are the two types of seismic waves?
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1. Body waves (within the earth)
- P waves - S waves 2. Surface waves - Rayleigh waves - Love waves |
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What are the characteristics of P waves and S waves?
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1. P waves
- Move back and forth - Fastest - Can travel through solids (fastest), liquids and gas 2. S waves - Slower - Side to side motion - Can only travel through solid materials |
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What are the characteristics of Rayleigh waves and Love waves?
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1. Rayleigh waves
- rolling motion - slower - damaging 2. Love waves - horizontal shaking at the surface - damaging |
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What is the difference between the number of recorded seismic events and the number felt?
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Many more recorded than felt; millions of minor, unfelt earthquakes annually
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How are earthquakes recorded?
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Seismographs record earthquake waves to produce seismograms
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How can the epicentre of an earthquake be located?
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Because they are faster, P-waves arrive at measuring stations first, and then are followed by S-waves. Due to the predictable speeds of the waves, the difference between the arrival of P-waves and the arrival of S-waves gives the station a measure of distance from the epicentre. Three stations or more combined can triangulate to measure precise epicentre location.
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What are two ways to quantitatively measure earthquake magnitude?
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1. Richter scale: measures amplitude of waves - not accurate, so obsolete
2. Moment Magnitude Scale: measures release of strain energy on a logarithmic scale. Each # on the scale represents 10 times more shaking and 32 times more energy release |
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How are earthquakes measured qualitatively?
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Modified Mercalli Index ranges from 1 to 12, estimates damage to structures, subjective feelings of shaking
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How does magnitude relate to earthquake intensity?
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Lower magnitude quakes are less intense, because less energy is released, and waves are less powerful
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How does distance from epicentre relate to earthquake intensity?
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The greater the distance from the epicentre, the less intense the earthquake, because seismic waves weaken as they travel
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How does foundational (ground) material relate to earthquake intensity?
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The more water-satured the sediment, the higher intensity (more shaking). Igneous rock most resistent, silt and mud least.
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How does structural resistance relate to earthquake intensity?
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The more resistant the building, the less intense (brick and concrete bad; wood, steel and reinforced concrete good)
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How does duration relate to earthquake intensity?
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Longer duration = more intensity
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What 7 hazards are caused by earthquakes?
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1. Shaking (Structural collapse)
2. Liquefaction 3. Subsidence 4. Landslides 5. Tsunami 6. Floods/Dam bursts 7. Fire |
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Why is earthquake forecasting easier than prediction?
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Forecasting takes into account probability of an earthquake based on historical events - probability that an earthquake of a given magnitude will occur in large time period (return period). Prediction is short-term and earthquakes are unpredictable in exact time and nature of quakes.
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How can damage from shaking be minimized?
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- Well-maintained and well-constructed buildings
- Resistent ground foundation (bedrock versus water-saturated sediment) |
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How can damage from liquefaction be minimized?
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Liquefaction: water-saturated loose sediments becomes liquid
- Minimized by not building on water-saturated sediment |
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How can damage from subsidence be minimized?
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Subsidence: Land lowering
Minimized by not building on water-saturated sediment |
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What is a tsunami?
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Large displacement of fault causes water to be displaced into massive wave
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How can fire be prevented in an earthquake?
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Turning off power and gas lines
Not having wooden buildings Narrow streets |
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What is the local tectonic setting?
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CASCADIA SUBDUCTION ZONE
Oceanic Juan De Fuca plate subducted under North America plate (convergent boundary; compressive stress; elastic strain) |
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What previous large earthquakes occurred in the local region?
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In the last 60 years, have been ~6 moderate/large quakes in West Coast region - low damage b/c in remote areas
~1700 huge >9 quake on BC coast |
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What are 3 methods of earthquake preparedness?
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1. Building codes
2. Seismic intensity maps (choose where to live, where to build) 3. Prepare home |
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What should you do during an earthquake?
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- Stay calm
- Turn off gas - Seek shelter under something sturdy - Stay in an open area w/o buildings, bridges etc. |
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Where does magma originate?
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Forms from partial melting of rocks inside the earth (intrusive)
Magma that reaches the surface is extrusive |
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What are the 3 components of magma?
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1. Melt: liquid portion composed of mobile ions
2. Solids: silicate materials that have already crystallized from the melt 3. Volatiles: Gases dissolved in the melt (mainly H2O, CO2) |
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How does magma reach the surface of the earth?
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Melted rocks from inside the earth released from volcanic vents, fumaroles and geysers
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What are the three types of igneous rock compositions?
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1. Felsic: high silica, low iron and magnesium rocks that are light in color and have visible crystals (intrusive)
2. Intermediate: medium silica, medium iron and magnesium, medium dark color 3. Mafic: low silica, high iron and magnesium, dark color (extrusive) |
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What are the typical settings of magma generation?
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- Temperature increases in upper crust result in melting of rocks
- Drops in pressure facilitate melting of rocks |
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How do plate tectonics relate to volcanism?
