The 7 major plates
- North American
- South American
Structure of the earth
Structure of the earth (2)
The inner core- liquid.
The outer core- solid iron and nickel.
The mantle- semi molten rock (moves slowly). Convection currents occur in the mantle.
Crust- thin outer layer of the earth, which is divided into tectonic plates.
- Plates are made up of two types of crust, Oceanic & Continental
- Oceanic crust is thinner and more dense.
- Continental crust is thicker and less dense.
Destructive Plate Margins
- An oceanic and continental plate collide.
- The oceanic plate is denser than the continental plate so therefore it sinks underneath the continental plate - this is called subduction.
- As the oceanic crust sinks down into the mantle it melts- forming magma.
- As energy builds up the magma may force its way through the continental crust and explode as a volcano.
- Friction may cause an earthquake.
Constructive Plate Margins
- Plates are moving apart.
- This allows magma from the mantle to rise up to the earths surface and construct new crust.
- This can cause volcanoes and earthquakes.
Collision Plate Margins
- Two continental plates moving together.
- Continental crust cannot sink or be destroyed so they push together until the land between the two plates is buckled and pushed upwards.
- This then forms high fold mountains (e.g. himalayas).
- There are no volcanic eruptions at collision margins but pressure created by the plates moving together can cause earthquakes.
Conservative Plate Margins
- Plates are moving past eachother.
- Same direction.
- If one plate is moving slightly faster than the other then pressure builds along the fault line until one plate jerks past another which causes an earthquake.
- No volcanoes.
Fold Mountains are formed when Plates collide at Constructive Margins
1. When tectonic plates collide, layers of sedimentary rock rises up creating a fold mountain.
2. Therefore Fold mountains are found at constructive plate margins
3. You can also get Fold Mountains where the Continental and the Oceanic plates collide (destructive).
4. You can also get Fold mountains where the two continental plates collide (constructive).
A geocyncline is a huge depression where sedimentary rocks form.
Syncline- downfolds in sedimentary rock.
Anticline- upfolds in sedimentary rock.
Overfold- pushing the anicline on top of the syncline.
Sedimentary rocks form by rivers carrying and depositing sediments into geosynclines. Over millions of years the sediments are compressed to form sedimentary rocks.
Case Study - The Alps- Fold Mountain
Where: Europe, France/Italy border
Formation: 30 million years ago by a collision between African and Eurasian plate
Population: 12 million
- On the sunnier, warmer side of slopes.
- Uses transhumance (seasonal movement of animals).
- summer- cattle taken to high Alps to graze allowing crops to grow on valley floor.
- winter- return to valley floor in cattle sheds.
- Change over years:
- Cable cars used to transport milk to dairy's
- Farmers buy additional food so can remain on valley floor all year
Case Study - The Alps - Tourism
- 100 million tourists visit each year
- In the winter tourists visit for skiing, snowboarding and ice climbing.
- In the summer tourists visit for walking, mountain biking, climbing.
- New villages have been built to cater for tourists.
- Worry is that winters are warming up so there is less snow:
- more people skiing on worn slopes
- damages vegetation and the surface below
- increases number of bare slopes and risk of soil erosion
Case Study - The Alps - Hydro electric power & min
Hydro-Electric Power (HEP)
- Steep slopes, high precipitation and summer melting of glaciers makes fast flowing rivers which are ideal for generating HEP.
- Valleys are narrow
- Easier to dam and there are lots of lakes to store water
- Some cheap HEP is used by industries which require high input of electricity.
Mining- salt, iron ore, gold, silver and coper are mined.
Problems of Fold Mountains
Relief: high and steep
- mountain valleys=narrow and gorge like.
- little flat land for forming settlements.
Climate: increasing height becomes colder, windier, wetter and more snow
- short growing season.
- oftenimpossible to grow cropsat such high levels.
soils- stoney, thin and infertile
Accessibility: roads and railways= expensive and difficult to build
- Found at destructive and constructive plate margins
- A volcano is a cone shaped mountain formed by surface eruptions from a magma chamber inside the earth.
A volcano produces-
- Pyroclastic flower (super-heated ash and steam)
How volcanoes are formed
- Magma escapes through a crack in the earths crust (called a vent)
- Lava and other products are thrown out from the circular hole at the top called the crater.
