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BSc Environmental Science > LEC.185 Natural Hazards > Flashcards

LEC.185 Natural Hazards Flashcards

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1
Q

Which are the 2 most commonly occurring natural disaster types?

A

Floods and storms

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2
Q

What is the CRED definition of a natural disaster?

A

10+ people reported killed OR 100+ people reported affected OR call for international assistance OR declaration of a state of emergency

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3
Q

What are 5 reasons why number of killed has decreased but number of people affected and number of reported disasters has increased between 1900-2010?

A
  1. More public awareness + reporting (less deaths, more reports)
  2. Larger population so more people forced to live in hazardous areas
  3. More poverty + urbanisation so more people in poorly constructed shanty towns
  4. Proliferation of sensitive structures e.g. nuclear power plants (interaction between natural + technological hazards)
  5. Environmental degradation + climate change
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4
Q

Define risk

A

Probability that harmful effects will actually follow from a natural hazard

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5
Q

What is the risk equation?

A

Risk = hazard level x exposure x vulnerability

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6
Q

What is the difference between weather and climate?

A

Weather = Short term changes in atmosphere
Climate = Long term average of weather conditions

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7
Q

Define heatwave

A

Period of abnormally hot weather with respect to some threshold value (but there is no universally adopted definition because of varied preparedness)

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8
Q

Define heat index

A

Measure of ‘how it feels’ or the ‘apparent’ temperature + factors in relative humidity

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9
Q

What are 4 reasons why the perception of heat may differ between different regions?

A
  1. Meteorological factors (e.g. wind speed, relative humidity)
  2. Differences in body composition/shape
  3. Metabolic differences
  4. Levels of hydration
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10
Q

Why does higher relative humidity make heat feel hotter?

A

Less perspiration evaporates in humid conditions

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11
Q

What conditions are needed to be met for a UK heatwave?

A

When a location records a period of 3+ consecutive days with a daily max. temp. higher or equal to the heatwave temp. threshold (derived from distribution of July max. temps. seen over a 30-year reference period)

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12
Q

What does air pressure arise from?

A

Weight of the atmosphere (larger closer to Earth’s surface and decreases with increasing altitude)

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13
Q

What are horizontal pressure gradients smaller than and why are they important?

A

Smaller relative to vertical pressure gradients but are important as drive winds

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14
Q

What do isobars join?

A

Areas of equal pressure (closer spacing denotes stronger pressure gradient + increased wind speeds)

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15
Q

What is an alternative name for high pressure systems and what do they involve?

A

Anticyclones, involve air descending, forming a high pressure area at the surface

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16
Q

What is an alternative name for low pressure systems and what do they involve?

A

Depressions, involve air ascending, forming a low pressure area at the surface

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17
Q

Define heat dome

A

Descending air in a persistent high pressure system with stagnant conditions and light winds which traps heat close to surface

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18
Q

Define urban heat island

A

Region where tarmac/stone absorbs + stores heat during daytime + emits heat at night

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19
Q

What are 6 reasons why the intensity, duration, frequency, and areal extent of heatwaves is important?

A
  1. Heat-related illness/death
  2. Pressure on services
  3. Water/energy demand
  4. Critical infrastructure impacts
  5. Ecological impacts (droughts/forest fires)
  6. Co-occurrence of heatwaves + air pollution episodes
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20
Q

What are 4 ways of mitigating heatwaves?

A
  1. Heat-health alert systems (5 alert levels in UK)
  2. Increased healthcare capacity
  3. Address urban heat islands
  4. Protect critical agriculture + vulnerable groups
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21
Q

Which direction do hurricanes rotate in in the Northern/ Southern hemispheres and what is the cause of this?

A

Northern: Anti-clockwise
Southern: Clockwise
Coriolis force

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22
Q

What is the difference between a hurricane/cylcone/typhoon and a tropical storm?

