LEC.185 Natural Hazards Flashcards
1
Q
Which are the 2 most commonly occurring natural disaster types?
A
Floods and storms
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
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
- More public awareness + reporting (less deaths, more reports)
- Larger population so more people forced to live in hazardous areas
- More poverty + urbanisation so more people in poorly constructed shanty towns
- Proliferation of sensitive structures e.g. nuclear power plants (interaction between natural + technological hazards)
- Environmental degradation + climate change
4
Q
Define risk
A
Probability that harmful effects will actually follow from a natural hazard
5
Q
What is the risk equation?
A
Risk = hazard level x exposure x vulnerability
6
Q
What is the difference between weather and climate?
A
Weather = Short term changes in atmosphere
Climate = Long term average of weather conditions
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)
8
Q
Define heat index
A
Measure of ‘how it feels’ or the ‘apparent’ temperature + factors in relative humidity
9
Q
What are 4 reasons why the perception of heat may differ between different regions?
A
- Meteorological factors (e.g. wind speed, relative humidity)
- Differences in body composition/shape
- Metabolic differences
- Levels of hydration
10
Q
Why does higher relative humidity make heat feel hotter?
A
Less perspiration evaporates in humid conditions
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)
12
Q
What does air pressure arise from?
A
Weight of the atmosphere (larger closer to Earth’s surface and decreases with increasing altitude)
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
14
Q
What do isobars join?
A
Areas of equal pressure (closer spacing denotes stronger pressure gradient + increased wind speeds)
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
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
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
18
Q
Define urban heat island
A
Region where tarmac/stone absorbs + stores heat during daytime + emits heat at night
19
Q
What are 6 reasons why the intensity, duration, frequency, and areal extent of heatwaves is important?
A
- Heat-related illness/death
- Pressure on services
- Water/energy demand
- Critical infrastructure impacts
- Ecological impacts (droughts/forest fires)
- Co-occurrence of heatwaves + air pollution episodes
20
Q
What are 4 ways of mitigating heatwaves?
A
- Heat-health alert systems (5 alert levels in UK)
- Increased healthcare capacity
- Address urban heat islands
- Protect critical agriculture + vulnerable groups
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
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
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’
24
Q
Which regions call hurricanes ‘typhoons’ and ‘cyclones’?
A
Typhoons: SE Asia
Cyclones: Australia + Indian Ocean
25
When is hurricane 'season' in the N.Atlantic basin, when is peak activity, where do these hurricanes form, and which direction do they travel?
June-November, September, coast of Africa, steered East by trade winds
26
What 6 things does hurricane formation require?
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)
27
Describe the 8-step formation process of a hurricane (positive feedback loop)
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)
28
What is important to differentiate between within a hurricane?
Rotation wind speed and forward propagation wind speed
29
What are the 3 structures of a hurricane?
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
30
Define hurricane wind velocity and how is this measured?
Speed of rotating winds, measured using Saffir-Simpson scale (categories 1-5)
31
Define storm centre velocity
Speed of entire storm (typically 15-20mph), affected by atmospheric flows that steer storm system, can exceed 60mph particularly at high latitudes
32
When is hurricane intensity at its strongest?
When storm centre velocity + hurricane wind velocity are in the same direction
33
What are 6 consequent hazards of hurricanes?
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
34
Define storm surge
Change in sea level caused by high winds + low pressure
35
How will climate change affect hurricanes?
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
36
How are hurricanes detected?
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)
37
What are 3 types of wind/storm surge defences?
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
38
When does a funnel cloud become a tornado?
When it reaches the ground (can sometimes form multiple tornadoes)
39
Why are tornadoes often visible?
Has a condensation funnel in which dust/debris is picked up + rotated
40
Define waterspouts
Tornadoes that are formed over water (generally weaker)
41
What is a key step of tornado formation?
Mesocyclone formation with a parent thunderstorm ('supercell' thunderstorms)
42
How do thunderstorms form?
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
43
What are examples of specific conditions that need to be met for severe thunderstorms to form?
Significant vertical wind shear + large instability
44
Which is the only continent where tornadoes haven't been observed and where do most tornadoes form?