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1. Divergent margins: Result in spreading centres where magma rises due to decompression; leads to balsatic rocks
2. Convergent margins: Water in subduction zone lowers melting temperature, facilitating magma generation - felsic rocks 3. Intraplate: hot spots in oceanic (balsatic) and continental (felsic) crust |
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How does silica composition relate to the explosivity of a volcano?
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The higher the silica content, the more explosive
Silica -> Lower temperature -> High viscosity |
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How does gas content relate to the explosivity of a volcano?
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The more volitite (i.e. the more gases), the higher explosivity
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How does viscosity relate to the explosivity of a volcano?
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The higher viscosity, the higher explosivity
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What are the 4 types of volcanos?
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1. Shield volcano
2. Composite volcano 3. Volcanic dome 4. Cinder cone |
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What are the characteristics of a shield volcano?
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- Gentle arch or dome with gentle slopes (largest)
- Low silica content - Low viscosity - Basalt rocks - Lava flows, some explosive activity |
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What are the characteristics of a composite volcano?
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- Cone-shaped with steep sides (medium)
- Intermediate silica content - Intermediate viscosity - Andesite rocks (intermediate) - Combination of lava flows and explosive activity |
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What are the characteristics of a volcanic dome?
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- Dome-shaped
- High silica - High viscosity - Rhyolite rocks (felsic) - Highly explosive |
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What are the characteristics of a cinder cone?
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- Steep cone, commonly with summit crater (small)
- Low silica - Low viscosity - Basalt rocks - Explosive activity |
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What happens when magma reaches the surface?
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1. Crystallization of rocks
2. Volatiles set free from solution 3. Bubbles form in magma and rise, causing an eruption |
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How are shield volcanoes formed?
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By mild, effusive eruptions of large volumes of lava
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How are cinder cones formed?
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By ejected lava fragments
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How are composite volcanoes formed?
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From interbedded lava flows (surface magma) and layers of pyroclastic (ash, gas and volcanic rock) debris
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What are the 5 types of volcanic eruptions from least explosive to most explosive?
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1. Hawaiian (lava flows)
2. Strombolian (bombs, lava) 3. Vulcanian (ash) 4. Pelean (ash) 5. Plinian (ash) |
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What are calderas?
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Circular oval depressions that form during explosive ejection of magma and subsequent collapse of a volcano
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What are lava flows?
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- Slow-moving magma that has reached the surface
- Low threat to people, but can damage property and are hard to stop |
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What is ash?
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- Formed from liquid magma that has been blow up by decompressed gas bubbles and frozen in mid-air
- Can be small or large - Problems if breathed in - can be fatal - Darkness - Roof collapse - Clog engines |
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What are pyroclastic flows?
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- Avalanches of gas, ash and volcanic rock driven by gas and gravity
- Fast and very hot - Most common cause of volcanic-related deaths |
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What are lahars?
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- Volcanic mudflows that erode material and can result in massive flooding
- Fast and can cause death |
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What are volcanic landslides?
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Huge landslides caused by eruptions; can travel huge distances
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What are volcanic tsunamis?
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Tsunamis produced by eruptive or non-eruptive volcanic processes
- Responsible for 25% of volcanic fatalities |
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What are the effects of volcanic gases?
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Toxic concentrations of gases emitted from inside the earth that can cause death directly and indirectly (through crop destruction leading to starvation and disease)
- Lots of CO2 can cause suffocation - Can lead to climate change |
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What are two core methods used to monitor volcanoes?
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1. Seismic: measures shaking generated by volcanic activity. Volcanoes tend to have a pre-eruption swarm.
2. Ground deformation: Measure amount of deformation (bulge) in volcano to estimate eruption of magma reservoir; can be precise leveling, GPS, satellite radar |
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How can gas monitoring be used to predict volcanic eruption?
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- Greater levels of acids and gases indicative of new magma
- Can be direct, via UV examination, satellite |
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What variables are considered in evaluating volcanic risk?
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1. The volcanic HAZARDS an area is exposed to (resulting in human and monetary losses)
2. The VULNERABILITY of the elements of the environment |
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How can volcanic hazards be mitigated?
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1. Containing structures
2. Active degassing 3. Emergency response, including training and warning system 4. Risk education |
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How might BC be affected by volcanoes?
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Mount Baker closest volcano to lower mainland
Ash could potentially hit Abbotsford, Chilliwack areas |
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What are mid-ocean ridges?
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Large, underwater mountain ridges produced by new lithosphere in divergent boundaries. Mid-ocean ridges offset from one another at transform boundaries.
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How can magmas change composition after they are generated?
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1. Fractional crystallization: as it cools, minerals crystallize out of the melt, changing the composition
2. Assimilation: foreign matter (country rock) is incorporated 3. Mixing: 2 different magmas mix and result in a change in composition |
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What is the Volcanic Explosivity Index based on?
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1. Volume of ash produced
2. Height of eruption cloud around the vent 3. Duration of eruption |
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What is an eruption column?
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Hot volcanic ash emitted during a volcanic eruption
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Why do eruption columns collapse?
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Eruption column is too dense to be lifted high into the air by air convection, and instead forms a pyroclastic flow
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