A

Hurricane: Sustained wind speeds > 74mph
Tropical storm: Sustained wind speeds < 74mph but > 39mph

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23
Q

Define tropical storm and hurricane

A

Tropical storm = Low pressure weather system with high winds + heavy rainfall
Hurricane = Severe tropical storm characterised by a rotating organised system of clouds + a warm ‘core’

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24
Q

Which regions call hurricanes ‘typhoons’ and ‘cyclones’?

A

Typhoons: SE Asia
Cyclones: Australia + Indian Ocean

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25
Q

When is hurricane ‘season’ in the N.Atlantic basin, when is peak activity, where do these hurricanes form, and which direction do they travel?

A

June-November, September, coast of Africa, steered East by trade winds

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26
Q

What 6 things does hurricane formation require?

A
  1. Low pressure zone (inward converging winds)
  2. Warm oceans (>27°C)
  3. High relative humidity
  4. Atmospheric instability
  5. Location > 5° from equator (sufficient Coriolis force)
  6. Low vertical wind shear (change in wind speed with height)
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27
Q

Describe the 8-step formation process of a hurricane (positive feedback loop)

A
  1. Wind blows over warm ocean
  2. Sucks up heat + water vapour
  3. Warm, moist air rises
  4. Water vapour condenses to form clouds
  5. Condensation releases latent heat
  6. Causes air to expand + rise further
  7. Decreases air pressure at surface
  8. Increases wind speed
    (Wind blows over warm ocean)
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28
Q

What is important to differentiate between within a hurricane?

A

Rotation wind speed and forward propagation wind speed

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29
Q

What are the 3 structures of a hurricane?

A
  1. The ‘eye’ - central innermost area with calm, clear skies, low air pressure/wind speed/rainfall, and dry air descending
  2. The ‘eyewall’ - dense thunderstorms, rainfall/wind speeds at maximum
  3. Outer rainbands - zones of intense cloud/rainfall extending from eye, wind speeds decrease + pressure increases towards storm edge
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30
Q

Define hurricane wind velocity and how is this measured?

A

Speed of rotating winds, measured using Saffir-Simpson scale (categories 1-5)

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31
Q

Define storm centre velocity

A

Speed of entire storm (typically 15-20mph), affected by atmospheric flows that steer storm system, can exceed 60mph particularly at high latitudes

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32
Q

When is hurricane intensity at its strongest?

A

When storm centre velocity + hurricane wind velocity are in the same direction

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33
Q

What are 6 consequent hazards of hurricanes?

A
  1. Extreme wind speeds
  2. Storm surges
  3. Torrential rain/flooding/mudslides (slower-moving, larger storms produce most rainfall)
  4. Rip currents
  5. Tornadoes
  6. Death from other factors e.g. disease
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34
Q

Define storm surge

A

Change in sea level caused by high winds + low pressure

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35
Q

How will climate change affect hurricanes?

A

No evidence for increased hurricane frequency but strong evidence for increased hurricane intensity, increased storm surges, more rain as more water vapour in atmosphere, potentially changed path of tropical cyclones

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36
Q

How are hurricanes detected?

A

Satellite images, observations fed into statistical models to predict path, landfall, + height of storm surge –> issue ‘Hurricane Watch’ alert (72-hour forecast has margin of error of ~160km but 24-hour forecast has margin of error of 65km)

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37
Q

What are 3 types of wind/storm surge defences?

A
  1. Natural defences e.g. wide beaches, high dunes, mangroves
  2. Artificial defences e.g. concrete shelters, sea walls, levees
  3. Building regulations e.g. rounded walls/pitched roofs to promote wind flow around structure, anchor bolts between foundations/walls/roofs
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38
Q

When does a funnel cloud become a tornado?

A

When it reaches the ground (can sometimes form multiple tornadoes)

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39
Q

Why are tornadoes often visible?

A

Has a condensation funnel in which dust/debris is picked up + rotated

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40
Q

Define waterspouts

A

Tornadoes that are formed over water (generally weaker)

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41
Q

What is a key step of tornado formation?

