3.1.1.2 Tectonic Hazards Flashcards
What are earthquakes and volcanic eruptions the result of?
physical processes
What is the internal structure of the Earth?
Plate boundary/margin:
the boundary or margin between two tectonic plates
Tectonic plate:
a rigid segment of the Earth’s crust which can “float” across the heavier, semi-molten rock below
Crust:
outer layer of the Earth
Continental crust:
the thicker, less dense part of the Earth’s crust
Oceanic crust:
the thinner, more dense part of the Earth’s crust
Asthenosphere:
the weak upper layer of the Earth’s mantel, which can deform like plastic
Lithosphere:
includes the brittle upper portion of the mantle and the crust, the outermost layers of Earth’s structure
Mantle:
the area beneath the Earth’s crust which is made of solid material, that can flow slowly
Core:
the centre of the Earth, mainly made from iron and nickel, and with a solid inner core and outer liquid core
What is tectonic plate theory?
- Earth’s outer shell (lithosphere) is divided into several plates that glide over the Earth’s rocky inner layer above the soft core (mantle)
- Earth once had a huge supercontinent called Pangea that split off to form today’s continents, tectonic plates drifted apart and are still constantly moving
Slab pull:
plate is forced back into mantle due to gravity
Ridge push:
pushes plates from mid-ocean ridge
Trench/slab suction:
plate gets pushed back into mantle due to small convection currents
Where do tectonic hazards tend to take place in general?
- tectonic hazards (earthquakes and volcanoes) tend to occur to plate margins
- there are a clear pattern of volcano and earthquake distribution along plate margins e.g. along west of North America and South America, or in the Atlantic Ocean between Africa and South America
What is an example of an area with high volcanic activity?
- The ‘Ring of Fire’ locates in the pacific oceans
- the earthquakes and volcanoes follow the margins between the Pacific tectonic plate and the other plates
Why do earthquakes and volcanoes occur along plate margins?
- earthquakes generally occur along plate margins due to plate movements causing vibrations
- volcanoes occur along certain plate margins as magma (molten rock found underground) feeds volcanoes, and this magma can get ti the surface at certain plate margins
Why might volcanoes not always occur on plate margins?
- e.g. volcanoes in middle of Pacific plate
- this is where magma breaks through the middle of the plate and travels up to the surface - knows as a hotspot
Are ocean or continental plates heavier?
oceanic because of its rock composition and rapid cooling
What takes place at constructive/tensional/divergent plate boundaries?
- constructive / tensional / divergent plate boundary the plates move apart
- when the two plates are pulled apart, magma rises in between the gap left by the two plates separating
- The plates are forced apart at mid-ocean ridges because of either convection currents or ridge push, both as a result of rising magma from the Earth’s core
- often there are large cracks (faults) in the crust or either side of a constructive plate margin caused by the massive pressure of the moving plates
- When the plates move apart magma rises to fill the gap created by the ridge (forming volcanoes)
- lava (magma above ground) pours out into the surface
- new crust is formed, volcanoes also form in areas where lava pours out
- The lava is usually free-flowing and runny, over time this will accumulate and create a broad and flat volcano, usually a shield volcano
- If it has contact with water means that the magma cools rapidly and turns to rock
- earthquakes also occur here as the plates shake and vibrate when they move apart
- when new land is formed on the ocean floor, this is known as sea floor spreading
- over time, this rock builds up and can form islands
Where can constructive plate boundaries occur?
on continental or oceanic crust
What landforms form at constructive plate boundaries
shield volcanoes, mountains, cracks/faults
Example of a constructive plate boundary:
- Atlantic Ocean - Mid-Atlantic Ridge
- Eurasian + North American plates
Diagram of constructive plate boundary:
What takes place at destructive plate boundaries/collision plate boundaries/compression zones?
- when 2 continental plates meet, neither subduct below the other (neither gives way) causing pressure to increase
- the crust is instead crumpled upwards by the pressure building between 2 plates, creating fold mountains
- gives rise to earthquakes but no volcanoes
What landforms are formed at destructive plate boundaries/collision plate boundaries/compression zones?
- fold mountains
- no volcanoes
Example of destructive plate boundaries/collision plate boundaries/compression zones:
Himalayas formed due to the Indian plate and the Eurasian plate colliding
Diagram of destructive plate boundaries/collision plate boundaries/compression zones:
What takes place at destructive plate boundaries/subduction zones/subductive plate boundaries?
