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Types of Weathering

There are three different types of weathering: mechanical, chemical, and biological. Mechanical weathering refers to the direct break-up of a material. Next, chemical weathering is the weakening of a material on the atomic level. Biological weathering combines the two. It includes any action taken by a living thing that wears down a material.

Over time, plant roots can weather a wall.

Three Types of Weathering

As stated, there are three types of forces which weather materials. But, these are huge categories and they overlap. Let’s try and focus on each one in-depth, one at a time.

Mechanical Weathering

Mechanical weathering is the simplest type of weathering. It’s when materials are forcefully broken into smaller pieces. That said, the ‘force’ isn’t always so obvious. As we’ll see, mechanical weathering often works in the long-term.

Examples

Temperature Shocks
 
In most northern states, roads are subject to temperature shocks. This is a form of physical weathering that happens over the course of several months. During the summer, when the sun is out, it’s relatively hot. This causes the material which makes up a road to expand. As it does, it will crack and fracture. Several months later, in the winter, temperatures drop. The road will then contract which is another source of cracking. 
Road cracked from temperature.

A weathered road. Weathering makes for a bumpy ride!

 
Sandstorms
 
In desert environments, heavy winds tend to pick up lots of sand. This creates what is known as a sandstorm. Importantly, sandstorms spew out sand as they collect it. While each sand particle is tiny, lots of them make for a powerful force. They’re thrown against boulders, each one damaging the rock a little. Over time, this can chip pieces off of the boulder.

Chemical Weathering

This next type of weathering is a little more complex. Physical weathering isn’t that hard to explain: rocks can be broken with force. But, chemical weathering is different. It takes place at the level of atoms and molecules. As a result, it’s invisible to us. Yet, its impact is not. Let’s look at a few examples of what it can do.

Examples

 
We don’t usually think of rain as dangerous or destructive. And for the most part, it’s not. But, sometimes it’s more than water that rains down. Above industrial zones, for example, chemicals float up into the sky. When it rains, they mix with the water coming down. 
A stone angel eroded by rain.

A statue which has been weathered by acid rain. Acid creates openings in rocks and makes them weak.

 
This makes the raindrops very acidic. As they land, they’ll react with metals in buildings and minerals in rocks. This softens them up so that water can wash them away (an erosional process).
 
Rust
 
Have you ever left something metallic out in the rain, say a bike? If you did, you may have received an unpleasant surprise: the metal rusted. Rusting is something that happens to metals exposed to rain or open air. It’s when oxygen (in water and air) reacts with metal. So, we also call the process oxidation. 
A rusted bicycle.

A statue which has been weathered by acid rain. Acid creates openings in rocks and makes them weak.

 
Of course, our atmosphere is full of oxygen. While that’s great for us, it’s very bad for metals. It discolors them and makes them weak. Notably, this is also how most ores form. Ores are actually large groups of oxidized minerals. They were exposed to oxygen while the earth was forming.

Biological Weathering

Now, our final type of weathering is much easier to observe. That’s because it has to do with living things! For example, some animals tunnel through dirt to find food. Additionally, most plants release waste chemicals into the environment. Both of these behaviors are examples of biological weathering.

Examples

Molehills
Moles are animals that we rarely ever see. Yet, we can see their impact pretty clearly. They dig holes all over the place, breaking up soil. This weakens the soil so that it’s much easier for runoff to carry it away.
A molehill

A mole coming out of a molehill.

 
Plant Acids
All organisms have what we call a metabolism. This means they produce chemicals which help them survive (usually for energy). In our case, plants release chemicals called acids into their environment. They do this to dissolve and absorb minerals. Of course, this also weathers rocks.

Other Great Resources:

Geography4Kids on the Types of Weathering: http://www.geography4kids.com/files/land_weathering.html
 
‘Weathering Facts for Kids’ by Kiddle: https://kids.kiddle.co/Weathering