Tectonic Hazards Flashcards
1
Q
What are the 2 types of tectonic plate?
A
Continental
Oceanic
2
Q
What is the asthenosphere?
A
Part of the mantle below the lithosphere where the rock is semi molten.
3
Q
What are the different processes that affect plate movement?
A
Mantle convection.
Slab pull
Subduction
Sea floor spreading
Paleomagnetism.
4
Q
What is mantle convection?
A
Heat produced by the decay of radioactive elements in Earths core heat the lower mantle and creates convection currents.
Hot liquid magna currents thought too be in circles in the asthenosphere thus causing the plates to move - now less accepted.
5
Q
What is slab pull?
A
Newly formed oceanic crust at mid ocean ridges become denser and thicker as it cools.
This causes it to sink into the mantle underneath its own weight pulling the rest of the plate down with it.
Increasingly seen as a major factor in plate movement.
6
Q
What is subduction?
A
Plate destruction.
As two oceanic plates or an oceanic and continental plate move towards eachother one slides under the other into the mantle where it melts into the subduction zone.
7
Q
What is sea floor spreading?
A
Process of new crust pushing tectonic plates apart. In middle of oceans there are mid ocean ridges or underwater mountain ranges which form when hot magma is forced up from the asthenosphere and gardens forming new oceanic crust.
8
Q
What is paleomagnetism?
A
Confirmed sea floor spreading. Every 400,000 years the earths magnetic fields change direction. When lava cools and becomes rock, minerals inside the rock line up with the Earths magnetic direction (polarity) at the time.
9
Q
What is a plate boundary?
A
Where 2 tectonic plates meet.
10
Q
What are the 3 types of plate boundary?
A
Convergent
Divergent
Conservative
11
Q
What is a convergent plate boundary also known as?
A
Destructive margins
12
Q
What is a divergent plate boundary also known as?
A
Constructive margin
13
Q
What is a conservative boundary also known as?
A
Transform margin.
14
Q
Explain divergent plate boundaries.
A
Two plates are moving apart (diverging) leading to formation of new crust.
In oceans this divergence forms mid ocean ridges and on continents it forms rift valleys.
15
Q
Name example of mode ocean ridge
A
Mid Atlantic ridge
16
Q
Describe the tectonic hazards at mid ocean ridges?
A
Earthquakes are shallow focus and occur frequently, pose little threat to humans as they are small and underwater.
Volcanoes, submarine volcanoes can occur some one which can be above sea level to form new islands, eg Iceland on mid Atlantic ridge. Generally less explosive and more effusive:
17
Q
What does effusive mean?
A
A type of eruption where lava steadily flows out of a volcano.
18
Q
How does a Rift Valley form?
A
Continental plates move apart the crust stretches and breaks into sets of parallel cracks (faults). The land between these faults then collapses forming steep sided rift valleys
19
Q
Name example of Rift Valley?
A
East African Rift Valley.
20
Q
Describe tectonic hazards at rift valleys?
A
Earthquakes, similar to mid ocean ridges, shallow and low magnitude
Volcanoes- don’t occur here as magma never reaches the surface.
21
Q
What is the subduction zone?
A
Broad areas where two plate are moving together. Often thinner more dense oceanic plate descends beneath the continental plate.
22
Q
What is a locked fault?
A
In a subduction zone as plates move together they can get stuck due to frictional resistance. These faults may store strain for extended periods, eventually released in a large magnitude earthquake.
23
Q
What is the Benioff zone?
A
An area of seismicity corresponding with the slab bearing thrust downwards into a subduction zone where the pressure is released form locked fault.
24
Q
Explain how an earthquake occurs at subduction zone?
A
Two plates collide, heaviest plate sinks (oceanic) at the subduction zone. Plates do not slide smoothly over eachother, they create friction. Frictional resistance causes a locked fault to form where the plates get stuck. Energy is stored here and builds up, finally in the Benioff zone, the frictional pressure is released causing an earthquake.
25
What forms when the oceanic plate subducts?
The continental plate folds and is pushed upwards forming fold mountains. Caused by melting of oceanic plate in asthenosphere, molten rocks rise to the surface of mantle and release out of fold mountains.
26
Which plate subducts where oceanic meets oceanic?
Either the faster moving one
Ore the one with the largest crust.
27
Explain what happens when oceanic meets oceanic?