- The plates move towards one another
- Oceanic crust is denser (heavier) than continental crust so the continental crust forces the oceanic crust underneath it - this is a process called subduction
- At the subduction zone an ocean trench is formed where the plate is being forced downwards under the continental plate
- The plate that is subducting leaves a deep ocean trench
- Friction between the two plates cause strong, deep earthquakes
- When the oceanic crust begins to melt as it is pulled deeper into the hot mantle it forms magma
- This magma causes pressure to build up under the crust
- The magma starts to float back up, because it is made up of lighter material than the mantle (the magma created from the melted oceanic plate is less fluid than at a constructive margin)
- Eventually the magma pushes out through weaknesses in the crust
- This means that the magma erupts back to the surface to form steep-sided composite volcanoes (explosive)
- Eruptions are often violent and very explosive
- This process can also happen between 2 oceanic crust plates where the denser plate sinks below and islands in the ocean can form
What landforms do destructive plate boundaries/subduction zones/subductive plate boundaries form?
- mountains
- composite volcanoes (explosive, violent)
- ocean trenches
Example of destructive plate boundary/subduction zone/subductive plate boundary:
- at the West Coast of South America
- the Nazca plate is subducting below the South American plate
Diagram of destructive plate boundary/subduction zone/subductive plate boundary:
What is the difference between subduction zones/subductive plate boundaries and collision plate boundaries/compression zones?
- Collision plate boundary/compression zone – where two continental plates meet
- Subduction zone/subductive plate boundary – where oceanic and continental plates meet
What takes place at conservative/transform/transverse plate boundaries?
- When parallel plates move along side each other in opposite directions or in the same direction but at different speeds earthquakes are created
- The plate margins are made up of rock that is brittle and jagged so it is difficult for the plates to slide past each other and friction between the plates builds up
- Sometimes the plates get stuck and pressure builds and builds until eventually the pressure is released and causing the plates to suddenly jolt
- This sudden movement and release of pressure is the cause of earthquakes at this type of margin - it releases a lot of energy which sends vibrations through the ground
- On oceanic crust this movement can displace a lot of water, which causes large waves called tsunamis
Example of a conservative plate boundary:
- The most famous conservative plate margin is the San Andreas Fault on the western coast of North America
- The faster-moving Pacific Plate is sliding in the same direction next to the slower-moving North American Plate
What landforms do conservative plate boundaries form?
- on continental crust fault lines/cracks can occur where the ground is cracked by the movement
- mountains
- no volcanoes on conservative plate margins as no magma is being generated
Diagram of conservative plate boundaries:
How do medical facilities affect the impact of an earthquake?
the more medical resources the easier it is for the injured to get treatment
How does transport infrastructure affect the impact of an earthquake?
the better the transport network the quicker it is to evacuate and for aid to arrive
How does monitoring and predicting affect the impact of an earthquake?
more resources available to monitor and predict earthquakes should reduce the risks
How do construction standards affect the impact of an earthquake?
buildings with strict building regulations have less chance of collapsing
How does training affect the impact of an earthquake?
more training so the public and emergency services know what to do to reduce casualties
How do resources and finances affect the impact of an earthquake?
the more resources and money available the quicker it is to rebuild homes and businesses
How do emergency services affect the impact of an earthquake?
more skilled emergency services, armies and volunteers reduce casualties
How does corruption affect the impact of an earthquake?
corrupt government and organisations divert aid and supplies away from areas that need it most
How does planning in an earthquake prone area affect the impact of an earthquake?
planning, preparation and protection is more likely in areas that expect earthquakes
How does depth of focus affect the impact of an earthquake?
the shallower the focus the more energy to cause damage
How does population density affect the impact of an earthquake?
the more people the more potential risk of injuries and fatalities
How does building density affect the impact of an earthquake?
the more buildings the greater the likelihood will collapse
How do plate margins affect the impact of an earthquake?
some plate margins are more destructive than others
How does the distance from the epicentre affect the impact of an earthquake?
the closer to the epicentre the greater the magnitude will be
How does the magnitude affect the impact of an earthquake?
the stronger the earthquake the greater the impact
How does the time and day of the week affect the impact of an earthquake?
buildings and roads that collapse when they are empty reduce casualties
How does the time of the year affect the impact of an earthquake?
climate in difference seasons can make impacts and responses harder e.g. monsoon
How does the type of event affect the impact of an earthquake?
secondary effects e.g. tsunamis, avalanches and landslides can cause further devastation
Monitoring:
using scientific equipment to detect warning signs of events e.g. volcanic eruptions
Prediction:
using historical evidence and monitoring, scientists can make predictions about when a where a tectonic hazard may happen
Protection:
designing buildings that will withstand tectonic hazards
Planning:
identifying and avoiding places most at risk
How are volcanoes monitored?