- Each time an eruption takes place, a new layer of lava is added to the surface of the volcano.
- Laval accumulates at the top of the crater to form the cone shape.
Types of Volcano
- Lava is usually thick and flows slowly
- It hardens quickly, forming a steep sided volcano
- Made up of ash and lava in alternate layers
- Tall cone with narrow base
- Irregular with violent explosions
- Subsidiary cones and vents form
- Lava is runny and flows quickly
- Lava spreads over a wide area forming a low, flat volcano, made only of lava
- Frequent non violent eruptions
Types of Volcano pictures
Case Study- Mount St Helens - MEDC Volcano
When: 10th May 1980
Case Study- Mount St Helens - MEDC Volcano - Effec
- Gas steam and ash burst out and flowed down the side of the volcano.
- Sideways eruption.
- 61 people killed.
- Animals killed.
- Flattened and burnt trees.
- Mudslides (due to melted snow).
- Top of mountain collapsed and side blown out.
- Roads blocked.
- Houses destroyed.
Case Study- Mount St Helens - MEDC Volcano - Respo
Short Term Responses:
- Rescuers saved lives.
- Search & rescue.
Long Term Responses
- Buildings & bridges rebuilt.
- Forests replanted.
- Roads rebuilt.
- Government provided money.
A supervolcano is a volcano that is much bigger than a normal volcano. They do not form a cone shape, they form a large depression called a caldera (there is a higher rim of land around the edges). Emits atleast 1000km3 of magma.
- Magma rises through cracks in the crust forming a large magma chamber below the surface.
- The pressure of the magma causes a circular bulge on the surface.
- The bulge cracks, creating vents for lava to escape through.
- Lava erupts out of vents causing earthquakes and sending up ash and rock.
- As the magma basin empties, the bulge is no longer supported so collapses
- When the eruption finishes there is a big crater (caldera) left where the bulge collapsed.
Case Study- Yellowstone Supervolcano
Size? Measures 34 mile by 45 miles
Last eruption? 70,000 years ago
Possible effects if yellowstone erupted?
- Land destroyed.
- People would be killed.
- Crops would fail.
- Ash would effect transport, electricity, water and farming.
Volcanoes- Hazard or Blessing?
- Loss of life.
- Poisonous gases.
- Buildings destroyed.
- Public services distrupted.
- Fertile soils.
- Hot water supplies.
- Valuable minerals.
Warning signs of volcanic eruptions
- Small earthquakes.
- Increased emissions of steam and gases.
- Visual signs of bulging around crater.
- Electronic tiltmeters- measure very small changes in the profile of mountain.
- Satellites are used to measure the infra-red radiation and look for changes in heat activity.
Case Study- Montserrat- LEDC Volcano
When: 25th June 1997
Why: Destructive boundary - North and south american plates subducted under the caribbean plate.
Case Study- Montserrat- Responses- LEDC Volcano
- People evacuated to North of island.
- Shelters built.
- Uk sent £17 million of emergancy aid.
- Temporary infrastructure built.
Long Term Responses:
- UK funded a 3 year redevelopment programme.
- South of island remained out of bounds in 2005.
- Red Cross built a home for the elderly.
Case Study- Montserrat- Effects- LEDC Volcano
- 20 villages destroyed by pyroclastic flow.
- Areas covered in volcanic material.
- Schools, hospitals and the airport destroyed.
- Farmland destroyed.
- 23 people died.
- Fires destroyed buildings (government offices, police hq and petrol station).
- Tourists stayed away (disrupting the economy).
- Population decline.
- Although, tourism has now increased and soil is fertile.
What are they?
Vibrations in the earths crust which shake the ground surface.
Why do they happen?
Friction. When plates try to move they are held still by friction. This can be with another plate or with the mantle. The forces pushing the plate keep pushing until there is so much force that it overcomes friction and the plate suddenly jerks forwards.
Focus = Where the plate moves underground, where the earthquake originates.
Epicentre = The point on the surface straight above the focus.
Shockwaves = Radiate out in all directions which get less powerful the further away from the epicentre.
The Richter Scale
- Measures magnitude (energy released) of an earthquake.
- Measured using a seismograph.
