Hazards Flashcards
(162 cards)
1
Q
What is the VEI ?
A
Volcanic eruption index
2
Q
What three things do the VEI measure ?
A
- Volume of ejecta
- Height of the eruption column
- Qualitative observations
3
Q
GIve three criticisms of the VEI ?
A
- Gas emissions
- Atmospheric / climate impacts
- All tephra considered alike despite differences in densities and impact
4
Q
Give five ways in which volcanic eruptions vary ?
A
- Frequency
- Magnitude
- Regularity
- Predictability
- Duration
5
Q
What is a super volcano ?
A
An unusually large volcano having the potential to produce an eruption with major effects on the global climate and ecosystems.
6
Q
What is tephra
A
Solid material of varying grain size ranging from volcanic bombs to ash all ejected into the atmosphere during a volcanic eruption that then falls back down.
7
Q
What is pyroclastic flow
A
Very hot gas charged high velocity flows made up of a mixture of super-heated gas and tephra
8
Q
What are lava flows
A
Molten rock that flows from a volcanic vent
9
Q
What are volcanic gases
A
carbon dioxide, sulphur dioxide, hydrogen sulphide, carbon monoxide and chlorine
10
Q
How are lahars formed
A
Melted snow and ice as a result of the eruption or heavy rainfall following an eruption combines with volcanic ash and forms mud flows.
11
Q
How are tsunamis formed
A
Sea waves generated by violent volcanic eruptions underwater or pyroclastic flows/lahars/landslides displacing water which often result in much more widespread impacts than the volcano itself
12
Q
How is acid rain formed
A
Volcanoes emit gases which include sulphur, this then combines with atmospheric moisture and results in acid rain.
13
Q
What is climate change
A
The ejection of huge amounts of volcanic debris into the atmosphere can reduce global temperatures.
Sulphur dioxide emitted from volcanoes when combining with water vapour creates droplets of sulphuric acid which reflect sunlight.
14
Q
What is the impact of a lahar
A
1985 - Nevado del Ruiz, Amero, Colombia - 23, 000 people killed. Impacts include: destruction of natural habitats/settlements/farmland; economic benefits of lahar deposits. Long-term impacts can occur many years post eruption.
15
Q
What is the impact of a tsunami
A
Wide-spread destruction
16
Q
What is the impact of acid rain
A
- Damages and kills trees
- Leaches toxic metals from soils and then accumulates in rivers/lakes
- Kills fish stocks and damages ecosystems
- Damages buildings and monuments by accelerating weathering
17
Q
What is the impact of climate change
A
Unusually cold weather > crop failures and resultant food shortages. The eruption of the Laki fissure system and ash/gas cloud has been linked to the start of the French Revolution in 1789
18
Q
Give three methods of preparedness to reduce the risk of volcanic hazard
A
- Hazard mapping
- Have emergency kits prepared
- Set up search and rescue teams
19
Q
Outline how the following warning signs of volcanic hazards can be predicted
Sulphur/radon gases
Ground deformation
Energy release
Surface temperature changes
A
Sulphur/radon gases = Spider robots
Ground deformation = Tiltmeters
Energy release = Seismometers
Surface temperature changes = Thermal Heat sensors
20
Q
How do earthquakes result in tsunamis
A
Earthquakes vertically move the seabed up by several metres.
Displacing (moving) the water above. The greater the movement of the sea floor the greater the volume of water displaced and the bigger the wave produced - hence greater intensity at destructive plate boundaries as higher magnitude earthquakes.
Large waves radiate outwards across the ocean away from the epicentre of the earthquake.
In deep water no energy is lost to frictional drag with the seabed.
As wave approaches shore > water becomes shallower and the base is slowed down by friction, forcing the circular wave motion into an elliptical form, which heightens until it can no longer be maintained and breaks. This is called shoaling.
A large wave hits the coast, a tsunami.
21
Q
How do the following factors affect the intensity of impacts of a tsunami?
The height of the waves:
The distance the waves have travelled:
Shape of coastline:
A
The height of the waves: the level of movement of the sea floor - the greater the movement the greater the volume of water displaced and the bigger the wave produced.
The distance the waves have travelled: waves lose energy as they travel towards the land, so the closer to the coast the waves start, the less energy they will lose, therefore tsunamis tend to be more powerful when they start closer to the coast.