A

Mesocyclone formation with a parent thunderstorm (‘supercell’ thunderstorms)

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42
Q

How do thunderstorms form?

A

When warm, moist air rises rapidly (instability from warm air below cold air) –> warm air cools + condensation occurs, resulting in cumulonimbus clouds with strong updrafts

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43
Q

What are examples of specific conditions that need to be met for severe thunderstorms to form?

A

Significant vertical wind shear + large instability

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44
Q

Which is the only continent where tornadoes haven’t been observed and where do most tornadoes form?

A

Antarctica, mid-latitudes (in contrast to hurricanes in tropics)

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45
Q

When is tornado season in ‘Tornado Alley’?

A

Spring to early summer

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46
Q

Why does Tornado Alley get so many tornadoes?

A

Has the key ingredients for supercell thunderstorms (low level winds bring warm, moist air from S.E and high level winds bring cool, dry air from Rocky Mountains)

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47
Q

In which direction do tornadoes rotate in the northern hemisphere?

A

Anti-clockwise

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48
Q

What is the Fujita scale based on and what is the scale?

A

Based on tornado-inflicted damage to human-built structures/vegetation + assigned wind speed, EF 0-5

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49
Q

What 3 things are used to assimilate data for tornado detection?

A
  1. Spotters (look for characteristic cloud formations e.g. mammatus clouds)
  2. Satellites (visible, infrared, moisture)
  3. Doppler radar
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50
Q

Describe how doppler radar is used to assimilate data for tornado detection?

A

Emits radio waves from transmitter –> pulse strikes an object e.g. raindrop + waves scattered –> some scattered energy directed back to radar –> computer algorithms determine strength of returned signal, time taken to travel to object and back, + frequency shift of pulse (changes depending on object motion + can be used to calculate speed of object towards/away from radar)

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51
Q

Define biohazard

A

Hazard caused by exposure to living organisms + their toxic substances or vector-borne diseases carried by living organisms

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52
Q

What must a biohazard do in order to become a natural hazard?

A

Must greatly exceed human expectation in terms of magnitude/frequency, causing human hardship or a negative economic impact

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53
Q

What % of global deaths is accounted for by infectious diseases (human hardship endpoint for many biohazards is human disease)?

A

> 25% (likely to increase under future climate scenarios)

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54
Q

What are the 3 types of biohazard?

A
  1. Microorganisms (airborne/blood/body fluid borne/vector borne/food borne/zoonotic/water borne)
  2. Biohazards that indirectly impact human society (infectious diseases in animals/fungal diseases affecting plants/insect infestation affecting crop production)
  3. Others (deadly nightshade/parasites/animal attacks)
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55
Q

What are the 3 types of disease classification?

A
  1. Endemic (always present)
  2. Epidemic
  3. Pandemic
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56
Q

What % of known diseases are zoonotic?

A

60%

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57
Q

What are the 4 types of biohazard mitigation?

A
  1. Surveillance + data (challenging for new diseases, potential political interference)
  2. Disease prevention (vaccines, limited availability)
  3. Treatment (of clinical symptoms, limited by public health infrastructure)
  4. Education
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58
Q

What are 2 key biohazards that are transmitted through water and are of significant concern?

A
  1. Cholera (intestines infection, bacterial, diarrhoea + dehydration, can lead to death if left untreated)
  2. Typhoid fever (bacterial, bacteria multiply in human blood/intestines)
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59
Q

What are many waterborne biohazards associated with?

A

The contamination of water be faecal matter e.g. E.coli

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60
Q

What are 2 naturally-occurring biohazards that can multiply in response to environmental conditions?

A
  1. Legionella bacteria (natural hazard when grow in water systems within buildings, can cause Legionnaire’s disease - serious case of pneumonia)
  2. Cyanobacteria (blue-green algal blooms, some blooms can be harmful + produce neurotoxins, hepatotoxins (liver), or dermatoxins)
61
Q

What are 3 lower cost strategies to reduce risk of waterborne biohazards?

