The restless earth Flashcards
What is the crust?
The outer layer of the earth.
What is the crust split into?
Plates of varying size and at plate margins.
Why are the plates at plate margins able to move?
Due to the slabs of crust floating on the semi-molten upper mantle.
What determines plate movement?
Convection currents within the mantle.
What are the two types of crust? 2
- oceanic
* continental
What is the mantle?
The dense, mostly solid layer between the outer core and the crust.
What are the properties of the oceanic crust? 4
- newer
- denser
- can sink
- can be renewed and destroyed
What are the properties of the continental crust? 4
- older
- less dense
- cannot sink
- cannot be renewed or destroyed
What are the types of plate margin? 3
- destructive
- constructive
- conservative
What occurs at a destructive plate margin?
The denser oceanic crust sinks under the lighter continental crust through subduction. Great pressure is exerted and the oceanic crust is destroyed as it melts to form magma.
What is the collision boundary?
If two continental plates meet each other, they collide.
What happens at a constructive plate margin? 4
- plates pull away from each other
- cracks and fractures form between the plates where there is no solid crust
- magma forces its way into the cracks to the surface to form volcanoes
- new land is formed as the plates gradually pull apart
What happens at a conservative plate margin? 6
- plates are sliding past each other
- moving in similar direction
- moving at slightly different speeds/angles
- plates tend to get stuck
- build-up of pressure causes them to release
- sudden release of pressure cause an earthquake
What are fold mountains and ocean trenches a result of?
Plates moving together.
What mountain ranges include young fold mountains? 4
- Himalayas
- the Rockies
- the Andes
- the Alps
Why are older ocean trenches less high?
Due to erosion.
What do older fold mountains include? 2
- Cambrian mountains
* Cumbrian mountains
Where do ocean trenches form?
In some of the deepest parts of the ocean.
What are the 2 types of volcano?
- composite
* shield
Where do composite volcanoes occur?
Destructive plate margins.
Where do shield volcanoes occur?
Constructive plate margins.
Can you describe a composite volcano? 7
- crater
- steep slopes
- narrow base
- eruptions infrequent
- eruptions violent
- secondary cones
- layers of thick lava and ash
Can you describe a shield volcano? 7
- low, rounded peak
- wide base
- gentle slopes
- eruptions frequent
- eruptions non-violent
- layers of runny lava, with little ash
- crater
What case study will you use for fold mountains?
The Andes and its people.
What are the ways in which the Andes are used? 4
- farming
- mining
- hydroelectric power
- tourism
How is farming used in the Andes? 5
- grow potatoes which are main source of food
- use of terraces
- llamas carry materials for irrigation and buildings into inhospitable and inaccessible areas
- llamas can carry over 25% of their body weight
- female llamas used for meat and milk, their wool is used in clothes and rugs
What advantages does terracing in the Andes offer? 3
- retain water in an area that receives little
- limit the downward movement of the soil
- cash crops are produced
How are the Andes used for mining? 5
- rank in the top ten for tin, nickel, silver and gold
- half of Peru’s exports
- has the largest gold mine
- Cajamarca has grown from 30,000 inhabitants to 240,000 in 2005 bringing source of jobs
- growth led to lack of services and increased crime rate
How are the Andes used for hydroelectric power? 4
- steep slopes and narrow valleys
- they can be more easily dammed
- relief encourages the rapid fall of water
- melting snow increases the supply of water
How are the Andes used for tourism? 2
- many natural attractions
* show how people settled in these inhospitable areas (Macchu Picchu)
Where are volcanoes located?
Relates closely to plate margins. The area around the Pacific Ocean is prone to volcanoes.
What caused the eruption of Nyiragongo?
Disturbed by the movement of plates along the East African rift valley.
What were the primary effects of Nyiragongo volcano?
