Weathering

• weathering 


  the breakdown of rock in situ by the action of rainwater, extremes of temperature, biological activity
• Mechanical weathering 


  the breakdown of rock without changing its chemical structure (composition)
• Freeze-thaw weathering 


  occurs when rocks are porous or permeable. 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
• Describe characteristics of rocks that have recently gone through freeze-thaw weathering

  recently weathered rocks can be seen at the foot of chalk and limestone cliffs and are easily identified because it is angular
• Salt weathering 


  when salt spray from the sea gets into a crack in a rock. It may evaporate and crystallise, putting pressure on the surrounding rock and weakening the structure.
• Chemical weathering 


  the breakdown of rock through changin gits chemical composition
• Carbonation weathering 


  When rainwater hits rock, it decomposes or eats it away, a process known as carbonation. Carbonation occurs when slightly acidic rain or sea water comes into contact with sedimentary rock, such as limestone or chalk, and causes it to dissolve. A chemical reaction occurs between the acidic water and the calcium carbonate, forming calcium bicarbonate. This is soluble and is carried away in solution. Carbonation weathering occurs in warm, wet conditions.