A
  1. Solar water disinfection
  2. Chlorination
  3. Biosand filtration
62
Q

What are the 4 key chemical pollutants of water sources?

A
  1. Arsenic
  2. Lead
  3. Nitrate
  4. Salinisation
63
Q

What are 2 natural processes that can mobilise arsenic?

A
  1. Weathering
  2. Volcanic activity
64
Q

Where in the world does groundwater from alluvial/deltaic aquifers represent the most serious risk of arsenicosis and why?

A

Bangladesh + West Bengal, concentration of >3000 µg/L arsenic when WHO drinking standard is 10 µg/L

65
Q

What caused the concentration of arsenic to increase in groundwater aquifers in Bangladesh + West Bengal?

A

High organic matter content in aquifers used in 1970s/80s resulted in strongly reducing conditions + the release of arsenic in solution

66
Q

What negative human effect can lead exposure cause?

A

Cognitive effects on young children

67
Q

Why is lead a potentially significant chemical contaminant in drinking water?

A

Infrastructure used to supply water historically was manufactured using lead so potential for dissolution of lead corrosion products

68
Q

What is the case study for lead being a significant chemical contaminant in drinking water?

A

Flint, Michigan - switched water supply to untreated water sourced from River Flint + no corrosion control i.e. dosing with phosphate

69
Q

What is a potential health effect of nitrate exposure in drinking water?

A

Infant methemoglobinemia (blue baby syndrome) - nitrate oxidies ferrous iron to ferric form and produces methehaemoglobin which can’t bind O2

70
Q

What are 2 natural and 2 human sources of nitrate?

A

Natural: Lightning, biological N fixation
Human: Wastewater, fertiliser

71
Q

Why will nitrate be a globally persistent + potentially growing problem in the future?

A

Due to legacy stocks of nitrate that are yet to reach receiving waters (our groundwater abstraction boreholes)

72
Q

Define salinisation

A

An increase in the conc. of total dissolved solids in water (often detected by Cl- conc.)

73
Q

What are 2 direct effects and 1 indirect effect of salinisation of a water source?

A

Direct: Increased hypertension + infant mortality
Indirect: Increased corrosivity of water supplies + release of lead

74
Q

What are 2 natural processes and 2 anthropogenic activities that contribute towards salinisation?

A

Natural: Chemical weathering + climate change (sea level rise)
Anthropogenic: Road de-icing + over-abstraction of ground water

75
Q

What are 4 ways of mitigating chemical pollution of water?

A
  1. Identify + access new, unpolluted raw water sources (cost is a problem)
  2. Treat raw water to remove pollutants (cost/technology is a problem)
  3. Establish a monitoring regime to ensure risks are identified
  4. Engage with pop. regarding risks + appropriate responses
76
Q

What are 2 ways of treating raw water to remove/prevent pollutants within supplies?

A
  1. Adsorption for pollutant removal
  2. Corrosion control to prevent lead dissolution by dosing phosphate
77
Q

What are the 3 types of flood?

A
  1. River floods
  2. Coastal floods
  3. Surface water floods (‘flash floods’) - heavy rainfall overwhelms drainage capacity of local area, more difficult to predict
78
Q

What 3 factors is climate change changing which in turn alters the probability of flooding?

A
  1. Sea level
  2. Frequency + magnitude of storm surges
  3. Distribution + intensity of rainfall
79
Q

What % of UK coastal defences are predicted to be overtopped by 2100?

A

20%

80
Q

What are 4 immediate hazards of flooding?

A
  1. Drowning/hit by debris
  2. Electrocution
  3. Hypothermia
  4. Mudflows/debris flows
81
Q

What are 5 long term hazards of flooding?

A
  1. Epidemics of waterborne diseases
  2. Chemical contamination of drinking water
  3. Damage to agricultural land + products –> food shortages
  4. Damage to properties –> economic + social impacts
  5. Mental health effects e.g. financial stress
82
Q

What are 6 strategies to reduce vulnerability to flooding?

