Unit 3 - Tectonic hazards Flashcards
(143 cards)
1
Q
What’s the Earths structure?
A
Inner core, outer core, mantle and crust.
2
Q
Characteristics of the core?
A
- iron and nickel at 6200*c
- inner core is 1250km thick
- outer core is 2200km thick
3
Q
Characteristics of the mantle?
A
- rich in silicate rocks
- 2900km thick, 1000*c
- rocks are semi molten
4
Q
What is the asthenosphere?
A
- apart of the mantle, 80-200km
- solid, but rocks can deform under pressure
5
Q
What are the 2 types of crust?
A
- oceanic crust (6-10km)
- continental crust (70km)
6
Q
What is the lithosphere?
A
The rigid outer layer of the Earth consisting of the crust and solid outermost layer of the upper mantle.
7
Q
What is the Moho Discontinuity?
A
The boundary between the crust and the mantle.
8
Q
What are the 3 types of plate boundary?
A
-converging/destructive
-diverging/constructive
-transform/conservative
9
Q
Movement of converging boundaries?
A
Pulling together, causing push mountains (South america)
10
Q
Movement of diverging boundaries?
A
Pulling apart, creating new land (Iceland)
11
Q
Movement of conservative boundaries?
A
Moving next to each other (san andreas fault)
12
Q
What is the theory of convection currents?
A
- heat is moved towards the crust by circuling convection currents
- spread out the surface, like a conveyer belt
- the plates move on the asthensphere
13
Q
What data is against convection currents?
A
modern scientific technologies have been unable to identify any convection cells in the mantle that would be strong enough to move plates.
14
Q
What is ridge push?
A
-molten magma rises at a midocean ridge divergent boundary
- rocks are heated, expand and rise above the seafloor, forming a slope away from the ridge
- as rock cools, it becomes denser, causing it to slide down the pkates, exerting a force
- the gravitational sliding is the active driving force
15
Q
What is slab pull?
A
-at the convergent plate boundaries, one plate is denser than another
- the denser plates subducts under the less dense plate
- the subducting plate is colder and heavier than the mantle, so it continues to sink, pulling the rest of the plate with it.
16
Q
What happens to the plates at diverging plate boundaries at oceanic plates?
A
- diverging plates under oceans driven by slab pull, bring magma to the surface to form a ridge
- can form volcanoes and new islands
17
Q
What happens to the plates at diverging plate boundaries at continental plates?
A
- mountain ridges are found at the plate margins as hot magma forces the crust to bulge
- parallel faults are found, forming rift valleys
18
Q
What happens to the plates at converging plate boundaries at oceanic plates?
A
-the colder, denser plate will subduct beneath the other, forming an ocean trench
- some magma may be able to rise, forming island arcs.
19
Q
What happens to the plates at converging plates boundaries at continental/ocean margins?
A
- the denser oceanic plate is subducted by slab pull
- less dense continental crust gets buckled and folded, to form mountain chains
20
Q
What happens to the plates at converging plate boundaries at continental margins?
A
- continental plates have similar densities so no subduction
- fold mountains are created to relieve pressure
- earthquakes can occur at these
21
Q
How are hotspots formed?
A
- plumes of magma rise to the crust
- forms volcanoes at the surface
- as the plate continues to move, more volcanoes form
- as continental volcanoes move, they become extinct
22
Q
What are earthquakes along diverging plate boundaries like?
A
Shallow and related to volcanic activity
23
Q
What are earthquakes like at oceanic boundaries?
A
Frequent and powerful, may cause tsunamis
24
Q
What are earthquakes like at continental boundaries?
A
Mainly shallow, can be powerful and hazardous if humans inhabit the area
25
Why can earthquakes occur away from plate margins?
Stress creating movements at old fault lines
26
What human activity can cause Earthquakes?
Fracking for gas extraction, unnatural movement of gas causes movement of plates.
27
What are eruptions like at divergent plate margins?
Usually non-violent and most are in the deep ocean
28
What are eruptions like at convergent plate margins?
Can be violent and hazardous if close to urban settlements
29
What is the definition of magnitude?
The size or physical force of a hazard event
30
What are the 3 scales for earthquake magnitude?
Richter, movement magnitude and mercalli.
31
What is the richter scale?
- based on seismic waves on a seismic graph
- uses a logarithmic scale, 1-9
- widely used
32
What is the movement magnitude scale?
