Tectonics Flashcards
How are volcanoes formed?
Magma rises through cracks or weaknesses in the Earth’s crust.
Pressure builds up inside the Earth.
When this pressure is released, eg as a result of plate movement, magma explodes to the surface causing a volcanic eruption.
The lava from the eruption cools to form new crust.
Over time, after several eruptions, the rock builds up and a volcano forms.
What is a constructive plate margin?
Two plates move away from each other. Molten rock or magma immediately rise to fill any possible gap and forms a new oceanic crust
What is a conservative plate boundary?
Two plates slide next to each other, they can go in the same direction but go at separate speeds.
What is a destructive plate margin?
A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes.
What is a collision plate boundary?
A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes.
Give me the three types of seismic waves
P waves- vertical movements
S waves- horizontal movements
Surface waves- rippling waves
How do volcanoes function?
A volcano is formed by eruptions of lava and ash.
Volcanoes are usually cone shaped mountains or hills.
When magma reaches the Earth’s surface it is called lava. When the lava cools, it forms rock.
Volcanic eruptions can happen at destructive and constructive boundaries, but not at conservative boundaries.
Some volcanoes happen underwater, along the seabed or ocean floor.
Give me three things that come out of volcanoes
Lahars-mud flows
Ash cloud- toxic
Pyro clastic flows- boiling ash and fire travelling at 200km/hr
Give me 3 causes of the Japanese earthquake
The cost of Sendai, was really close to the epicentre
Wednesday the 9th earthquake happened of 7.2
Made the plate margin move at 2.4m and lifted upwards at 9m
Give me 3 causes of the Japanese tsunami
Happened 2 days after the earthquake hit
More people died in the tsunami
Came in at 800kph
How many casualties of Japan?
Deaths 15,500
Injuries 5,700
Missing 4,800
Social effects of the tsunami
32,000 casualties and left people homeless
Economic effects of the tsunami
$122 billion to repair
Most manufacturing stopped
Plantations lost 40%
Nuclear crisis of the tsunami
Fukushima power plant was hit
killed 50 volunteers
Everyone in a 20km radius most likely to develop cancer
What is the crust?
Outer most layer also as the lithosphere
Solid rock split into tectonic plates
What are the two types of crust?
- Continental crust: forms land granite, low density, between 30 - 50 km in thickness
- Oceanic crust: under the oceans basalt, more dense, between 6 - 8 km in thickness
What is the asthenosphere?
Semi molten upper part of the mantle on which the plates float
Below the lithosphere and 100 - 200 km below the surface
What is the mantle?
Composed of rock called peridotite
The top layer is between 75 250 km thick and is partially molten
The bottom layer is around 2200 km thick and is sold
What is the outer core?
Around 2300 km thick and composed of iron and nickel
This is liquid
What is the inner core?
Around 1000 km thick and composed of iron and nickel
It is solid
What are seismic waves, the focus and epicentre?
During an earthquake SEISMIC WAVES move out from the point where the rocks of the tectonic plates move
This point is called the FOCUS
The EPICENTRE is directly above the focus on the earths surface
What is the Richter scale?
Measures the magnitude of earthquakes
What are primary effects of an earthquake?
The immediate damage that occurs i.e. Collapsing buildings, cracks in roads, death, panic
What are the secondary effects of an earthquake?
After affects of an earthquake i.e. Fires, tsunamis, disease, longer term economic impacts
When was the Sichuan earthquake?
12 May 2008
Magnitude 8.0
What were the social impacts of Sichuan?
70,000 dead
375,000 injured
5 million homeless
What were the economic impacts of Sichuan?
Over 1 million people lost their job due destruction of work places
Rebuilding costs estimated around $75 billion
200 large after shocks
27th May magnitude 6.0 caused 420,000 buildings collapsed
What are the local responses of Sichuan?
Heavy rain, landslides and aftershocks made the rescue effort difficult:
• 50,000 soldiers sent to dig for survivors
• helicopter were used to reach the most isolated areas
• Chinese people donated $1.5 billion aid
What are the international responses to Sichuan?
China quickly asked the rest of the world to help:
• some countries sent moment, UK GAVE $2 million
• Finland sent 8000 six person tents and Indonesia sent 8 tonnes of medicines
• rescue teams flew in from Russia, Hong Kong, South Korea and Singapore
give me 3 factors to a composite volcano
- viscous, sticky and thick
- steep volcanoes
- magma runs slowly, and can freeze through the central vent
- infrequent and unpredictable
give me 3 factors to a shield volcano
- gentle slopes
- lava is fluid
- flows quickly
- very frequent and generally gentle eruptions
how can tsunamis be formed?
large volcanic eruptions or earthquakes can cause a tsunami as a secondary impact
series of destructive waves
sub-sea earthquakes can displace the sea which can cause tsunamis
Explain how the Earths tectonic plates move
High temperature in the core caused by gradual radioactive decay create rising limbs of material in the mantle called convection currents
These cool and spread out as they rise before sinking again and some this material moves into sheets creating movements in the crust above it, which is pulled apart to form new crust - in other places it rises as columns, creating hotspots
What do the impacts of any hazard, including earthquakes and volcanoes depend on ?
- size of the event
- the vulnerability of the population - poverty and high density increase vulnerability
- the capacity of the population to cope - how prepared they are
What are the different factors that influence a volcano or earthquake?
- because plate margins are essentially lines, so most volcanoes are found in lines
- volcanic eruptions generate earthquakes but earthquakes also occur on conservative margins and sometimes happen in regions many thousands of miles from plate margins
- not all volcanoes are found on plate margins. Some are found at hotspots where the crust is moving over a column of rising magma
How can a tsunami occur?
Large volcanic eruptions and earthquakes can both cause a tsunami as a secondary hazard
Tsunamis are a series of very destructive ocean waves
Sub-sea earthquakes can displace seabed which causes tsunamis to form
The waves travel at speeds up to 900 km/h and when they strike land, waves can be 20-30 m high and flood far inland
How can volcanoes be predicted?
- gas emissions, earth tremors and ‘bulging’ of a volcano’s flanks can be measured and used to predict
- in 1991 about 120,000 people were evacuated from the area around Mt Pinatubo before it erupted
How do you prepare yourself for an earthquake?
- emergency plans, well trained and funded emergency services, warning systems and evacuation routes
- reducing impact by mitigation such as hazard resistant buildings, disaster kits and land use planning
What are examples of mitigation in a developed world?
Making new buildings better:
- foundations very deep but allow movement
- shock absorbers built into structure
- cross bracing to prevent floors collapsing
What are examples of mitigation in a developing world?
Make existing buildings better:
- reduce the weight of the roofs
- lightweight, hollow bricks used
- strengthen wall corners with wire mesh and cement
