GEOGRAPHY

GEOGRAPHY

TERM 3 2026

SURFACE FORCES THAT SHAPE EARTH

Earth’s surface is continually worn away by the forces of nature such as wind, rain, frost, and waves.

·         Rivers carve out valleys, and in some places, they leave fertile mud over wide areas.

·         Waves produce cliffs and beaches along the coast.

·         Water/ ice break up rocks in high areas, creating high pointed peaks.

·         In cold areas, ice moves over the land, carving deep valleys with steep sides.

·         Wind blows sand across deserts, producing sand dunes and sand carved rocks.

1. WEATHERING

What is weathering?

Weathering is the wearing away of rocks and soil by the action of weather. It affects the shape and composition of rocks and soil.

There are 3 main types of weathering:

1.    PHYSICAL WEATHERING- physical forces such as frost/ temperature change.

2.    CHEMICAL WEATHERING- chemical changes that weaken rocks.

3.    BIOLOGICAL WEATHERING- the action of plants and animals.

1. PHYSICAL WEATHERING

o   Involves physical forces that break up rocks.

o   Examples: ice, water, temperature changes.

a.) Freeze thaw action

ü 

This happens when water collects in the cracks in rocks.

ü  As water freezes it expands.

ü  As water turns into ice, it increases its volume and puts pressure on the

sides of the cracks.

           b.) Exfoliation

ü  Common in dry areas.

ü  The outer layers of rock expand in the heat of the day.

ü  The outer layers of rock contract due to the cooler night.

ü  The constant expanding and contracting of rocks during the day and night weakens the outer layers of rocks. (large pieces can peel off the outer surface)

2. CHEMICAL WEATHERING

o   Changes the chemical composition of rocks.

o   Weakens rocks, causing them to break.

o   Chemical reactions cause chemical weathering.

a.) Carbonation

ü  There is dissolved carbon dioxide in rain droplets, making rain a weak acid called carbonic acid.

ü  When rain comes into contact with rocks that contain calcium carbonate (limestone), the rain changes the insoluble calcium carbonate into the soluble calcium bicarbonate.

ü  The calcium bicarbonate is dissolved by the rainwater and is washed away.

ü  Carbonation is greater in colder climates.

          b.) Oxidation

ü  Occurs in rocks and objects that contain iron.

ü  Water contains oxygen that mixes with the iron inside rocks to form iron oxide.’

ü  Oxidation changes the chemical structure of the rock, making it weaker and more easily broken down.

         c.) Hydrolysis

ü  A sequence of chemical reactions that involve water, and minerals called silicates.

ü  Certain silicate minerals absorb water and change into clay.

ü  Clay is easily washed out of rocks.

ü  When clay exits the rocks, it becomes unstable and can crumble.

3.BIOLOGICAL WEATHERING

o   Weathering caused by plants, animals and people.

o   Animals dig in the soil, weakening it and exposing it to other kinds of weathering.

o   The tips of plant roots can penetrate in small cracks in roads, pavements and rocks.

o   The roots put pressure on the cracks, causing them to expand and break.

o   A group of plants called lichen grow on rocks.

o   The roots of lichens penetrate in between the cracks of rocks, loosening them so that the grains eventually fall away.

o   Lichens also produce an acid that breaks down minerals in rocks.

2. EROSION AND DEPOSITION

DIFFERENCE BETWEEN WEATHERING, EROSION AND DEPOSITION.

·         All a set of linked processes that create natural features on the land.

·         Weathering and erosion wear away Earth’s surface.

·         Deposition builds up Earth’s surface with the materials produced from weathering and erosion.

1.Weathering

§ 

Breaking down of rocks and soil by the action of the weather.

§  Very little movement occurs during the process.

2. Erosion

§  Always involves movement in many places, unlike weathering.

3. Deposition

§  Weathering/ erosion produce rocks/ sand/ soil.

§  This material is deposited on the land.

