Tectonics Flashcards
Tectonic processes, hazards, trends and modification
1
Q
When was Tohoku earthquake?
A
March 2011
2
Q
Magnitude of Tohoku earthquake
A
9.0 Richter Scale
3
Q
Plates involved in Tohoku earthquake
A
Subduction zone between the Pacific and Eurasian plates
4
Q
Height of the Tohoku tsunami
A
10-20m
5
Q
Deaths from the Tohoku earthquake
A
16,000
6
Q
Number of people missing from the Tohoku earthquake
A
3,000
7
Q
Number of injured people from the Tohoku earthquake
A
6,000
8
Q
Amount of debris from Tohoku earthquake
A
26m tonnes
9
Q
Economic losses from Tohoku earthquake
A
$300bn
10
Q
Why was the Fukushima Power Plant a major issue in the Tohoku earthquake?
A
It was flooded during the tsunami and had the potential to explode, causing a nuclear disaster. The area has since been permanently evacuated due to the high levels of radiation.
11
Q
What did the government in Japan do following the Tohoku earthquake?
A
Produced a report on how to avoid future disasters. It suggested:
- More safety measures, such as higher tsunami walls
- Better planning, such as avoiding flat coastal areas
- Long-term support for those who had lost relatives or been affected
12
Q
Features of destructive plate margins
A
- Oceanic plate slides under the continental plate
- Oceanic crust destroyed
- Friction between the plates can cause earthquakes
13
Q
Features of constructive plate margins
A
- Plates move apart
- Pushed by convection currents
- Magma rises to fill the gap that is created
- New crust generated
14
Q
Features of conservative plate margins
A
- Plates slide past each other horizontally
- No crust destroyed or produced
- Friction between the plates builds until they can’t take the stress and they slip past each other
15
Q
Features of oceanic crust
A
- High density
- Made of basaltic rock
- Only 7-10km thick
- Can subduct
16
Q
Features of continental crust
A
- Thicker (25-75km)
- Less dense than oceanic plates
- Made of granitic rock
- Do NOT subduct
17
Q
Tectonic hazard definition
A
A natural event that has the potential to threaten both life and property
18
Q
At what type of plate boundaries do tectonic hazards occur?
A
All 3 of them!
19
Q
What is a geological hotspot?
A
A hot mass of rising heat under a weakness in a plate
Magma rises to fill this weakness
20
Q
Example of a geological hotspot?
A
The Hawaiian islands formed as a result of a mid-Pacific hotspot
21
Q
How do intra-plate volcanic islands form?
A
- Isolated plumes of convection heat rise towards the surface of the Earth
- Basaltic volcanoes created
- The plume remains stationary as the tectonic plate moves over it
- Continuing plate movement over time produces a chain of volcanic islands
22
Q
How do intra-plate earthquakes occur?
A
Ancient fault lines are re-activated by tectonic stresses and this causes minor earthquakes.
23
Q
What is the name given to the impact of the Indo-Australian plate with the Eurasian plate?
A
A collision zone
24
Q
Features of the Earth’s core
A
- Central part of the Earth
- Made up of an inner core and an outer core
- Inner core = solid; Outer core = liquid
- A source of radioactive heat
25
What is the Earth's mantle?
A semi-molten body of rock between the Earth's crust and its core
26
Features of the asthenosphere?
- Part of the mantle
- Semi molten
- Below the lithosphere, which floats on top of it
27
Features of the lithosphere?
- The crust and upper mantle which form tectonic plates
- Around 80-90km thick, but this changes depending on whether the crust is oceanic or continental
28
Order of the layers of the Earth, starting in the centre
Core, outer core, mantle (including asthenosphere), lithosphere (including crust)
29
Which is more solid: the inner core or the outer core?
The inner core is more solid
30
Explain sea-floor spreading theory
In the 1960s, there was a discovery of magnetic stripes in the oceanic crust of the seabed.
Palaeomagnetic signals from the past reversal of the Earth's magnetic field prove that new crust is created through the process of sea-floor spreading at mid-ocean ridges.
31
What is gravitational sliding?
Elevated altitudes of crust at ridges at destructive plate boundaries.
Creates a 'slope' down where oceanic plates slide
32
What was Holmes' hypothesis?
