Earth's Surface
Discover how weathering, erosion and geological processes shape Australia's incredible landscapes over time.
What Is Weathering?
Weathering is the breaking down of rocks, soil and minerals on Earth's surface. It happens slowly over hundreds or thousands of years. There are three main types of weathering.
Physical Weathering
Rocks crack and break apart due to temperature changes, wind, water freezing in cracks, or plant roots growing into gaps.
Chemical Weathering
Rainwater (which is slightly acidic) slowly dissolves minerals in rocks, changing the rock's structure. This creates caves and sinkholes.
Biological Weathering
Living things break down rocks. Tree roots push into cracks, lichens grow on rock surfaces, and burrowing animals loosen soil and rock.
Australian example: The Twelve Apostles along Victoria's Great Ocean Road were carved by millions of years of physical weathering from wind and waves crashing against the limestone cliffs.
What Is Erosion?
Erosion is when weathered rock, soil and sediment are picked up and moved to a new location by water, wind, ice or gravity. Weathering breaks rock down; erosion carries it away.
Agents of Erosion
Water
Rivers, rain and ocean waves carry sediment. This is the most powerful agent of erosion.
Wind
Blows sand and dust, wearing down rocks and reshaping deserts and coastlines.
Ice (Glaciers)
Glaciers grind over rock, carving valleys and carrying huge boulders. Less common in Australia today.
Gravity
Pulls loose rock and soil downhill in landslides and rockfalls.
Did you know? Uluru (Ayers Rock) in the Northern Territory has been shaped by hundreds of millions of years of weathering and erosion. Its red colour comes from iron in the rock rusting (oxidising) on the surface.
Geological Changes Over Time
Earth's surface is always changing, but most changes happen so slowly that we cannot see them happening. Some changes, however, can be sudden and dramatic.
Slow Changes
- Mountain building -- Tectonic plates push against each other, slowly forming mountain ranges over millions of years
- River valleys -- Rivers cut deeper into rock over thousands of years
- Coastal erosion -- Waves gradually reshape cliffs and beaches
- Soil formation -- Rock breaks down into tiny particles that become soil
Rapid Changes
- Earthquakes -- Sudden shaking when tectonic plates shift
- Volcanic eruptions -- Molten rock (lava) erupts from below Earth's surface
- Landslides -- Large amounts of rock and soil slide downhill suddenly
- Floods -- Heavy rain causes rivers to overflow, moving large amounts of sediment
Deposition: Where Does the Sediment Go?
When water or wind slows down, it drops the sediment it has been carrying. This process is called deposition. Over time, deposited layers of sediment can form new landforms like deltas, sand dunes and floodplains. The Murray-Darling river system in Australia deposits sediment that creates rich farming soil.
Key Vocabulary
Weathering
The breaking down of rocks and minerals on Earth's surface by natural forces like water, wind, temperature and living things.
Erosion
The process of weathered rock and soil being carried away by water, wind, ice or gravity to a new location.
Sediment
Tiny pieces of rock, sand, silt and soil that are carried by water or wind and deposited somewhere new.
Deposition
When water or wind slows down and drops the sediment it has been carrying, building up new layers of material.
Worked Examples
Explain the difference between weathering and erosion.
Step 1: Weathering is the breaking down of rocks in the same place (the rock does not move).
Step 2: Erosion is when the broken pieces are picked up and moved somewhere else by water, wind, ice or gravity.
Answer: Weathering breaks rock apart; erosion carries the pieces away. Weathering must happen first before erosion can occur.
How were the Twelve Apostles in Victoria formed?
Step 1: Ocean waves constantly crashed against the limestone cliffs along the coast (physical weathering and erosion).
Step 2: Over millions of years, the waves wore away softer rock, creating caves, arches and eventually tall stacks standing alone in the sea.
Answer: The Twelve Apostles were formed by wave erosion gradually wearing away the coastline, leaving behind isolated rock stacks.
Give an example of a rapid change to Earth's surface.
Step 1: Heavy rain falls on steep, burnt bushland after a bushfire in Australia.
Step 2: Without plant roots holding the soil in place, the waterlogged soil slides downhill quickly.
Answer: A landslide is a rapid change -- it happens in seconds or minutes and can reshape the landscape dramatically.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
What is the process of rocks breaking down in the same place called?
Question 2
Which of these is the most powerful agent of erosion?
Question 3
Tree roots growing into cracks in a rock is an example of:
Question 4
What is deposition?
Question 5
Which of these is a rapid change to Earth's surface?
Key Concepts Summary
- ●Weathering breaks rocks down in place (physical, chemical and biological types).
- ●Erosion moves weathered material to new locations via water, wind, ice or gravity.
- ●Deposition occurs when sediment is dropped, building new landforms like deltas and sand dunes.
- ●Earth's surface changes both slowly (mountain building, river valleys) and rapidly (earthquakes, landslides).
- ●Australian landmarks like the Twelve Apostles and Uluru show the effects of weathering and erosion over millions of years.