Subducts plate melts and magma rises to form under water volcanoes. Over millions of years these grow above sea level to form island volcanoes called island arcs.
Earthquakes often occur, often shallow to deep and can be very powerful
Tsunamis also occur.
28
What forms when continental meets continental?
A collision margin forms.
29
Explain what happens when a continental plate meets a continental plate?
Both plates have same density and these plates are less dense than the asthenosphere, neither plate is subducted. Instead these plates collide and the sediments between them are crumpled and forced up to form high fold mountains.
Any earthquakes that occur here are shallow.
Eg Himalayas.
30
What happens at conservative plate margin?
Two plates are sliding past eachother resulting in major breaks in the crust between them as they move.
31
What are earthquakes like at conservative plate margins?
Big and powerful earthquakes as there is no subduction, no Benioff zone. The earthquakes are shallow and result from friction between the two plates.
32
Example of conservative plate margin?
San Andreas Fault
33
What is the focus / hypocentre?
The point inside the crust from which the pressure is released.
34
What is the epicentre?
The point on Earths surface that is directly above the focus / hypocentre.
35
What are the 3 types of seismic wave?
Primary P waves
Secondary S waves
Love L waves
36
Describe primary P waves
Body waves - travel through earths body
Fastest and first to reach the surface (8km/sec)
Travel through solids and liquids
Move backwards and forwards (left to right)
Only damaging in most powerful earthquakes
37
Describe secondary S waves?
Also body waves - travel through earths body
Slower than P waves (4km / sec)
Only travel through solids.
Move up and down in motion perpendicular to direction of travel
Do more damage than P waves.
38
Describe Love L waves?
Surface waves only travel on earths surface
Slowest if 3 waves, last to arrive
Move side to side motion, perpendicular to direction of travel.
Larger and do the most damage
39
What does the overall severity of an earthquake depend on?
Links to the amplitude and the frequency of the wave types.
Ground surface may be displaced horizontally, vertically or obliquely (slanted) during an earthquake
40
How can you predict earthquakes?
Cannot be predicted.
Can us epilate boundary knowledge to forecast where an earthquake is likely to happen, eg areas that have had large earthquakes before
Research focuses on precursors which may indicate an earthquake is going to happen eg Foreshocks
41
What physical factors affect the impact of an earthquake?
Magnitude
Depth
Distance from epicentre
Geology (soft rocks amplify shaking)
42
What human factors impact effect of earthquakes?
Level of development
Population
Levels of preparation
Effectiveness of emergency response
Impact of secondary hazards
43
What are primary effects of earthquakes?
Ground shaking causing buildings etc to collapse
Crustal fracturing - when Earths crust cracks due to the energy that is released.
44
What are secondary effects of earthquakes?
Landslides or avalanches
Tsunamis
Liquefaction : where surface rocks lose strength and become more liquid than solid. Buildings sink into the ‘soil’
45
What are the primary hazards from volcanic eruptions?
Lava flows
Pyroclastic flows
Tephra and Ash Falls
Gas Eruptions
46
What are lava flows?
Streams of lava flowing across earths surface
Can reach 1170 degrees C and take years to cool fully, destiny everything in their path.
Generally not the eating as they move slowly so people can move out of the way.
47
What are pyroclastic flows?
Mix of dense hot rock ash lava and gases ejected from volcano. Can each 700 degrees C
Move up to 100mk/h
Destroy everything in path
48
What is tephra and Ash falls?
Tephra are pieces of volcanic rock that blast into the air during eruptions.
Large pieces fall near to volcano where they cause injury / death as well as structural damage; and ash can travel for thousands of kilometres.
Ash fall causes disruption through poor visibility, slippery roads. Roots can collapse under weight a d engines can get clogged up with Ash
49
What are gas eruptions?
Magna contains dissolved gases that are released into the air during eruptions.
Gases include water vapour, carbon dioxide and sulphur dioxide.
Once gases are in the air they can travel for thousands of kilometres.
Gases can be harmful and hazardous to people animals and structures
50
What are the secondary hazards of volcanic eruptions?
Lahars
Jökulhlaup
51
What are Lahars?
Masses of rock mud and water that travel quickly down the sides of volcano and they vary in size and speed.
Caused when eruptions quickly melts snow or ice or when heavy rainfall has occurred either during or after an eruption.
52
What are jökulhlaup?
Glacial outburst floods.
