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 to fill the gap and cool, this constructs new crust.
- This can cause volcanoes and earthquakes.
Conservative Plate Margins
- A conservative plate boundary, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.
- If one plate is moving slightly faster than the other then pressure builds (friction) along the fault line until one plate jerks past another which causes shockwaves which produce an earthquake.
- There are no volcanoes made by this plate margin
The formation of fold mountains:
- An area of sea separates two plates, sediments settle on the sea floor in depressions called geosynclines. These sediments gradually become compressed into sedimentary rock.
- When the two plates move towards each other again, the layers of sedimentary rock on the sea floor become crumpled and folded.
- Eventually the sedimentary rock appears above sea level as a range of fold mountains.
Where the rocks are folded upwards, they are called anticlines. Where the rocks are folded downwards, they are called synclines. Severely folded and faulted rocks are called nappes.
Fold mountains are found at Destructive plate margins.
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- Farming+Fore
Where: Central Europe- it stretches across Austria, France, Germany, Italu, Liechtenstein, Slovenia and Switzerland.
Formation: 30 million years ago by a collision between African and Eurasian plate
Population: 12 million
1) The steep upland areas are used to farm animals such as goats for milk, cheese and meat.
2) Some sunnier slopes are terraced to plant vineyards.
Scots pine is planted all over the Alps because its more resiliant to muching goats, which kill native tree spalings, This means trees arent damaged and so can be logged and sold to make things like furniture.
Case Study - The Alps - Tourism
- 100 million tourists visit each year
- In the winter tourists visit for skiing, snowboarding and ice climbing. - 70% of tourists visit in winter.
- In the summer tourists visit for walking, mountain biking, climbing.
- New villages have been built to cater for tourists. - e.g Tignes in France
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
- 60% of Switzerlands electricity is from HEP stations in the Alps
- Some cheap HEP is used by industries which require high input of electricity.
Mining- salt, iron ore, gold, silver and coper are mined. However mining has dropped dramatically sue to cheaper foreign sources.
Adaptations made due to Problems with fold mountai
1) Steep Relief-
- Goats are farmed there- they are well adapted to live on steep mountains.
- Trees and man-made defences are used to protect against avalanches and rock slides.
2) Poor soils-
- Animals are grazed in the highest areas as the soils there arent great for growing crops.
3) Limited communications-
- Tunnels have been cut through the mountains to provide fast transport links as passes created over lower points btween mountains took a long time to drive over and had the risk of being blocked by snow.
Volcanoes- How are they formed?
Volcanoes are formed at Destructive and Constructive plate margins
1) At Destructive plate margins the oceanic plate goes under the continental platebecause its more dense.
- The oceanic plate moves down into the mantle, where its melted and destroyed.
- A pool of maga forms
- The magma rises through the cracks in the crust called vents.
- The magma erupts onto the surface (where its called lava) forming a volcano.
2) At constructive plate margins the magma rises up into the gap created by the plates moving apart- forming a volcano.
3) Some volcanoes also form over parts of the mantle that are really hot (called hotspots) e.g in Hawaii
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- steep sided.
- 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
- Lava is thick and flows slowly- Made up of only lava that hardens quickly
- Forms a steep-sided volcano.
Types of Volcano pictures
Case Study- Montserrat - Volcano
Date of eruption- June 25th 1997 (small erruptions started in JUly 1995)
Size of eruptions: Large- 4-5 million m(cubed) of rocks and gas released.
Death toll: 19 killed.
1) Montserrat is above a destructive plate margin, where the Atlantic plate is being forced under the carribean plate.
2) Magma rose up through weak points under the soufriere hills forming an underground pool of magma.
3) The rock above the pool collapsed, opening a vent and cuasing the eruption.
Case Study- Montserrat - Volcano - Impacts
- Large area were covered with volcanic material- the capital city Plymouth was burried under 12m of mud and ash..
- Over 20 villages and two thirds of homes on the island were destroyed by pyroclastic flows (fast- moving clouds of super-heated gas and ash)
- 19 people died and 7 were injured
- Schools, hospitals, the airport and the port were destroyed.
- Vegetation and farmland were destroyed.
- Fires destroyed many buildings including local government offices, the police headquaters and the town's central petrol station.