Antarctica, mid-latitudes (in contrast to hurricanes in tropics)
45
When is tornado season in 'Tornado Alley'?
Spring to early summer
46
Why does Tornado Alley get so many tornadoes?
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)
47
In which direction do tornadoes rotate in the northern hemisphere?
Anti-clockwise
48
What is the Fujita scale based on and what is the scale?
Based on tornado-inflicted damage to human-built structures/vegetation + assigned wind speed, EF 0-5
49
What 3 things are used to assimilate data for tornado detection?
1. Spotters (look for characteristic cloud formations e.g. mammatus clouds)
2. Satellites (visible, infrared, moisture)
3. Doppler radar
50
Describe how doppler radar is used to assimilate data for tornado detection?
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)
51
Define biohazard
Hazard caused by exposure to living organisms + their toxic substances or vector-borne diseases carried by living organisms
52
What must a biohazard do in order to become a natural hazard?
Must greatly exceed human expectation in terms of magnitude/frequency, causing human hardship or a negative economic impact
53
What % of global deaths is accounted for by infectious diseases (human hardship endpoint for many biohazards is human disease)?
>25% (likely to increase under future climate scenarios)
54
What are the 3 types of biohazard?
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)
55
What are the 3 types of disease classification?
1. Endemic (always present)
2. Epidemic
3. Pandemic
56
What % of known diseases are zoonotic?
60%
57
What are the 4 types of biohazard mitigation?
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
58
What are 2 key biohazards that are transmitted through water and are of significant concern?
1. Cholera (intestines infection, bacterial, diarrhoea + dehydration, can lead to death if left untreated)
2. Typhoid fever (bacterial, bacteria multiply in human blood/intestines)
59
What are many waterborne biohazards associated with?
The contamination of water be faecal matter e.g. E.coli
60
What are 2 naturally-occurring biohazards that can multiply in response to environmental conditions?
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
What are 3 lower cost strategies to reduce risk of waterborne biohazards?
1. Solar water disinfection
2. Chlorination
3. Biosand filtration
62
What are the 4 key chemical pollutants of water sources?
1. Arsenic
2. Lead
3. Nitrate
4. Salinisation
63
What are 2 natural processes that can mobilise arsenic?
1. Weathering
2. Volcanic activity
64
Where in the world does groundwater from alluvial/deltaic aquifers represent the most serious risk of arsenicosis and why?
Bangladesh + West Bengal, concentration of >3000 µg/L arsenic when WHO drinking standard is 10 µg/L
65
What caused the concentration of arsenic to increase in groundwater aquifers in Bangladesh + West Bengal?
High organic matter content in aquifers used in 1970s/80s resulted in strongly reducing conditions + the release of arsenic in solution
66
What negative human effect can lead exposure cause?
Cognitive effects on young children
67
Why is lead a potentially significant chemical contaminant in drinking water?
Infrastructure used to supply water historically was manufactured using lead so potential for dissolution of lead corrosion products
68
What is the case study for lead being a significant chemical contaminant in drinking water?
Flint, Michigan - switched water supply to untreated water sourced from River Flint + no corrosion control i.e. dosing with phosphate
69
What is a potential health effect of nitrate exposure in drinking water?
Infant methemoglobinemia (blue baby syndrome) - nitrate oxidies ferrous iron to ferric form and produces methehaemoglobin which can't bind O2
70
What are 2 natural and 2 human sources of nitrate?
Natural: Lightning, biological N fixation
Human: Wastewater, fertiliser
71
Why will nitrate be a globally persistent + potentially growing problem in the future?
Due to legacy stocks of nitrate that are yet to reach receiving waters (our groundwater abstraction boreholes)
72
Define salinisation
An increase in the conc. of total dissolved solids in water (often detected by Cl- conc.)
73
What are 2 direct effects and 1 indirect effect of salinisation of a water source?
Direct: Increased hypertension + infant mortality
Indirect: Increased corrosivity of water supplies + release of lead
74
What are 2 natural processes and 2 anthropogenic activities that contribute towards salinisation?
Natural: Chemical weathering + climate change (sea level rise)
Anthropogenic: Road de-icing + over-abstraction of ground water
75
What are 4 ways of mitigating chemical pollution of water?