Shape of coastline: Indented coastlines with long, narrow bays concentrate energy on the bay head due to a funnelling effect as the wave travels up the bay. Irregular coastlines and offshore islands can set up interference patterns in the waves which, when they coincide perfectly, can accentuate the waveform.
22
Q
How do the following factors affect the intensity of impacts of a tsunami
Relief of coastline:
Presence of natural defences:
Population density
A
Relief of coastline: Cliffs present a natural barrier to a tsunami.
Presence of natural defences: Coral and mangroves act as natural defences by dissipating wave energy through their large surface areas.
Population density: High population density - greater intensity. Also, the young and old are the most vulnerable, and there may be a gender disparity.
23
Q
What is a natural hazard ?
A
Naturally occurring phenomena that occurs in the lithosphere, hydrosphere and atmosphere. That is a threat to both life, the built and natural environment.
24
Q
What are the three types of natural hazard ?
A
- Geophysical
- Hydrological
- Atmospherical
25
What are the five characteristics of natural hazards?
- Origins are clear and their effects are distinctive
- Most only offer short or little warning before the event
- Exposure to risk is involuntary in LIC and some NIC’s whilst in HIC’s they are aware of hazards however choose to minimise or ignore them
- Most losses to life and damage to property occurs shortly afterwards even though the effects of natural hazards can be felt in communities long after that time
-The scale and intensity of the event requires an emergency response
26
Define vulnerability
How susceptible a population is to damage caused by a hazard - potential for loss which varies over time and space.H
27
Define risk
The likelihood that people will be seriously affected by a hazard
28
Define multi-hazard environment
places where two or more natural hazards occur and may interact to form more complex disasters
29
Describe the spatial distribution of tropical storms
- 5-20N/S of equator
- Hurricanes: North Atlantic and NE pacific - Caribbean sea, Gulf of Mexico and Western Central America
- Cyclones: Southern Pacific/ Indian
- Typhoons: NW pacific affect SE Asia
- Found in areas with oceans over 27 C and 70+m deep, low level convergence of air in lower atmospheric circulation systems
30
Why do people consciously put themselves at risk of natural hazards?
- Hazard events are unpredictable - We cannot predict the frequency, magnitude or scale of a natural hazard event.
- Lack of alternatives - Due to social, political, economic and cultural factors, people cannot simply uproot themselves from one place and move to another, giving up their homes, land and employment.
- Changing the level of risk - Places that were once safe many have become through time far more at risk . - Cost/benefit - Advantages of living somewhere outweigh the disadvantages - Perception
31
Define fatalism
People cannot influence the shape or outcome therefore nothing can be done to mitigate against it. People with such an attitude put in place limited or no prevention measures. ‘God’s will’
32
Define adaptation
Attempts by people or communities to live with hazard events. By adjusting their living conditions to live with the hazards and to reduce their vulnerability.
33
Define mitigation
Attempts to lessen the severity of hazards.
34
Why is perception important in the context of hazards?
People’s perception will ultimately decide and determine the course of action that individuals take or the response they expect from governments and other organisations
35
What are the three ways people may perceive natural hazards?
Fatalism
Adaption
Fear
36
How does socioeconomic status affect perception of risk
Wealthier areas better prepared/protected/consider hazards more controllable/voluntary > lower risk. Poorer areas: less able to afford protections etc/may be involuntary, lack of alternatives means cannot move away > risk seems greater
37
How does level of education affect perception of risk
People with a better education may better understand the risk of hazards or believe they are able to reduce the risks.
38
How does religion affect perception of risk
If hazards are an act of god > people may perceive them as uncontrollable and be less likely to mitigate them
39
How does past experience affect perception of risk
Prison of experience - limit perception of risk to past experiences - more likely to fully understand. Vs 'lightning never strikes the same place twice’ approach
40
Define community preparedness
Involves prearranged measures that aim to reduce the loss of life and property damage through public education and awareness programmes, evacuation procedures, the provision of emergency medical supplies and the taking out of insurance
41
Define integrated risk management
The process of considering the social, economic and political factors involved in risk analysis; determining the acceptability of damage/disruption; deciding on the actions to be taken to minimise damage/disruption
42
Define resilience
The ability of individuals or communities to be able to utilise available resources to respond to, withstand and recover from the effects of natural hazards events.
43
What are the four stages of the disaster risk management cycle ?
Preparedness
Response
Recovery
Mitigation
44
Give two positives and two negatives of the disaster risk management cycle
- Less reflective of slow onset disasters as no obvious event to trigger movement between stages
- Generic - no specific figures
+ Risk management is an ongoing process - hence a cycle.