- Tourists stayed away and businesses were destroyed, disrupting the economy.
- Population decline- 8000 of the island's 12000 inhabitants have left since the eruptions began in 1995.
- Volcanic ash from the eruption has improved soil fertality
- Tourism on the island is now increasing as people come to see the volcano.
Case Study- Montserrat - Volcano - Responses
- People were evacuated from the south to safe areas in the north.
- Shelters were built to house evacuees.
- Temporary infrastructures was also built, e.g. roads and electricity supplies.
- The Uk provided £17 million of emergancy aid (Montserrat's an overseas territory of the uk).
- Local emergancy services provided support units to search for and rescue survivors.
Long Term Responses
- A risk map was created and an exclusion zone is in place. The south of the island is off-limits while the volcano is still active.
- The Uk has provided £41 million to develop the north of the island- new docks, an airport and houses have been built in the north.
- The Montserrat Volcano observatory has been set up to try and predict future eruptions.
A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta volume greater than 1,000 km³. This is thousands of times larger than normal volcanic eruptions. THere usually ound at destructive plate margins or over parts of the mantle that are really hot (called hotspots).
How are they former at a hotspot?
- Magma rises through cracks in the crust forming a large magma basin below the surface.
- The pressure of the magma causes a circular bulge on the surface (several km wide).
- 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 spewing up more lava
- When the eruption finishes there is a big crater (caldera) left where the bulge collapsed.
Characteristics of a supervolcano-
*Flat- unlike normal volvanoes which are like mountains. *Cover a large are. *Have a caldera.
Supervolcanoes- what affect does it have? + Yellow
1) A supervolacno eruption will throw out thousands of cubic kilometres of rock, ash and lava ( a normal volcano will only produce a couple of cubic kilometres
2) A thick cloud of super-heated gas and ash will flow at high speeds from the volcano, killing, burning and burying everything it touches. -Everything within tens of miles will be destroyed.
3) Ash will shoot kilometres into the air and block out almost all daylight over whole continents. This can trigger miny ice ages as less heat energy from the sun reaches the Earth.
4) The ash will also settle over hundreds of square kilometres, burying fields and buildings.
Yellowstone is one example of a supervolcano.
it was 1,000 times bigger than the Mount St Helens eruption in 1980.
The large volume of material from the last Yellowstone eruption caused the ground to collapse, creating a depression called a caldera. The caldera is 55 km by 80 km wide.
Earthquakes occur at all 3 types of plate margin-
1) earthquakes are caused by the tension that builds up at all 3 types of plate margin:
- Destructive margins- tension builds up when one plate gets stuck as it's moving down past the other into the mantle.
- Constructive margins- tension builds along cracks within the plates as they move away from each other.
- Conservative margins- tension builds up when plates that are grinding past each other get stuck.
2) the plates eventually jerk past eatchother, sending out shock waves (vibrations). These vibrations are the earthquake.
3) The shock waves spread out from the focus- the point in the Earth where the earthquake starts. Near the focus the waves are stronger and cause more damage.
4) The epicentre is the point on the Earth's surface straight above the focus.
Earthquakes can be measured;
Earthquakes can be measured using 2 different types of scale:
The Richter Scake:
- 1) This measures the amount of energy released
- 2) Magnitude is measured using a seismometer- a machine with an arm that moves with the vibrations of the Earth.
- 3)The Richter Scale doesnt't have an upper limit and it's logarithmic- this means that an earthquake with a magnitude of 5 is 10x more powerful than one with magnitude 4.
- 4) Most people don't feel earthquakes of magnitude 1-2. Major earthquakes are above 5.
The Mercalli Scale:
- 1) This measures the effects of an earthquake.
- 2) Earthquakes are measured by asking eye witnesses for observations of what happened. Observations can be in the form of words or photos.
- 3) It's a scale of 1 to 12.
Case study- Earthquakes- L'Aquila, Italy
The effects of earhquakes and the responses to them are different in different parts of the world. A lot depends on how wealthy the part of the wrold is:
- place: L'Aquila, Italy
- Date: 6th of April, 2009
- Size: 6.3 on the Richter scale
- Cause: Movement along a crack in the plate at a destructive plate margin.