Holmes (1930s) said that the Earth's internal radioactive heat was the driving force of convection currents in the mantle, which move tectonic plates
33
Explain Wegener's theory of continental drift
His hypothesis from 1912 suggested that our continents had once been joined together as supercontinents (i.e. Pangea).
34
What is slab pull?
At destructive boundaries, the high density ocean floor is being dragged down by a downward gravitational force beneath the adjoining continental crust
35
What are volcanic eruptions at constructive plate boundaries like?
- Basaltic eruptions
- Produce low viscosity lava
36
What are volcanic eruptions at destructive plate boundaries like?
Violent due to high viscosity lava
37
What are earthquakes at constructive plate boundaries like?
- Low in magnitude
- Shallow focus (less than 70km deep)
38
What are earthquakes at destructive plate boundaries like?
- High magnitude
- Deep focus (up to 700km deep)
- Frequent
39
Example of a place with destructive plate boundaries?
Western South America
40
At what plate boundary do deep-sea trenches and fold mountains form?
Destructive
41
What is a collision plate boundary?
The meeting of two continental plates resulting in the formation of a fold mountain belt
42
Example of a mountain range caused by a collision plate boundary
The Indo-Australian plate and Eurasian plates have created the Himalayan mountain range
43
What is volcanic activity like at collision plate boundaries?
There is no volcanic activity
44
What are earthquakes at collision plate boundaries like?
- Rare
- High magnitude
- Shallow focus (less than 70km deep)
45
What is volcanic activity at conservative plate boundaries like?
There is no volcanic activity
46
What are earthquakes at conservative plate boundaries like?
- High magnitude
- Shallow focus (less than 70km deep)
- Common
47
Example of a conservative plate boundary
The San Andreas Fault, California
48
What is the focus of an earthquake?
Where the pressure is released underground and where the energy radiates out from.
This is the place with the strongest waves that cause the most damage.
49
What is the epicentre of an earthquake?
The point directly above the centre of an earthquake on the Earth's surface
50
What are seismic waves?
When energy is released from the focus in shock waves
51
True/false - The Earth's plates are always moving
True
| Tensions build up between them over time
52
How are earthquakes caused?
- Tension builds up between two plates
- The stress can suddenly be released when the strain overcomes the elasticity of rock
- This release of stress can cause parts of the surface to experience an intense shaking motion
53
Where is energy transferred in an earthquake?
Mostly transferred vertically to the surface, then moves outwards from the epicentre as seismic waves
54
How deep are shallow focus earthquakes?
0-70km under the Earth's surface
55
How deep are deep focus earthquakes?
70-700km under the Earth's surface
56
What causes deep focus earthquakes?
- Previously subducted crust moving towards the Earth's core
- Previously subducted crust heating up
- Previously subducted crust decomposing
57
Why are deep focus earthquakes less damaging than shallow focus ones?
The shock waves have had to travel further and so cause less shaking at the surface
58
What are P waves?
Primary waves
59
Features of P waves
- Fastest
- Cause the least damage
60
What are L waves?
Love waves
61
Features of L waves
- Create significant damage, including crustal fracturing
- Only travel across the surface
- Have a large amplitude
62
What are S waves?
Secondary waves
63
Features of S waves
- Slower
- Make the ground shake violently
64
What do we call series of enormous waves caused by underwater earthquakes?
Tsunamis
65
What is crustal fracturing?
The Earth visibly separating and deep fissures in the ground are created
66
What are some primary hazards of earthquakes?
- Ground shaking
- Crustal fracturing
67
What are some secondary hazards of earthquakes?
- Landslides (in mountainous areas)
- Liquefaction
- Tsunamis (in submarine earthquakes)
68
What is liquefaction?
When earthquakes shake loose sediment (silt, sand and gravel) that is waterlogged. The compact ground forces water to rise to the surface. Damage to buildings and infrastructure is common.
69
Example of a tsunami
Boxing Day Tsunami, 2004
70
What is an ash fall?
A solid material of varying grain size ejected into the atmosphere (known as tephra)
71
How do ash falls damage buildings?
Buildings often collapse under the weight of ash falling onto their roofs
72
How can ash falls harm people?
Air thick with ash causes breathing difficulties
73
Example of an ash fall
The eruption of Mount Merapi in Indonesia in 2010
74
What are some examples of volcanic gases?
