Tectonics Flashcards
1
Q
What is a tectonic hazard?
A
A natural event formed by tectonic processes which has the potential to threaten both life and property.
2
Q
What are the three types of plate boundary?
A
- Divergent
- Convergent
- Conservative
3
Q
Example of divergent plates
A
North American and Eurasian
4
Q
Example of convergent boundary
A
Nazca and South American
5
Q
Example of conservative boundary
A
North American and Pacific
6
Q
Features of a divergent boundary
A
- Shallow earthquakes
- Volcanic is the eruptions - effusive
- Rift valleys
- Runny basaltic lava
- Gassy eruptions
- Mid Ocean Ridge
- Transform faults
- Island volcanoes
7
Q
Features of a convergent boundary
A
- Medium to deep earthquakes
- Fold mountains
- Ocean trenches
- Explosive volcanoes (oceanic to continental)
- Batholiths - a mass of intrusive igneous rock (continental to continental)
- Dangerous eruptions of viscous lava
- Pyroclastic flows
- Slab pull
8
Q
Features of a conservative boundary
A
- Medium to shallow earthquakes
* Some show a pattern of earthquakes - transform faults
9
Q
Why is the lava viscous at a convergent oceanic to continental boundary?
A
- Introduction of silica from millions of years of sediment and sand deposited onto the ocean bed.
- The partial melting of the continental crust.
10
Q
What is the Benioff Zone?
A
Area of seismicity that relates to the slab pull of a plate as it subducts below another
11
Q
Why is there no volcanic activity at a continent to continent convergence?
A
The lava is too viscous
12
Q
Why is there no ocean trench at a continent to continent convergence?
A
There is almost no subduction due to buoyancy of the continental crust
13
Q
What are intraplate earthquakes?
A
They occurs in the middle of tectonic plates where the pressure of the plate being squashed and forced to move builds up and is released through the cracks in the rocks associated with fault zones.
This results in an earthquake.
14
Q
Example of intraplate earthquake
A
New Madrid between 1811-1812 4000 earthquakes were recorded.
1811 - 7.5
1812 - 7.3
1812 - 7.5
15
Q
Earthquakes at the North American plate
A
Faults were left after North America split from Rodina.
When the plate is under strain as the plates move, the fault zone takes some of the brunt and releases strain energy in the form of earthquakes.
16
Q
The crust
A
- The thinnest layer - 75km
- Relatively cold
- Solid but brittle
- Oceanic and continental
17
Q
The lithosphere
A
Top layer of crust
18
Q
The Asthenosphere
A
- Top layer of crust
* Where the convection currents are
19
Q
What is rheid?
A
Molten/semi solid
20
Q
The core
A
Mostly nickel and iron
21
Q
The inner core
A
- Solid
* Under intense pressure
22
Q
The outer core
A
- Liquid/molten
* 4000 - 6000 ‘C
23
Q
The mantle
A
The largest section
24
Q
The inner mantle
A
- Mostly non metals
- Solid because of high pressures
- 3000’C
25
The outer mantle
* Bottom layer is liquid rock - 1400-1300’C
| * Upper layer is rheid - lower temperature
26
What is ridge push
Magma that rises pushes the plates apart.
| It is a continuous process which is thought to have lead to sea floor spreading.
27
What is slab pull?
* Gravitational pull of subducted lithosphere is a driving force of plate movement
* Cold, dense lithosphere sinks at an ocean trench, pulling the rest of the plate with it
28
What is sea floor spreading?
When convection currents force the plates to move apart and material rises
29
Fissure eruptions
Evidence of active rifting on MOR.
| The lava is basalt
30
What is palaeomagnetism?
* The earth traps any iron and lines itself with the north pole at that time
* Magnetic field reverses roughly 4 times every million years
* A striped pattern is left behind - white stripes showing the reversal
31
What is happening to the MOR?
* The crust either side of the MOR is moving apart
| * Radiometrically date them to calculate the rate of spreading
32
What is magnitude?
The size or extent of an event.
| Each unit releases about 32 times more energy.
33
Hotspot volcanoes
* Occur in the centre of plates
* The surface expression for a mantle plume in the centre of a plate
* E.g. Hawaii
34
What is a mantle plume?
Stationary area of high heat flow from the mantle, which rises from depth and produces magma that feeds a hot spot volcano.
35
Factors affecting magnitude
* Seismic gap
* Types of movement/boundary
* Depth of the focus
36
What is a seismic gap?
