SOSE Chapter 8
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SOSE Chapter 8

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Chapter 8

Chapter 8
Landforms of the earth
credits to Marshall Cavendish Education

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SOSE Chapter 8 SOSE Chapter 8 Presentation Transcript

  • Chapter 8 Landforms on the Earth
  • The earth surface • Earth’s surface is not flat or smooth. It has been shaped and changed into many different features over years • Made up of many different landforms.
  • Types of Landforms
  • Mountain • Usually taller than 600 m in height with steep slopes and a narrow top or peak
  • Hill • Usually less than 600m in height, rounded in shape with gentle slopes
  • Valley • A low area of land between hills or mountains
  • Plain • A broad, flat and low area on the Earth’s surface
  • Plateaux • A raised area of land, usually flat with a broad top and steep slopes • another type of landform associated with vulcanicity • A plateau is formed when a large quantity of magma escapes from a fault in the Earth’s crust and spreads over a wide area • Layers of hardened lava form a plateau
  • Volcanoes • a mountain or hill, typically conical, having a crater or vent through which lava, rock fragments, hot vapor, and gas are being or have been erupted from the earth's crust. • Volcanoes commonly occur at the boundaries of plates where the impact of plate movements is the greatest
  • The internal structures of the Earth Layers of the Earth
  • The Core • Centre of the earth • Temperature of up to 5 000 Degrees Celsius • Solid due to intense pressure exerted on the center by the outer layers of the Earth.
  • The Mantle • Layers of rock that surrounds the core • 2 900 km in thickness • 80% of the earth total volume • Temperature 2 000 degrees Celsius • Semi-molten or semi-liquid state
  • The Crust • Outermost layer of the earth • Solid state • Varies in thickness 6 to 7 km • Made up of several pieces called plates which floats on the semimolten mantle beneath them
  • The Internal Structure of The Earth • Core: the centre of the Earth • Mantle: the layer above the core and makes up nearly 80% of the Earth’s total volume • Crust: the outermost layer which is made up of many separate pieces called plates
  • Internal Forces That Create Landforms Folding, Vulcanicity
  • Internal Forces that Create Landforms • The Earth’s plates are always moving Ocean Plate • The movement of plates is known as crustal movement Mantle • As the plates move, they may slide past, pull apart from or push towards each other, resulting in the creation of many landforms on the Earth Ocean Plate Mantle Plate Plate
  • Folding • Some plates collide with each other • When this happens, some of the layers of rocks buckle and form folds • When the amount of folding is large, mountains may form • Examples of fold mountains: • The Himalayas • The Appalachian Mountains • The Andes • The Alps Some plates push towards each other and form folds
  • Vulcanicity • When the temperature beneath the Earth’s surface is so great, magma (molten mantle) is formed • Magma that reaches the Earth’s surface is called lava • Vulcanicity is the process in which magma and other materials reach the Earth’s surface
  • Vulcanicity • The outpouring of the lava onto the Earth’s surface is called an eruption • At the Earth’s surface, the lava hardens due to the cooler temperature • Hardened lava from eruptions through a single hole or vent may result in a cone-shaped mountain called a volcano
  • Volcanoes • A volcano consists of a vent, pipe, crater and cone:  Vent: An opening in the Earth’s surface  Pipe: A channel which allows the magma to rise to the top of the volcano during an eruption  Crater: A bowled-shaped opening at the top of the volcano  Cone: The shape of the volcano
  • Volcanoes • Volcanoes commonly occur at the boundaries of plates where the impact of plate movements is the greatest • There are three types of volcanoes:  Active volcano: erupted from time to time and will most likely erupt again in future - e.g. Mount St Helens, USA  Dormant volcano: presently inactive but may erupt again - e.g. Mount Rainer, USA  Extinct volcano: unlikely to erupt again - e.g. Mount Kilimanjaro, Tanzania
  • External Forces that Modify Landforms Weathering
  • Weathering • Weathering refers to the process by which rocks are progressively broken down into fragments where they are • Weathering is mainly caused by:  Large changes in temperature  Action of water  Action of freezing water  Plant growth
  • Cracks appearing on a Weathering - Large changes in temperature of changes rock because in temperature  Heat causes the surface layer of the rock to expand during the day  During the night, the surface of the rock cools and contracts faster than the interior of the rock  This constant expansion and contraction weakens the surface of the rock
  • Weathering – Action of water  Rainwater combines with carbon dioxide in the air to form carbonic acid which dissolves certain types of rocks such as limestone How would you describe the formation of the physical features of this limestone cave?
  • Weathering -Action of freezing water  Water from melting snow or rain may enter cracks in rocks  When water freezes, it expands and causes the cracks in the rocks to widen Can you describe how the action of freezing water has caused the physical features of this mountain?
  • Weathering - Plant growth  The wind may carry seeds of plants into the cracks in rocks  As the seeds grow into plants, the roots grow into the rocks and force the cracks in the rocks to widen  Overtime, the rocks can fall apart if the force is strong enough
  • Erosion • Erosion refers to the process of wearing down surface materials and moving them from one place to another • Erosion is mainly caused by:  Action of running water  Action of waves  Action of wind
  • Erosion - Action of running water Running Water  Water in streams and rivers carries a lot of sediments or small particles  The sediments in the water wears down rocks as the water flows over them  The action of the water and its sediments will gradually erode the Earth’s surface
  • Erosion - Action of waves  The constant breaking of waves against the shore, together with the grinding action of sand and stones in the waves, erodes the seashore  It results in landforms such as sandy beaches, caves and cliffs Waves
  • Erosion - Action of wind  Wind erosion occurs in areas with little water and few plants to hold the soil in place  Strong winds carry large amounts of sand which wear away the surfaces of rocks in their path  Erosion tends to take place mainly at the base of rocks Wind
  • How Do Landforms Affect Us? • Location of homes  The relief of the land affects where people build their settlements  People living near volcanoes and areas which are prone to floods bear the risk of losing their lives and property when disaster strikes This picture shows how people are able to build houses even on the slopes of a hill
  • How Do Landforms Affect Us? • Human activities  People have adapted to the environment by cutting terraces into the slopes to grow crops  Recreational activities such as trekking and mountain climbing take place on hills and mountains  Scenic places attract both local and foreign tourists