SOSE Chapter 8

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