Teaching Students About Weathering

What is Weathering?

Weathering is breaking down or dissolving rocks on the Earth’s surface. The process of weathering breaks down and removes material from the coastlines. Weathering wears away exposed surfaces over time.

There are many types of rocks; some are more vulnerable to weathering than others. Weathering is also the first step to producing soils, as rocks’ angular or harsh edges become rounded and more minor. The tiny bits of weathered material sometimes mix with plants, animal remains, bacteria and other organisms to create soil. A single type of weathered rock makes infertile soil, whereas weathered materials from different rocks produce more fertile ground.

5 Facts About Weathering

  • Weathering should not be confused with erosion. Erosion describes the moving of rocks via water, wind, or gravity, whereas weathering describes the breaking down of rocks through direct contact.
  • There are three types of weathering: biological, chemical, and mechanical.
  • Rain is mildly acidic and slowly eats away at rocks – this is an example of chemical weathering.
  • Plants and animals also cause rocks to erode – this is an example of biological weathering.
  • Water can seep into the cracks of rocks, and as the temperature cools and this water freezes, this causes stones to break away – this is mechanical weathering.

What are the Three Types of Weathering?

The three types of weathering can break down any exposed rocks along the coastline.

The three types of weathering are:

  • Mechanical weathering
  • Chemical weathering
  • Biological weathering

What are Weathering Agents?

There are different weathering agents. Weathering agents are the things that contribute to the process of weathering.

What is Biological Weathering?

Biological weathering is the weakening and removing rock by plants, animals, and microbes. For example, plant roots can enter a small crack in a rock, and then as the root grows larger, the gap in the rock gets larger. It weakens the structure of the stone until it eventually breaks away.

What is Chemical Weathering?

Chemical weathering changes the molecular structure of rocks and soils, becoming weaker and eroding.

Chemical weathering is usually a result of rain or saltwater being slightly acidic. However, sometimes coastlines are made up of rocks such as limestone or chalk, and these types of stones can be affected by the acid in the water, which then dissolves the rock over time.

One example is carbonic acid, which is weak but effective at dissolving limestone. When carbonic acid seeps through a limestone underground, it can create huge cracks or even open up many little caves.

Another type of chemical weathering involves rocks that contain iron. These rocks rust due to a process called oxidation. Rust is created by the interaction of oxygen and iron with water. As the rust expands, it can weaken the rock and break it apart! The image below shows an example of rust.

What is Mechanical Weathering?

Mechanical weathering is sometimes called physical weathering, describing the process of rock crumbling. Water is the critical agent in mechanical weathering. Temperature changes are also the primary agent in mechanical weathering. The main type of mechanical weathering is freeze-thaw weathering.

Freeze-thaw weathering is when rocks have holes (also called porous), and water can pass through the rocks. If water can pass through the rock, it is called a porous rock. Freeze-thawing happens when water goes into a rock crack and freezes when the temperature drops below freezing. The frozen water then expands, widening the rock. The ice then melts when the temperature rises again, and the water makes it’s way further into the cracks in the rock. The process then repeats over and over again until the rock completely breaks apart.

Another type of mechanical weathering is a process called thermal stress. It is when temperature changes cause rocks to expand and contract. For example, stones grow in the head and contract in the cold. The process repeats over and over again and weakens the rock each time. It is common in rocky deserts, where temperatures change drastically day to night.

Another type of mechanical weathering is when materials such as clay that are porous are near rocks. The clay will absorb lots of water and expand, eroding the more complex rock around it. Salt is another agent which can affect weathering. For example, saltwater can sometimes get into the cracks or holes of rocks, and then when the water evaporates, it can leave behind salt crystals. The salt crystals will then grow, which puts pressure on the rock and causes it to break eventually.

Clay in minerals, such as quartz, is some of the most common by-products of weathering, mainly chemical and physical weathering. So it is because clay makes up around 40% of the chemicals in all sedimentary rocks on earth!

Animals also play a part as an agent of weathering. For example, animals that live or roam underground, such as moles, might also break apart rock and soil. Some animals also dig and trample rock above ground, causing the rocks to crumble or break away.

Can Humans Impact Weathering?

Weathering is a natural process, but humans can cause the process to speed up due to certain human activities. The primary example of this is air pollution. Air pollution can speed up the process of weathering because when we burn fossil fuels, natural gas, and coal, it releases chemicals into the atmosphere. These chemicals then change into acids and fall back to earth in the rain. This type of rain is called acid rain.

Acid rain has a significant impact on rocks such as limestone and marble. In addition, acid rain has damaged many buildings and monuments and can affect gravestones.

What are Weathering, Erosion, and Deposition?

Weathering, erosion, and deposition have occurred over billions of years to wear down and build up the Earth’s surface. All these processes act together in a continual cycle.

  • Weathering is the breaking down of rocks. Rocks get broken down by agents, including water, ice, wind, animals, and growing plants.
  • Erosion is the movement of material from broken-down rocks. This material is called sediment and is made of rocks, minerals, and plant and animal remains. Erosion agents include water, ice, wind, and gravity.
  • A deposition is the dropping of sediment in a new place. Some examples of deposits are the formation of an island or dunes.

So, the material is broken down by weathering, moved by erosion, and deposited in a new place by deposition.

Gravity pulls everything towards the Earth’s core, causing rock and other materials to move downhill. Some effects of weathering, erosion, and deposition are changes in the shape and size of landforms and the formation of different landforms. These include mountains, beaches, and riverbeds.

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