Occur when heat of volcano melts the snow and ice of a glacier causing heavy and sudden floods.
These occur suddenly and release large amounts of water rocks and ice that can be very dangerous as they flood and damage land and structures.
53
Can you predict volcanic eruptions?
Use gps and satellite based radar placed in and around volcanoes to monitor the signs
Monitoring of small earthquakes, changes to the surface of volcano and changes to the tilt of a volcano can indicate that an eruption is about to occur.
54
How are most tsunamis caused?
Underwater earthquakes, some caused by underwater landslides.
Energy released during the earthquake causes the sea floor to uplift, displacing the water columns.
55
Explain how a tsunami occurs?
Tsunami forms in deep ocean, difficult to detect, long wavelength and short in height.
Water column rises as the ocean gets shallower (towards land)
The nature / size of the wave depends on the cause, distance travelled from source, water depth on route and the topography of the shoreline.
The depth and destruction of the tsunami depends on the land use, population, and the level of warnings given.
56
How to predict tsunamis?
Very hard to predict.
Early warning can be possible due to signals and DART monitoring etc
57
How are tsunamis monitored?
Early warning systems in place.
Use seismic detectors to detect submarine earthquakes, and additional equipment also used eg
DART used sea bed detectors and surface buoys to monitor changes in sea level and pressure.
When waves detected the into is sent to scientists via satellite where the data can be analysed and the correct people can be informed if necessary.
58
Pros and cons of computer modelling for monitoring tsunamis?
Can save lives
Info can reviewed regularly due to multiple sensors / buoys
Cons:
Faulty equipment can result in inaccurate data
Shallow earthquakes can damage equipment
59
What is hazard?
A percieved natural / geophysical event that had the potential to threaten both life and property
60
What is a disaster?
The realisation of a hazard when it causes a significant impact on the vulnerable population,
61
When does a hazard become a disaster according to CRED?
When 10 or more people are killed
100 or more people are affected.
62
What is the formular for Hazard Risk?
Risk(R) = Hazard (H) x Vulnerability(V)
———————————————-
Capacity to Cope
63
What is resilience?
The ability to protect lives, livelihoods and infrastructure from destruction and to restore areas after a natural hazard has occurred.
64
How can you increases resilience?
Improving infrastructure
Monitoring systems
Warning systems
65
What political factors effect vulnerability to hazards?
Existence and enforcement of building codes and regs
Efficiency of emergency services and response teams
Existence of public education and practices hazard responses
Corruption levels
Existence of disaster preparedness plans
Quality of infrastructure
66
What social factors impact vulnerability?
People without access to education
Poor quality housing
Communities with poor health and healthcare
Age of a population
67
What environmental factors impact levels of vulnerability?
Accessibility of an area
Rapid urbanisation increases demand for housing
Areas with high population density have poorer quality housing
68
What does the pressure and release model show?
The progression of vulnerability through the root causes which lead up to unsafe conditions in the event of a hazard or disaster
69
How can you measure tectonic hazards?
Richter Scale
Mércalli Scale
Moment Magnitude Scale (MMS)
Volcanic Explosivity Index
70
What does the Richter scale measure?
Measures the amplitude of the waves produced by an earthquake.
71
What does the MMS measure?
Describes the event in terms of the energy released. Based on the seismic moment which is calculated from the amount of slip of the fault, the area affected and and Earth rigidity factor.
72
What does the Mercalli Scale Measure?
Measures the experienced impacts of an earthquake on a scale of I - XII (Roman numerals)
Relative scale, not fact based.
73
What does the volcanic explosivity index measure?
A relative measure of explosiveness of a volcanic eruption which is calculated from the volume of the products, height of the eruption cloud and also qualitative observations.
74
Advantages of hazard profiling?
Can be used to compare hazards
Simple
Easy to compare / make comparisons
Help governments to develop disaster plans
Can show multiple hazards.
75
Disadvantages of hazard profiling?
Non specific
Subjective = lost reliability
76
What is a multiple hazard zone?
Places where a number of physical hazards combine to create an increased level of risk for the country and its population.
77
Example of MHZ?
The Philippines
78
What is the hazard management cycle?
Covers 4 areas; mitigation, preparedness, response and recovery, which can be used by governments to protect people from natural hazards that threaten their communities.
Useful as cycle involves all key players, and all key factors that can reduce impact so effective use SHOULD manage the impact.