- seismographs used to detect and record earthquakes
- tiltmetres are used along with laser beams to measure changes in the shape and tilt of the volcano - monitor ground deformation as volcanoes tend to swell near an eruption
- gravity metres to measure changes in density
- measure temperature - volcanoes become hotter when magma begins to rise through the main vent
- satellites used to detect volcanic activity and changes to the shape of them
- instruments used to monitor gas emissions and changes in water chemistry (when magma rises)
- can use robots called Spiders
- there is often an increased release of sulphur dioxide near an eruption
What happens if a volcanic eruption seems likely?
warnings are issued and people are evacuated
How are the eruptions of volcanoes predicted?
the prediction of a volcanic eruption is based on scientific monitoring and patterns in activity
Why is it difficult to protect against volcanoes
- Protecting against a volcanic eruption is extremely difficult
- Buildings cannot be designed to withstand the lava flows, lahars or weight of debris and ash falling on roofs, especially if this mixes with water
- Therefore people need to evacuate their homes to a safe location under the instruction of the authorities
How can you protect against volcanic eruptions?
- can use earth embankments or explosives to divert lava flows away from property
- this has been done on the slopes of Mount Etna in Italy
- can design buildings to withstand the effects of volcanic ash falls which, when mixed with water, can cause roofs to collapse
- steep-pitched, smooth-tiled roofs prevents the build-up of ash and when reinforced with strong lateral supports are less likely to fall
- window shutters can prevent ash entering homes
How can you plan for the effects of a volcanic eruption?
- hazard maps used to help protect the 500 million people at risk from volcanic eruptions
- based on scientific evidence from previous eruptions hazard maps plot the likely extent of hazards e.g. ash falls, pyroclastic flows and lahars
- maps can be used to control development and evacuation routes
Lahar:
- A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water
- The material flows down from a volcano, typically along a river valley
How are earthquakes monitored?
- seismometres monitor and record earthquakes - can detect minor tremors before main earthquake
- laser beams can be used to detect plate movement
- Aseismometeris used to pick up thevibrationsin the Earth’s crust - an increase in vibrations may indicate a possible earthquake
- Radon gasescapes from cracks in the Earth’s crust
- levels of radon gas can be monitored - a sudden increase may suggest an earthquake
- tsunami monitoring systems in the Pacific and Indian Oceans use floating buoys to detect early tsunami waves following an earthquake
- warnings issued to coastal areas enabling people to be evacuated to higher ground
Why is it harder to predict when earthquakes will take place?
- It is harder to predict earthquakes, partly because they do not happen at a single visible point, like volcanic eruptions
- They can occur anywhere along the length of the plate margin
- There is also a lack of clear warning signs and short amount of time to react to them if they are clear
- However, scientists studying historical records of earthquakes at plate margins have identified locations that they believe are at the greatest risk
- An example of this is the city of Istanbul, which scientists identified as at risk from an earthquake and were correct
How can buildings be protected from earthquakes (earthquake-resistant)?
- rolling weights on roof to counterbalance shaking and shock waves
- cross bracing to provide extra support for the frame
- large open areas for evacuees and emergency services to gather
- several emergency staircases and exits to speed up evacuation
- shock absorbers (made of lead) in foundations to absorb seismic waves
- deep foundations into solid rock
- roof covering area immediately outside building to prevent pedestrians being shower with glass
- shatter resistant glass windows
- strong steel frame with girders interlinked
- earthquake resistant buildings are also being built in LICs
- bamboo is a very shock resistant material and is being used in the building of houses in LIC countries.
How can you plan for the effects of an earthquake?
- shakemaps show impact of ground shaking
- can be used by planning authorities to locate high-value developments e.g. hospitals, power stations and office blocks away from high risk areas
- regular training of public and emergency services on how to respond to earthquake
- On Disaster Prevention Day in Japan (September 1st), emergency drills organised by local governments are held throughout the country
- Some of these drills consist of ducking under desks to escape falling objects and evacuating from buildings
- At many elementary and middle schools, 1st September is the first day of school after the summer holidays
- So a lot of schools carry out an evacuation drill as part of the back-to-school ceremony
- drop, cover and hold on training