Time period since last earthquake
37
Earthquake waves
* Primary waves
* Secondary waves
* Love waves
38
Primary waves
* Arrive first
* Compression and extensional movement
* Travel within the Earth
39
Secondary waves
* Arrive second
* Up-down movement
* Travel within the earth
40
Love waves
* Arrive last
* Long waves
* Surface waves
* Most damaging waves
41
Secondary hazards of earthquakes
* Liquefaction
* Landslides
* Tsunamis
42
Liquefaction
* Waves cause water pressures to increase in sediment and grains to lose contact with each other
* Water saturated sediment temporarily loses strength and acts as a fluid
* The most vulnerable areas are bays or marshland that we’re pumped with material
43
Landslides
* Large mass of material moves downslope
* Can be triggered by liquefaction
* 87,000 killed in Kashmir in 2005
44
Tsunami
* Wave of water which is usually caused by an earthquake.
| * Usually caused by a dislocation of a larger section of crust on the sea floor, causing displacement of water.
45
Primary hazards of volcanoes
* Lava flows
* Pyroclastic flows
* Ash flows
* Gas eruptions
46
Secondary hazards of volcanoes
* Lahars
| * Jokulhaups
47
Lava
* Viscosity is determined by temperature and chemical composition
* Hotter, low-silica lava flows fastest
48
Basaltic lava
* Hottest lava - 1000-1200’C
* Low silica
* Flows readily and travels far
* The Hawaiian islands were built up from the sea floor from successive basaltic lava flows, forming large shield volcanoes
49
Rhyolitic laval
* Lower temperatures - 800-1000’C
* Highly viscous - slow
* Produces explosive volcanic domes
50
Andesitic lava
* Viscosity depends on quantity of sediment subducted
* Eruptions are characterised by a mixture of explosive activity and lava flows
* Very dangerous
51
Effusive eruption
* Non explosive release of lava
* Lava gently wells up from the ground and overflows, cooling on its way down the slope
* Common in a Hawaiian type event
52
Peléan eruption
* Type of explosive eruption
* Large amount of gas, dust, ash, and lava fragments are blown out of the volcano and the andesite lava dome collapses
* Pyroclastic flows
* Landslides
* Andesitic lava
* Very dangerous
53
Plinian/Vesuvian eruption
* Eruptive columns reach up to 2-45 km into the atmosphere
* Can last days
* Regions affected are subjected to heavy pumice/ashfall - which eventually settles in a thick layer on the ground
* E.g. Mt St Helens
54
Pyroclastic flows
* Most dangerous eruptive feature
* Move down side of the mountain at extreme speeds
* Incredibly hot - can melt snow Bank and ice deposits, which mixes with tephra to form lahars
55
Lahar
* Fast moving mudslides
| * E.g. Nevada Del Ruiz, 1985
56
Haiti earthquake 2010 information (developing example)🇭🇹
* Magnitude of 7.0
* Large seismic gap - 1770
* Epicentre 16 miles west of the capital, Port au Prince
* Shallow focus - 13km
* Had been hit by a storm in 2008 which killed 800 people
* Country has national debt and poverty
* GDP per capita $674
* Doctor:patient - 1:4000
* High risk of water and vector borne diseases
57
Social impacts of the Haiti earthquake🇭🇹
* 230 000 deaths
* 300 000 homeless
* Crush injuries - gangrene -amputation
* No utilities
* Gangs - unfair distribution of resources
* Lack of ongoing education
* Mass burials and burnings create risk of disease spreading
* Lack of organisation lead to cholera outbreak which killed 7000
58
Environmental impacts of the Haiti earthquake🇭🇹
* Damaged infrastructure
* Hospitals collapsed
* 20 million cubic metres of rubble and less than 5% was cleared
* 100 000 damaged buildings that are still usable but many can’t afford them
59
Cause of Nevado Del Ruiz event, 1985🇨🇴
* An eruption released ash and pyroclastic material
* This melted 5-10% of snow and ice on the Arena Crater
* This mixed with ash to form a lahar
60
Social impacts of Nevado Del Ruiz, 1985🇨🇴
* 23,000 deaths
* 10,000 homeless
* Many traumatised - bodies discovered a week after the event
61
Environmental impacts of Nevado Del Ruiz, 1985🇨🇴
* 85% of the town of Amero covered
* Roads and bridges destroyed which made aid supplies and access difficult
* Water contaminated with materials such as lead
* 1000 head of cattle killed
* 30,000 cattle stressed which decreased milk production
62
What is a jokulhlaup?