A
  1. Land use planning
  2. Flood risk reduction measures
  3. Flood diversion/defence measures
  4. Flood resistant/resilient buildings
  5. Forecasting + warning
  6. Education
83
Q

What is the case study for flooding?

A

Bangladesh (world’s most flood-prone country + densley-populated)

84
Q

What causes rivers to swell in Bangladesh during the spring and summer?

A

Snow melt from Himalayas in spring and heavy monsoon rains in summer

85
Q

What % of Bangladesh is normally inundated during the monsoon season?

A

20-25%

86
Q

What has reduced vulnerability to flooding in Bangladesh in recent decades?

A

Cyclone Preparedness Programme (1972) - thousands of cyclone shelters constructed + large network of volunteers trained to disseminate warnings + assist with evacuation

87
Q

Define a megadrought

A

Persistent, multi-year drought events that are exceptional in terms of severity/duration/spatial extent

88
Q

Define ‘flash drought’ (very recent research suggests emergence under climate change)

A

Moving from drought-free conditions to extreme drought within a matter of weeks

89
Q

What are 3 reasons why droughts present a particular risk in semi-arid regions?

A
  1. Low mean rainfall + associated high variability of total rainfall
  2. Lack of rainfall reliability
  3. Duration of drought is usually longer in drier regions
90
Q

What are the 4 types of drought?

A
  1. Meteorological (rainfall deficit)
  2. Hydrological (streamflow deficit)
  3. Agricultural (soil moisture deficit)
  4. Famine (food deficit)
91
Q

What is meteorological drought based on?

A

Palmer Drought Severity Index (PDSI)

92
Q

Define hydrological drought

A

Shortfall of water supply compared to water demand

93
Q

What is agricultural drought based on?

A

Indirect calculations e.g. PDSI - looks at precipitation + temp.

94
Q

What is an example of a country where agriculture is a significant part of economic output (agricultural drought)?

A

Australia

95
Q

What are the 2 causes of drought?

A
  1. Physical factors (evidence that large-scale interconnections between atmosphere + oceans are important for triggering drought)
  2. Human factors
96
Q

What is drought most likely triggered by?

A

Negative (cold) sea surface temps. –> descending air + anticyclonic weather

97
Q

What are the 3 strategies in mitigating drought?

A
  1. Protection (e.g. cloud seeding, use of dams/water transfer schemes)
  2. Mitigation (crisis management e.g. food aid)
  3. Adaptation
98
Q

What are 3 ways of adapting to drought?

A
  1. Community preparedness (e.g. diversifying livestock herds, using irrigation, hosepipe bans)
  2. Predictions/forecasts/warnings (e.g. Global Information + Early Warning System)
  3. Land use planning (e.g. adopting drought-resistant crops)
99
Q

How do earthquakes occur?

A

Faults constantly moving due to plate tectonics but sometimes “lock up” due to friction –> stress builds up until it overcomes friction –> fault releases suddenly in an EQ

100
Q

Define fault plane

A

Area that ruptures

101
Q

Define focus/hypocentre

A

Point on fault plane at which rupture starts (defined by latitude, longitude, + focal depth)

102
Q

Define epicentre

A

Point on Earth’s surface directly above focus

103
Q

What is the difference between shallow, intermediate, and deep EQs?

A

Short = 0-70km deep, intermediate = 70-300km deep, deep = 300-700km deep

104
Q

Where can EQs occur?

A

Convergent plate boundaries, sites of continental collision, + intraplate EQs (related to crustal loading/unloading)

105
Q

Why are MOR EQs less destructive (divergent boundaries)?

A

Relatively small + away from populations, mostly along transform faults (type of strike-slip fault), little displacement of ocean so less chance of tsunamis

106
Q

How many seismographs are needed to measure ground displacement/velocity/acceleration vs. time?

A

One vertical and two horizontal (N-S and E-W)

107
Q

What are the 4 types of seismic waves?

