Tectonic processes and hazards Flashcards
The global distribution of earthquakes, tsunamis and volcanoes is linked to what?
Plate boundaries
What are the different types of plate boundaries?
Divergent, convergent, transform and collision
What is a divergent plate boundary?
Where two plates (usually oceanic) move away from each other
Give an example of a divergent plate boundary
Between the Nazca and Pacific plates
What is a convergent plate boundary?
Where an oceanic and continental plate converge, and the oceanic crust subducts
Give an example of a convergent plate boundary
Along the west coast of South America
What is a transform plate boundary?
Where two plates move alongside each other, either in opposite directions or same direction at differing speeds
Give an example of a transform plate boundary
Between the Pacific and North American plates
What is a collision plate boundary?
When two continental plates converge
Give an example of a collision plate boundary
between Altiplano and South American plates
At what types of plate boundary do volcanoes occur?
Divergent and convergent plate boundaries
At what types of plate boundary do earthquakes occur?
Divergent, convergent, transform and collision
At what types of plate boundary do tsunamis occur?
Divergent, convergent, transform and collision
What is an intra-plate process?
A process that occurs towards the middle of the plate rather than the boundary
How do intra-plate earthquakes occur?
Small movements along fault lines (cracks in the plate caused from previous plate movements) build up friction and strain over time, which is suddenly released, causing low magnitude earthquakes
How do intra-plate volcanoes occur?
Magma rising through the mantle from the edge of the outer core is able to melt its way through, forcing molten material to the surface, therefore creating volcanoes
Name and describe the intra-plate earthquake case study
UK
-The UK experiences minor earthquakes despite being 1500km from the nearest plate boundary under the centre of the Atlantic Ocean
-There are about 25 earthquakes in the UK each year that are felt by people
-The largest occurred in 1931 under the North Sea at Dagger Bank
-6.1 on the Richter scale
Name and describe the intra-plate volcano case study
Hawaii
-The Hawaiian islands have 15 volcanoes, which are the youngest of 130 found along a 6000km line to their north-west
-Kilauea and Mauna Loa are the most active volcanoes on the planet
-The submarine volcano Lo’ihi is the youngest in the Hawaiian chain, being created as the Pacific plate moves north-westwards over the hotspot
Where are the two massive mantle plumes in the Earth’s mantle layer?
Under the Pacific plate, and under the African plate
What is a mantle plume?
An area under the crust, where magma is hotter than surrounding magma
How are hotspots created?
Erupted mantle plumes once broken through the crust will form hotspots
What are the four layers of the earth, from innermost to outermost?
Inner core, outer core, mantle, crust
What are the 4 components of plate tectonic theory?
1) Characteristics of the Earth’s structure
2) Mantle convection
3) Palaeomagnetism and sea floor spreading
4) Subduction and slab pull
Evaluate mantle convection (Plate tectonic theory)
-Heat radiating from the inner core causes it to convect
-Convection may be in several layers or just one
-The convection cells make contact with the base of the crust which causes friction
-Friction drags the crust along in the general direction of the convection
Evaluate palaeomagnetism and sea floor spreading (Plate tectonic theory)
-The outer core is mostly liquid and it convects; this movement creates a magnetic field for the earth
-When new igneous rocks cool to solidify, they trap in the magnetic field direction
-Geological records of magnetic directions are symmetrical either side of divergent plate boundaries
-This proves that the oceanic crust has been diverging in places for a long time
Evaluate subduction and slab pull (Plate tectonic theory)
-At subduction zones (convergent boundaries), as the oceanic plate subducts it pulls the rest of the plate down with it
At what type of plate boundary are seismic waves the greatest?
Convergent plate boundaries
What is a body wave?
A wave that travels through the Earth
What is a surface wave?
A wave that travels through the top of the crust
What are the 2 types of body waves?
Primary (P) waves and Secondary (S) waves
Describe characteristics of Primary (P) waves
Arrives first, fast, moves through solid rocks and fluids, pushes and pulls in the direction of travel
Describe characteristics of Secondary (S) waves
Slower than P waves, only moves through solid rock, up and down movement
Describe characteristics of Love (L) waves
Only travels through the surface of the crust, fastest of the surface waves and moves from side to side as it moves forward
Name 4 hazards caused by earthquake waves
1) Crustal fracturing
2) Ground shaking
3) Liquefaction
4) Landslides
Describe crustal fracturing
-Primary hazard
-Shockwaves travel fast through solid rock and can increase stress in it
-Stress causes strain until the rock fractures
Describe ground shaking
-Primary hazard
-Shockwave ground movements include:
Pushing and pulling (P)
Up and down (S)
Side to side (L)
Describe liquefaction
-Secondary hazard
-Occurs when shockwaves travel through loose unconsolidated material, shaking it so it acts like a fluid
Describe landslides
-Secondary hazard
-Occur when there are steep slopes
-The shockwaves loosen rock and cause it to move downslope under the influence of gravity
Give an example of when/where liquefaction has occurred
Christchurch, 2011
Give an example of when/where a landslide has occurred
Kashmir, 2005
Why can L waves be the most damaging?
