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IGCSE Geography - Revision guide: Weathering

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Types of weathering - mechanical, biological, influence of weathering on climate

Hydrological cycle, profile of river, river processes, land forms, deltas, erosion, Niagara falls formation, river deposition (Bangladesh), flooding 

Coasts, changing coastlines, erosion - 12 apostles, deposition, bays and headlands, sea defences, holderness coast

Coral reefs, the great barrier reef, coral reef regions of the world, threats to coral reefs

Weathering and Climate

Click on image to access interactive weathering module.

World's fresh water sources

Click on image and then click on different sources on this interactive map. 

What is the 'Water Cycle' ?

What is the water cycle?

The water cycle describes the existence and movement of water on, in, and above the Earth. Earth's water is always in movement and is always changing states, from liquid to vapor to ice and back again. The water cycle has been working for billions of years and all life on Earth depends on it continuing to work. 

Click on image to see an interactive Water Cycle process

Animations of river processes

click this image to watch an 'Erosion' animation
click this image to watch a 'Transport' animation

Delta: Words to Know

Alluvial fan: A fanlike deposit of sediment that forms where an intermittent, yet rapidly flowing canyon or mountain stream spills out onto a plain or relatively flat valley.
Alluvium: A general term for sediment (rock debris such as gravel, sand, silt, and clay) deposited by running water.
Bed load: The coarse sediment rolled along the bottom of a river or stream.
Bottomset bed: A fine, horizontal layer of clay and silt deposited beyond the edge of a delta.
Dissolved load: Dissolved substances, the result of the chemical weathering of rock, that are carried along in a river or stream.

Bays & headlands - animation

click on image to watch an animation!

OR Watch this video 

Great Barrier Reef - World Heritage Site

The Great Barrier Reef is a site of remarkable variety and beauty on the north-east coast of Australia. It contains the world’s largest collection of coral reefs, with 400 types of coral, 1,500 species of fish and 4,000 types of mollusc.

Click on image to read more from World Heritage Site

What are the threats to the Great Barrier reef

What will happen to coral reefs in 2050?

Exploring Threats to Coral Reefs - A World Resources Institute Study

Coastal defences

Why defend the coast?
Coastlines tend to be very heavily populated. They are areas of high economic value due to tourism. Coastlines are particularly prone to flooding. Finally, they are fragile ecosystems which take a long time to recover if they are destroyed. 
Hard Engineering
Hard engineering approaches tend to be expensive, last only a short amount of time, are visually unattractive and unsustainable. They often increase erosion in other places further down the coast. Examples are groynes, sea walls, reventments etc
Soft Engineering
Soft engineering approaches are less expensive, are more long term, attractive and sustainable as they work with natural processes. Examples are beach nourishment, managed retreat. 

Read about Hard Engineering and Soft Engineering methods HERE

Hydrologic Cycle

The hydrologic cycle begins with the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns to the surface as precipitation. Once the water reaches the ground, one of two processes may occur; 1) some of the water may evaporate back into the atmosphere or 2) the water may penetrate the surface and become groundwater

Weathering Types and processes

How are main river features formed?

click on image to read more about rivers, formation and features

Rivers data



Avg. Discharge at Mouth (kilo cubicfeet /sec)
































River Deltas

 A river often creates a delta at the spot where the river enters the sea or a large lake because, as the river reaches the shore, the speed of its water flow slows way down.  At the shore, the river’s water is no longer briskly moving, confined between its banks, but instead it spreads out into the sea in the shape of a fan and becomes just a part of the much larger volume of water that is the sea.

As the delta grows the river tends to separate into multiple smaller streams flowing individually through the low-lying fan. The symbol for the Greek letter “D” is an equilateral triangle, which is, of course, fan shaped.  In English the Greek letter “D” is called “Delta.” 

Watch an animation of wave types

click on image!


Abrasion -This occurs when rock particles already being moved by the river strike or are dragged along the rock bed. The impact removes small particles. 