+ Shows effects of preparedness before/after event
45
What are the five stages of the Park Model?
Pre-disaster
Disruption
Relief
Rehabilitation
Reconstruction
46
What does the following tell you about a country's response to a disaster?
Depth of curve: intensity of impacts
Steepness of upward curve: Effectiveness /speed of recovery
Steepness of downward curve: type of hazard (rapid or slow onset).
47
The Park Model shows changes of ____ over time?
Quality of life
48
Give two positives and two negatives of the Park Model
- Doesn’t show quantitative data making comparisons difficult
- Doesn’t show pre-onset mitigation methods for example evacuation - so cannot compare these
+ Allows for comparison between events to show what was effective in recovery
+Helps planners plan for future events as can rehabilitate to a higher standard and implement mitigation strategies
49
Explain the rehabilitation stage of the Park model
Immediate impacts are under control so people start to resolve longer term problems
50
The distribution of a hazard through time is called the…
Frequency
51
The assessment of the size and impacts of a hazard event is known as the …
Magnitude
52
The ability of individuals to withstand and recover from a disaster is known as …
Resilience
53
How will incidence affect the level of management needed following a disaster
A high incidence = frequent, expected and more likely to have a management plan in place.
High incidence hazards also tend to be less intense > so less of a need for a large management response.
54
How will intensity affect the level of management needed following a disaster
High magnitude, high intensity hazards tend to have worse effects and therefore require more management
55
How will distribution affect the level of management needed following a disaster
areas with a high hazard distribution are likely to have lost management strategies, those living there will be more adapted to the hazardous landscape > less intense
56
How will a high level of development affect the level of management needed following a disaster
LICS less able to afford effective mitigation strategies > more disastrous/less management
57
How will a multi-hazard environment affect the level of management needed following a disaster
Lack of money for multiple hazards so may lack management strategies for the less frequent events.
58
What is prediction in the context of hazards?
Using scientific research and past events to forecast when and where hazards will occur and provide warnings to aid in evacuation to reduce the impacts of a hazard.
59
Give an example of methods of prediction.
The tsunami warning system
60
Give three factors needed to make prediction an effective management technique
- Information must be successfully distributed
- Information must be accurate
- Recipients must trust warnings and know how to effectively respond
61
What is ‘protection’ in the context of hazards?
Protect people from the impact of the event by modifications to the built environment
62
What are the three ways people and organisations manage natural hazards?
Prediction
Protection
Prevention
63
What is a primary hazard
Hazards that are directly related to the hazard event.
64
What is a secondary hazard
Hazards that occur due to the occurrence of another are indirectly related and occur after the primary hazard.
65
Give three examples of primary VOLCANIC hazards.
Tephra
Pyroclastic flows
Lava flows
Volcanic gases
66
Give three examples of secondary VOLCANIC hazards
Lahars
Flooding
Volcanic landslides
Tsunamis
Acid rain
Climate change
67
How was the earth formed?
- Accretion (gravitational attraction and collision of meteorites.
- Meteorite collision, radioactive decay and planetary compression caused temperatures to rise above 2000C the melting point of iron
- Earth cooled > layers formed > heavier materials sank and lighter rocks rose above.
68
What are the two reasons why the earth’s core is so hot?
- Primordial heat
- Radiogenic heat
69
What is the asthenosphere?
Semi-molten mantle, nearer the core that plates move on.
70
What is the lithosphere?
Crust and rigid upper section of the mantle
71
Give three differences between oceanic and continental crust
Oceanic
- 6-10km (thinner)
- Less than 200 million years old (younger)
- Denser (3.0)
- Basalt, SIMA (silicon, magnesium and oxygen)
Continental
- 30-70km (thicker)
- Over 1500 million year old
- Less dense (2.6)
- Granite, SIAL (silicon, aluminium and oxygen).
72
What theory did Alfred Wegener suggest?
Continental drift
73
Give two pieces of geological and two pieces of biological evidence used by Alfred Wegener to support his theory.
Geological
- Fit of continents together
- Glaciation striation patterns in Brazil and West Africa are similar - indicating close together during the ice age.
Biological
- Fossil brachiopods found in Indian limestone and similar fossils in Australia
- Fossil remains of reptile Mesosaurus in both South American and South Africa. - previous theories suggested a landbridge between the two, however many organisms couldn’t have crossed the vast oceans that exist today.