- Preperation: There are laws on construction standards, but some modern buildings hadn't been built to withstand earthquakes.
- Italy has a civil preperation department that trains volunteers to help with things like rescue operations.
Case study- L'aquila, Italy continued
- Around 290 deaths, mostly from collapsed buildings.
- Hundreds of people were injured.
- Thousands of buildings were damaged or destroyed
- A bridge near the twon of Frossa collapsed, and a water pipe was broken near the twon of Paganica.
- Aftershocks hampered rescue efforts and caused more damage
- Fires in some collapsed buildings caused more damage.
- The broken water pipe near the town of Paganica caused a landslide.
- Camps were set up for homeless people with water, food and medical care.
- Ambulances, fire engines and the army were sent in to rescue survivors
- Money was provided by the government to pay rent+ gas+ electricity bills were suspended.
Long term reponses: The Italian priminister prmomised to build a new town+ an investigation is going on to find out why buildings weren't built to withstand earthquakes.
Case study- Earthquakes- Kashmir, Pakistan
- Place: Kashmir, Pakistan
- Date: 8th of October, 2005
- Size: 7.6 on Richter scale
- Cause: Movement along a crack in the plate at a destructive plate margin.
- No local disaster planning was in place
- Buildings were not designed to be earthquake resistant
- Communications were poor- few roads+ badly contructed.
- Around 80,000 deaths, mostly from collapsed buildings
- HUndreds of thousands of people injured
- Entire villages+ thousands of buldings were destroyed.
- Around 3 million people were homeless
- Water pipelines+ electricity lines were broken.
Case study- Kashmir, Pakistan continued...
- Landslides buried beuildings+ people. They also blocked access roads and cut off water supplies, electricity supplies and telephone lines.
- Diarrhoea and other diseases spread due to little clean water.
- Freezing winter conditions shortly after the earthquake cause more casualties and meant rescue and rebuilding operations were difficults
- Help didn't reach many areas for days or weeks.
- Tents, blankets and medical supplies were distributed within a month, but not to all areas affected.
- International aid and equipment such as helicopters and rescue dogs were brought in, as well as teams of people from other countries.
- Around 40,000 people have been relocated to a new town.
- Government money has been given to people whos homes had been destroyed so they can rebuild them themeselves.
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- Tsunamis
An earthquake caused a tsunami in the Indian Ocean in 2004;
- 1) There's a destructive plate margin along the west coast of Indonesia in the Indian ocean.
- 2) on the 26th of December 2004 there was an earthquake off the west coast of the island of Sumatra measuring around 9.1 on the Richter scale.
- 3) The plate that's moving down into the mantle cracked and moved very quickly, which caused a lot of water to be displaced. This triggered a tsunami with waves up to 30m high.
The Indian ocean tsunami was one of the most destructive natural disasters that's ever happened. It affected most countries bordering the Indian ocean, e.g. Indonesia, Thailand, India and Sri Lanka. The effects of the tsunami were so bad because there was no early warning system:
- 1) Around 230,000 people were killed or are still missing.
- 2) whole towns+ villages were destroyed- over 1.7 million people lost their homes.
- 3) The infrastructure (roads, waterpipes+ electricity lines) were severly damaged.
- 4) 5-6 million people needed emergancy food, water+ medical supplies.
- 5)There was massive economic damage. Millions of fishermen lost their livelihoods, and the toruism industry suffered because of the destruction+ of being afaid to go there.
- 6)There was massive environmental damage.
Case study- tsunamis continued
The response invlved a lot of international aid:
Short- term responses:
- Within days hundreds of millions of pounds had been pledged by foreign governments, charities, individuals and businesses to give survivors acess to food, water, shelter and medical attention.
- Foreign countries sent ships, planes, soldiers and teams of speacialists to help rescue people, distribute food and water and begin clearing up.
- Billions of pounds have been pledged to help re-build the infrastructure of the countries affected.
- As well as money, programmes have been set up to re-build houses and help people get back to work.
- A tsunami warning system has been put in place in the Indian ocean.
- Disaster management plans have been put in place in some countries. Volunteers have been trained so that local people know what to do if a tsunami happens again.