- measure the energy released
- takes into account geology, area and fault movement
- scale 1-9
- used since 2002 for large quakes
33
What is the Mercalli scale?
- a quanlitative scale that measures intensity based off visual damage
- from I to XII
34
What is the magnitude of volcanoes measured with?
Volcanic Explosivity Index (VEI)
35
What is the volcanic explosivity index?
- the volume of materia ejected, eruption cloud height, and direction used to determine explosivity value
36
What does the VEI not take into account?
Sulphur dioxide emissions, so limited in describing the effects on the atmosphere.
37
What can accurate/inaccurate predictions of hazards allow?
- reduce the impact of a hazard by allowing the evacuation of danger zones
- too many inaccurate predictions may increase the impact of future hazards as people will begin to ignore warnings
38
What is the seismic gap theory?
Over a period of time, all parts of a fault must attain the same average level of movement. A seismic gap with no quakes could result in a significant quake.
39
Why is there greater prediction for volcanoes?
There are usually warning signs before the eruption
- gas emissions
- hydrology
- temp changes
- seismic activity
40
What is the link between frequency and magnitude?
The higher the frequency, the smaller the magnitude.
The smaller the frequency, the larger the magnitude.
41
What can be put in place to manage the impact of frequent earthquakes?
Earthquake proof buildings and earthquake resistant drills, for example in Japan
42
What is the link between duration and impact of earthquakes?
The longer the duration, the more impact is caused on land.
43
What can extend the duration and impact of an earthquake?
The causation of secondary factors, like lahars, tsunamis and aftershocks.
44
What is speed of onset?
Speed of onset refers to how quickly the peak of the hazard arrives.
45
What is the speed of onset like for an earthquake?
Its almost instant, allowing no time to issue warnings, hence creating a larger damaging impact.
46
What is the speed of onset like for a volcanic eruption?
Usually slower speed of onset, which allows avasive action, thus reducing impact.
Example - 20,000 lives saved by evacuating in the pinatubo eruption of 1991.
47
What is areal extent?
The size of the geographical area effected by the tectonic event.
48
What increases the potential impact?
Increasing the area covered by the hazard.
49
What 6 factors are included in a tectonic hazard profile?
- magnitude
- speed of onset
- duration
- areal extent
- spacial predictability
- frequency
50
Name the 5 types of volcanoes.
- shield
- composite/stratovolcano
- cinder/ash
- acid/dome
- caldera
51
Shape and formation of a shield volcano?
- effusive eruption where large quantities of lava pour from the central vent
- lava travels a long way before solidifying
- produces tall volcanoes with gently sloping sides
- eruptions tend to be frequent, but not explosive
- occurs at diverging margins and hotspots
52
Shape and formation of stratovolcanoes?
- many layers of solidified lava and volcanic ash
- lava is slow flowing and solidifies quickly
- produces steep sloping sides
- ash occurs in explosive eruptions, often after the vent has become blocked with solidified lava
- occur at converging plate margins
53
Shape and formation of cinder volcanoes?
- gas forces lava high into the air, where it breaks into small fragments
- fragments cool and fall as cinders
- produces a short, symmetrical cone with relatively steep sides and a crater at the top
- often occurs at the sides of shield or composite volcanoes
- many are formed from one eruption
54
Shape and formation of acid volcano?
- viscous, acidic lava erupts effusively but cannot travel far before solidifying
- lava builds up to form a steep sided cone
55
Shape and formation of a caldera volcano?
- gasses trapped in a magma chamber eventually causes an extremely explosive eruption
- the upper part of the volcano can be destroyed
- the ground above magma chamber can subside, leaving a large depression, which can eventually flood
56
What are icelandic eruptions like?
Effusive - Lava flows freely from the open fissure
57
What are hawaiin eruptions like?
Effusive - fluid lava flows from a vent, some maybe thrown into the air
58
What are strombolian eruptions like?
Distinct eruptions, forcing lava into the air, occur frequently, the least violent explosive eruption
59
What are vulcanian eruptions like?
Short, relatively small, violent eruptions of viscous lava
60
What are vesuvian eruptions like?
Powerful blasts of gas pushing gas into the air, with some lava flows
61
What are plinian eruptions like?
Huge, violent eruptions, blasting ash and fragments high into the air, creating huge ash clouds, gas clouds and lava can rush down the slopes, part of the volcano may be blasted away.
62
What is a pyroclastic flow?