74
What is sea floor spreading?
- Theory that the ocean floor was created at mid-ocean ridges and has then been gradually expanding sideways due to volcanic activity.
- Plates must be being destroyed somewhere to accommodate the increase in their size at mid-oceanic ridges.
75
What evidence did Vine and Matthews use to support their theory?
Mirroring patterns of paleomagnetism either side of ocean ridges.
76
Outline the process of convection currents in the asthenosphere:
- Hot spots in the earth’s core create thermal plumes in the asthenosphere.
- Hot magma rises as it is less dense, it spreads out underneath the lithospheric plates. This basal drag (friction/lateral pressure) moves the plates.
- Magma cools, becoming more dense and sinking, creating a continuous cycle.
77
Outline the process of Gravitational sliding at ocean ridges:
- At constructive plate boundaries magma rises to the surface to form a new crust.
- Rising magma is very hot and heats surrounding rocks which expand and become elevated above the surrounding sea floor forming a slope.
- As the new crust cools and becomes denser, gravity causes it to move downslope away from the mid-oceanic ridge.
- This puts pressure on the tectonic plates causing them to move apart. The process repeats.
78
Outline the process of slab pull at ocean trenches:
- At destructive plate boundaries the subducting oceanic plate (usually composed of basalt) is denser than surrounding material.
- Downward gravitational force acts upon the cold dense descending plate as it sinks into the mantle.
- This pulls the rest of the plate behind it
79
How do plates move at each of the following plate boundaries
Constructive: plates move apart
Destructive: plates move towards each other
Conservative: plates move alongside each other in opposite directions or the same direction at different speeds.
80
Outline the formation of ocean ridges:
- Plates diverge in oceanic areas (due to convection currents and gravitational sliding) - sea floor spreading.
- As plates move apart this leaves cracks and fissures, lines of weakness that allows magma from the mantle to escape from the highly pressurised interior of the planet.
- This magma fills the gap and eventually erupts onto the surface and cools as new land. Creating ridges of undersea mountains and volcanoes.
81
Outline the formation of rift valleys
- When plates diverge beneath land, rising magma causes the continental crust to bulge and fracture, forming fault lines,
- As the plates keep moving apart the crust between the parallel faults drop down to form a rift valley.
- The crust here is thinner due to tension in the crust causing the plate to thin as it starts to split. Through this thinning crust, magma forces its way to the surface to from volcanoes
82
Outline the processes at oceanic-continental destructive plate boundaries.
- Denser oceanic plate subducts under the less dense continental plate > downwarping forms an ocean trench.
- As the oceanic plate descends, friction with the plate above and increasing pressure and heat in the asthenosphere melts the subducting ocean plate at the benioff zone.
- Some of this molten material works its way up through the continental plate above through fissures, as molten material is less dense than the asthenosphere.
- Magma eventually re-emerges at the surface to create explosive composite volcanoes (explosive as they have silica-rich andesitic lava).
- Sediments on the edge of the continental crust cumple upwards as the oceanic plate subducts forming fold mountains.
- As one plate is subducted, plates can become stuck > pressure builds up > suddenly jerk past each other > earthquakes.
83
Outline the processes at oceanic-oceanic destructive plate boundaries.
- Denser oceanic plate subducts under the less dense oceanic plate > downwarping forms an ocean trench.
- As the oceanic plate descends, friction with the plate above and increasing pressure and heat in the asthenosphere melts the subducting ocean plate at the benioff zone.
- Some of this molten material works its way up through the less dense oceanic crust through fissures.
- Magma eventually re-emerges at the surface to create an island arc of explosive composite volcanoes
84
Outline the processes at continental-continental destructive plate boundaries.
- Neither plate subducts into the mantle because of their similar density. Instead, the two plates crumple into one another and fold upwards into fold mountains.
- As neither is subducted there are no volcanoes but the pressure build up can cause earthquakes
85
Outline the processes at conservative plate boundaries
- Two plates move alongside each other (in opposite directions or the same direction at different speeds).
- Plates get stuck (‘lock’) due to friction and pressure builds up.
- Plates suddenly jerk past each other or crack forming fault lines, this releases the pressure sending shockwaves through the earth’s crust as earthquakes
86
Give three characteristics of a hotspot:
Stationary area of crust
High heat flow (rising magma plume due to concentration of radioactive elements below the crust).
