Tectonic Hazards Flashcards
What is the theory of plate tectonics?
The earth’s lithosphere (crust and upper mantle) is broken into several slabs known as tectonic plates, which can either be oceanic or continental, which float on the mantle and move very slowly due to convection currents in the mantle generated by radioactive decay
Describe the earth’s structure
Picture
What is a plate margin?
A long, narrow belt, which is the boundary between two tectonic plates (where they meet), which are either moving apart from (constructive), moving alongside (Conservative) or moving towards one another (destructive).
Describe the global distribution of volcanoes and earthquakes
Generally found along plate boundaries, e.g. the Pacific Ring of Fire
Volcanoes may also be found at hotspots, which are far from plate boundaries, but where the mantle is simply very hot, e.g. Hawaii (far from the edge of the Pacific Plate)
Where are plate boundaries generally found?
Along coastlines, e.g. West North and South American coastlines, south and East Asian coastlines
What is a hotspot?
An area far from the edge of a plate boundary where the mantle is very hot. Volcanoes may occur here.
Give an example of a constructive plate boundary
Eurasian and North American plates
Give an example of a destructive plate boundary
Nazca and South American plates (oceanic and continental)
Give an example of a conservative plate boundary
Are the plates moving in different directions, or the same direction at different speeds?
Pacific and North American Plate (San Andreas Fault Line)
Moving in the same direction at different speeds
Why do Earthquakes occur at destructive plate boundaries?
Tectonic plates move towards each other at a destructive boundary due to converging convection currents in the mantle.
If the plates are both continental, the collision of plates and crumpling and folding of the crust will cause tension, release energy as shock waves.
If one plate is oceanic and one is continental, when the oceanic is subducted under the continental (due to being less dense), it may become stuck, creating tension due to friction and eventually causing it to fracture, sending out shock waves.
Why do Earthquakes occur at constructive plate boundaries?
At constructive plate boundaries, the plates are moving away from each other due to diverging convection currents in the mantle below. As the plate moves, there is tension which builds up along cracks in the plates which may cause them to fracture and send out shock waves.
New plate material may also fracture and send out shock waves as it moves.
Why do earthquakes occur at Conservative boundaries?
Plates may become stuck when moving past each other, causing tension to build up, which may cause them to fracture and send out shockwaves
Why do volcanoes form at destructive plate boundaries?
When oceanic plates move down into the magma, they are melted and destroyed, forming a pressurised pool of magma.
Since the magma is less dense than the mantle above, it rises, and due to the pressure, rises through cracks in the crust known as vents.
The magma erupts onto the surface as lava at high pressure, forming a linear belt of composite volcanoes
Primary Effects of Earthquakes
- buildings and bridges collapse, and homes are destroyed
- people are injured or killed by collapsed buildings and falling debris
– roads, railways, ports and airports are damaged, e.g. roads can buckle and crack
– electricity cables, gas, water pipes and communications networks are damaged, cutting off supplies
Why do volcanoes form at constructive plate boundaries?
Magma rises up to fill the gap created by the plates moving apart, and erupts nonviolently onto surface as non-viscous lava, forming shield volcanoes
Secondary Effects of Earthquakes
Earthquakes can trigger landslides and tsunamis- please destroy more buildings and cause more injuries and deaths
Leaking gas can be ignited, starting fires
People left homeless and could die, e.g. from cold
There is a shortage of clean water and lack of proper sanitation – this makes it easier for waterborne diseases such as cholera spread
Due to blocked or destroyed roads, aid and emergency vehicles can’t get through, and trade is difficult
Businesses are damaged or destroyed, causing unemployment and lost income, and tourists can be put off visiting the area
Repairs and reconstruction can be very expensive, so can weaken a country‘s economy
Do volcanoes form at conservative plate boundaries?
No
Immediate Responses to Earthquakes
Rescue people trapped by collapsed buildings, and treat injured people
Recover dead bodies to prevent spread of disease
Put out fires
Set up temporary shelters for people whose homes have been damaged or destroyed
Provide temporary supplies of water, food, electricity, gas and communication systems if regular supplies have been damaged
Foreign governments or charities may send aid workers, supplies, equipment or financial donations the areas affected
Tech companies may set up disaster response tools, allowing damage to be recorded and allowing people to confirm their safety, e.g. Google Crisis Response™️ service
Long-term Responses To Earthquakes
Rehouse people who lost their homes
Repair and rebuild damaged buildings, roads, railways and bridges
Reconnect broken electricity, water, gas and communications connections
If necessary, improve building regulations so that buildings are more resistant to damage from earthquakes
Set up initiatives to help economic recovery, e.g. promoting tourism
What is the difference between a composite volcano and a shield volcano?
Composite Volcano in comparison to a shield volcano:
- Longer periods between eruptions
- More violent eruptions
- Alternate layers of ash and lava (whereas shield is just lava)
- Steep sides - lava doesn’t flow far before solidification
- Acidic lava - v. viscous
- Found at destructive plate margins (whereas shield are found at constructive)
Primary Effects of Volcanic Eruptions
Buildings and roads are destroyed by lava flows and pyroclastic flows. Buildings may also collapse if enough ash falls on them
People and animals are injured and killed by pyroclastic flows, lava flows and falling rocks
Crops are damaged and water supplies are contaminated when ash falls on them
People, animals and plants are suffocated by volcanic gases
Secondary Effects of Volcanic Eruptions
Mudflows (lahars) form when volcanic material mixes with water, e.g. from heavy rainfall or snowmelt. Mudflows and landslides cause more death, destruction and injury
Flooding can be caused by hot rocks, ash and gas melting ice and snow on the volcano. Rock and ash clog up reviews and downs, making flooding worse
Transport networks are blocked or destroyed so aid and emergency vehicles can’t get through, and trade is difficult
People left homeless. Damaged or destroyed businesses can cause unemployment and loss of income
Tourism can be disrupted straight after an eruption – but often it can be increased afterwards with tourists interested in seeing volcanoes
Ash makes fields more fertile once broken down
Recovering after eruption can take a very long time and cost a huge amount of money, which can weaken the country’s economy
Immediate Responses to Volcanic Eruptions
Evacuate people before the eruption, if it was predicted, or evacuate as soon as possible after the eruption starts
Provide food, drink and shelter for the evacuated people
Treat people injured by the eruption, e.g. from falling debris or ash inhalation
Rescue anyone cut off by damage to roads or buildings
Provide temporary supplies of electricity, gas and communication systems if regular supplies have been damaged
Foreign governments or charities may send aid workers, supplies, equipment or financial donations to the areas affected
Tech Companies may set up disaster response tools allowing damage to be recorded and people to confirm their safety, e.g. Google Crisis Response™️ service
Long-Term Responses To Volcanic Eruptions
Repair and rebuild if possible, or resettle affected people elsewhere
Repair and reconnect infrastructure (roads, rail, power lines and communication networks etc.)
Improve, repair and update monitoring and evacuation plans
Boost economy if possible, e.g. by attracting tourists to see the volcano and its effects