79
What does parks model show?
Shows how a country or region may respond after a hazard event.
Can be used to compare how areas at different levels of development mug he recover from a hazard event.
Analyses the response to a disaster with a time scale
Shows responses - improvements or not
Shows how time can change quality of life.
Can compare different events in different countries and the differing impacts of the event and can help governments to plan for the future.
80
What are theoretical frameworks?
Models that governments and organisations can use to predict, reduce the impact and manage situations in the event of a natural disaster.
81
Examples of theoretical frameworks?
Predictions of tectonic hazards using DART or sensory equipment etc
Hazard response curve - Parks Model
Hazard Management cycle
82
What are hazard mitigation strategies?
Meant to avoid, delay or prevent hazard events
83
What are hazard adaption strategies?
Strategies designed to reduce the impact of hazard events
84
Give examples of hazard mitigation strategies for tectonic events?
Land Use Zoning
Diverting Lava Flows
GIS Mapping
Hazard Resistant Design and Engineering Defences
85
How can land use zoning reduce, delay or prevent impacts of disaster?
Protects people and property
Land divided into zones dependent on risks. Areas at high risk will be under strict regulations. Settlements limited if allowed at all, communities may be resettled in a safer place, certain building types / structure prohibited as they may pose danger in event.
86
How do diverting lava flows work?
Building barriers and digging channels to divert lava flows in directions away from causing harm.
Fairly ineffective because path taken by lava difficult to predict.
Terrain has to be suitable
Saving one community may put others in danger.
87
How does GIS mapping work to mitigate risk?
Identifies where evacuation routes should be placed.
Can show areas worst affected by hazards
The locations of airports and airstrips etc
Locations and rough population sizes of major towns / cities
Helps direct aid where it’s needed most and find nearest drop off locations etc
88
How is hazard resistant design useful at mitigation?
New buildings can be built to resist ground shaking and therefore will not collapse
Roofs build near volcanoes can be sloped so ash slides off them rather then building up in the roof
Buildings at risk from tsunami can be built well above sea level.
Existing buildings can be modified.
Protective structures like sea walls can be built
Generally expensive but work well and there are cheaper alternatives that work similarly.
89
Name some examples of hazard adaption strategies?
High tech monitoring
Crisis mapping
Modelling hazard impact
Public education.
90
Explain high tech monitoring
Early warning systems
Satellite communication technologies
Mobile phone warnings technology - eg in Japan
91
How does crisis mapping work?
Uses crowd sourced information as well as setllite technology and maps to accurately map areas struck by disaster
Pre mapping the vulnerable areas helps to get aid responses there rapidly in the event of disaster.
92
Modelling hazard impacts what is it?
Computer modelling allows scientists to predict the impact of hazard events on communities. Info is fed into computer systems and then model the effects of a disaster and preparation plans can be put into place.
93
What does public education involve?
Teaching evacuation routes
What to do in event of earthquakes etc
Creation of emergency preparedness kits in schools and workplaces
Regularly practicing emergency procedures.
94
Who are the key players in the response to natural disasters?
Aid donors
NGO’s
Insurance Companies
Communities
95
What role does aid play in the response to natural disasters?
Emergency aid
Short term aid
Long term aid
Provided as cash personnel or services
Reconstruction or providing food or temporary shelters
+ helps massively
- prone to corruption
- can create dependency in long term
96
What role do NGO’a play?
Important to disasters where local governments find it difficult to respond - no money or funds
Providing shelters food helping with reconstruction
Re-establishing water supplies etc
Providing funds and co-ordinate search and rescue efforts and also help to develop reconstruction plans
- lead to dependency
- doesn’t always reach the most rural areas
97
What role does insurance play in responses to hazards?
Insurance coverage can help communities to recover from disasters providing individuals and businesses with the money they need to rebuild their lives
Costs can be covered by groupings of insurance companies.
- not everyone has insurance
- insurance very rare in developing countries
- government and bank partnerships do not occur in developing countries so there is little support.
98
What role do communities play in the response to a disaster?
Crucial to search and rescue efforts
In remote or isolated communities aid may not reach them for days/weeks so villagers undertake the responsibilities themselves, saving lives etc
First in the scene
Community groups heavily involved in long term strategies for rebuilding
- little financial backing
- less impact than aid etc
- requires support from others.
