sose chapter 8
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Chapter 8 Landforms of the earth credits to Marshall Cavendish EducationTRANSCRIPT
Chapter 8Landforms 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 EarthLayers 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 semi-molten 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 LandformsFolding, Vulcanicity
Internal Forces that Create Landforms
• The Earth’s plates are always moving
• The movement of plates is known as crustal movement
• 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
Plate
OceanPlate
Mantle
OceanPlateMantle
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 LandformsWeathering
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
Weathering - Large changes 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
Cracks appearing on a rock because of changes
in temperature
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
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
Running Water
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