- Carbon dioxide
- Carbon monoxide
- Hydrogen sulphide
- Sulphur dioxide
- Chlorine
75
Why are volcanic gases dangerous?
They can be poisonous
76
Example of an eruption which produced lots of volcanic gases
1986 eruption of Lake Nyos, Cameroon
77
Features of pyroclastic flows
- Very hot (800 degrees)
- High velocity (200km/h)
- A mixture of gases and tephra
- Destroy everything in their path
78
Ancient example of a pyroclastic flow
AD79 eruption of Mount Vesuvius in Pompeii, Italy
79
Modern example of a pyroclastic flow
1980 eruption of Mount St. Helens in the USA
80
Why are lava flows not usually a major threat?
They are slow moving
81
What are some examples of land masses created by lava turning into rock?
Hawaii
82
What is a jökulhlaup?
Flooding that happens when glaciers or ice caps melt
83
What are lahars?
When rain mobilises deposits of volcanic ash to create a fast mudflow
84
Example of a lahar
Nevado del Ruiz eruption in Colombia, 1985
| Four lahars killed around 20,000 people in the town of Armero
85
Primary hazards of volcanoes
- Pyroclastic flows
- Lava flows
- Gases
- Ash
86
Secondary hazards of volcanoes
- Lahars
- Jökulhlaups
87
What causes a tsunami?
Submarine earthquakes at subduction zones.
| The sea bed is moves up or down, displacing a large volume of water.
88
Example of a tsunami
2004 Boxing Day tsunami in Indonesia
89
What are some characteristics of tsunamis at sea?
- Long wavelength
- Short amplitude (height)
- High velocity (up to 700km/h)
90
What are some characteristics of tsunamis near land?
- Drawback: the sea appears to move back as water is sucked to form a tsunami wave
- High amplitude (height)
- They hit in a series of waves called a wave train
91
How tall are tsunami waves?
At sea: very short, 1m
Near land: tall, up to 25m
92
Define risk
The probability of a hazard happening and it creating damage
93
Define vulnerability
The risk of exposure to hazards combined with the inability to cope with them
94
Define resilience
The degree to which a population or environment can absorb a hazard and stay organised and functioning
95
Define disaster
When a hazard has a significant impact on people
96
Risk equation
Risk = (Hazard x Vulnerability) / Resilience
97
What features increase an area's disaster resilience?
- Having emergency evacuation systems
- Hazard-resistant buildings
- Disaster education
98
What is the PAR model?
Pressure-and-release model
99
What does the PAR model show?
Many socio-economic factors impact how bad a disaster is, not just the hazard itself
100
What are some root causes in the PAR model?
- Low access to resources
- Poor government or economy
101
What are some dynamic pressures in the PAR model?
- Lack of education and training
- Rapid population change and urbanisation
102
What are some unsafe conditions in the PAR model?
- Poor construction standards
- Poverty
- Unsafe infrastructure
- Lack of social safety net
103
Order of the PAR model
1. Root causes
2. Dynamic pressures
3. Unsafe conditions
+ The hazard itself
= DISASTER
104
Benefit of the PAR model
Focus on socio-economic causes for the disaster. This helps governments to work out how they can reduce the impact of a disaster, particularly in hazardous areas.
105
Why is it difficult to compare disasters from different countries?
Some countries may have better government and be financially better-off, so they are not affected by hazards equally.
106
What is the Moment Magnitude Scale and what does it measure?
Measures the amount of energy released by an earthquake. Ranges from 1-10 (each number is 10x more violent than the last one as the scale is logarithmic)
107
What is the Mercalli scale and what does it measure?
Measures the intensity of an earthquake shaking on a scale of 1-12
108
How are volcanic eruptions measured?
Volcanic Explosivity Index (VEI)
109
What factors does the Volcanic Explosivity Index include?
- Volume
- Duration
- Column height
110
How does a plate boundary affect VEI?
Lower VEI = less explosive eruption, usually at constructive plate boundaries
Higher VEI = more explosive, usually at destructive plate boundaries
111
3 earthquake measuring scales
- Richter scale
- Moment magnitude scale (MMS)
- Mercalli scale
112
What do hazard profiles show?
