GCSEPlate tectonics Year 11
Learning intention The Earth’s crust is unstable: • The tectonic plates may move together or move apart • At plate boundaries earthquakes, volcanoes and fold mountains occur. • There are different types of volcano –composite or shield (basic lava)
Three zones • The Earth’s structure has 3 parts: • Core – at the centre • Mantle – a large mass of molten rock surrounding the core • Crust – the surface of the Earth. A thin layer ‘floating’ on the mantle.
Crust • Two types of crust • Oceanic crust – denser, about 5km thick • Continental crust – less dense (lighter), about 30km thick
Earth’s crust - not one continuous layer • Crust made up of 7 large tectonic plates and many smaller ones. • Crust is unstable. Plates move according to rising currents called convection currents within the mantle. • The plate movement has its greatest impact where the plates meet. The further from these boundaries between plates the more stable they tend to be.
Tensional plate boundaries • Plates move apart eg. N. American and Eurasian plates • Gap filled by rising magma from the mantle • Rising magma forms shield volcanoes • Most common under oceans so submarine volcanoes or volcanic islands are formed. • Plates buckle to form ridges. Eg Mid-Atlantic Ridge
Constructive plate margin This is when 2 plates move apart, usually under oceans. As the plates move away from each other, cracks and fractures form between the plates where there is no solid crust. Magma rises into the cracks and forces its way to the surface to form volcanoes. New land is formed as the plates gradually pull apart. Example: Mid Atlantic Ridge – N. American and Eurasian plates.
Destructive plate boundariesSubduction boundary Convection currents in the mantle cause the Plates to move together. If an oceanic plate (Nasca plate) meets a continental plate (South American plate) then the oceanic plate sinks under. This is called Subduction. The reason the oceanic plate sinks is it is denser and the continental crust is lighter. The oceanic plate melts in the subduction zone where there is great heat, friction and pressure. The destroyed plate forms magma. The magma will rise to the surface to form a volcanoe.
Energy may be released as an earthquake. The molten rock or magma may rise forming composite volcanoes. The lighter the crust at the surface may crumple to form fold mountains.
Destructive plate marginsCollision boundary If 2 continental plates meet they collide, they do not sink beneath each other. This type of boundary creates fold mountains.
Conservative plate margins At Conservative plate margins the plates slide past each other. They move in a similar (but not the same) direction, at different angles and speeds. When one plate moves faster than the other and in a slightly different direction the plates can get stuck. A build up of pressure will eventually cause them to be released. This sudden release of pressure causes Earthquakes. At a Conservative plate margin, crust is neither destroyed nor made. Eg. Pacific Plate and N.American plate (San Andreas Fault).
Passive plate boundaries • Plates slide past each other at a passive plate boundary (Pacific and N.American). An example of a passive plate boundary is the San Andreas fault in California. Earthquakes occur along the fault.
How are fold mountains formed? • Fold mountains form along plate boundaries as a result of great Earth movements. • The general theory is:Two plates with landmasses on them move towards each otherThe plates push layers of accumulated sediment in the sea into folds between themThis becomes a fold mountain range. Most fold mountains continue to grow as the plates constantly moveExamples: the Himalayas (Asia), Rockies (USA), Andes (South America), Alps (Europe)
Good geography resource for plates etc • http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm • Andes • 7000 km long • Longest fold mountains in the world • Extend length of S.America • 300km wide • Andes in Argentina, Bolivia, Columbia, Peru, Ecuador, Chile • Tallest peak Aconcagua (Argentina) 6960 metres high.
Major Fold Mountains of the world Alps Urals Appalachian Rockies Andes Himalayas http://www.platetectonics.com/book/page_11.asp
Fold Mountains Sediments compressed and folded into Fold Mountains Geosyncline Sea Plates Plates Compression Over millions of years, the sediments were compressed (squeezed), by their own weight, into sedimentary rocks eg. Sandstone, limestone. Large depressions called Geosynclines form between plates. Seas filled the geosynclines. Rivers flowing into the geosynclines carried sediments (sand and silt) which built up on the sea bed
How fold mountains are formed? • Large depressions called geosynclines form between plates. • Seas filled the geosynclines and rivers flowing into them carried sediments (sand and silt) which built up on the sea bed. • Over millions of years the sediments were compressed, by their own weight, into sedimentary rocks, eg. Shells into Limestone, sand into sandstone. These rocks form fold mountains today. • The tectonic plates moved toward each other forcing the sediments to be pushed upwards. This forms the fold mountains with a series of anticlines (upfolds) and synclines (downfolds).
Fold mountains and Ocean Trenches • Fold mountains are some of the highest places on the planet. • Mt Everest is 8,850m high. • Ocean trenches form some of the deepest parts of the world. • Both ocean trenches and fold mountains form as 2 plates move together. If both occur together they are a result of Subduction. If only fold mountains occur then Collision is taking place.
The Alps – a range of fold Mountains Why are they there? • The Alps lie along a compressional plate boundary where, for ten million years, two plates pushed together. • The rocks were folded upwards forming simple folds, overfolds and nappes. • The Alps are young fold mountains formed 30-40 million years ago.
What are the physical features of the Alps? • High mountains eg. Mont Blanc (4810m) • Steep slopes • Deep valleys eg. Lauterbrunnen • Lakes, eg. Lake Como, Lake Garda • Source area for rivers eg. The Rhine.
