Tectonic Processes and Hazards Flashcards
How do the plates move at a conservative margin?
Plates move parallel to each-other
How do plates move at a divergent margin?
Move apart
How do plates move at a constructive margin?
Move apart
How do plates move at a convergent margin?
Move towards each-other
Which plate is denser: oceanic or continental?
Oceanic plate
What happens at a convergent margin between an oceanic and continental plate?
The oceanic plate subducts underneath the continental plate. This forms a deep ocean trench
What happens to the oceanic plate after subduction?
It melts in the asthenosphere. This causes slab pull
What happens to the continental plate after the oceanic plate subducts?
The continental crust is squashed together and forced upwards, forming fold mountains
What is the Benioff zone?
The part of a subducted oceanic plate at which the friction with the continental plate causes deep earthquakes
Describe the traditional theory of tectonic plate movement?
Mantle convection; convection currents in the magma causes the plates above the mantle to move
What is the seafloor-spreading theory?
Hot magma forced out of the asthenosphere hardens to form mid-ocean ridges, forming new oceanic crust
What is the modern theory of tectonic plate movement?
Slab pull
What is slab pull?
Subducting crust is denser than the mantle around it because it is cooler; it sinks and pulls the rest of the plate with it
Who proposed the theory of continental drift, and when?
Wegener, 1912
Who proposed the movement of plates by convection current, and when?
Holmes (1930)
When was paleomagnetism introduced?
1960s
How did paleomagnetism advance plate tectonic theory?
Polar shifts show the age of the rocks; getting older the further away they are from mid-ocean ridges
What type of volcano is formed at fold mountains?
Composite volcano
What is the other name for hotspots?
Mantle plume
What type of volcano is formed at constructive margins?
Shield volcano
What type of waves are P-Waves?
Longitudinal
What type of wave are S-Waves?
Transverse
How do L-Waves move?
Transverse; oscillate parallel to the surface
How fast does an S-wave move?
60% the speed of a P-Wave
Which is faster - S-Wave or L-Wave?
S-Wave
What is jökulhlaup?
Glacial flooding caused by a volcanic eruption
What is a Lahar?
A hot mudflow moving down a volcano’s river valley.
What is pyroclastic flow?
Hot gas and tephra moving at 700km/h
What is tephra?
Volcanic matter
What is Degg’s disaster model?
Venn diagram with Hazard and Vulnerable population, intersecting to cause a disaster
What is the Disaster Risk Equation?
(Hazard x Vulnerability) ÷ Capacity to Cope
What are the criteria for a disaster?
10+ deaths
100+ affected
£1m
What are the factors of the Pressure and Release model?
Root Causes
Dynamic Pressures
Unsafe Conditions
(Hazard Event)
What are the components of a Hazard profile?
Magnitude, Speed of Onset, Duration, Areal Extent, Spatial Predictability, Frequency
What is liquefaction?
Surface rocks lose strength and become almost liquid. They can’t support foundations
What is a mantle plume?
A rising convection current in the mantle pushes up through the crust. Can be in middle of plate (Hawaii) or on a boundary (Iceland)
How do plates move at a collision margin?
Move towards each-other
What kind of plates are involved at a collision margin?
Two continental plates
Give an example of a collision margin
Himalayas
What kind of mountains are formed at a collision margin?
Fold mountains
Which kind of earthquake wave causes the most damage?
Love waves
How fast does a tsunami move at deep sea?
800 km/h
How large is a tsunami at deep sea?
1m high, 100km wide
How have the number of people affected by disasters changed over time?
Increased
How have the number of reported disaster events changed over time?
Increased
How have the cost of disasters changed over time?
Increased
How have the number of people killed by disasters changed over time?
Decreased
How can you predict a volcanic eruption?
Changes in the types of gas emitted
Magma moves nearer to the surface; can cause small earthquakes
What is the drawback to volcanic eruption prediction?
Not an exact science - 3 evacuations before Mt St Helens
What are the stages of the hazard management cycle?
Hazard Event, Response, Recovery, Mitigation, Preparedness
How are poorer countries limited in terms of the hazard management cycle?
They can only perform the response stage with the help of aid
What is the Park model?
A graph of Quality of Life against Time for a hazard event
How does the Park model suggest Quality of Life changes after a hazard event?
Sharp decline, gradual return to normality
How can wealthy countries use the Park model?
To improve their situation compared to normality
How are poorer countries affected by the Park model?
Slower return to normality; lower Quality of Life
What are the three stages of the Park model?
Response (weeks)
Reconstruction (months)
Mitigation (years)
What methods are there for modifying a hazard event?
Land-use zoning, tsunami defences (walls), lava flow diversion, cross bracing (aseismic buildings)
What methods are there for modifying the vulnerability of the population?
Education (community preparedness), high-tech monitoring, earthquake survival kits
What factors affect the impact of a hazard event?
Population Growth, Urbanisation, Ageing Population, HDI, Loss of Community Memory, Corrupt Governance, Technology
How effective is international aid in the short-term after a hazard event?
A lot of money/support provided; good organisation
How effective is international aid in the long-term after a hazard event?
The world “forgets” because of less media coverage
How does the effect of insurance differ between countries?
People in poorer countries can’t afford it
It is a luxury for richer nations
What theory of plate movement is related to seafloor-spreading?
Ridge push
It is now proven to provide negligible force
When was ridge push shown to provide negligible driving force for tectonic plate movement?
1983
Where is an earthquake’s epicentre?
The point on the surface directly above the focus
Where is an earthquake’s focus?
The origin of the earthquake
What physical damage do earthquake waves cause?
Crustal fracturing
What are the criteria for a disaster?
10 people dead
100 people affected
£1 million damage
How often does a VEI 4 eruption occur?
18 months
How often does a VEI 6 eruption occur?
50 - 100 years
