I Bet You Don’t Know What Weathering of Rocks is


The Wind River Range of the Rocky Mountains have been shaped by weathering.

Weathering of rocks is not something that most people hear about.  Despite it’s lack of fame, it plays an important role in the shaping of landscapes, including the Rocky Mountains.

Contrary to what many people think and say, the breaking down of rock into smaller pieces is called weathering, not erosion.  It is an important part of the rock cycle.  Weathering of rocks can be done by different means – physical or  chemical.  Here is an explanation of what the different kinds are.

Physical Weathering

Physical changes break down large rocks into smaller ones but the rocks are made of the same stuff.  Here are a couple of examples of different types of physical processes that can break down rocks.

Frost Wedging

It may be hard to believe, but water is responsible for breaking apart many rocks.  This is due to the fact that when water freezes it expands by 9%.

Water can get into tiny cracks in rocks during the day.  Then at nighttime that water freezes and expands, which makes bigger cracks in the rock.  This continues until part of the rock breaks off.


An example of root wedging – a physical process that breaks apart rocks.

Biological Activity

Another unlikely powerful force that can break up rocks is plants.  It is possible for plant roots to grow into small cracks in rocks in search of water and nutrients.  Over time those roots grow larger and larger, widening the crack in the rock.  Eventually, if the roots get large enough or the crack large enough the rock may break off or apart.

chemical weathering

Chemical weathering of limestone. Photo via Flickr.

Chemical Weathering

In contrast to physical processes, which break apart the rocks, chemical processes change the make-up of the rock itself.  The chemical processes break down the bonds or glue that hold rocks together and cause them to fall apart.

These chemical processes may occur when rain or oxygen from the air chemically reacts with the minerals in the rock to change it.  For example, acid in rainwater can create a cave in the rock.  This is common in limestone.