Glacial outburst floods when a volcano erupts underneath a glacier
63
How were the impacts of the 1996 joklhlaup in Iceland reduced?🇮🇸
The government had an effective hazard plan and had already evacuated nearby areas, preventing any deaths
64
Impacts of the 1996 joklhlaup in Iceland🇮🇸
* Destruction of the southern road in Iceland which left problems for many months as there was no alternative road
* 1 billion kroner to repair the road but with a low population of 265,000, the countries had a lower GDP to pay for it
65
New Zealand earthquake 2010 information🇳🇿
* Magnitude of 7.1
* Shallow focus of 10km
* Epicentre was 40km from Christchurch
* GDP per capita was $30,500
* Large seismic gap - 1922
66
Impacts of New Zealand earthquake🇳🇿
* 1 death and 2 major injuries
* Private insurance prices rose as high as $4 billion
* Damaging aftershocks up to Magnitude 6.3
67
How were the impacts of the New Zealand earthquake reduced?🇳🇿
* Most buildings were under reinforced construction
* $20M was spent on soil compaction previously to reduce chance of liquefaction
* Residents were asked to boil water until no contamination was found
* 16 ambulances operational within 30 minutes of the earthquake
* Hospital has emergency generators
* 90% of electricity was restored on the same day
* The army was deployed to the worst affected areas
68
What is a disaster?
When a hazard causes significant impact on a vulnerable population
69
What is a vulnerable population?
* A population that wouldn’t be able to deal with the hazard.
* Factors are: finance, governance, dealing with a prior event, emergency services, population density and preparation and education
70
What is the pressure release model?
Risk = hazard + vulnerability
71
Hazard risk equation
Risk = hazard x exposure x vulnerability/manageability
72
What is the resilience of a country?
* The ability to recover from a disaster
| * Factors are: community cohesion, GDP, insurance and governance
73
Sichuan, China earthquake 2008 information (emerging example)🇨🇳
* Population of 15 million
* Magnitude of 7.9
* Epicentre 80km from capital city
* Shallow focus of 19
* Highly industrial region
74
Social impacts of Sichuan earthquake 2008🇨🇳
* 69,000 deaths
* 4.8 million homeless - 1 million tents, water and medical supplies provided by government
* Most schools collapsed
* 3 year rebuild
75
Economic and environmental impacts of Sichuan earthquake 2008🇨🇳
* 40% of chemical factories damaged
* 80 tonnes of ammonia leaked, causing major water contamination
* $137.5 billion spent on rebuilding
76
Japan earthquake 2011 information (developed example)🇯🇵
* Magnitude of 9
* Triggered tsunami
* Fukushima Daiichi nuclear power plant was hit
77
Impacts of Japan earthquake 2011🇯🇵
* 16,000 deaths from tsunami (60% elderly)
* Some cracking and liquefaction
* High radioactive releases which contaminated water in the ocean and fishing grounds
* Liquefied natural gas prices rose
* Other countries shut down some of their nuclear reactors
78
How were the impacts of the 2011 Japan earthquake reduced?🇯🇵
* Land use zoning
* Earthquake proof buildings
* Text message system
* Regular earthquake drills
79
Haiti - potential factors🇭🇹
* 61% attend school
* Gangrene caused over 1000 deaths
* 7% have HIV
* Few have access to good healthcare
* 47% vaccinated against tetanus which has a high fatality rate of 70-100%
* 16% of secondary deaths from diarrhoea
* 90% of buildings in Port au Prince collapsed or were severely damaged due to no building regulations
* Weak government neglected building standards and agricultural- cash crops
80
Heimeay, Iceland 1973🇮🇸
* In 6 hours, 5,300 residents were evacuated
* Icelandic State Civil Defence Organisation had an evacuation plan ready
* Sprayed sea water onto lava flows
* No deaths or panic
* National bank released funds
* Parliament increased taxes
* Government gave $2 million
81
Measuring earthquakes
* Moment Magnitude
* Size of waves
* Amount of rock moved
* Area of the fault broken by earthquake
* Resistance of the affected rocks
82
Duration of an event
* How long it will last
| * Volcanic events typically last longer than earthquakes
83
Speed of onset
How much warning time before an event occurs
84
Areal extent
Area that the event has affected
85
Spatial predictability
How predictable the event is likely to be
86
Difficulties of hazard profiling
* Consider comparability of hazards
* Consider scale
* Can suggest severity but does not always relate to death rate
87
Hazard profiling
* Magnitude
* Duration
* Speed of onset
* Areal extent
* Spatial predictability
* Frequency
88
Natural factors of the Bam, Iran earthquake🇮🇷
* Shallow focus of 7km
* Directly under city
* Shaking vertically
* 5.26 am - early morning
* Cold January temperatures
89
Human factors of the Bam, Iran earthquake🇮🇷
* Recent construction was of poor quality
* Wooden structures had already been weakened
* Buildings were unstable and had old heavy roofs
* The 3 main hospitals were destroyed
* Emergency services struggled - facilities and infrastructure destroyed
* Lack of specialised medical training
90
Natural factors
* Magnitude
* Depth of focus
* Distance from coastline
* Tile of day and year
* Recent floods
* Steep relief
91
Why might death rate data be unreliable?