Summarises the physical processes of all hazards on a scale so decision-makers can see which ones are most at risk
113
6 factors in a hazard profile
- Magnitude
- Speed of onset
- Areal extent
- Duration
- Frequency
- Predictability
114
Where do the most high risk events happen?
At subduction and collision zones
115
What is 'areal extent'?
The area affected by a disaster
116
What year was the Kashmir earthquake?
2005
117
MMS of Kashmir earthquake
7.6
118
Mercalli ground shaking measure of the Kashmir earthquake
VII (severe)
119
Why was it hard for people to escape the Kashmir earthquake?
Speed of onset was very rapid so it was hard for people to get to safety
120
Where is Kashmir?
Northern India
121
How long did the ground shake during the Kashmir earthquake?
30-45 seconds
122
What secondary disaster was caused by the Kashmir earthquake?
Landslides
123
How many people died in the Kashmir earthquake?
79,000
124
Why did many people not know how to react to the Kashmir earthquake?
The last earthquake was in 1905 so nobody was expecting or prepared for one
125
What is the 'seismic gap'?
An area of known risk that has not experienced an earthquake for a long time
126
Why are more deprived areas worse affected by natural disasters?
- Many people lack basic necessities like food and water, even in 'normal times'
- A lot of housing is poorly constructed
- Poor population health and access to healthcare
- Education levels are lower so people don't know the risks of disasters
- Government may not be wealthy or stable enough to help citizens following a disaster
127
What are some methods governments can use to be more prepared for natural disasters?
- Land-use planning and zoning to prevent house construction in dangerous areas
- Having effective monitoring systems
- Preparing their population
- Environmental management to prevent factors such as deforestation
128
How can urbanisation increase a population's vulnerability to hazards?
High population density
129
How can urbanisation increase a population's resilience to a hazard
They have better access to food, healthcare and transportation
130
Why can a high population density put people at risk from disasters?
- Hard to evacuate
- Disease spreads easier
- Those living in slums often have very poor living conditions
131
Why can a low population density put people at risk from disasters?
Isolated areas are difficult to reach so it may take a very long time for them to be evacuated or receive resources
132
What type of hazards have become more common as a result of climate change?
Hydro-meteorological (weather events)
133
Why does the number of deaths from earthquakes vary so much each year?
Large disasters with extremely high death counts skew the figures
134
Why are disasters becoming more and more expensive each year?
There is more to lose as global affluence increases
135
How many eruptions have killed more than 100 people since 1980?
7
| this isn't very many compared to earthquakes
136
Example of an area which gets lots of earthquakes
The Himalayas
137
3 major earthquakes in the Himalayas since 2005
- Kashmir (2005)
- Sichuan (2008)
- Nepal (2015)
These 3 events account for 40% of all earthquake deaths since 2005
138
2 earthquakes with deaths over 100,000
- Banda Aceh (2004)
- Haiti (2010)
139
Economic impact of the Iceland 2010 eruption
The ash cloud from the eruption disrupted flights all over the world
140
What is a multi-hazardous zone?
Where two or more different hazards occur
141
Characteristics of multiple hazard zones?
Usually:
- Geologically young with unstable mountain zones (prone to landslides)
- Tectonically active
- On major storm tracks, usually in the mid-latitudes
142
What does ENSO stand for?
El Nino Southern Oscillation
143
What is ENSO?
A warm current that replaces the usual cold current off the Pacific coast of South America. It is becoming more common due to climate change
144
What are the effects of ENSO?
- Heavier rain than usual on the coast
- Drought inland
145
Define prediction
Knowing when and where a hazard will strike so that meaningful action can be taken
146
What does a tiltmeter measure?
Volcanoes 'bulging' as magma rises
147
What does a seismometer measure?
Seismic waves, indicating tectonic movement
148
What does a gas spectrometer measure?
Analyses gas emissions from volcanoes. More gas suggests an eruption is likely.
149
How can volcanoes be monitored?
- Tiltmeters
- Seismometers
- Gas spectrometers
150
Why are earthquakes so hard to predict?
They give little advance warning
151
How can tsunamis be predicted?
Seismometers can detect ocean earthquakes and warn nearby coastal areas
152
4 parts of the hazard management cycle?
