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Mechanical Weathering (Physical Weathering)

Mechanical weathering is defined as a natural process. It occurs when big rocks are broken down into smaller rocks. Sometimes you will hear it referred to as “physical weathering.” There are lots of different things that can cause physical weathering. For example, temperature changes and rain can both cause weathering.

What is Mechanical Weathering?

Mechanical weathering is a specific kind of weathering. Weathering is a process that breaks down rocks on the Earth’s crust into smaller pieces. Other types include chemical weathering and biological weathering
Watch this video to learn more about weathering!  

While these types of weathering all break down rocks, they are each unique. Unlike chemical weathering, physical weathering does not change the chemical make-up of rocks. 
Weathering is an important process because it can lead to changes on the Earth’s surface. It’s important to remember that weathering is a slow process. It takes a long time to make significant changes to the Earth’s landscape. 

Types of Mechanical Weathering

There are a few main physical forces that can cause weathering. These include water, salt, and temperature. 


Water can cause weathering through a process called the “freeze-thaw cycle.” In this cycle, water enters into tiny cracks in rocks. When the water freezes it expands and can force the rock to split. Later, when the ice melts, the water carries away tiny pieces of the rock through the process of erosion


Salt can cause weathering through a process called “haloclasty.” In this process, saltwater enters the tiny cracks in rocks. Then the water evaporates and the salt is left behind. Over time, salt crystals grow and can cause the rock to break. 


Temperature can cause weathering through a process called “thermal stress.” Rocks expand when the temperature increases and contract when the temperature decreases. Over time, this process weakens the rocks. Eventually, they break into smaller pieces. 
Additionally, weathering by temperature is common in desert biomes. During the day, the hot sun bakes rocks. Then, at night, the temperature drops. This cycle causes rocks to expand and then rapidly contract.

Examples of Mechanical Weathering 

You can find examples of mechanical weathering all around you! For example, have you ever seen cracks in the sidewalk? These cracks are created over time through physical forces wearing down the sidewalk. 
Sidewalk with cracks.

Weathering can cause small changes likes cracks in the sidewalk.

Mechanical weathering can also cause large changes on the Earth’s surface. The Grand Canyon was created by many, many years of physical weathering and erosion!
The Grand Canyon.

The Grand Canyon

This is a great example of how weathering and erosion can change the Earth’s landforms.  

Other Great Resources 

Geography4Kids on Mechanical Weathering: http://www.geography4kids.com/files/land_weathering.html
ScienceStruck on ‘What Causes Mechanical Weathering:’ https://sciencestruck.com/what-causes-mechanical-weathering
Written By: Leah Tolby.