A
  1. P-waves (body) - primary, compressional, oscillate parallel to direction of wave propagation
  2. S-waves (body) - shear waves, oscillate perpendicular to direction of wave propagation
  3. Rayleigh waves (surface)
  4. Love waves (surface)
108
Q

How is the epicentre of an earthquake located?

A

Time difference between first P- and S-wave arrivals on seismogram is proportional to distance between EQ + seismograph so S-P time interval measured and used to calculate distance for at least 3 stations (epicentre is where circles overlap)

109
Q

How is the focus of an earthquake located?

A

pP phase identified on seismogram, time interval pP-P used to compute depth-of-focus tables

110
Q

Define pP waves

A

P-waves that have been reflected from surface of Earth at a point relatively near to the focus

111
Q

What is the equation for Moment Magnitude (Mw) scale?

A

Mw = 2/3 (log10 M(0) - 9.1)

112
Q

What is M(0) determined by and what is the equation for calculating it?

A

Magnitude of force which acts on Earth’s lithosphere + strength of block that fractures, M(0) = μAd

113
Q

What do μ, A, and d mean in the M(0) equation?

A

μ = modulus of rigidity, N m-2 (shear stress/shear strain)
A = area of fractured plane
d = average displacement along fault, m

114
Q

What 4 things does the strength of which an EQ is felt depend on?

A
  1. Magnitude
  2. Distance from epicentre
  3. Focal depth (shallower EQs more damaging)
  4. Ground type (soft rock/sediment shakes more)
115
Q

What are 2 primary effects of an EQ?

A
  1. Fault rupture
  2. Ground shaking
116
Q

What are 4 secondary effects of an EQ?

A
  1. Ground settlement
  2. Liquefaction
  3. Landslides + rockfall
  4. Tsunamis
117
Q

Define ground acceleration

A

How quickly ground changes velocity during an EQ (usually expressed as fraction of acceleration due to gravity)

118
Q

Describe liquefaction

A

Solid medium soil turns into a fluid medium due to shaking, houses can sink + pipes can rise, soils prone to liquefaction are sandy/silty/gravelly and water-saturated

119
Q

How are fires caused by EQs?

A

Overturned stoves/broken gas mains/short-circuited electricity cables

120
Q

How are floods caused by EQs?

A

Diverted rivers/burst dams/changes in land elevation/tsunamis

121
Q

How are tsunamis caused by EQs?

A

Occur where fault movements in vertical plane (not strike-slip) offshore lead to a sudden vertical change in seabed which displaces sea water

122
Q

Which EQ scale is used in N.America?

A

Modified Mercalli Intensity (MMI), ranges from I-X+

123
Q

What is the equation for the intensity of an EQ?

A

Intensity = K(1)M + K(2)/D + K(3)/R + G
K(x) = constant
M = moment magnitude
D = focal depth
R = distance from epicentre
G = ground factor (zero for solid rock, higher for soft ground)

124
Q

What are the 5 ways of reducing vulnerability to an EQ?

A
  1. EQ hazard assessment (probabilistic forecasting)
  2. Land use planning
  3. Anti-seismic design + structures
  4. Education, training, + emergency planning
  5. Earthquake Early Warning System (EEWS)
125
Q

What are the 2 different approaches of the EEWS?

A
  1. Single station approach (detect first P-waves from EQ + sound alarm)
  2. Network approach (combine data from several seismograph stations to rapidly compute approximate magnitude etc.)
126
Q

What does lava chemistry depend on and what does it affect?

A

Plate tectonic location, affect volcano morphology/explosivity

127
Q

Define an active, dormant, and extinct volcano

A

Active volcano = Has erupted in historical times
Dormant volcano = Hasn’t erupted since end of Ice Age (10k years)
Extinct volcano = Not considered to erupt again

128
Q

What are 3 signs a volcano is active/dormant?