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
What are 2 ways of treating raw water to remove/prevent pollutants within supplies?
1. Adsorption for pollutant removal
2. Corrosion control to prevent lead dissolution by dosing phosphate
77
What are the 3 types of flood?
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
What 3 factors is climate change changing which in turn alters the probability of flooding?
1. Sea level
2. Frequency + magnitude of storm surges
3. Distribution + intensity of rainfall
79
What % of UK coastal defences are predicted to be overtopped by 2100?
20%
80
What are 4 immediate hazards of flooding?
1. Drowning/hit by debris
2. Electrocution
3. Hypothermia
4. Mudflows/debris flows
81
What are 5 long term hazards of flooding?
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
What are 6 strategies to reduce vulnerability to flooding?
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
What is the case study for flooding?
Bangladesh (world's most flood-prone country + densley-populated)
84
What causes rivers to swell in Bangladesh during the spring and summer?
Snow melt from Himalayas in spring and heavy monsoon rains in summer
85
What % of Bangladesh is normally inundated during the monsoon season?
20-25%
86
What has reduced vulnerability to flooding in Bangladesh in recent decades?
Cyclone Preparedness Programme (1972) - thousands of cyclone shelters constructed + large network of volunteers trained to disseminate warnings + assist with evacuation
87
Define a megadrought
Persistent, multi-year drought events that are exceptional in terms of severity/duration/spatial extent
88
Define 'flash drought' (very recent research suggests emergence under climate change)
Moving from drought-free conditions to extreme drought within a matter of weeks
89
What are 3 reasons why droughts present a particular risk in semi-arid regions?
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
What are the 4 types of drought?
1. Meteorological (rainfall deficit)
2. Hydrological (streamflow deficit)
3. Agricultural (soil moisture deficit)
4. Famine (food deficit)
91
What is meteorological drought based on?
Palmer Drought Severity Index (PDSI)
92
Define hydrological drought
Shortfall of water supply compared to water demand
93
What is agricultural drought based on?
Indirect calculations e.g. PDSI - looks at precipitation + temp.
94
What is an example of a country where agriculture is a significant part of economic output (agricultural drought)?
Australia
95
What are the 2 causes of drought?
1. Physical factors (evidence that large-scale interconnections between atmosphere + oceans are important for triggering drought)
2. Human factors
96
What is drought most likely triggered by?
Negative (cold) sea surface temps. --> descending air + anticyclonic weather
97
What are the 3 strategies in mitigating drought?
1. Protection (e.g. cloud seeding, use of dams/water transfer schemes)
2. Mitigation (crisis management e.g. food aid)
3. Adaptation
98
What are 3 ways of adapting to drought?
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
How do earthquakes occur?
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
Define fault plane
Area that ruptures
101
Define focus/hypocentre
Point on fault plane at which rupture starts (defined by latitude, longitude, + focal depth)
102
Define epicentre
Point on Earth's surface directly above focus
103
What is the difference between shallow, intermediate, and deep EQs?
Short = 0-70km deep, intermediate = 70-300km deep, deep = 300-700km deep
104
Where can EQs occur?
Convergent plate boundaries, sites of continental collision, + intraplate EQs (related to crustal loading/unloading)
105
Why are MOR EQs less destructive (divergent boundaries)?
Relatively small + away from populations, mostly along transform faults (type of strike-slip fault), little displacement of ocean so less chance of tsunamis
106
How many seismographs are needed to measure ground displacement/velocity/acceleration vs. time?
One vertical and two horizontal (N-S and E-W)
107
What are the 4 types of seismic waves?
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
How is the epicentre of an earthquake located?
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
How is the focus of an earthquake located?
pP phase identified on seismogram, time interval pP-P used to compute depth-of-focus tables
110
Define pP waves
P-waves that have been reflected from surface of Earth at a point relatively near to the focus
111
What is the equation for Moment Magnitude (Mw) scale?
Mw = 2/3 (log10 M(0) - 9.1)
112
What is M(0) determined by and what is the equation for calculating it?