Thinner crust (low pressure and high heat allow magma plume to melt and thin the lithosphere)
Located away from plate boundaries
87
Give two examples of hotspots
Hawaiian hotspot
Reunion hotspot
88
Outline the formation of a hotspot
- Intense radioactivity (due to concentration of radioactive elements) below the crust creates a magma plume (column of extra-hot upwelling lava).
- Plume from the asthenosphere rises upwards and high heat and low pressure allows molten rock to melt the plate above (so plate is thinner than average) and push through the crust above.
- Lava breaks through the surface forming active volcanoes above the plume.
- The magma plume remains stationary but the tectonic plate moves. Upwelling lava creates a steady succession of new volcanoes.
- Volcanoes above the hotspot are active and the remainder form a chain of islands of extinct volcanoes. The oldest volcanoes put pressure on the crust causing subsidence and marine erosion results in old volcanoes becoming seamounts.
89
Give three differences between shield and composite volcanoes.
Shield
- Constructive plate boundary and hotspots.
- Gentle slopes and wide base.
- Eruptions are frequent, not explosive.
- Formed with layers of runny lava but no ash.
Composite
- Destructive plate margins
- Steep slopes and narrow base
- Eruptions infrequent but violent
- Formed with layers of ash and rock
90
Give three methods of diverting lava flows?
- Digging/using explosives to create earth trenches and use concrete: Mt Etna Sicily
- Bombing lava tubes
- Use of ice water/cooling lava: 1973 Heimaey Iceland
91
How might people adapt to the risk of volcanic eruptions?
- Strengthen buildings to reduce the chance of collapse from ash on roofs
- Capitalise on the opportunities of living near volcanoes e.g. farming fertile soils or working in the tourism industry.
92
Give three primary impacts of volcanic events:
- People are killed and buildings are destroyed by pyroclastic flows
- Ash causes damage to agricultural land
- Ash causes flights to be grounded
- Death due to volcanic gasses
93
Give three secondary impacts of volcanic events:
- Acid rain acidifies aquatic ecosystems killing some plants/animals
- Volcanic debris reflects sunlight resulting in crop destruction due to colder winters
- Flash floods due to glacial melts
- Tsunamis due to volcanic landslides
- Death due to lahars
- Fires started by lava and pyroclastic flows puts lives at risk
- Conflict and political unrest due to food shortages
- Homelessness
94
Outline how earthquakes are formed?
- At all plate boundaries, plates move due to gravitational sliding, slab pull and convection currents. Plates get stuck due to friction and tension and pressure builds up.
- When plates suddenly jerk past each other or crack forming fault lines, this releases the pressure sending shockwaves through the earth’s crust as earthquakes.
95
How are seismic events distributed?
- Found along plate boundaries
- Particularly: destructive and conservative plate boundaries.
- The Ring of Fire accounts for 90% of the world’s Earthquakes.
- The Alpine-Himalayan belt accounts for 5-6% of the world’s earthquakes
96
How does the depth of focus affect nature and magnitude of earthquakes?
- Deep focus earthquakes tend to be higher magnitude than shallow focus earthquakes.
- Deep focus earthquakes generally do less damage than shallow focus earthquakes as shock waves have to travel further to reach the surface reducing their power.
97
Why are earthquakes of higher magnitude at destructive plate boundaries?
High pressure builds up between plates as subduction.
98
Why are earthquakes lower magnitude at constructive plate boundaries?
Fracturing (as plates move apart), injection of magma and eruption is frequent. So, tensional stresses do not have time to accumulate.
99
What are the three factors affecting the magnitude of earthquakes?
Type of plate boundary
Depth of focus
Rate of movement
100
Give three reasons why earthquakes may occur away from plate boundaries?
- Reactivation of old fault lines - potentially due to deferred stress release OR...
- Large dams and reservoirs - pressure on underlying rocks reactivates old faults
- Hydraulic fracturing
- Subsidence of old deep mines
101
What is the difference between primary and secondary waves?
P (Primary/pressure) waves: alternately compress and expand, so particle motion is parallel to direction of wave movement. Can travel through ALL substances, fastest.
S (Secondary/shear/shaking) waves: transverse, movement of particles is perpendicular (90 degrees) from movement of wave (up and down). Cannot travel through air or water, slower but cause more damage (greater amplitude).
102
What does the Richter scale measure?
Logarithmic scale measures the magnitude of an earthquake based on the amplitude of secondary waves.
103
What does the Moment Magnitude Scale measure?