What are the human activities in the Alps? B Tourism Tourists are attracted by: • Winter resorts e. Chamonix, St Moritz • Summer resorts eg. Lake Garda • Winter sports eg. Skiing. Tobogganing • Beautiful scenery and the Alpine climate • Ease of access through good communications eg. Simplon pass, Geneva airport
What are the human activities in the Alps? A Farming • Mostly on the valley floor where it is flatter, more sheltered, warmer, with deeper soils • Traditional dairying • Main crops are hay and cereals with some vines and fruit in warmer areas • Use upland pastures in summer
What are the human activities in the Alps? C HEP and Industry • Industry needing large amounts of electricity eg. Sawmills, smelters, locate near to HEP stations which generate cheap electricity from the fast flowing streams • Traditional industries include clock making, paper and furniture
What are the human activities in the Alps? D Forestry • Conifers cover the slopes up to about 1800 metres. The wood is used for fuel, building chalets and for paper-making.
Influence of Fold Mountains on human activities • They often act as climatic barriers. Regions on one side of a mountain range may have an entirely different climate form that on the region on the other side. • They often receive heavy rain/snow which may give rise to important rivers. These rivers may be used for irrigation or for developing hydro-electric power (HEP). • Some mountains and their plateaus may contain minerals. • They may act as barriers to communications or they can make the construction of communications 9 (roads etc) difficult. • Some mountain ranges have valuable timber resources.
Problems of Fold Mountain areas • Fold Mountains, like the Andes, tend to have low population densities because:- • The high altitude and steep slopes make it difficult to build houses and communication links, and to locate industries. Roads and railways need expensive tunnels and passes. • There is little flat land for farming and the use of machinery is difficult. • The climate is also cold and wet with heavy snowfall and strong winds, especially at high altitudes. The growing season is therefore short and travel can be difficult, especially in the winter. Avalanches and rock falls can block roads. • However, the population density in the Andes is higher than in many Fold Mountain areas because the soil in the valley floors is reasonable fertile and the region is attractive to tourists from nearby wealthy countries.
Volcanoes Types of volcano http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/volcanoes/volcano-lava.html http://news.bbc.co.uk/2/hi/science/nature/4972366.stm http://videos.howstuffworks.com/discovery/7153-volcanoes-pyroclastic-flow-video.htm Composite cone volcanoes usually form at compressional plate boundaries (plates meeting) Shield volcanoes usually form along tensional plate boundaries (plates pulling apart)
MEDC – More Economically developed country (Rich) Richer Able to afford Satellite and Early warning systems to predict earthquakes and volcanoes. Buildings are off a good standard to cope with volcanoes (ash) and Earthquakes (Earthquake proof) – use hi-tech materials and do not fall down easily. Better and quicker aid to help people quickly after a natural hazard happens (eg. Helicopters to rescue people, fire brigade, ambulances, better hospitals, army etc) Better roads, bridges, airports etc (better infrastructure) More money and better professionals to rebuild roads, bridges, buildings quickly and to a high standard LEDC – Less Economically Developed Country (Poor) Poorer Can not afford Satellite and Early warning systems to predict earthquakes and volcanoes. Buildings off a poor standard made out of mud, wood or corrugated iron sheets – fall down easily. Aid and help slower to arrive for after a natural hazard happens (eg. No Helicopters to rescue people; poor standard of fire brigade, ambulances, hospitals, army etc) Poor roads, bridges, airports etc (poor infrastructure) May be years before bridges, roads and buildings are repaired (if at all).
Draw a volcanoe and label parts of it Lahars – mudflows and landslides caused by melting ice due to volcanic activity Pyroclastic flow – Flow of hot ash, steam and rock down the side of a volcano after it erupts. It can travel at 300 miles per hour and cook a person in a millisecond.
Volcanoes A volcano is a cone shaped hill or mountain of lava. Active volcanoes are ones which have erupted recently. Dormant volcanoes have not erupted in 2000 years but they could still erupt. Extinct volcanoes are unlikely to ever erupt again.
Volcanoes They are natural hazards – just like Tsunamis and Earthquakes. Volcanoes are magma that has risen to the surface through cracks in the earth’s crust. Each eruption adds a new layer to the volcanoe, seeing it grow larger and larger. Composite volcanoes occur at destructive plate margins. They are created by thick lava that does not move much giving rise to a tall cone shape with a narrow base. They give very violent eruptions eg. Mt St Helen’s, USA; Vesuvius, Italy. Shield volcanoes occur at constructive plate margins. They are created by runny lava giving them a wide base, but they are not very tall as a result. They erupt often but gently eg. Mauna Lau, Hawaii; Heimaey, Iceland.
Volcanoes occur at plate boundaries – where two plates meet. Most of the world’s volcanoes are around the edges of the Pacific Plate. We call this area the ‘Ring of Fire’.
Homework – Past Paper Questions Use the diagram showing the world’s volcanoes Describe the distribution of the world’s Volcanoes.(4 marks) How is the distribution of supervolcanoes different from that of volcanoes? (2 marks) Explain why volcanoes are found at destructive plate boundaries. (3 marks) Describe the ways in which a supervolcano is different from a volcano. (4 marks) Using case studies of volcanoes in rich and poor parts of the world, compare and describe the immediate responses. (8 marks)