RIVERS 

Ø  River erosion happens when a river flows over the land.

Ø  The weathered material transported in a river is called the rivers load, containing mostly of sand stone and silt.

Ø  The rivers load wears away the river bed and the sides of the river.

Ø  Only some of the worlds rivers actually flow into the sea.

Ø  The rest flow into other rivers as tributaries.

FEATURES OF EROSION AND DEPOSITION IN THE MIDDLE AND LOWER CIURSE OF A RIVER

Ø  Rivers often have large bends, called meanders.

Ø  1. Meanders

·         Meanders are formed by erosion and deposition.

·         Erosion= the river flowing faster on the outside of the bend.

·         Deposition= river flows more slowly on the inside of the bend.

Ø  2. Ox-bow lakes

·         Erosion pushes the bend of the meander downstream.

·         This narrows the gap between different meanders. (meander neck)

·         The river eventually erodes through the meander neck and make a new channel.

·         Deposition from the meander will cut off the original meander, making it an ox-bow lake.

·         In time the lake will dry up and be left as a meander scar.

Ø  3. Levees and deltas

·         Levees are natural mounds on river banks.

·         Formed when a river floods and deposits sand and silt on the river bank

·         Frequent floods increase the height of levees.

Ø  4. Deltas

·         Formed at the place where a river flows into the sea/lake.

·         The loss of energy of the river when it flows into another body of water causes the river to deposit the remainder of its load.

·         If the river channel is blocked by silt, it will split up into smaller channels.

·         As more silt is deposited, the delta grows outwards.

SEAS (WAVE ACTION)

Ø  Ocean waves release large amounts of energy when they wash against the land.

Ø  They also carry a load of sand, silt and stones.

Ø  Wave erosion is much greater when waves are larger, during storms and strong winds.

Ø  1.Headlands and bays

·         Headlands: pieces of land that stick out into the sea.

·         Bays: curved areas in between headlands.

·         Rocks of different hardness and resistance are the main cause of headlands and bays.

Ø  2. Cliffs

·         A steep wall of rock formed by wave erosion.

·         Waves erode the base of rocks on the coast, causing the rocks above to collapse.

·         As erosion continues, the cliff face retreats inland.

Ø  3.Caves

·         When waves attack weak points in a cliff, small caves form around them.

Ø  4. Arches

·         When 2 caves form back-to-back on either side of a headland.

Ø  5. Stacks

·         A column of rock that stands apart from the land.

WIND

Ø  Wind picks up and transports soil and sand, causing it to bounce along the ground.

Ø  Wind erosion and deposition mostly occurs in areas where there is little vegetation cover.

 FEATURES PRODUCED BY WIND EROSION

Ø  Loose particles blown by the wind knock against each other and cause erosion, known as abrasion.

Ø  Abrasion mostly takes place close to the ground as this is where the materials ac=re carried to by the wind.

Ø  Examples: mushroom rock- the base is narrower than the rock above the ground.

                  Yarding- long ridge carved by wind erosion.

FEATURES PRODUCED BY DEPOSITION

Ø  Material carried by the wind is deposited once the speed of the wind drops.

Ø  Sand dunes are the most common kind of deposition features.

Ø  Sand dunes can never stay in 1 place for very long.

3.THE IMPACT OF PEOPLE ON SOIL EROSION

o   Soil erosion is only a problem when more soil is eroded than is replaced by natural soil farming processes.

o   Human activities disturb the natural processes of erosion.

o   The main contributors to soil erosion is agriculture, industry, deforestation, and construction.

HOW AGRICULTURE CONTRIBUTES TO SOIL EROSION

o   Removing natural vegetation and ploughing the land weakens soil.

o   Animals contribute to soil erosion when their legs break up the soil.

HOW CONSTRUCTION CONTRIBUTES TO SOIL EROSION

o   Road building/ construction of buildings requires large areas of vegetation to be cleared.

o   Soil can be eroded, removed or covered with concrete.