- destroyed many homes
- destroyed roads and water pipes
- set off explosions in fuel stores
- killed 45 people
What were the secondary effects of Nyiragongo? 7
- 0.5 million people fled to Rwanda so to escape the lava
- no shelter, electricity or clean water as area couldn’t cope with the influx
- diseases such as cholera were a huge risk
- people were frightened of going back
- looting was a problem
- many residents returned within a week in the hope of aid
- Oxfam were involved in the distribution of food, medicine and blankets
What were the immediate responses to the eruption of Mt Helens? 7
- mobilising helicopters for search and rescue
- rescuing survivors was a priority
- emergency treatment at nearby towns
- ash clogged air-conditioning
- ash blocked roads
- ash was cleared within 3 days of eruption
- Carter promised to send 2 million masks
What are the positive impacts of the eruption of Mt Helens? 4
- ash improved quality of soil by increasing its fertility
- sterile moon has been transformed to be bursting with life
- has become a better-known area after the eruption
- $1.4 million spent to transform area
What were the long-term responses to the eruption of Mt Helens? 6
- buildings and bridges needed rebuilding
- drainage in the area had to be looked at to see that flooding would not occur
- forest began to be replanted
- removal of fallen timber
- roads need to be rebuilt
- attempts to bring tourists back
How was the eruption of Mt Helens monitored? 5
- bulge that appeared on northern flank was evidence of moving magma
- tiltmeters can identify small, subtle changes in the landscape
- GPS use satellites to detect movement of as little as 1mm
- change in temperature can be seen on satellite images
- digital cameras can photograph events relatively safely
How was the eruption of Mt Helens predicted? 7
- samples were collected from the crater entrance
- “spiders” can monitor changes
- past frequency of eruptions
- gap between eruptions
- pattern of lava flows
- ash movement
- lahars
What are the characteristics of a supervolcano? 3
- much bigger scale than volcanoes
- emit at least 1,000km3 of material
- have calderas
What are the likely effects of a supervolcano eruption? 8
- destroy 10,000km3 of land
- kill 87,000 people
- 15cm of ash would cover buildings with 1,000km
- 1 in 3 people affected would die
- ash would affect transport, electricity, water and farming
- lahars are a probability
- global climates would change
- crops would fail
How do earthquakes occur at destructive plate margins?
Pressure resulting from the sinking of the subducting plate and its subsequent melting can trigger strong earthquakes as this pressure is periodically released.
How do earthquakes occur at constructive plate margins?
Tend to be less severe. The friction and pressure caused by the plates moving apart.
How do earthquakes occur at conservative plate margins?
Great strength. Where the plates slide past each other, they tend to stick. This causes stress and pressure to build. The release of pressure occurs in a sudden, quick release and the result is an earthquake.
What is an earthquake’s focus?
The place where the earthquakes begin, deep within the earth’s crust.
What is the epicentre of an earthquake?
The point at the earth’s surface directly above the focus.
What are an earthquake’s shock waves?
Seismic waves generated by an earthquake that pass through the earth’s crust.
What caused the Kobe earthquake?
Philippines Plate shifted uneasily beneath the Eurasian Plate along the Nojima fault line that runs beneath Kobe.
What were the primary effects of the Kobe earthquake? 5
- 5000 died
- 300,000 made homeless
- 102,000 buildings destroyed
- worst affected area was the centre
- estimated cost for rebuilding £100billion
What were the secondary effects of Kobe? 4
- emergency aid for the city needed to use damaged roads
- raised motorways collapsed during the shaking
- many small roads were closed by fallen debris from buildings, cracks or bumps
- 300 fires took 2 days to put out
What were the immediate responses? 3
- clean, fresh water supply was in short supply until April
- many people had to sleep in cars or tents in cold winter conditions
- government was criticised for being slow to rescue people
What were the long-term responses? 5
- water, electricity, gas and telephone services were fully working by July 1995
- railways were back in service by August 1995
- 80% of the port was working a year after
- by January 1999, 134,000 housing units had been constructed
- new laws were passed to make buildings and transport structures even more earthquake proof
What caused the Haiti earthquake?
Caribbean Plate south of the fault line was sliding east and the smaller Gonvave Plate north of the fault was sliding west.
What were the immediate impacts of the Haiti earthquake? 8
- 316,000 people died
- 1 million people made homeless
- Port Au Prince crumbled to dust
- 3 million people affected
- 250,000 residences damaged
- 30,000 commercial buildings damaged
- rubble blocked roads and rail links
- roads were littered with cracks
What were the short term responses to Haiti earthquake? 4
- many countries responded to appeals for aid, pledging funds and dispatching rescue and medical teams
- communication systems had been damaged which slowed rescue and aid efforts
- there was much confusion over who was in charge, air traffic congestion complicated early relief work
- supplies, medical care and sanitation were priorities
What were the long term responses? 5
- EU gave $330 million and the World Bank waived the countries debt repayments for 5 years
- 98% of rubble remained un cleared 6 months later
- $1.1 billion had been collected for Haiti for relief efforts
- 1 million people remained displaced a year later
- Dominican Republic offered support and accepted some refugees
What caused the Indian Ocean tsunami?
Info-Australian Plate subducting beneath the Eurasian Plate.
What were the effects of the Indian Ocean tsunami? 7
- 220,000 people died
- 650,000 seriously injured
- 2 million made homeless
- public buildings were wiped out
- pictures were posted in the hope that loved one had survived
- identification of the dead on such a scale was an issue
- 1,500 settlements were believed to have been wiped out completely in Banda Aceh
What were the responses to the Indian Ocean tsunami? 8
- rescue services were swamped
- injured people were untreated for days
- bodies littered the streets
- fresh water, water purification tablets, food, sheeting and tents all poured in as aid
- UK government promised £75 million
- £372 million had been donated by the British public
- £128 million had been sent out by DEC
- plans to spend £190 million building 20,000 homes for 100,000 homeless people