A high density mix of hot volcanic ash, volcanic fragments, pumice and ash, which moves at a high speed down volcanic slopes.
63
How can eruption collumns cause pyroclastic flows?
- the eruption collumn collapses, during an explosive eruption, material is ejected into the atmosphere, the gas and particles are denser than than the surrounding air and fall back to earth, flowing down the mountain
64
How can boiling cause pyroclastic flows?
- boiling over at the dome, material is emitted in eruption and cascades down the slope
65
How can dome collapses cause pyroclastic flows?
- the slopes of volcanoes become so steep they collapse due to gravity
66
Case study of Aa lava?
- high flow volume
- up to 10km/h on steep slopes
-thickness of flow 2-20m
- surface is rough
67
Case study of Pahoehoe lava?
- low flow volume
- 1-2km/h on steep slopes
- thickness of flow 0.2-2m
- surface is smooth
68
What is a tephra?
Refers to all explosive eruption materials, including those over 2mm in diameter, some descriptions and estimations of the amount of volcanic ash will include it
69
How can ashfall affect human activity?
- the weight of ash collapses buildings
- interrupts transport by blocking roads and railways
- clogs engines and machinery, affecting jet planes
- destroys crops and farmlands
- circuit failures of electricity
70
What are lahars?
A lahar is a mixture of volcanic ash, debris, and water that travels down a slope, usually along a valley
71
What are jokulhlaups?
- Icelandic glacial outbursts of floods
72
What are volcanic landslides?
A volcanic landslide is a mass of volcanic rock or debris that moves rapidly under the force of gravity
73
How can volcanic landslides be triggered?
- volcanic eruptions
- earthquake in the area
- heavy rainfall saturating the ground
- rising magma causing the ground to deform and resulting in instability
74
How can toxic gases be harmful to those around an erupting volcano?
- co2 is colourless and odourless and is denser than air, so it sinks and collects in depressions (causing asphyixiation)
- sulphur dioxide can be a skin irritant and causes acid rain, playing a role in climate change
75
What are some primary environmental impacts of volcanic hazards?
-reshaping the land
- destruction of vegetation
- increased precipitation
- reduction in temperature from ash clouds
76
What are some primary demographic/social impacts of volcanic hazards?
- 91000 dead between 1900 and 2016
- 4.7 million people affected between 1900 and 2016
- 15000 injured between 1900 and 2016
77
What are secondary environmental impacts of volcanic hazards?
- green house gasses lead to global warming
- sulphur dioxide leads to acid rain
-
78
What are secondary demographic/social impacts of volcanic hazards?
- 15000 left homeless every year
- stress related illness and disease
- lack of food from crop damage
79
What are secondary economic impacts of volcanic hazards?
- loss of income from loss of business
- financial loss from agriculture and trading
- damage to business
- repairs cost $65 million a year
- economic loss from 1900 to 2016 thought to be $3.5 billion
80
When do earthquakes occur?
The result of gradual build up of stresses due to crustal movement
81
What is elastic rebound?
When the deformation from stress is too great the rock fractures and returns to its original shape, creating seismic waves.
82
What are seismic body waves?
-travel through the interior of the earth
- higher frequency and arrive before surface waves
83
What are the 2 types of body waves?
P waves (primary) and S waves (secondary)
84
What are P waves?
- fastest waves and first to arrive
- can move through solid rock and liquid
- caused by compression, pushing and pulling the rocks as it moves
85
What are S waves?
- slower than P waves and only move through solid rock
- move rock particles at right angles to the direction of wave travel
- second wave to arrive, responsible for much damage
86
What are surface waves?
- travel only through the crust
- lower frequency and arrive after the body waves
- responsible for most destruction
87
What are the types of surface waves?
L waves (love) and R waves (rayleigh)
88
What are L waves?
- fastest surface waves
- move the ground horizontally from side to side
- often generate the greatest damage
89
What are R waves?
- waves follow an elliptical motion, which moves the ground up and down and side to side
- can be larger than other waves and result in most of the shaking that is felt
90
What are the 4 hazards of an earthquake?
-ground shaking
- liquefaction
- landslides
- tsunamis
91
What is ground shaking?
Shaking of the ground caused by the passage of seismic waves, causing most danger to humans due to collapsing structures
92
What does the intensity of ground shaking depend on?
- intensity and duration of the earthquake
- distance from the epicentre
- geology - solid bedrock is less subject to intense shaking than loose sediment
93
What is the epicentre?