Logarithmic scale measures earthquake magnitude based on the total amount of energy released. Distance a fault has moved x force required to move it.
104
What is the relationship between magnitude and frequency of seismic events?
Negative relationship - as magnitude increases frequency decreases.
105
What are the two primary impacts of seismic events?
Ground rupture (displacement of the earth’s surface along fault lines).
Ground shaking
106
Give three factors affecting the severity of ground shaking from seismic events.
Dependent on magnitude
Depth of focus
Distance from the epicentre
Geological conditions
107
What is the difference between body and surface waves?
Body: travel: Travel through the earth can be divided into primary (p) waves or secondary (s) waves.
Surface: Travel along the Earth’s surface, these cause the most damage, as cause more ground movement and travel more slowly so take longer to pass
108
What is the difference between Rayleigh and Love waves?
Rayleigh: ground roll, similar to surface water waves. Rock moves in an elliptical motion as the wave passes and breaks up the surface.
Love: horizontal shear waves, move the ground from side to side at right angles to the direction of the movement. This can damage infrastructure and buildings.
109
What does the Mercalli scale measure?
Intensity of an event and its impact - 12 point scale, subjective.
110
What is the difference between the epicentre and the focus of an earthquake?
Epicentre: Point on the earth’s surface directly above the focus - where the earthquake is first felt.
Focus: Point in the earth’s crust where the earthquake starts.
111
How do earthquakes result in tsunamis?
- Earthquakes vertically move the seabed up by several metres.
- Displacing (moving) the water above. The greater the movement of the sea floor the greater the volume of water displaced and the bigger the wave produced - hence greater intensity at destructive plate boundaries as higher magnitude earthquakes.
- Large waves radiate outwards across the ocean away from the epicentre of the earthquake.
In deep water no energy is lost to frictional drag with the seabed.
- As wave approaches shore > water becomes shallower and the base is slowed down by friction, forcing the circular wave motion into an elliptical form, which heightens until it can no longer be maintained and breaks. This is called shoaling.
- A large wave hits the coast, a tsunami.
112
How does the height of the waves affect the intensity of a tsunami ?
The level of movement of the sea floor - the greater the movement the greater the volume of water displaced and the bigger the wave produced.
113
How does the distance the waves have traveled affect the intensity of a tsunami ?
Waves lose energy as they travel towards the land, so the closer to the coast the waves start, the less energy they will lose, therefore tsunamis tend to be more powerful when they start closer to the coast.
114
How does the shape of a coastline affect the intensity of a tsunami ?
Indented coastlines with long, narrow bays concentrate energy on the bay head due to a funnelling effect as the wave travels up the bay. Irregular coastlines and offshore islands can set up interference patterns in the waves which, when they coincide perfectly, can accentuate the waveform.
115
How does relief of coastline affect the intensity of a tsunami ?
Cliffs present a natural barrier to a tsunami.
116
How does presence of a natural defence affect the intensity of a tsunami
Coral and mangroves act as natural defences by dissipating wave energy through their large surface areas.
117
How does the population density affect the intensity of a tsunami ?
High population density - greater intensity. Also, the young and old are the most vulnerable, and there may be a gender disparity.
118
What is liquefaction?
- Weakening of water saturated sediment during an earthquake causing it to act as a liquid.
- May lead to eruptions of pressurised water and sand at the surface called sandblow - may result in localised flooding.
- Causes the lateral movement of the ground damaging underground pipelines, causing buildings to topple etc.
119
How do seismic events result in landslides (and avalanches)?
- The earthquake destabilised a hillside and caused it to fall
- Can occur months or years later as seismic shaking damages the rock making it more prone to failure in later earthquakes or rainstorms
- Shaking loosens ground material making it easier for water to infiltrate, the weight of extra water may then trigger a landslide even after shaking has stopped.
120
Why are landslides induced by earthquakes a hazard?
- Cause debris flows
- Debris flows may result in natural dams and resultant flash flooding when dams break
121
What are the four secondary hazards of seismic events?
- Tsunamis
- Landslides
- Liquefaction
- Fires
122
Is prediction effective for seismic events?
No- although regions generally at risk can be identified using plate tectonics it is difficult to know when a hazard will occur
123
Give three methods used when attempting to predict seismic events?
- Monitoring of groundwater levels
- Release of radon gas
- Unusual animal behaviour
- Using foreshocks
- Tilt-metres to show ground formation.
124
What is seismic gap theory?
