When rock is exposed to weather conditions it becomes subject to processes, such as freeze-thaw weathering, that cause it to change and break down.
The freeze-thaw weathering process is also known as frost shattering.
Mount Snowdon in Snowdonia, Wales
- Water - eg from rainfall or melting snow and ice - becomes trapped in a crack or joint in the rock.
- If the air temperature drops below freezing, the water will freeze and expand by 9-10 per cent putting pressure on the rock.
- The ice will melt when the temperature rises above freezing.
- If this process happens repeatedly, the rock will weaken and eventually shatter into angular fragments.
- The fragments may then be deposited as scree at the foot of a slope.
- It is most effective where the temperature fluctuates around 0°C, eg on north-facing high altitude slopes in Snowdonia.
Exposed rocks along the coastline can be broken down by the processes of weathering.
Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through).
- Water enters cracks in the rock.
- When temperatures drop, the water freezes and expands causing the crack to widen.
- The ice melts and water makes its way deeper into the cracks.
- The process repeats itself until the rock splits entirely.
Plants and animals can also have an effect on rocks. Roots burrow down, weakening the structure of the rock until it breaks away.
- Plant roots can get into small cracks in the rock.
- As the roots grow, the cracks become larger.
- This causes small pieces of rock to break away.
Rainwater and seawater can be a weak acid. If a coastline is made up of rocks such as limestone or chalk, over time they can become dissolved by the acid in the water.