Rock is broken down by chemical and mechanical weathering.
What is mechanical weathering?
Mechanical weathering is the breakdown of rock without changing its chemical composition. This means the rock breaks up without its chemical makeup changing. Freeze-thaw weathering is the main type of mechanical weathering that affects coasts.
Freeze-thaw weathering occurs when rocks are porous (contain holes) or permeable (allow water to pass through). Water enters the rock and freezes. The ice expands by around 9%. This causes pressure on the rock until it cracks. Repeated freeze-thaw can cause the rock to break up.
Recently weathered rock can be seen at the foot of chalk and limestone cliffs and is easily identified because it is angular. Over time it will become smoother, forming peddles and then eventually sand.
What is chemical weathering?
Chemical weathering is the breakdown of rock through changing its chemical composition. Carbonation weathering occurs in warm, wet conditions.
Carbonation weathering is a type of chemical weathering that happens in warm and wet conditions. When slightly acidic (carbonic) rain or sea water comes into contact with sedimentary rock it causes it to dissolve.
The role of weathering is to weaken cliffs. This weakening speeds up the rates of erosion.