A
  1. Recent eruptions evidenced by known historical eruptions, ¹⁴C (radiocarbon) dated eruptions, young-looking volcanic rocks
  2. Thermal signs e.g. fumaroles, hot springs
  3. Frequent local earthquakes
129
Q

What increases lava viscosity (resistance to flow)?

A

Increased SiO2 content and decreased temp.

130
Q

Define volatiles

A

Gases dissolved in magma at high pressures (i.e. deep underground)

131
Q

How do volatiles cause an explosive eruption?

A

When pressure decreases, volatiles exsolve + form bubbles –> if bubbles can’t easily escape (e.g. blocked vent), cause explosive eruptions

132
Q

Where do most explosive eruptions occur?

A

At subduction zones as magmas contain higher proportions of volatiles derived from subducted oceanic lithosphere + magmas tend to have higher silica content so more viscous

133
Q

Define a phreatic eruption (external water can cause explosve eruptions)

A

Explosion of superheated steam due to heating of groundwater in close proximity to magma

134
Q

Define a phreatomagmatic eruption (external water can cause explosve eruptions)

A

Direct interaction of water with magma (fresh magma included in erupted material)

135
Q

What is VEI based on?

A

How much material is ejected, to what height, and eruption duration

136
Q

What are 4 hazards of volcanic eruptions?

A
  1. Lava flows
  2. Air fall deposits, pyroclastic fall deposits, tephra
  3. Flow deposits (lahars, pyroclastic flows)
  4. Sector collapse
137
Q

What are 5 ways of reducing vulnerability to volcanic eruptions?

A
  1. Risk assessment (hazard maps)
  2. Appropriate land use (exclusion zones, evacuation routes)
  3. Hazard defences (crater lake drainage, strong shelters)
  4. Advance emergency planning
  5. Monitoring + forecasting (detect ground deformation e.g. bulges using tiltmeters + thermal anomalies using remote sensing e.g. satellite-based IR)
138
Q

Define mass movement

A

Downslope movement of material under the influence of gravity

139
Q

What are 6 processes involved in mass movement and which are the most destructive?

A
  1. Creep
  2. Heave
  3. Subsidence
  4. Fall
  5. Slide (occurs along well-defined shear plane)
  6. Flow (shear occurs throughout moving mass of material + no well-defined shear plane)
    Last 3 are most destructive
140
Q

What does driving force do (mass movement)?

A

Encourages failure + downslope motion

141
Q

Define threshold angle of stability (mass movement)

A

Shear plane angle at which failure occurs

142
Q

Define angle of repose (mass movement)

A

Maximum slope angle that can be attained before it slides

143
Q

Define regolith

A

Layer of loose heterogeneous superficial deposits covering Earth’s solid rock (fragments of rock, sediment, + soil)

144
Q

What is the response of a slope to stress determined by?

A

Shear strength (ability to resist deformation + fracture without failure)

145
Q

What 4 things influence the shear strength of a slope?

A
  1. Frictional resistance between constituent particles (unconsolidated)
  2. Stress applied
  3. Cohesion of material (unconsolidated)/intact strength (consolidated)
  4. Clay content (of soil)
146
Q

Define Safety Factor, F(s) and give the equation for F(s)

A

Safety Factor = Ratio between a slope’s shear stress + shear strength, F(s) = shear strength / shear stress

147
Q

What are 3 natural factors that can trigger change from a stable to an unstable slope?

A
  1. Rainfall
  2. Earthquakes
  3. Volcanoes
148
Q

What are 3 anthropogenic factors that can trigger change from a stable to an unstable slope?

A
  1. Loading (e.g. building)
  2. Undercutting (e.g. road construction)
  3. Deforestation (removes binding agent)
149
Q

What are 2 ways of mitigating mass movement?

A
  1. Decrease likelihood (e.g. slope stabilisation by drainage/reforestation, land use laws)
  2. Mitigate impact (e.g. sabo (catchment) dams, boulder catchment nets + ditches, EWS)

BSc Environmental Science (13 decks)

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