* Location - did it occur in a remote place?
* Political bias - over or understate death rate
* Level of development - LIC of high density
* Time - data collection methods change
92
What is a HILP event?
High impact, low probability event
93
Local human impacts of 2010 mega hazard in Eyjafjallakull🇮🇸
Grounded flights
94
Global human and economic impacts of 2010 mega hazard in Eyjafjallakull🇮🇸
* 100 000 cancelled flights
* Produce from Africa rotted-$65 million
* Imports and exports were affected
95
Local human and economic impacts of 2011 mega hazard in Japan🇯🇵
* 16,000 dead
* 4,000 missing
* 63% of dead were 60 or over
* Disabled power supply
* Nuclear energy became less trusted
* Contaminated fishing grounds
96
Global human and economic impacts of 2011 mega hazard in Japan🇯🇵
* Reduced availability and affordability of LNG
* Less people trusted nuclear energy and many plants were shut down
* Contaminated fishing grounds
* Asian market affected
* Increasing costs for new, safe nuclear reactors
97
What is a multiple hazard zone?
An area in the world where there are a number of different physical hazards that combine to create and increased level of disaster
98
What is a disaster hotspot?
A country or area extremely prone to disasters due to its range of physical hazards
99
Hazards in California🇺🇸
* Earthquake: active faults
* River flooding: winter storms and deforested hillsides
* Coastal flooding: subsiding area
* Drought: Mediterranean climate - Lack of water for rising population
* Wildfires: LA expanding into rural areas
* Landslides/mudslides: winter storms and burnt and eroded hillsides
* Fog/smog: cold sea air meets warm air and car pollution
100
Signs of an earthquake
* Changes in ground level
* Measurement of gases
* Changes in water levels
* Coloured skies
* Animal behaviour
101
The stages of the hazard management cycle
* Mitigation (prevention)
* Preparedness
* Response
* Recovery
102
What are players?
* The different groups of people who are involved in a hazard
* E.g. governments, NGOs, private donors
103
What is the Park’s Model?
It shows the stages of recovery from disruption based on development
104
What is the difference between micro techniques and macro techniques?
* Strengthen individual structures
| * Large scale protective measure
105
What’s the difference between hazard mitigation and hazard adaptation?
* Strategies to avoid/delay/prevent
| * Strategies to reduce impact
106
What is land use zoning?
* Local governments use a GIS map to consider areas at risk
| * They can them decide what it is safe to use that area of land for
107
Diverting lava flows
* Building barriers and digging channels
* Usually unsuccessful as lava is unpredictable, landscape may not be suitable and stopping lava in one area may put others at risk
108
Building design
* Reinforced concrete
* Cross braved steel frames
* Steel pendulum
* Bass isolation
* Retrofitting - fitting after it has been built
109
Modifying vulnerability
* Prediction and warnings
* Improved community preparedness
* Changing a populations behaviour
110
Modifying the loss
* Emergency services
* Insurance
* NGOs/charities
111
Negatives of disaster aid
* Poor or corrupts distribution systems could be present
| * Doesn’t encourage self help
112
What is the VEI?
* Volcanic explosivity index
| * Relative measure of the explosiveness of volcanic eruptions
113
Why is it difficult for buildings to remain intact during an earthquake?
* Each type of seismic wave moves through the ground differently
* The waves all arrive within seconds of each other
* Anything attached to the ground would also move
114
Explain the geographical criteria that can be used to decide if a tectonic event is a hazard, disaster or mega disaster
* Definitions by the UN
| * Suggestions if impacts contained within the scales for measuring volcanoes, tsunamis and earthquakes
115
An example of a multiple hazard and risk zone
* Vanuatu - 65 Pacific islands
* Vulnerable due to cyclones earthquakes, volcanic eruptions and the fact that they are isolated islands spread over a large area
116
Developed examples
* New Zealand🇳🇿
* Japan🇯🇵
* Iceland🇮🇸
117
Developing examples
* Iran🇮🇷
| * Haiti🇭🇹
118
Emerging examples
* Colombia🇨🇴
| * China🇨🇳
