Coastal Processes: Weathering 

Weathering is best described as the process of the atmosphere and weather breaking down rocks on the coastline in situ (in the original place). The process differs from erosion as it doesn’t involve the movement of material and is a process that doesn’t necessarily involve action from the ocean.  

There are three main types of weathering:

  • Mechanical
  • Chemical
  • Biological

Each form of weathering has examples that you could draw on to provide evidence of weathering as a coastal process that affects the coastlines of the UK.


Mechanical weathering physically breaks up the rock. The most common example of this is freeze-thaw weathering

This process requires porous or permeable rocks – water needs to be inside of a rock to carry out freeze-thaw-weathering. Let’s look at the process below:

  1. Water enters rocks through cracks and joints.
  1. As temperatures drop, the water freezes, which causes it to expand in volume, forcing the crack to increase in size.
  1. Temperatures rise again and the water melts. It sinks deeper into the crack or joint.
  1. As time goes on, the process of melting and freezing repeats until pieces of the rock break from the rock face. This leads to large rocks or boulders being broken into small rocks or even gravel. 


Chemical weathering is when rocks are broken down by a chemical process, which usually results from the interaction with rainfall. 

Rainwater is slightly acidic, through absorbing carbon dioxide from the atmosphere, and it can react with certain types of rock. If a coastline is made of rocks such as limestone or chalk (weak sedimentary rock) then they can be dissolved by the rain over time.

The rock undergoes a chemical reaction with the acidic rain, forming new minerals and breaking down the rock face on the coastline. The warmer the temperatures, the faster this reaction will take place. 

Stronger rocks, such as granite, are still impacted by rainfall, but at a far slower rate. 


Biological weathering is a process in which rocks are worn away by living organisms. Notably, plant roots contribute to this as they grow into and widen cracks in the rock.

  1. Plant roots grow downwards, finding their way into small cracks in the rock
  1. The roots continue to grow, and the cracks become larger
  1. As cracks continue to grow, small pieces of rock break away. 

Animals can also influence the integrity of rock on the coast. Animals, such as rabbits, burrow into the ground, disturbing the soil and increasing pressure on the rocks above their burrows. This puts more pressure on any existing cracks, leading to pieces falling off. 

Key Terms

PorousContaining holes.
PermeableAllows fluids, like water, to pass through.
Sedimentary rocksOne of the three main rock types, made from the accumulation of sediment and minerals. tend to be less dense and less hard than igneous and metamorphic rocks, which can make them more susceptible to weathering processes.