Weathering and erosion

• Rocks are broken down in situ

• In situ means at the original place

• Causes of weathering

Extreme temperature change

Freeze-thaw action

Action of plants

Action of water

In the day, very high temperature heats up the surface of the rock and causes it to expand.

At night, very low temperature cools the surface of the rock and causes it to contract.

Alternate expansion and contraction of the rock surface weakens the rock.

Over time, the rock surface will peel off.

Joints

When temperature falls below freezing point, water in the cracks of rock turns into ice.

The ice will expand, widening the cracks.

When temperature rises above freezing point, the ice in the crack will melt.

Repeated freezing and melting will cause the cracks to become wider and the rocks will break apart.

Water freezing

in the joint

Joint is widened

and deepened

Rock breaks down

• Rain will combine with carbon dioxide in the air to form acid rain.

• The acid rain will seep into the cracks of rocks and dissolve part of the rocks.

• Over time, the acid rain can corrode landforms and buildings.

• Seeds can be carried by wind into cracks of rocks.

• Roots can grow into the cracks of rocks and widen the cracks.

• Over time, the rocks may break apart.

• Rocks are broken down and are removed from their original site

• Causes of erosion

Waves Wind River Flow

• Waves will hit the rocks on the beach constantly.

• The rocks will be broken down either by the force of the water or by the materials carried by the waves.

• The broken rocks will be removed.

• Over time, features such as cliff, cave and arch may be formed.

• Wind picks up sand in the deserts and hits against the rock surface.

• As sand is heavy, it can only be carried by wind to a certain height.

• Wind erosion can therefore take place near the base of rocks.

• Rivers have energy to carry small materials like sand and silt, as well as large materials like pebbles.

• These materials will erode river beds and river banks along the path of the river.

• Over time, the river will deepen and lower the Earth’s surface.

Broken rocks together with decomposed leaf litter will form fertile soil which is good for farming. (+)

Beautiful landscapes such as river valleys, will be formed and attracting tourists. The country’s economy will prosper from the earnings from tourism. (+)

However, erosion can bring negative impact too. Landslides may occur and there will be a loss of lives and houses will be destroyed. (-)

Statues will be corroded and destroyed. Government has to spend large sum of money to maintain the statues regularly. (-)

Physical landscapes will be destroyed and fewer tourists will visit the areas. The country’s economy will be affected as less income is earned from tourism. (-)