They arrive after P and S waves have already weakened buildings
What are some effects of crustal fracturing?
Causes faults, which can rupture the surface
Anything on these faults can get moves and damaged
What are some effects of ground shaking?
Buildings that are not aseismic may only survive some types of shaking, and will be damaged
What are some effects of liquefaction?
Causes buildings to tilt over or collapse and the ground to crack
Underground infrastructure such as cables and pipes may be ruptured
What are some effects of landslides?
Landslides may hit settlements directly or destroy/block transport and communication infrastructure
What are 6 hazards that a volcanic eruption could cause?
1) Ash falls
2) Pyroclastic flows
3) Gas eruptions
4) Lava flows
5) Lahars
6) Jokulhaulps
Describe the characteristics and effects of ash falls
-Ash are forced to a high altitude and are so light that they can be carried around the planet in the atmosphere
-A lot of ash can fall locally which causes roofs to collapse
-It gets into machinery and causes them to collapse
-Ash clouds disrupt flight paths of aeroplanes as it damages engines and fuselages
Describe the characteristics and effects of pyroclastic flows
-Considered the most dangerous
-Flows consist of a dense mixture of superheated solid particles and poisonous gases
-These move down the slopes with speeds of up to 700km/h
-Any buildings or people in the way are destroyed by impact/burying/incineration/poisoning
-The deposition of material may also block river channels and cause flooding
Describe the characteristics and effects of gas eruptions
-Water vapour (a common volcanic gas) is condensed locally with other erupted material (lahars)
-Other gases include sulphur dioxide which is poisonous in high concentrations and can cause ‘acid rain’ when combined with water vapour
-SO2 may also cool the Earth when carried high into the atmosphere, blocking the suns energy; historical eruptions have caused crop failures/famine this way
Describe the characteristics and effects of lava flows
-Erupted molten magma flows down the sides until it cools
-Buildings/infrastructure cannot move out of the lavas path, so the lava sets fire/buries them
Describe the characteristics and effects of lahars
-A mixture of water and erupted volcanic material which flow fast (60km/h) down river valleys
-Water may come from rainfall/crater lake/melting of a snow cap on the top of a volcano
-Poses a risk to settlements as they are deceptively fast, so people struggle to escape
Describe the characteristics and effects of jokulhlaups
-Where a volcano erupts under an ice cap, and so this cap is melted
-The melted water is trapped by remaining ice, so when the remaining cap is lifted by the meltwater the water bursts out from under the ice and flows rapidly to the ground
-When this happens anything in its path is washed away or covered by volcanic and glacial deposits
What causes a tsunami?
Submarine earthquakes at subduction zones that displace a column of seawater, which causes a tsunami
Give 4 features of a tsunami
1) A sequence of large waves of varying heights
2) Long wavelength in open ocean, but short in shallow water
3) Very fast speeds in deep water but slower in shallower
4) Low height in open ocean but significant height in shallow water
How do tsunamis form?
-An undersea earthquake at a subduction zone that causes a rapid movement of the sea bed
-If this movement is up and down, then a column of seawater above the epicentre is displaced
-This creates a powerful wave motion
Name and describe the tsunami case study
Tohoku, 2011
-Undersea earthquake at junction of Pacific and Okhotsk plates
-Mw 9.0.
-Lowland east coast of Japan only 130km away from epicentre facing the tsunami
-18,500 killed
-$220 billion of damage, including failure of nuclear power plants and release of radioactivity
-Category VI (highest) on the Tsunami Intensity Scale
-Tsunami reached Hawaii about 8.5 hours later
Define a natural hazard
A natural event that causes a disruption to daily lives or death and disruption
How is the scale of a disaster measured?
By the number of deaths (500+) or the cost of damage (millions of $)
Define a mega-disaster
A disaster that has over 2000 deaths and a GDP reduction of over 5%
Define the term adaptation
Changes to ways of doing things so future hazards have less impact
Define the term recovery
Ways of returning to normal after the impacts of a hazard