Theory that over the long run all parts of the fault must average about the same level of movement per time. This can either happen through the cumulative efforts of a very large number of very small earthquakes. Therefore, 1 large and long standing ``seismic gap''suggests that a significant earthquake should be expected
125
Give two methods used to attempt to prevent earthquakes?
- Nuclear explosions at depth
- Pumping water/oil into a fault line to prevent plates from sticking
- Use of boreholes to change the properties of soil and reflect incoming earthquake energy waves.
126
Give three methods of creating hazard resistant structures ?
- Concrete weights on the top of buildings to move in the opposite direction ti the force of the earthquake to counteract stress (with computer programme)
- Rubber shock absorbers in the foundations
- Cross bracing the structure to hold it together better when it shakes
127
Give a pieces of evidence demonstrating the effectiveness of hazard resistant structures
Haiti - substandard building design, shoddy construction and inadequate materials, no building code 7.0 magnitude 12.01.2020 - 230, 000 killed and 3 million affected vs Chile 2010 8.8 MMS 521 people killed.
128
Give two factors limiting the effectiveness of hazard resistant buildings in reducing risk to a population
- Need to retrofit even if new strict building regulations are put in place the older buildings remain vulnerable to an earthquake - e.g. Kobe 1995 Japan where it was mainly due to the collapse of older wooden buildings that 6,300 people were killed that were the homes of the poorest people.
- Need to enforce building regulations effectively e.g. 1985 Mexico city where many multi-storey buildings collapsed leading to a total death toll of 30,000 - building regulations had not been enforced.
129
What does FEMA stand for?
Federal emergency management agency’s
130
Give the four objectives of FEMA to reduce hazard risk in the USA.
- To promote understanding of earthquakes and their effects
- To work to better identify earthquake risk
- To improve earthquake-resistant design and construction techniques
- To encourage the use of earthquake safe policies
131
How does education minimise the risks of seismic hazards? AND Give an example.
Minimise loss through use of drills (so the population knows how to respond effectively reducing injury/death - e.g. staying away from buildings where possible and finding strong door frames etc. to shelter under if inside) - Disaster Prevention Day (1st September) Japan. Ensure people have emergency supplies prepared - e.g. The Red Cross issued a list of supplies e.g. food stuff, clothing, first aid kits post 1989 Loma Prieta earthquake.
132
How does fire prevention minimise the risks of seismic hazards? AND give an example.
Smart metres cut off the gas if an earthquake of a sufficient magnitude occurs reducing the risk of death by fire. E.g. In Tokyo the gas company has a network that transmits seismic information to a computer which then informs employees where to switch off major pipelines.
133
How does emergency planning minimise the risks of seismic hazards. AND give an example
Careful organisation to tackle the impacts of a hazard more efficiently and effectively reducing the intensity of impacts. E.g. heavy lifting gear needs to be available and many people should be given first aid training as it could be some time after an event that trained medical personnel can arrive. Much of the preparation in California involves the establishment of computer programs to identify which areas the emergency services should be sent to first.
134
How does early warning systems/tsunami protection minimise the risks of seismic hazards. AND give an example.
While not entirely predictable automated systems can give out warnings if foreshocks or if undersea earthquakes increase tsunami risk so people can take evasive action. E.g. The pacific warning system.
135
How do sea walls minimize the risks of seismic hazards. AND give an example.
Prevention walls along the coast to protect the land behind from oncoming tsunamis - e.g. Japan. N.b. often ineffective as large tsunamis are likely to overwhelm them.
136
How does insurance minimise the risks of seismic hazards. AND give an example.
People take out insurance to cover their losses and help recover faster
137
How does land-use planning minimise the risks of seismic hazards?
Identifies the most hazardous areas and regulates land use - e.g. should not build hospitals etc. and should ensure sufficient open space as this forms a safe area away from fires and aftershock damage to buildings.
138
What is micronzonation?
Microsonation: mapping out the variability of hazards through urban areas to identify areas that are more or less hazardous with respect to some geological and geophysical characteristics. As these will affect the likelihood/severity of: ground shaking, liquefaction susceptibility, landslides and flooding.
139
What factors should be considered when land-use planning?
- Known fault lines
- Geology - soft sediment layers can amplify wave magnitudes and result in liquefaction (1985 Mexico City)
- Topography - e.g. Port Au Prince Haiti 2010 some of the most dramatic damage was associated with amplification by small scale topographical features such as hills and ridges.