Attrition - This is the reduction in the size of particles in transport as they strike one another or the bed and banks of the channel. The consequence is that as particles are moved downstream, there is a steady reduction in size. In addition, the angular edges of the particles become more rounded, since they are more exposed. 

Corrosion (or solution) -This is most important on carbonate rocks such as limestone and chalk where carbonic acid (rainwater) dissolves the rock, which is carried away in solution.

Cavitation (or hydraulic action) - This process moves material into the river channel through the impact of moving water, and its frictional drag, on the bed and banks f the river. Usually, only unconsolidated material, such as sand and fine gravel can be removed. 

Read more HERE

Three stages of Coral reef formation

A new oceanic island in the tropics has no terrestrial or marine life when it is first formed. Life forms may arrive by flying, floating or swimming. 

A fringing reef The reef building coral animal is one of the few marine organisms that can survive in the warm, nutrient-poor surface tropical waters. The coral animal reproduces and needs to attach to a solid surface that will stay in the warm, sunlit, clear tropical water. So a coral reef forms along the edge of this new island, right next to the island and is called a fringing reef.

A barrier reef forms as the oceanic island begins to sink into Earth's crust due to the absence of volcanic island building forces, the added weight of the coral reef, and erosion at the surface of the island. As the island sinks, the coral reef continues to grow upward. The coral animals lay down tremendous amounts of calcium carbonate. Their living tissue remains in the upper part of the reef in the warm, clear, tropical water. The lower part of the reef is composed of the calcium carbonate skeletons left by the reef building coral.

An atoll forms when the oceanic island sinks below the surface of the ocean but the coral reef continues to grow upward. The atoll is usually circular in shape. 

Coastal defence mechanism


Weathering in general refers to a group of processes by which surface rock disintegrates into smaller particles or dissolve into water due to the impact of the atmosphere and hydrosphere. The weathering processes often are slow (hundred to thousands of years). The amount of time that rocks and minerals have been exposed at the earth's surface will influence the degree to which they have weathered.

Weathering processes can be: physical  chemical  biological 

Types of weathering explained

Mechanical Weathering
Expansion and Contraction - the thermal heating and cooling of rocks causing expansion and contraction.
Frost Action - Water freezes at night and expands because the solid occupies greater volume. Action wedges the rocks apart. Requires adequate supply of moisture; moisture must be able to enter rock or soil; and temperature must move back and forth over freezing point. 
Exfoliation - process in which curved plates of rock are stripped from a larger rock mass. Example Half Dome. Exact mechanism uncertain but probably due to unloading.
Other types - Cracking of rocks by plant roots and burrowing animals.
Chemical Weathering
Factors which effect the rate of chemical weathering are:
Particle size - Smaller the particle size the greater the surface area and hence the more rapid the weathering
Type and amount of vegetation

River profile

The River changes as it travels from its source to its mouth. The course of a river is divided into three main sections: 

Upper Course 

Middle Course

Lower Course

click on image to read more about river profile, erosion, hydrological cycle

What are waves?

What causes waves? 

Measuring waves

Types of waves

Click on image to find answers to these topics and more...

Coasts - Process, features

Click this image to explore, play and read about some coastal features

Formation of a Spit - in animation

click on image to see an animation!


Niagara Falls formation

The layers of rock that comprise the Niagara Gorge at the point of the falls are integral to sustaining a waterfall on the Niagara River. There are several layers of different compositions, colors and hardness; but the bottom line is: the hard, erosion-resistant layer on top and the softer, wear-easy layers on the bottom are what create the falls. Click image to read more

Threats to Great Barrier Reef

Aerial View of Great Barrier Reef


Ocean Acidification
Ocean warming and Coral bleaching
Carbon dioxide
Water Pollution
Coastal Development
Destructive Farming practices
Coral mining
Careless tourism
Ozone depletion

The Holderness Coast, NE Yorkshire Coast

The coastline is mainly made up of cliffs (20-30m high), consisting of soft, easily eroded boulder clay. Where the cliff line meets the Humber Estuary, a spit has formed due to the change in the direction of the coastline - Spurn Head. Click image to read from the webpage