The epicentre is the point on the Earths surface directly above the focus
94
What is liquefaction?
Loose sediments such as sand and silt combine with groundwater and behave like a fluid or quicksand
95
What are landslides?
Earthquakes create stresses that make weak slopes fail triggering landslides as well as rockfalls and avalanches
96
What is the focus of an earthquake?
The focus is the point where rocks fracture.
97
How are tsunamis formed?
Caused by a shallow focus, underseas earthquake at a plate margin, creating a sudden rise or fall in the ocean floor, which displaces the water above it.
98
What are the primary environmental impacts of an earthquake?
- landslides,liquefaction,tsunami
- land uplift or subsidence
- damage and destruction to infrastructure
99
What are the primary demographic/social impacts of an earthquake?
- earthquakes killed 804000 between 00 and 17, mainly due to collapsed structures
- many people injured
100
What are the secondary environmental impacts of an earthquake?
- damage and flooding from primary impacts
- fires can start
- atmosperic pollution from fires
101
What are the secondary demographic/ social impacts of an earthquake/
- destruction leaves people homeless
- loss of personal belongings
- unemployment
- spread of disease
- lawlessness such as looting
- lack of education and health facilities
102
What are the secondary economic impacts of earthquakes?
- costs of repairing and rebuilding
- loss of production and economic activity
103
What is the risk equation?
risk = hazard (frequency and or magnitude) x level of vulnerability / resilience level
104
What is a risk?
The probability of a hazard occuring and causing loss of life and livelihoods
105
s meant by vulnerability?
The ability of a communitiy to cope with the impacts of a hazard
106
What is a hazard?
A natural event that threatens or causes injury, death and destruction.
107
What is a disaster?
The result of a hazard seriously disrupting the functioning of a vulnerable community, causing loss of life and material and economic damage
108
What does povery result in?
- lack of education
- poor quality building standards
- limited ability to cope with aftermath
- lack of alternatives to reduce the risk
109
What social hazards can impact a persons perception of a hazard?
- acceptance that it might happen and that they will bear the loss
- complanency due to false alarms from warning systems
- fear of the unknown
110
Ow can political factors increase vulnerability?
- A lack of development or enforcement of building codes
- bureaucracy and corruption, which may prevent aid from reaching certain areas
- a lack of hazard mitigation planning
111
What 4 geographical factors can increase risk from hazards?
- rural areas - harder to rescue
- urban areas - greater population density
- time of the hazard
- the probability of a secondary hazard forming
112
What is the pressure and release model?
Shows how the level of impact is due to the level of vulnerability, which in turn is influenced by the socio-economic characteristics of the area
113
What 2 types of responses are there to tectonic hazards?
- monitoring and attempting to predict and warn of a hazard event
- mitigating the hazard by modifications
114
How can you reduce a communities vulnerability to a hazard?
- evacuation to areas of safety
- preparations for the event
- risk assessment by authorities and insurance companies
- allowing providers of post-event aid to be prepared
115
What devices can monitor small movements along a fault?
Laser reflector
creep meter
gravity meter
tilt meter
116
What is a strain meter?
Measures the stress in rocks
117
What do well levels and groundwater measurements help do?
monitors groundwater movements and height of the water table, which can change just before an earthquake
118
WHat does a radon gas meter do?
Levels of radon gas dissolved in water can increase before an earthquake
119
What does a magnetometer do?
Changes in the earths magnetic field have been recorded before an earthquake
120
What does a seismograph do?
Records smaller foreshocks that could give warning to a larger plate movement
121
How can animal behaviour be used to monitor earthquakes?
Anecdotal evidence abounds, for example rats and snakes leaving homes and heading for safety before an earthquake
122
What does the United States Geological Survey suggest an earthquake prediction must include?
- date and time
- the location
- the magnitude
123
How can seismic activity aid volcanic eruption predictions?
- may show an increase in seismic activtiy
- if earthquakes are mitigating towards the surface, this could suggest rising magma fracturing rocks
124
How can ground deformation aid volcanic eruption predictions?
Tilt meters and laser measures can detect minute changes in slope and angle and the distance between points, suggesting that rising magma is displacing the ground above
125
How can gas emissions aid volcanic eruption predictions?
- ground based, airborne and satellite detectors can measure changes in the amount and composition of gas emissions
- if gases pass through lakes, changes in colour and acidity of the water can be recorded
126
How can thermal changes aid volcanic eruption predictions?