140
Describe the frequency of seismic events ?
Earthquakes are frequent around the world and occur every day at boundaries. N.b. Negative relationship between magnitude and frequency.
141
Describe the regularity of seismic events ?
Earthquakes follow no pattern and are random so there is irregularity between events.
142
describe the predictability of seismic events ?
Earthquakes are almost impossible to predict. Microquakes may give some indication but the magnitude cannot be predicted as how strong they are is random - see above for methods used.
143
Distribution of tropical storms.
Tropical maritime areas between 5-20N/S but not on the equator.
144
WHere are hurricanes located ?
North Atlantic (Caribbean sea and Gulf of Mexico) (11% of tropical storms) and NE Pacific (western side of central America) (17% of tropical storms)
145
Where are cyclones located ?
South Pacific/Indian - Arabian sea and Bay of Bengal (8% of tropical storms). Off of Madagascar (southeast Africa) 11%
146
Where are typhones located ?
Northwest Pacific (off of southeast asia) 33%.
147
Where are willy willies located ?
Off north-western and north-eastern Australia (20%)
148
Give five conditions needed for the formation of a tropical storm:
- Warm ocean above 27C to at least 70m below the surface
- continuous source of heat in order to maintain rising air currents and allow for latent heat to be released by condensation powering the storm. And less frictional drag over the ocean
- At least 5-20N/S of the equator so coriolis force can bring about the maximum rotation to the area.
- Low level convergence of air forces warm air to rise.
149
Why do tropical storms decay upon reaching land?
- Lose source of heat and moisture which provides latent heat when evaporating
- Increased frictional drag with the land surface slows down the storm
150
In what direction do tropical storms spin in:
Northern hemisphere: anticlockwise
Southern hemisphere: clockwise
151
What are the four stages of tropical storm formation?
- Tropical Disturbance winds less than 23mph
- Tropical depression 23-39mph
- Tropical storm 39-73 mph
- Hurricane: 74 mph +
152
What scale is used to measure the magnitude of tropical storms?
Saffir-simpson scale
153
What are the four factors are measured by the Saffir-simpson scale ?
- Central pressure
- Wind speed
- Storm surge
- Damage potential
154
Describe the frequency of tropical storms ?
- Northern hemisphere > June - Nov.
- Southern hemisphere > Nov. - April
- Frequent, but FEW are a major hazard - as they don't develop into strong storms or reach land.
155
How has the frequency of tropical storms changed ? Give example.
Little evidence of increased hurricane frequency.
- North Atlantic 1966-2009 average 11 tropical storms vs 2000-2014 average 15 tropical storms.
Arguably increasing temperatures allow the conditions for storm formation to be met more frequently.
156
Describe the regularity of tropical storms ?
Irregular - occur in the same areas but no clear spatial or temporal pattern.
157
Describe the predictability of tropical storms.
Fairly predictably with use of satellite tracking of cloud formations.
158
What are the three primary hazards of tropical storms ?
- Strong winds
- Heavy rain
- Storm surges
159
Give two secondary hazards of tropical storms
- Flooding
- Landslides
160
Outline the formation of tropical storms.
- In the tropics, solar radiation warms the ocean to 27 degrees. The ITCZ is usually overhead.
- Warms moist air rises through the air in thermals. This creates an area of low pressure at the centre of the storm.
- As rising air cools > condensation > cumulonimbus clouds and heavy rainfall. The latent heat given off when the air cools powers the tropical storms.
- The coriolis effects causes rising air to spin upwards around a central eye.
- Air rushes in from areas of higher pressure outside the storm to replace the rising air - creating strong winds.
- Cold air sinks in the eye of the storm > no cloud, drier and calm.
- Tropical storms are carried across the ocean by prevailing winds - building in strength by evaporating water.
- When te tropical storm meets land, it is no longer fueled by a source of moisture and heat from the ocean and slowed down by friction with land so it loses power and weakens.
161
What are storm surges ?
Tropical storms (rising air) create low barometric pressure causing a localised temporary rise in sea level.
Strong winds create larger onshore waves and push a bulge of water inland increasing the damage potential relative to the potential damage caused by surge-induced high water levels alone.
162
Give five factors that increase the severity of storm surges ?
- Low lying coastal area (relief)
- Coastal configuration (funneling effect of estuaries/deltas)
- Storm track - creation of onshore waves
- Intensity of storm - stronger winds = stronger waves.
- High tide