- It's logarithmic- means that an earthquake with magnitude of 5 is 10 times more powerful than one with a magnitude of 4.
- Most people don't feel earthquakes of magnitude 1-2.
- Major earthquakes are above 5.
The Mercalli Scale
- Used to indicate intensity/effects of an earthquake
Effects are measured by asking eye witnesses of what happened, and takes into account effects on Earth's surface, people and buildings.
Given a number between 1-12, sometimes Roman numerals:
I (1)- Rarely felt by humans.
II-IV (2-4)- Moderate effects- felt by people indoors.
V-VII (5-7)- Strong effects, causing panic felt by everyone, structural damage.
VIII (8)- Destructive to poorly built structures, only slight damage to those well designed.
IX-XII (9-12)- Disastrous, total destruction.
Effects Of Earthquakes
- Collapsing roads and buildings
- Deaths (trapped people)
- ((Primary effects are worse if there is a shallow focus and in a poorer urban area due to large population and non earthquake proof buildings.))
- Fires (fallen electricity wires)
Types of Responses
Immediate/ short term = what happens straight away after the earthquake (medical teams help injured).
Medium term = to get back to normal life asap (rebuilding what has been lost).
Long term = to be prepared for another (earthquake proof buildings).
Case Study- Kashmir - LEDC Earthquake
When? 8th October 2005
Collision zone? Eurasian & Indian plate (collision boundary)
Richter scale? 7.6
Case Study- Kashmir - Effects - LEDC Earthquake
- 3.3 million homes destroyed.
- Buildings collapsed, roads cracked, bridges fell down.
- 79,000 people killed.
- 100,000 injured.
- Disease (contaminated water caused diarrhoea).
- People died of cold due to thin tents to live in.
Long term Effects:
- Jobs lost.
- Schools damaged.
- Electricity wires brought down so reconstruction was made harder.
- Overall cost of damage - £5 billion.
Case Study- Kashmir - Responses - LEDC Earthquake
Immediate / short term responses:
- Locals tried to rescue trapped people.
- Army and emergancy services helped.
- Charities (like muslim aid) gave out tents.
- Helped eachother mainly (self help).
Long term responses:
- Red cross re-established water supplies.
- Teachers trained for counsilling.
- Thin tents replaced with temporary housing by army.
- Building laws were tightened to ensure less damage next time.
A short term response in an MEDC is often a long term response in an LEDC.
Case Study- Los Angeles - MEDC Earthquake
Where? Los Angeles, USA
When? 7th january 1994
Plate boundary? Pacific & North American plates grind past eachother.
Richter scale? 6.7
Case Study- LA - Effects - MEDC Earthquake
- 15 seconds of shaking.
- People crushed.
- Highways and bridges broke/collapsed.
- Landslides moved houses down slopes.
- Broken gas mains caught fire.
- Cars exploded.
- People left homeless.
- 57 killed.
- $15 billion of damage.
((People live in LA despite the risk of earthquakes because they don't want to lose their job, friends and family live there and the technology is advanced etc..))
Case Study- LA - Responses - MEDC Earthquake
Immediate / short term responses:
- Fire crews rescued 30 people from collapsed buildings and freeways.
- Food handed out.
- Red cross handed out emergancy food and shelter.
Long term responses:
- Public given leaflets and training to prepare for earthquakes.
- People have earthquake huts at home with food, water and radio.
- Government compensated home owners.
- 80,000 new houses built.
A tsunami is a special type of wave where the entire depth of the ocean is set in motion by an event - often an earthquake - which displaces the water above it and creates a huge wave.
Case Study- Boxing day Asian Tsunami
Where? Indonesian island of Sumatra in Asia.
Earthquake richter scale? 8.9
How? Pressure from the indo-australian plate pushing under the eurasian plate.
Case Study- Boxing day Asian Tsunami - Effects
Short term effects:
- Buildings destroyed.
- Flash floods.
- High waves.
- Initial earthquake.
Long term effects:
- Dead/missing people.
- 5,000 houses destroyed.
Case Study- Boxing day Asian Tsunami - Responses
Short term responses:
- Blankets and aid flown in.
- Water provided.
- Bulldozers cleared dead bodies to prevent disease.
Long term responses:
- International tsunami warning put in place.
- £100 million donation.