- detectors like satellites, can register changes in temperature at the surface and in lakes, suggesting increase in activity
- increasing discharge from hotsprings and death in vegetation are visible signs
127
How can lahar monitoring aid volcanic eruption predictions?
observations of lahars including by remote video cams drones and seismometers recording vibrations from an active lahar can allow short-term warnings
128
What devcies can help predict the arrival of a tsunami?
- tide gauges
- tsunami detection buoys
- pressure recorders
129
What 3 strategies are used to reduce the impact of tectonic hazards?
- modifying the event
- modify human vulnerability to the event
- modify the loss from the event
130
What are the physical factors that affect hazard response?
- geographical accessibility of location
- type of hazard
- topography of region
- climate
131
What are the human factors that affect hazard response?
- population density
- degree of community preparedness
-technological resources, quality of engineering
- scientific understanding
- education and training
- economic wealth
- infrastructure
- social and political framework
132
examine the graph of plate activity (4)
- higher hazard along the coasts
- higher hazard along plate margins
- Indonesia, Myanmar and the Philipines have the highest hazard risk
- North-west to South-east have linear patterns
133
Examine the relationship between the location of tectonic margins and theblevel of earthquake hazard risk in South East Asia (9)
- the higher risk areas are along tectonic margins
- at destructive boundaries earthquakes are caused by...
- at constructive boundaries earthquakes are caused by
- at transform boundaries earthquakes are caused by..
- the areas that are less at risk are further away from the plate boundaries (give examples)
134
Outline how earthquakes produce liquefaction and landslides (8)
Liquefaction
- soil layers are shaken
- water is absorbed in the soil travels through the layers- water goes to the top of the surface because it is less dense than soil
- soil the turns semi solid and then loses strength
- causes foundations and building to sink
Landslides
- an earthquake can cause vibrations on a steep slope
- unconsolidated material moves down the slope
- shaking overcomes cohesion in the soil
- water acts as a lubricant as material travel down the slope, creating mass movement of material
135
How do you work out the interquartile range?
- put numbers in order
- find the median
- put brackets around the other numbers
- find median of both brackets
- q3-q1 = the interquartile range
136
Suggest possible reasons why there is variation in the number of destroyed buildings between the selected minicipalities of Bohol shown on figure 6a (10)
- population density
- quality of buildings/preparedness
- strength of hazard/distance from the epicentre
- geology/locational material
137
Use figures 6a and 6d to suggest how the earthquake could have impacted on the economy of Bohol (9)
- 5761 destroyed buildings
- 135 dead missing people
- bridge between Manbojoc and Tagbilaron destroyed, meaning transport and trade is affected
- the church adds to building damage, economic damage from lack of tourists
- death leads to the loss of labour
- loss of employment so negative multiplier affect
138
Outline one or more short-term response to the effect of volcanic hazards (10)
- evacuation
- redirecting lava flow
- cooling lava flow
- aid and safety measures
- emergency services
- seismic monitoring stations
- warning services
139
Suggest why explosive volcanic eruptions are the most hazardous (4)
- magnitude (high on VEI)
- types of hazard, pyroclastic, ash, gas, landslides, tsunamis ect
- covers a large land mass (large areal extent)
- looses dependant on preparedness
140
What do you have to think about when a question asks about success or the effective nature of a response?
- alleviate impact
- spacial variation
- temperate variation
- success in selective case studies
141
Examine the success of one or more long term responses to the effect of earthquake hazards (8)
- monitoring and prediction
- insurance
-education
- hazard resistant buildings
- planning and prevention
- land use planning
- emergency supplies and long term financial plans
- communication and warning
- retrofitting and renovation
142
Outline 2 social impacts of a named earthquake (10)
- nepal 2016 death (8600)
- resulting in trauma and grief
- people aren't employed so draws out recovery process
- nepal homelessness (300000)
- was not quickly alleviated by financial funding, due to lacking insurance
- this economic effect may last for years
-so in conclusion... continued damage ect ect
143
Examine the success of one short term response used to manage the impacts of an earthquake (8)
- army search and rescue teams
- japan 2015, successful as helped people out of rubble
- nepal 2011, less effective not very well trained
- nepal was geographically closer to the epicentre bet due to its location was further away from emergency services
-japan always has had plans regarding the search and rescue responses, so they knew what to do