- Response
- Recovery
- Mitigation
- Preparedness
153
Hazard management cycle: response
Immediate help
Examples:
- Rescue missions
- Emergency aid like food and water
154
Hazard management cycle: recovery
Rebuilding infrastructure and services after the disaster and rehabilitating injured (physically and mentally) people
155
Hazard management cycle: mitigation
Acting to reduce the scale of the next disaster
Examples:
- Land-use zoning
- Resistant infrastructure
156
Hazard management cycle: preparedness
Ensuring the population is prepared for future hazards
Examples:
- Warning and evacuation systems
- Education
157
What is the Park Disaster Response Model?
Shows the response to a disaster in 5 stages. Curved shape
158
5 stages of the Park Disaster Response Model
```
1- Normal before disaster
2- Disaster strikes
3- Immediate response
4- Rehabilitation process
5- Reconstruction of society
```
159
Advantages of the Park Disaster Model
- Shows the impact of a range of management strategies
- The impact on QoL
160
2 ways of modifying tectonic disasters
- Land-use zoning
- Physical defenses
161
What areas do land-use planners try and avoid
- Close to sea in potential tsunami area
- Areas prone to liquefaction
- Areas near volcanoes
162
What are aseismic buildings?
They have deep foundations and use cross-bracing and counterweights to resist earthquake damage
163
What physical defenses can limit tsunami effects?
Seawalls and breakwaters
164
What physical defenses can limit volcanic eruption effects?
- Building lava channels
- Cooling areas with water
165
What is 'modifying loss'?
Reducing the scale of loss from a disaster
166
How can loss be modified?
- Emergency aid
- Monetary compensation e.g. insurance
167
What is 'modifying vulnerability'?
Reducing the risk people have before the disaster occurs
168
How can vulnerability be modified?
- Monitoring
- Community preparedness and education
- Living in a non-dangerous area
169
Where is Mount Merapi?
Indonesia
170
When did Mount Merapi erupt?
November 2010
171
How many died in the Mount Merapi eruption?
353
172
How many were injured in the Mount Merapi eruption?
500
173
How many people successfully evacuated the Mount Merapi eruption?
350,000
174
Worth of damage from the Mount Merapi eruption
$600m
175
Environmental damage caused by Mount Merapi eruption
- The rice harvest in the surrounding area was lost due to the ash fall
- Forests destroyed by pyroclastic flows
176
What secondary disaster was caused by the Mount Merapi eruption?
Lahar
177
VEI of Mount Merapi eruption
4.0
178
Plates involved in Mount Merapi eruption
```
Oceanic = Indo-Australian
Continental = Eurasian
```
179
How was the impact of the Mount Merapi eruption reduced before the eruption occured?
Monitoring schemes predicted an eruption was likely. Evacuation schemes were put into place for everyone within 20km of the volcano.
180
What were the responses to the Mount Merapi eruption?
- Refugee shelters
- Local airport closed due to ash
- Government agencies delivered aid (including masks so people didn't inhale ash)
181
When was the Nepal earthquake?
April 2015
182
Deaths from the Nepal earthquake
9,000
183
Number of people injured from the Nepal earthquake
22,000
184
Economic loss from the Nepal earthquake
$5bn
185
What secondary hazards were triggered by the Nepal earthquake?
Landslides and avalanches, including one on Mount Everest
186
Number of houses damaged in the Nepal earthquake
450,000
187
Number of people displaced from the Nepal earthquake
2.8m
188
Social impact of the Nepal earthquake
Increase of human trafficking, particularly teenage girls, caused by the displacement
189
Magnitude of Nepal earthquake
7.0
190
Plates in the Nepal earthquake
Collision zone between the Eurasian and Indo-Australian plate
191
Why does Nepal's geology increase its vulnerability to disasters?
Pre-historic valleys with lakes make the sediment soft
| Very hilly
192
Why does soft sediment make disasters worse?
It amplifies the waves which causes more violent swinging
193
Why was the Nepal government slow to respond to the earthquake?
They had their own political turmoil
194
How many people urgently needed aid following the Nepal earthquake?
1m
195
How much did the Asian Development Bank give Nepal following the earthquake?
$200m
196
Who was discriminated against in the response to the Nepal earthquake?
Women: men were prioritised with aid