Magnitude of force which acts on Earth's lithosphere + strength of block that fractures, M(0) = μAd
113
What do μ, A, and d mean in the M(0) equation?
μ = modulus of rigidity, N m-2 (shear stress/shear strain)
A = area of fractured plane
d = average displacement along fault, m
114
What 4 things does the strength of which an EQ is felt depend on?
1. Magnitude
2. Distance from epicentre
3. Focal depth (shallower EQs more damaging)
4. Ground type (soft rock/sediment shakes more)
115
What are 2 primary effects of an EQ?
1. Fault rupture
2. Ground shaking
116
What are 4 secondary effects of an EQ?
1. Ground settlement
2. Liquefaction
3. Landslides + rockfall
4. Tsunamis
117
Define ground acceleration
How quickly ground changes velocity during an EQ (usually expressed as fraction of acceleration due to gravity)
118
Describe liquefaction
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
How are fires caused by EQs?
Overturned stoves/broken gas mains/short-circuited electricity cables
120
How are floods caused by EQs?
Diverted rivers/burst dams/changes in land elevation/tsunamis
121
How are tsunamis caused by EQs?
Occur where fault movements in vertical plane (not strike-slip) offshore lead to a sudden vertical change in seabed which displaces sea water
122
Which EQ scale is used in N.America?
Modified Mercalli Intensity (MMI), ranges from I-X+
123
What is the equation for the intensity of an EQ?
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
What are the 5 ways of reducing vulnerability to an EQ?
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
What are the 2 different approaches of the EEWS?
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
What does lava chemistry depend on and what does it affect?
Plate tectonic location, affect volcano morphology/explosivity
127
Define an active, dormant, and extinct volcano
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
What are 3 signs a volcano is active/dormant?
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
What increases lava viscosity (resistance to flow)?
Increased SiO2 content and decreased temp.
130
Define volatiles
Gases dissolved in magma at high pressures (i.e. deep underground)
131
How do volatiles cause an explosive eruption?
When pressure decreases, volatiles exsolve + form bubbles --> if bubbles can't easily escape (e.g. blocked vent), cause explosive eruptions
132
Where do most explosive eruptions occur?
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
Define a phreatic eruption (external water can cause explosve eruptions)
Explosion of superheated steam due to heating of groundwater in close proximity to magma
134
Define a phreatomagmatic eruption (external water can cause explosve eruptions)
Direct interaction of water with magma (fresh magma included in erupted material)
135
What is VEI based on?
How much material is ejected, to what height, and eruption duration
136
What are 4 hazards of volcanic eruptions?
1. Lava flows
2. Air fall deposits, pyroclastic fall deposits, tephra
3. Flow deposits (lahars, pyroclastic flows)
4. Sector collapse
137
What are 5 ways of reducing vulnerability to volcanic eruptions?
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
Define mass movement
Downslope movement of material under the influence of gravity
139
What are 6 processes involved in mass movement and which are the most destructive?
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
What does driving force do (mass movement)?
Encourages failure + downslope motion
141
Define threshold angle of stability (mass movement)
Shear plane angle at which failure occurs
142
Define angle of repose (mass movement)
Maximum slope angle that can be attained before it slides
143
Define regolith
Layer of loose heterogeneous superficial deposits covering Earth's solid rock (fragments of rock, sediment, + soil)
144
What is the response of a slope to stress determined by?
Shear strength (ability to resist deformation + fracture without failure)
145
What 4 things influence the shear strength of a slope?
1. Frictional resistance between constituent particles (unconsolidated)
2. Stress applied
3. Cohesion of material (unconsolidated)/intact strength (consolidated)
4. Clay content (of soil)
146
Define Safety Factor, F(s) and give the equation for F(s)
Safety Factor = Ratio between a slope's shear stress + shear strength, F(s) = shear strength / shear stress
147
What are 3 natural factors that can trigger change from a stable to an unstable slope?
1. Rainfall
2. Earthquakes
3. Volcanoes
148
What are 3 anthropogenic factors that can trigger change from a stable to an unstable slope?
1. Loading (e.g. building)
2. Undercutting (e.g. road construction)
3. Deforestation (removes binding agent)
149
What are 2 ways of mitigating mass movement?
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)
